EVALUATION OF POWDERED ACTIVATED CARBON … · Evaluation of powdered activated carbon performance...

Environmental Engineering and Management Journal May 2016, Vol.15, No. 5, 1003-1008

http://omicron.ch.tuiasi.ro/EEMJ/

“Gheorghe Asachi” Technical University of Iasi, Romania

EVALUATION OF POWDERED ACTIVATED CARBON PERFORMANCE FOR WASTEWATER TREATMENT CONTAINING

ORGANIC (C6H6 AND C6H5-CH3) AND INORGANIC (Pb+2 AND Zn+2) POLLUTANTS

Cristina Ileana Covaliu1 , Ecaterina Matei2, Gabriela Georgescu3,

Teodora M l eru3, Sorin tefan Biri 1

1University Politehnica of Bucharest, Faculty of Biotechnical Systems Engineering, 313 Splaiul Independentei, 060042, Bucharest, Romania

2University Politehnica of Bucharest, Faculty of Materials Science and Engineering, 313 Splaiul Independentei, 060042, Bucharest, Romania

3National Institute of Research and Development for Electrical Engineering, INCDIE ICPE-CA, Bucharest, 313 Splaiul Unirii, 030138, Bucharest, Romania

Abstract The removal of toxic heavy metal ions such as lead and zinc from industrial and mining wastewaters has been widely studied because their existence in surface and underground water is responsible for several types of health problems caused to animals and human beings. Also, there are some organic compounds, which must be prevented from reaching in drinking water from various sources of pollution. For these reasons in this paper the experiments were conducted to study the ability of activated carbon for removal of Pb(II), Zn(II), C6H6, C6H5-CH3 from water. In addition to the data from the literature showing the actived carbon efficiency for removing of the organic nature pollutants from water, in this article the study is done also on inorganic toxic pollutants (lead and zinc heavy metals) that can exist in water. The removal efficiency of the tested activated carbon used as adsorbent towards the tested pollutants decreased in the following order: COD (benzene, toluene) > Pb(II) > Zn(II). Key words: activated carbon, inorganic pollutants, organic pollutants, wastewater treatment Received: June, 2015; Revised final: February, 2016; Accepted: April, 2016

Author to whom all correspondence should be addressed: e-mail: [email protected]

1. Introduction Activated carbon is applied in wastewaters

treatment resulted from industrial activities like textile, coke plant, pharmaceutical, chemical factories, munitions factories, food, pesticides manufacturing, herbicides manufacturing, petroleum refineries installations, storage installations, organic pigments and dyes, mineral processing plants, insecticides, pesticides, resins, detergents, explosives and dyestuffs (Kouachi et al., 2010; Syafalni et al., 2012).

Activated carbon includes a wide range of amorphous carbon based materials synthesized in such a way that is characterized by a high degree of porosity and an extended surface area (Chaudhary et al., 2013; Ignat et al., 2015).

Activated carbon is one of the most efficient adsorbant for removing a wide range of organic pollutants from water (Berar et al., 2012; Chen et al., 2014; Robescu et al., 2008). In Table 1 are presented some examples of chemical pollutants with high, very high, moderate and low probability of being adsorbed by activated carbon.

Covaliu et al./Environmental Engineering and Management Journal 15 (2016), 5, 1003-1008

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The potential application of activated carbon in wastewater treatment is sustained by its structure of pores presented in Fig. 1 which is suitable for retaining small, medium or large molecules.

Fig. 1. Scheme of retaining small, medium or large molecules of pollutants by one of the pores of activated

carbon

Examples of large or medium molecules are represented by organic compounds, whereas heavy metals are considered small molecules.

Toluene (also called methyl benzene) and benzene are colorless, flammable liquids, which are contained by petroleum crude oil. Toluene and benzene can enter in the environment during manufacture or use of these substances or products containing them. In United States, large amounts of the toluene recovered from crude oil is used for benzene production or in the composition of paint strippers, aerosol spray paints, adhesives, cosmetics, printing ink, perfumes, wall paints, lacquers, spot removers and antifreeze. The sources for benzene pollution could be combustion processes, industries producing or using it such as production of dyes, fibers, plastics, detergents, coatings pesticides, lubricants, adhesives and dry cleaning agents (http://www.epa.gov/chemfact/f_toluen.txt).

Table 1. Chemical pollutants with high, very high, moderate and low probability of being adsorbed by activated carbon

Chemical compounds with high probability of being

adsorbed by activated carbon

Chemical compounds with very high probability of being

adsorbed by activated carbon

Chemicals with moderate probability of

being adsorbed by activated carbon

Chemical compounds for which adsorption with

activated carbon is low and it is viable method for

low wastewater flow or concentration

Aniline

Aldrin

Acetic acid

Methyl chloride

Benzene

Anthracene

Acrylamide Acetone

Benzyl alcohol

Atrazine

Chloroethane

Acetonitrile

Benzoic acid

Azinphos-ethyl

Chloroform

Acrylonitrile

Bis(2-chloroethyl) ether

Bentazone 1,1-Dichloroethane

Dimethylformaldehyde

Evaluation of powdered activated carbon performance for wastewater treatment

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Excessive exposure to toluene may impair

hearing and affect the normal function of brain. Both benzene and toluene are considered harmful to aquatic organisms (http://www.epa.gov/chemfact/f_toluen.txt).

Effects of toluene on human health and the environment depend on some factors like: concentration, the length of time frequency of exposure, health of the person exposed and the conditions of the environment when exposure occurs (Segneanu et al., 2013). It was already proved that benzene is carcinogen.

In addition to the data from the literature showing the actived carbon efficiency for removing of the organic nature pollutants from water, in this article the study is done on two types of toxic pollutants that can exist in water: organic and inorganic type. The goal of our research was the study of the adsorption capacity of powdered activated carbon as a suitable tool for treatment of synthetic wastewater containing in the same time, inorganic pollutants such as Pb(II) and Zn(II) ions and as organic pollutants benzene (C6H6) and toluene (C6H5-CH3).

2. Materials and methods

The experiments were done with different heavy metals (Pb and Zn) concentrations (20, 40, 60, 80 mg/L for each pollutant) together with organic compounds consisting of 0.5% C6H6 and 0.5% C6H5CH3. Initial concentration of organic compounds was 100 mg/L expressed as chemical oxygen demand (COD). Solutions were put together with 1 g of activated carbon. Activated carbon powder was purchased from Sigma-Aldrich, with the following characteristics: vapor pressure < 0.1 mm Hg (20°C), resistivity 1375 -cm at 20°C, size dimension 37 – 149 m.

In order to measure Pb(II) and Zn(II) concentrations were used a 932 GBC Avanta Plus atomic absorption spectrometer with flame. The analytic conditions for Zn(II) and Pb(II) determination by atomic absorption spectrometry involved the use of Deuterium lamp as background correction and air/oxidized acetylene flame. Also, the specific wavelength for Pb was 217 nm and for Zn was 213.9 nm.

In order to evaluate the concentration of organic compounds as COD, before and after adsorption tests, the following procedure was applied: 100 mL of sample was poured into an Erlenmeyer flask together with 5 mL H2SO4 1:3 and 10 mL potassium permanganate accurately measured were added to the samples. All mixtures were boiled on a hotplate for 10 minutes. Into the hot mixture were added 10 mL oxalic acid precisely measured. Titration operation was made with potassium permanganate until a persistent pink color appeared.

Chemical oxygen consumption was calculated using the Eq. (1).

3

214

1000316.0/V

VfVVLmgKMnO (1)

where: V - volume of potassium permanganate initially added in the sample, mL; V1 - volume of 0.01 N potassium permanganate used for sample titration, mL; V2 - volume of oxalic acid added to the sample before titration, mL; f - the factor of the potassium permanganate solution; 0.316 - equivalent expressed in mg of KMnO4 of 1 mL of 0.01 KMnO4 0.01 N; V3 - volume of wastewater analyzed, in mL.

For adsorption tests 100 mL of sample with different concentrations of heavy metals and 100 mg/L organic compounds were added into contact with 1 g activated carbon. Samples were analyzed after 10 minutes, 1 hour, 2 hours and 24 hours. The time interval was chosen according to the previous researches regarding the adsorption tests (Matei et al., 2011) where adsorption appears after 10-15 minutes and the same results are observed after 2 hours. In order to evaluate tendency of desorption a sample was analyzed after 24 hours.

The analysis of the two heavy metals and organic compounds were done according to the SR ISO 8288/2001 standard for heavy metals.

Zn(II) and Pb(II) pollutants removal efficiency was calculated according to the Eq. (2):

%100i

ei

CCC

(2)

where: - removal effciency, %; Ci – initial concentration, mg/L; Ce - concentration at equilibrium, mg/L.

Based on the Langmuir equation, adsorption process can be described as monolayer process where adsorbent surface has a specific number of sites available for reaction and linking of retained molecules. Adsorption process is ended when all sites are occupied (Modrogan et al., 2013).

Langmuir model adsorption (Matei et al., 2011) is given by the Eq. (3):

qe = Qmax.KL.Ce (1+KLCe) (3) where: qe - adsorbed quantity at equilibrium, mg/g; Ce - concentration at equilibrium, mg/L; Qmax - maximum quantity adsorbed, mg/g; KL - Langmuir constant, L/mg.

Also, the adsorbed quantity at equilibrium, qe, was calculated with Eq. (4):

mVCCq e

e0

(4) where: qe - adsorbed quantity at equilibrium, mg/g; C0 – initial concentration, mg/L; Ce – equilibrium concentration, mg/L; V – volume, L; m – adsorbent quantity, g.


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Also, separation factor (RL), defined by the Eq. (5), can be used as dimensionless constant in order to evaluate the profile of the Langmuir isotherm (Modrogan et al., 2013; Ungureanu et al., 2015).

0LL CK1

1R (5)

According to RL values, the profile of the

isotherm could be: favorable (0<RL<1), unfavorable (RL>1), linear (RL=1) or irreversible (RL=0).

For a better description of adsorption process the Freundlich model (Hasani et al., 2015) was applied, given in the Eq. (6): log qe = log KF + 1/n log Ce (6) where: Ce - the equilibrium liquid phase ion concentration, mg/L; qe - the equilibrium solid phase ion concentration, mg/L; n - empirical constant Freundlich; KF - Freundlich constant.

According to Sun et al. (2014), Freundlich model indicates possibility of adsorption on a heterogeneous surface. The values of n indicate degree of nonlinearity between solution concentration and adsorption: n=1 for linear adsorption; n < 1 for chemical process; n > 1 for physical process.

The scanning electron image of the tested activated carbon were obtained by using a Quanta Inspect F scanning microscope, with a field emission gun (FEG) equipped with an EDAX spectrometer with a resolution at MnK of 133Ev (Fig. 2).

Fig. 2. The SEM image of the activated carbon used as

adsorbant

3. Results and discussion The SEM analysis shows the mean size of the

pores of the tested active carbon of 60 μm. The obtained results after contacting the

powder activated carbon with wastewater solutions were expressed as the average of five measurements. pH value was 3.17.

In Fig. 3(a) are presented the efficiency removal values for mixture solution of Pb(II), Zn(II) and COD as indicator for organic compounds, during experiments time (10 minutes and 24 hours). Initial concentration of heavy metals was 80 mg/L for each metal and 100 mg/L for organic compounds.

Also, in Fig. 3(b) equilibrium quantity (qe) for Pb, Zn and COD adsorbed at different time intervals is represented. As it can be seen from Fig. 3(a), tendency for organic compounds (COD) removal is higher than 90% in comparison with Pb (almost 70%) and Zn (higher than 15%). Also, results seem to be keeping the same tendency of removal from 10 minutes to 24 hours. This is the reason for which, the experiments were conducted until 2 hours and after this at 24 hours only an analysis for checking of the results was made. Results regarding the equilibrium quantity adsorbed (qe) onto solid material are presented in Fig. 3(b) where a tendency of retaining by a possible adsorption for organic compounds (as COD) could be observed. The time interval was the same as in the case of efficiency removal evaluation and the quantity was kept at the same values. Also, it can be observed the same tendency of Pb adsorption higher than Zn.

Within these observations, Langmuir model for monostrat adsorption was applied. Results are presented in Fig. 4. From Langmuir isotherm, correlation factors for COD were 0.91 and for Pb was 0.92 in comparison with Zn (0.81). These values indicate a quite well correlation between obtained data and Langmuir model for COD and Pb. It is possible that the adsorption takes place at upper layer of solid material. In accordance with RL values this process could be favorable one. RL are between 0 and 1, thus: COD: 0.004; Pb: 0.09; Zn: 0.43.

(a) (b)

Fig. 3. (a) Efficiency removal (%) for Pb, Zn and COD at different period of time and (b) Equilibrium quantity (qe) for Pb, Zn and COD adsorbed at different time intervals

Evaluation of powdered activated carbon performance for wastewater treatment

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Fig. 4. Langmuir model for Pb, Zn and COD adsorbed onto activated carbon

Freundlich isotherm indicates possibility of a

chemical process for Pb and COD and physical process for Zn, according to the n values. Obtained results are presented in Fig. 5.

Fig. 5. Freundlich model for Pb, Zn and COD adsorbed onto activated carbon

According to the correlation factors for COD

(0.9857), Pb (0.8236) and Zn (0.7649), obtained data are fitted with Freundlich model in case of COD. Values of n that indicate the degree of nonlinearity between solution concentration and adsorption are 0.676 for COD, 0.815 for Pb and 1.245 for Zn. In these conditions, Freundlich isotherm indicates a chemical process for Pb and COD (n < 1) and a physical process for Zn (n > 1). Also, KF values of 0.97 for Pb, 1.44 for COD and 0.88 for Zn indicate a greater adsorption capacity for COD and Pb in comparison with Zn.

For comparision in Fig. 6 are presented the results for Pb(II) removal from wastewater samples for a contact time between 10 minutes and 24 hours in presence of organic compounds (Pb1) and organic compounds and zinc (Pb2). The process became important in the first 10 minutes and the results for different concentration of Pb, Zn and COD were in accordance with two adsorption models, Langmuir and Freundlich. The maximum adsorbed quantity of Pb(II) by the tested activated carbon is presented in Fig. 7.

Fig. 6. The activated carbon wastewater treatment efficiency for Pb(II) removal during the experiments

Fig. 7. Maximum quantity of lead adsorbed by the activated carbon

In Fig. 8 are presented the results for Zn(II)

removal from wastewater samples for a contact time between 10 minutes and 24 hours in presence of organic compounds (Zn1) and organic compounds and lead (Zn2).

Fig. 8. The activated carbon wastewater treatment efficiency for Pb(II) removal during the experiments

Zn removal efficiency was 15.96% after 10

min and increases to 23.42% during 24h of study. After 24h, zinc removal efficiency is slightly lower in case of Pb(II) presence. Also, in Fig. 9 is presented the maximum quantity of zinc adsorbed in presence of organic compunds (Zn1) and organic compunds and lead (Zn2).


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Fig. 9. Maximum quantity of zinc adsorbed by the activated carbon

Chemical oxygen demand (COD) is an

important parameter regarding organic compounds content for aqueous solutions. It can be observed that the tendency of organic compounds removal is higher than for Zn(II) about 6 times and almost 1.28 times in comparison with Pb(II). In conclusion, the highest efficiency removals decrease in the following order: COD (as benzene, toluene) > Pb >Zn. Based on the experimental data we sustain the application of the powdered carbon as adsorbents for removal of lead, zinc, benzene and toluene from aqueous solutions. 4. Conclusions

Our research was based on the investigation of powdered activated carbon adsorption capacity for removing Pb(II) and Zn(II) from synthetic aqueous solutions in the presence of two organic pollutants (benzene and toluene).

The performance of the activated carbon for the removal of organic compounds was higher than for Zn(II) about 6 times and almost 1.28 times in comparison with Pb(II). The obtained experimental data sustain the application of powdered carbon as adsorbents for removal of lead, zinc, benzene and toluene from aqueous solutions.

References Berar (Sur) I.M., Micle V., Avram S., enil M., Oros V.,

(2012), Bioleaching of some heavy metals from polluted soils, Environmental Engineering and Management Journal, 11, 1389-1393.

Chaudhary D.S., Vigneswaran S., Jegatheesan V., Ngo H.H., Moon H., Shim W.G., Kim S.H., (2003), Granular Activated Carbon (GAC) adsorption in tertiary wastewater treatment: experiments and models, Water Science and Technology, 47, 113-120.

Chen X., Xiong C., Yao C., (2014), Evaluation of the adsorption of copper (II) from aqueous solution by D151 resin, Environmental Engineering and Management Journal, 13, 783-791.

Ignat M., Fortuna M.E., Sacarescu L., Zaltariov M.-F., Harabagiu V., (2015), PNiPAM-functionalized mesoporous carbon for the adsorption of vitamin B2, Environmental Engineering and Management Journal, 14, 607-615.

Kouachi R., Apostol D.G., Costache C., Constantinescu I., (2010), Study of precipitates growth in coagulation-flocculation based on inorganic commercial coagulants, Environmental Engineering and Management Journal, 9, 1547-1553.

Matei E., Predescu A.M., Predescu A., Vasile E., (2011), Characterization and testing of the maghemite nanoparticles used for removal of hexavalent chromium from aqueous synthetic solutions, Environmental Engineering and Management Journal, 10, 1711-1717.

Modrogan C., Apostol D.G., Butucea O.D., Miron A.R., Costache C., Kouachi R., (2013), Kinetic study of hexavalent chromium removal from wastewaters by ion exchange, Environmental Engineering and Management Journal, 12, 929-935.

Robescu D., Jivan N., Robescu D., (2008), Modelling chlorine decay in drinking water mains, Environmental Engineering and Management Journal, 7, 737-741.

Segneanu A.-E., Bandas C., Grozescu I., Cziple F., Slavici T., Sfirloaga P., (2013), Hybrid materials for the removal of organic compounds from water, Environmental Engineering and Management Journal, 12, 1071-1079.

Sun J., Li Y., Liu T., Du Q., Xia Y., Xia L., Wang Z., Wang K., Zhu H., Wu D., (2014), Equilibrium, kinetic and thermodynamic studies of cationic red X-GRL adsorption on grapheme oxide, Environmental Engineering and Management Journal, 13, 2551-2559.

Syafalni S., Ismail A., Irvan D., Chan K.W., Genius U., (2012), Treatment of dye wastewater using granular activated carbon and zeolite filter, Modern Applied Science, 6, 37-51.

Ungureanu G., Santos S., Boaventura R., Botelho C., (2015), Biosorption of antimony by brown algae, Environmental Engineering and Management Journal, 14, 455-463.

Digest Journal of Nanomaterials and Biostructures Vol. 6, No 3, July - September 2011, p. 1257-1263

SYNTHESIS AND CHARACTERIZATION OF NiTiO3 AND NiFe2O4AS CATALYSTS FOR TOLUENE OXIDATION

G. A. TRAISTARUa, C. I. COVALIUa*, V. MATEIb2, D. CURSARUb, I. JITARUa aPolitehnica University of Bucharest, Faculty of Applied Chemistry and Material Science; 1-5 Polizu St, 11061Bucharest, Romania bPetroleum-Gas University of Ploiesti, Faculty of Petroleum and Petrochemistry, Department of Petroleum engineering and Petrochemistry – Bucharest Boulevard, no. 30, 100680, Ploiesti, County of Prahova, Romania This paper presents the synthesis of nickel titanate and nickel ferrite by nonconventional procedures. Nickel titanate was obtained by autocombustion method using titanium isopropoxide – nickel nitrate-alanine system and nickel ferrite was obtained by co-precipitation method in Fe(NO3)3-Ni(NO3)2-NH4OH system. Both mixed oxides were characterized by FT-IR spectroscopy, X-ray diffraction, scanning electron microscopy (SEM) and catalytic activity tests. The catalytic activities were measured for toluene oxidation. (Received July 15, 2011; accepted August 26, 2011) Keywords: Nickel titanate, Nickel ferrite, Ilmenite structure, Catalytic tests, Toluene oxidation

1. Introduction The catalytic combustion, compared to an incineration process is one of the most

interesting technologies, from the economical point of view, for the destruction of volatile organic compounds (VOCs) emissions. Indeed, VOCs catalytic oxidation occurs at much lower temperatures than those needed for thermal oxidation. Moreover, there is no associated pollution by dioxins and NOx as they are exclusively formed under high temperature conditions [1-3].

Transition metal oxides are known for their capacity to catalyze the oxidation of hydrocarbons. In the last two decades, efforts have been spent on the activation and the fuctionalization of hydrocarbons catalyzed by mixed metal oxides [1-3].

The ilmenite type catalysts, such as nickel titanate have a good activity for the steam reforming reaction and have a structure relatively stable at various temperatures, towards CO2 and H2O and under oxidative conditions [1-3]. The use of these oxides for the purification of VOCs, such as toluene, total combustion of hydrocarbons for energetic conversion and reduction of nitrogen oxides (NOx) and automotive emission make them catalysts of futures. These systems are potential substitutes of catalysts containing platinic metals on different supported materials, like alumina, silica, in the total oxidation reaction of the hydrocarbons [4-6].

The main challenge in developing ilmenite catalysts is to obtain them with sufficiently high surface areas. The preparation of an ilmenite oxide involves a solid-state reaction of its precursors to form the characteristic ABO3 structure [4-6]. This requires a significant exposure of the oxide precursors to high temperatures, thus leading to a low specific surface area of the catalyst. To circumvent this limitation, a number of alternative preparation methods have been tested, in an attempt to lower the firing temperature for ilmenite oxide synthesis [6-9].

* Corresponding author: [email protected]

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This paper presents a comparison study of the catalytic activities on toluene oxidation of nickel titanate (obtained by autocombustion method) and nickel ferrite (obtained by co-precipitation method).

2. Materials and methods

Ti(OCH(CH3)2)4, Ni(NO3)2·6H2O, Fe(NO3)3 9H2O were purchased from Aldrich. NH3, C3H7OH and C6H5CH3 were purchased from S.C. Chimexin S.A. All reagents were used without further purification.

The NiTiO3 was obtained by the autocombustion procedure using a system formed by Ti(OCH(CH3)2)4 - Ni(NO3)2·6H2O - C3H7NO2 in molar ratio 1:1:20 in isopropyl alcohol solution. The amount of alanine (fuel) added in the mixture was established on the basis of a simple valence balance of the oxidizer (nickel nitrate) and reducer (alanine) components of the mixture. The solution of nitrate, isopropoxide and alanine was heated at 2000C on a sand batch in a capsule. Dark green product obtained was calcined at 6000C/3h .

NiFe2O4 was obtained by co-precipitation method, from Fe(NO3)3 9H2O-Ni(NO3)2 6H2O in a 2:1 molar ratio at pH = 12 obtained by adding ammonia 25% as precipitation agent. The reaction mixture was kept under reflux at 800C for 3 h, until a black precipitate was formed. After the purification process which implies washing five times with water and ethanol (10:1), the precursor was calcined at 6000C for 3 h in order to obtain a single phase NiFe2O4 powder.

Nickel titanate and nickel ferrite powders obtained by the precursors calcination at 6000C for 3h were characterized by FT-IR, XRD and SEM analyses.

Thermal decomposition of the catalysts was investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) in Netzsch 449C STA Jupiter apparatus. Samples were placed in open alumina crucible and heated with 10oC min-1 from room temperature to 900oC, under the flow of 10 mL min-1 in air. The specific surface areas were measured in Carlo Erba Sopty 1750 apparatus by using Brunauer-Emmet-Teller (BET) method with nitrogen at 77K. The oxide powders were analyzed by X-ray diffraction (XRD) on D8 Discovery Bruker diffractometer, using CuK (1.5406 Å) radiation with 30 mA and 40 kV in the 2 = 10–800 range with a scan rate of 100/ min. The Fourier transform infrared spectra (FTIR) were recorded using the KBr pellet technique on a Bruker Tensor 27 spectrometer in the 400-4000 cm-1 range. Morphological characterization was performed by scanning electron microscopy (SEM) in a HITACHI S2600N apparatus coupled with EDAX.

3. Results and discussion

Thermal analysis The TG-DSC analysis of NiTiO3 precursor revealed a complex process of decomposition

consisting in burning of reaction products and the reorientation of the lattice (fig.1). As it can be seen from the TG curve in temperature range of 1200C-1400C there is a loss mass of about 10% probably assigned to water molecules. The weight loss of about 20% in 200-450°C temperature range can be assigned to the thermal decomposition of organic compound (isopropoxide) molecules. The reorientation of the lattice took place between 4500-6000C temperature range and

finally the formation of crystalline NiTiO3 phase was observed at about 6000C.

Fig. 1. TG-DSC-DTG analysis of the NiTiO3 precursor obtained by autocombustion method

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X-ray diffraction analysis of obtained mixed oxides

Fig.2. XRD pattern of NiTiO3sample Fig.3. XRD pattern of NiFe2O4 sample

The XRD data of NiTiO3 powder sustain its ilmenite structure with rhombohedral symmetry (Fig.2). The calculated lattice constants are a = 5.03210 , b = 5.03210 , c = 13.79240

(JCPDS 75-3757). The average crystallites sizes of powders have been calculated by Scherer’s formula: d= k / cos where d is the crystallite size, assuming spherical particles, k=0.9, is the wavelength of radiation, is the full width at half maximum (FWHM) of the diffracted peak and is the angle of diffraction. The average crystallites size was estimated at 45 nm.

The XRD pattern presented in figure 3 corresponds to NiFe2O4 with spinel structure and cubic symmetry (JCPDS card 74-6507). The average crystallites size was estimated at 50 nm. The calculated lattice constants are: a = 8.28800 , b=8.28800 , c=8.28800 (JCPDS 74-6507). FT-IR analysis

The curves exhibiting the FE-IR spectrum are shown in Fig. 4 and 5

Fig.4. FT-IR spectrum of NiTiO3

The characteristic vibration bands corresponding to metal-oxygen bonds are in the range of 400-800 cm-1 in the FTIR spectra of oxide powders. The FT-IR spectrum of the nickel titanate powder (Fig.4.) presents a large splitted band at 500cm-1characteristic for Ni-O bond and a second band at 575cm-1 assigned to Ti-O bond.

Fig.5. FT-IR spectrum of NiFe2O4

At 609cm-1 appears the characteristic band of NiFe2O4, corresponding to the Fe-O bond

(fig.5). At 500 cm-1 appears the other characteristic band of NiFe2O4 corresponding to the Ni-O bond.

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SEM analysis of mixed oxides

Fig.6.a) SEM micrograph for NiTiO3 Fig.6.b) SEM micrograph for NiFe2O4

The morphology of NiTiO3 and NiFe2O4 powders, calcined at 6000C/3h, were evaluated by scanning electron microscopy (SEM) and were illustrated in Figs.6a and 6b. A higher tendency of the particles to form agglomerates it was observed in the case of NiFe2O4 (Fig.6a). Both samples present spherical shape particles. The average particles size is 45 nm for NiTiO3 and 50 nm for the NiFe2O4 and the average aglomerates size is 100 nm for NiTiO3 and 110 nm for the NiFe2O4.

Fig.7. EDAX for NiTiO3 calcined at 6000C/3h

Further evidence for the formation of NiTiO3 came from EDAX spectrum (fig.7). The EDAX analysis shows characteristic peaks and the composition of the NiTiO3 powder.

Catalytic tests on toluene oxidation Catalytic combustion of toluene on the obtained catalysts were carried out at

atmospheric pressure in a fixed-bed quartz tubular reactor with an inner diameter of 10 mm. Micro-pilot plant used in laboratory experiments consists in a quartz reactor, the reactor electric heating system, control system and automatic recording of temperature, feeding and dosing system for liquid hydrocarbons, condensation and cooling system and reaction by products capture system and dosing of CO2. An amount of catalyst was placed in the middle of the reactor, and a thermocouple was inserted near the outlet of the catalyst. Prior to the reaction, the catalyst was activated under air flow at 600°C for 2 h. After the catalyst bed was cooled to 100 °C, a reactant mixture consisting of 0.0625cm3/min toluene and 160cm3/min O2 was feed to the reactor by bubbling air at a rate of 800cm3/min. The temperature ramp of 5°C/min was considered to be sufficiently slow to reach a pseudo-steady state at every point. At the exit of condenser-separator, a bubbler with Ba(OH)2 saturated solution was attached and catalytic activity efficiency (CO2 conversion) was determined.

The catalytic reactions were investigated in 220-6000C range for NiTiO3 and 270-5300C range for NiFe2O4. Five experiments were made on nickel titanate catalyst at five different

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temperatures for establishing the minimum temperature at which the total combustion appears (Table 1). At the beginning of all the experiment were observed induction periods. These induction periods are levels of temperatures that are followed by pronouncedly increase of reaction temperature for NiTiO3. The reactions were investigated in 220-6000C range. The data presented in Table 1 show that the combustion was totally advanced and the higher efficiency was obtained in the 360-6000C temperatures range.

Table 1. The operation data and material balance for toluene oxidation on nickel titanate catalyst

Flow (cm3/min) Exp. no.

Reactor

feed

Ti ºC

Tf ºC

Toluene

Air

O2

BaCO3 precipitation

(g)

CO2

theoretical

CO2

practical

CO2

% 1 T+air 220 600 0,044 800 168 3,4743 0,0723 0,0176 24,42 T+air 310 600 0,049 800 168 2,8541 0,1052 0,0144 13,73 T+air 360 600 0,041 800 168 1,8665 0,0130 0,0094 72,14 T+air 400 600 0,046

800 168 1,8343 0,0460 0,0092 20,2

5 T+air 450 600 0,041 800 168 1,7243 0,0263 0,0087 33,2

The catalytic activities for different samples of NiTiO3 were appreciated based on the

starting temperature of the oxidation reaction and also based on the variation of the reaction temperature with the reaction time.

Table 2. The operation data and material balance for toluene oxidation on nickel ferrite catalyst

Flow (cm3/min) Exp. no.

Reactor

feed

Ti ºC

Tf ºC

Toluene

Air

O2

BaCO3 precipitation

(g)

CO2

theoretical

CO2

practical

CO2

%

1 T+air 270

300 0,046

800

168 - - - -

2 T+air 300

360 0,043

800

168 0,7284 0,0656 0,0036 5,48

3 T+air 350

390 0,041

800

168 1,2832 0,0858 0,0065 7,57

4 T+air 450

530 0,042

800

168 3,5092 0,0783 0,0178 22,7

4

Four experiences were made on NiFe2O4 catalyst obtained by co-precipitation method at four different temperatures (Table 2). The catalytic activity values of NiFe2O4 for toluene oxidation were measured in similar conditions with those for NiTiO3. The maximum feed flows at ambient condition were 0.046cm3/min toluene and 800cm3/min air. The reaction was investigated in 270-5300C range. Using CO2 practical and theoretical values we calculated the conversion yields of toluene oxidation reaction for both compounds tested.

1262

0 5 10 15 20 25 30

250

300

350

400

450

500

550

600

650Te

mpe

ratu

re (0 C

)

Reaction time (min)

NiTiO3

E1 E2 E3 E4 E5

-2 0 2 4 6 8 1 0 1 2 1 4 1 62 60

2 80

3 00

3 20

3 40

3 60

3 80

4 00

4 20

4 40

4 60

4 80

5 00

5 20

5 40

Tem

pera

ture

(0 C)

R e a c tio n tim e (m in )

N iF e 2O 4

E 1 E 2 E 3 E 4

a) NiTiO3 b) NiFe2O4

Fig. 6. The variation of temperature with reaction time for toluene oxidation on NiTiO3 (a) and NiFe2O4 (b) catalysts

Metal ions from the oxides have a strong influence on catalyst activity and its oxidizing

action. These experiments aimed to study some aspects of the oxidation reaction of toluene on spinel and ilmenit type oxide catalysts. From the variation of the starting temperatures of the experiments and reaction time were calculated the slopes values which indicates the most efficient catalyst tested. The 15,4 0C/min. slope obtained for NiTiO3 (fig.6.a) indicates a higher activity in comparison with 9,210C/min, obtained for NiFe2O4 (fig.6.b). The yields of toluene oxidation reactions calculated in terms of CO2 formation was 72% for NiTiO3 and 22% for NiFe2O4, respectively.

The best catalytic activity 72,1% (Table 1) was obtained for NiTiO3 because of the large surface area (32,6 m2/g). A much lower catalytic activity was obtained for NiFe2O4 (22%), which has a surface area value of 10,1 m2/g (table 2). Due to large specific surface area the NiTiO3 powder present the best catalytic activity and conversion of CO2 to 72,1%. A large specific surface area, leads to a corresponding catalytic activity.

In addition Fig. 6a shows that NiTiO3 powder has the active temperature window in the low temperature region ranging from 220 up to 600oC. It is advantageous to prepare NiTiO3 powder, compared to other catalysts for VOCs such as zeolites, Pt/Al2O3, PtSn/Al2O3 etc. It is also a technology aim on which researchers are focused to solve VOCs elimination from the air as well as from the industrial waste sources.

4. Conclusions NiTiO3 and NiFe2O4 were obtained by nonconventional methods: autocombustion and co-precipitation, respectively. The NiTiO3 has a higher catalytic activity (72%) with 45nm

average particle size and 32,6 m2/g surface area value in comparison with NiFe2O4 powder, which has an average particle size of 50nm and surface area value of 10,1 m2/g with a catalytic activity of about 22%

The catalytic activity results indicate that the combustion was totally advanced and the higher efficiency was obtained at 360ºC initial temperature for NiTiO3 and 4500C for NiFe2O4 respectively. The results of catalytic properties are preliminary, but attract considerable interest; especially NiTiO3 seems to be a promising and potential catalyst due to its low active temperature.

Aknowledgements The work has been funded by the Sectoral Operational Programme Human Resources

Development 2007-2013 of the Romanian Ministry of Labour, Family and Social Protection through the Financial Agreement POSDRU/6/1.5/S/19.

1263

References

[1] A. V. Murugan, V. Samuel, S.C. Navale , V. Ravi Materials Letters 60, 1791–1792 (2006). [2] M. Epifani, E. Melissano, G. Pace , M. Schiopa, Journal of the European Ceramic Society 27, 115 (2007). [3] M.S. Sadjadi, M. Mozaffari, M.Enhessari, K. Zare, Superlattices and Microstructures 47, 685 (2010). [4] A. Kale, S. Gubbala, R.D.K. Misra, Journal of Magnetism and Magnetic Materials 277, 350 (2004) [5] J.A. Jiang, Q. Ga, Z. Chen, J. Hu, Materials Letters 60, 3803 (2006). [6] Y.K. Sharma, M. Kharkwal, S. Uma, R. Nagarajan, Polyhedron 28, 579 (2009). [7] P. R. Liferovich, R. H. Mitchell, Phys Chem Minerals 32, 442 (2005) [8] N. Kasapoglu, A. Baykal, M. S. Toprak, Y. Koseoglu, H. Bayrakdar, Turk J. Chem. 31, 659 (2007). [9] U.S. Environmental Protection Agency, Integrated Risk Information System (IRIS) on Toluene. National Center for Environmental Assessment, Office of Research and Development, Washington, DC., 1999.

© copyright Faculty of Engineering Hunedoara, University POLITEHNICA Timisoara 325 | Fascicule 4

ANNALS of Faculty Engineering Hunedoara– International Journal of Engineering

Tome XII [2014] – Fascicule 4 [November]

ISSN: 1584 2673 [CD Rom, online]a free access multidisciplinary publication of the Faculty of Engineering Hunedoara

1. Gina Alina TR ISTARU, 2. Cristina Ileana COVALIU, 3. Gigel PARASCHIV,4. Georgios GALLIOS, 5. Valentin VL DU , 6. Drago MANEA, 7. Cristian SORIC

NITRATES IONS EFFICIENT REMOVAL FROM WATERUSING THREE NANOADSORBENTS1. S.C. ENECO Consulting S.R.L, sos. Pantelimon, 247, sector 2, Bucharest, ROMANIA2,3. University Politehnica of Bucharest, Faculty of Biotechnical Systems Engineering, 313 SplaiulIndependentei Street, 060042, Bucharest, ROMANIA4. University Aristotle of Thessaloniki, Department of Chemistry, GR 54124 Thessaloniki, GREECE5 7. INMA Bucharest, 6 Ion Ionescu de la Brad Blv., sect. 1, Bucharest, ROMANIA

Abstract: The increase of the input of nitrogen into environment as a result of human activities caused the increase ofnitrates concentration in surface water. Consequently, the nitrates inputs have exceeded the assimilation and eliminationcapability of the biosphere. Intensive agricultural production, domestic and industrial wastes and atmospheric nitrogenpollution are some of the main sources of nitrate pollution of water. This study presents an efficient way of nitrate ionsremoval from water by using three adsorbants: Pd Sn/ Al2O3, NiTiO3 and NiFe2O4. Also, we describe the preparation ofPd Sn/ Al2O3 by sol gel method starting from Al(OC3H7)3, PdCl2 and SnCl2. The obtained Pd Sn/ Al2O3 was structuraland morphological characterized by scanning electron microscopy (TEM), X ray diffraction (XRD) and BET analysis.Keywords: nitrate ions pollution, adsorbant nanomaterials, water treatment

1. INTRODUCTIONNitrate ions exist naturally in soil and water, but increased levels of nitrates are considered to bepollutant for groundwater and surface waters. In unpolluted areas, water has less than 1 mg/L ofnitrates. Higher levels of nitrates typically correspond to compromised water [1 3]. Nitrate levelsabove the EPA Maximum Contaminant Level of 10mg/L N NO3 or 45 mg/LNO3 may cause methemoglobinemia (also known as blue baby syndrome)in infants [4]. High levels of nitrate ions concentration in drinking water hasthe ability to impaired blood to carry oxygen throughout the body causingcancer, disruption of thyroid function, birth defects and other health risks.Only testing can determine nitrate in water, as nitrate has no taste, odor orcolor [5 7].One of the sources of excess nitrates besides human and animal wastes orindustry comes from agricultural activities. Nitrates are water soluble,easily carried by water and move freely through most soils. As regardingagriculture, nitrogen fertilizers (such as ammonium sulfate, ammoniumchloride, ammonium nitrate, urea etc.) are applied on land surface topromote the growth of plants. During the rainfall or irrigation, ammonia(NH4+) contained by fertilizer can leach into the ground below the rootzone, reaching into the groundwater and rivers converting to nitrates (NO3

) according to the following potential reactions (Fig. 1):NH4+ + 1.5 O2 2H+ + H2O + NO2 (1)

NO2 +0.5 O2 NO3 (2)Nitrate ions concentrations from surface water coming from agriculture are primarily fromgroundwater connections and other subsurface flows. Another agriculture practice which consist

Fig. 1 Schematicpresentation of leachingammonia from fertilizer

to groundwater asnitrates

ISSN: 1584-2673 [CD-Rom, online]

326 | Fascicule 4

of the utilization as fertilizers the animal manure is also a dominant source of nitrate pollution ofwater. Conventional water treatment methods, such as sedimentation, filtration, chlorination orneutralization, do not efficiently remove nitrates from water. Nitrates from water can be removedby specialized water treatment technologies, such as ion exchange, biochemical denitrification,reverse osmosis and so one.In this study we chose to study the removal of nitrates ions from water by adsorption on threedifferent adsorbents.2. MATERIALS AND METHODS2.1. Adsorbent materials preparationThe Pd Sn/ Al2O3 material was obtained in two steps.

Firstly Al2O3 was prepared by sol gel method in the presence of a template agent (lauricacid). The Al(OC3H7)3: C12H24O2 : C4H9OH molar ratio was 1: 0,15: 30. The aluminum precursorand water molar ratio was 1: 1,9. The reaction mixture was kept under reflux at 800C for 100h,until a white precipitate was formed. The precursor was washed several times with alcohol,filtered, dried in air and calcined at 6000C for two hours.

Secondly, the bimetallic material was prepared by sol gel method using the precursor saltsPdCl2 and SnCl2 in an ethylene glycol solution brought to pH 11 by addition of ammonia. ThePd Sn/ Al2O3 material contained 1 wt% noble metal (Pd) and 1 wt% Sn. The mixture wasstirred for 12 h, under reflux and then ammonia and ethylene glycol were removed by washingseveral times with alcohol. After drying overnight at 900C, the material was calcined at 2000Cfor 1h. The material finally obtained was analyzed by scanning electron microscopy (TEM), Xray diffraction (XRD) and BET analysis.

The preparation and characterization of NiFe2O4 and NiTiO3 was published elsewhere [8].2.2. Nitrates analysis methodThe analysis of nitrates from wastewater was determined using a standard method, no. SR ISO7890/3 1998 applied for drinking water, surface water and wastewater. Adsorption experimentswere carried out in Erlenmeyer flasks using a temperature controlled orbital shaker (stirring speedof 200 min 1) for 36h. Twenty miligrams of the adsorbent were contacted with 50 mL of nitratesolution solutions (concentration was 5 mg/L) representing the synthetic polluted water at 20 ±2 C.The nitrates ions adsorption capacity of the three prepared materials was calculated with theformula:

mCeCiVUptake )( (3)

where: Uptake adsorption capacity at time t, the concentration of nitrates retained per unit massof adsorbent materials (mg/L); V volume of solution containing nitrate ions (mL); Ci initialconcentration of the nitrate ions (mg/L); Ce equilibrium concentration (mg/L); m adsorbentweight (mg).In order to investigate the effect of pH on nitrateadsorption, the experiments were conducted in the 210 pH range. The pH of the water solution wasadjusted using 0.1M HCl or 0.1M KOH.3. RESULTS AND DISCUSSION3.1. Characterization of prepared adsorbent materialThe X ray diffraction (XRD) shows the distorsed spinelstructure of Al2O3 (Fig. 2). The characteristicdiffraction peaks observed for bimetallic particles PdSn are: 2 =38.50, 43.0. The average crystallite sizecalculated with the Scherrer formula was 40 nm.

Fig. 2 XRD for Pd Sn/Al2O3

ANNALS of Faculty Engineering Hunedoara – International Journal of Engineering

327 | Fascicule 4

Fig. 3 The adsorption desorption isotherm of the Pd Sn/Al2O3 material

Fig. 4 Pores size distribution of thematerial Pd Sn/ Al2O3

Based on figures 3 and 4 it could be observed that the specificsurface area of the material is Pd Sn/ Al2O3 275m2/g and thevalue of pores diameter is between 2 and 10 nm.The TEM image from figure 5 indicates that the Pd Sn/ Al2O3

mean particle size is of 100 nm.3.2. Nitrate ions adsorption studyIn figure 6 was presented the plot adsorption of nitrate ions onPd Sn/ Al2O3, nickel ferrite and nickel titanate used as adsorbentmaterials. Maximum adsorption capacity of nitrate was obtainedat pH 3.5.The maximum adsorption capacity values were 3.598 mg/L forPd Sn/ Al2O3, 3.176 mg/L for nickel titanate and 3.051 mg/L for nickel ferrite. The adsorption

equilibrium was obtained at pH = 3.5.SIPS isotherm modelThe SIPS isotherm model considers that the adsorptionefficiency is limited at high concentration of ions insolution. The model is similar to the Langmuir isotherm,with the exception of a parameter representingheterogeneous system.The SIPS model reduces to Langmuir s model when = 1.

)(1)(

maxeS

eS

CKCK

QQe (4)

where: eQ – the total adsorption capacity at equilibrium (mg/L); maxQ – maximum adsorptioncapacity of the adsorbent material (mg/L); eC – equilibrium concentration (mg/L); SK adsorptionconstant (dissociation parameter); n number ofvariable parameters (3);The following regression factors were obtained:0.9987 for Pd Sn/Al2O3, 0.9984 for NiTiO3 and0.9982 for NiFe2O4 (Fig.7). The regression factorsshow that the best results regarding nitrate ionsadsorption were obtained for Pd Sn/Al2O3

material. This fact could be explained based on thespecific surface area values are of the threeadsorbant materials: 275m2/g for Pd Sn/ Al2O3,32,6 m2/g for NiTiO3 and 10,1 m2/g for NiFe2O4 [8].

Fig. 5 TEM image of Pd Sn/Al2O3

Fig. 6 Adsorption plot for nitrate anionsfor Pd Sn/Al2O3, NiTiO3 and iFe2O4

Fig. 7 SIPS linear model representationfor nitrate ions adsorption of onto Pd Sn/Al2O3,

NiTiO3 and NiFe2O4

ISSN: 1584-2673 [CD-Rom, online]

328 | Fascicule 4

4. CONCLUSIONSThe experimental results of this study describe the adsoption capacity of Pd Sn/Al2O3, NiTiO3 andNiFe2O4 for nitrates removal from water. The results show that the adsorption effectiveness of PdSn/Al2O3 for nitrate removal was higher in comparison with those of nickel titanate and nickelferrite for a concentration of nitrate tested of 5 mg/L. The specific surface area and the pH valueshave influenced the adsorbtion capacity of the tested materials.REFERENCES[1.] Peña Haroa S., Llopis Albertb C., Pulido Velazquez M., Pulido Velazquez D., (2010), Journal of

Hydrology, 392, Issues 3–4, 15 October, 174–18;[2.] Mohammad Taher Nazami, Intl J Agri Crop Sci. Vol., 4 (19), 1410 1414, 2012;[3.] Traistaru G.A., Covaliu C.I., Gallios G.P., Cursaru D., Jitaru I., (2012), Removal of nitrate from water by

two types of sorbents: Characterization and sorption studies, Rev. Chim. (Bucharest), 63, no.3, 268271;

[4.] U.S. Environmental Protection Agency,(2000), Drinking Water Standards and Health Advisories, USEnvironmental Protection Agency, Office of Water, 822 B 00 001;

[5.] Ying W., Jiuhui Q., Huijuan L., Cheng Z. H., (2007), Adsorption and reduction of nitrate in water onhydrotalcite supported Pd Cu catalyst, Catalysis Today 126 476–482;

[6.] Zingg A., Winnefeld F., Holzer L., Pakusch J., Becker S., Gauckler L., (2008), Adsorption ofpolyelectrolytes and its influence on the rheology, zeta potential, and microstructure of various cementand hydrate phases, Journal of Colloid and Interface Science 323, 301–312;

[7.] Matis K. A., Zouboulis A. I., Gallios G.P., Erwe T., Blocher C.,(2004), Application of flotation for theseparation of metal loaded zeolites, Chemosphere 55 65–72;

[8.] Traistaru G. A., Covaliu C. I., Matei V., Cursaru D., Jitaru I., Digest Journal of Nanomaterials andBiostructures Vol. 6, No 3, 2011, p. 1257 1263.

ANNALS of Faculty Engineering Hunedoara – International Journal of Engineering

copyright © UNIVERSITY POLITEHNICA TIMISOARA, FACULTY OF ENGINEERING HUNEDOARA,5, REVOLUTIEI, 331128, HUNEDOARA, ROMANIA

http://annals.fih.upt.ro

1

Characterization and Application Results of Two Magnetic Nanomaterials

The presence of toxic heavy metals in surface waters and wastewaters represents a severe environmental and public health problem. The effluents discharged from

different industrial processes contain high concentrations of dis-solved metals, which have to be reduced according to legislative standards (Lo et al., 2009). One of the most efficient technolo-gies for reducing the concentration of heavy metals is through adsorption using different types of adsorbents, activated C being one of the most commonly used adsorbents (Manuel et al., 1995). Due to developments in nanotechnologies, nanoscale materials have been developed for wastewater treatment and soil remediation (Lo et al., 2009).

Recently, researchers have used magnetic Fe oxides at the nanometric scale to remove toxic heavy metal ions and organic pollutants from water (Liang et al., 2009). This is because magnetic Fe oxide nanoparticles possess not only strong adsorption capacities but also the capacity of being easily separated and collected by an external magnetic field (Booker et al., 1991; Orbell et al., 1997: Wang et al., 2009). Adsorption activity by magnetite nanoparticles for many heavy metal ions have been reported in the literature (Oliveira et al., 2003; Hu et al., 2004; Banerjee and Chen, 2007). Research regarding adsorption of Cr(VI) from single-component solutions onto magnetite nanoparticles has also been reported (Hu et al., 2004, 2005; Matei et al., 2011a). Recent studies have reported favorable responses of magnetite nanoparticles for the adsorption or reduction of several toxic metal ions (e.g., Ni�� , Cu2+, Cd2+, Zn2+, and Cr6+) and the catalytic degradation of some organic contaminants (Yuan et al., 2010). Metal ions (Cu2+, Ni2+, and Cr6+) from multicomponent solution were adsorbed with good results onto magnetite nanoparticles under acidic or basic conditions (Lo et al., 2009).

In addition, the preparation of coated nanoscale Fe oxides has gained attention recently. For example, zero-valent Fe nanoparticles supported on cellulose acetate for the dechlorination of trichloroethylene in water highlighted the successful preparation of reactive membranes by incorporation

Abbreviations: EDS, energy dispersive X-ray spectra; PAA, sodium alginate; SEM, scanning electron microscopy; TEM, transmission electron microscopy; XRD, X-ray diffraction.

Copyright © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.��J. Environ. Qual. 42 doi:10.2134/jeq2012.0147 Received 7 Apr. 2012. *Corresponding author ([email protected]).

Journal of Environmental QualityHEAVY METALS IN THE ENVIRONMENT

TECHNICAL REPORTS

Ecaterina Matei,* Andra Mihaela Predescu, Cristian Predescu, Mirela Gabriela Sohaciu,Andrei Berbecaru,and Cristina Ileana Covaliu

The toxicity of heavy metals for the environment can be solved by using of adsorption properties of magnetic nanomaterials. These types of nanomaterials can remove pollutants, especially from wastewaters. This study was conducted to determine whether two magnetic nanomaterials can be used as adsorbents for heavy metals (Cr, Cd, Cu, Zn, and Ni) from aqueous solutions under acidic conditions. Qualitative and quantitative elemental information and structural and surface characteristics before and after use as adsorbents were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The obtained data showed a good correlation with the Langmuir adsorption model using the two magnetic nanomaterials in aqueous solutions. The crystalline structure of the Fe3O4 powder was identified

with XRD. The TEM images of Fe3O4 nanoparticles indicated a good dispersion of particles of 85.5 nm. The SEM analysis for Fe3O4–PAA (magnetite covered with sodium alginate) showed spherical particles of magnetite wrapped into the polymer with dimension of ~200 nm. According to the adsorption Langmuir model, the removal efficiency for uncoated Fe3O4 decreased in order: Cr(VI) > Cu(II) > Zn(II) > Ni(II) > Cd(II). For the Fe3O4–PAA nanocomposite (45% w/w Fe in a mass of polymer), the adsorption phenomena appears as follows: Cr(VI) > Cd(II) > Cu(II) ~ Zn(II) > Ni(II). Langmuir parameters indicated a favorable monolayer adsorption at pH 2.5. The nanocomposite Fe3O4–PAA can be used as an adsorbent with the same performance as uncoated Fe3O4 but with the advantage of stability under conditions where industrial wastewaters have an acidic pH.

E. Matei, A.M. Predescu, C. Predescu, M. G. Sohaciu and A. Berbecaru, Faculty of Materials Science and Engineering, Univ. Politehnica of Bucharest, 313 Splaiul Indepedentei, 060042 Bucharest, Romania; and C.I. Covaliu, formerly Faculty of Chemistry and Material Science, Univ. Politehnica of Bucharest, 1-7 Polizu Street, 011061 Bucharest, Romania; currently Faculty of Biotechnical Systems Engineering, Univ. Politehnica of Bucharest, 313 Splaiul Indepedentei, 060042 Bucharest, Romania. Assigned to Associate Editor Andrew Tye.

2 Journal of Environmental Quality

of Fe(0) nanoparticles into cellulose acetate films. The Fe(0) nanoparticles were synthesized in a water–oil microemulsion, mixed with a cellulose acetate–acetone solution, and then formed into a porous membrane by phase inversion (Diallo and Savage, 2005).

In this study, two nanoscale products were synthesized: magnetite (Fe3O4) and a composite (magnetite covered with sodium alginate, denoted as Fe3O4–PAA). These products were used as adsorbents for Zn, Cd, Cu, Cr, and Ni from aqueous solutions. The dissolution capacity of Fe from uncoated Fe3O4 nanoparticles (average size of 7 nm) under acidic conditions has been reported, showing that ?40% of the Fe was dissolved (Matei et al., 2011a, 2011b). Sodium alginate is known as a flocculation additive with a high efficiency for removal of some pollutants such as Cd, Zn, Cu, Ca, and Pb from wastewater (Fourest and Volesky, 1997). By combining the two compounds to obtain a nanoscale composite, information regarding heavy metal removal under acidic conditions can be obtained when the tendency for Fe to dissolve from uncoated Fe3O4 is decreased. The adsorption experiments were conducted at pH 2.5 to obtain the appropriate conditions of acidic wastewater released from the iron and steel industries and from acid mine drainage treatment. The experimental data were correlated to the Langmuir adsorption model to evaluate the adsorption capacity of the two magnetic adsorbents.

Materials and MethodsAdsorbent PreparationSynthesis of Magnetite Nanoparticles

The magnetite nanoparticles were prepared by the conventional coprecipitation method. All commercial reagents were pure analytical grade (Merck). Distilled water was used. 0.4 mol/L Fe(NO3)3 9H2O and 0.4 mol/L FeCl2 9H2O were mixed at a molar ratio of 1:2 in the presence of 0.5 mol/L NaOH at room temperature.

The pH of the reaction mixture was maintained at 10 for 3 h. The precipitate formed was separated by centrifugation and washed several times with distillated water. The final pH was 7.

Synthesis of Magnetite–Sodium Alginate NanocompositeThe Fe3O4–PAA composite was produced by adding

synthesized Fe3O4 (45% w/w theoretical content of Fe3O4 in the composite) to 5% sodium alginate solution. The suspension was homogenized by mechanical stirring for 48 h at room temperature and the uncoated nanoparticles were separated by centrifugation. The water from the polymeric suspension was removed by rotary evaporation. The Fe content of the nanocomposite was established after mineralization of the polymer with 4:1 HNO3/HClO4, evaporation at 100 C, and dissolution into 37.5% HCl. The value obtained represents the Fe in the mass of polymer as a percentage and is the average of three replicates.

Adsorbents CharacterizationThe materials used as adsorbents, Fe3O4 and Fe3O4–PAA,

were characterized by X-ray diffraction (XRD) and transmission (TEM) and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectra (EDS) methods. A Panalytical

X’Pert PRO MPD X-ray diffractometer with high-intensity Cu–K radiation ( = 1.54065 Å) and 2 range from 10 to 90° was used to obtain XRD patterns. To evaluate the average dimension of the crystallites, the Debye–Scherrer equation was used (Milev et al., 2008):

Cu K

cos FWHMK

D [1]

where D is the crystallite dimension, K is a coefficient (0.89), Cu-K is the wavelength of the radiation from the diffraction

tube, FWHM is the full width at half maximum of diffraction in the 2 scale (rad), and is the diffraction Bragg angle.

The TEM images were obtained on a TECNAI F30 G2STWIN high-resolution transmission electron microscope with 1-Å line resolution. The SEM investigations were performed on a Quanta INSPECT F scanning electron microscope equipped with a field emission gun at a resolution of 1.2 nm and EDS with a resolution for Mn–K of 133 eV.

Adsorption ExperimentsAll stock standard solutions for Ni, Zn, Cd, and Cu were

prepared from Merck reagent-grade solutions by dissolving into ultrapure water. The Cr solution was prepared by dissolving reagent-grade K2CrO4 into ultrapure water. Each stock solution had an initial concentration of 1000 mg/L, and the pH was adjusted by adding HCl (0.1 mol/L). The adsorption studies were performed by measuring the initial and final concentrations of the metal on a GBC 932 AB Plus spectrometer (flame atomic absorption spectrometry) with spectral domain between 185 and 900 nm. For Cr(VI), a Cintra 202 GBC spectrophotometer, with spectral domain between 190 and 1000 nm was used. Each concentration of metal had five replicates. The values used to calculate the removal efficiency are the average values resulting from the five replicates associated with each metal.

The efficiency of removal (Ozmen et al., 2010) was calculated as

0 e

0100

C CC

[2]

where C0 is the initial concentration (mg/L) and Ce is the equilibrium concentration (mg/L).

The equilibrium concentration was considered to be the final concentration when no variation occurred. The adsorbed metal amount at equilibrium is given by the ratio between the adsorbed metal (mg) and adsorbent mass (g) expressed as qe (Wang et al., 2009) according to

0 ee

C C Vq

m [3]

where V is the volume of the solution (L) and m is the adsorbent quantity (g).

The quantities of adsorbents used were 0.5, 0.1, and 0.2 g. The concentration of metal ions in the synthetic solutions varied between 20 and 100 mg/L after mixing each quantity of adsorbent with each solution consisting of all metal ions at room temperature (21.5 C). The contact time between adsorbent and solution was between 10 and 100 min at pH adjusted to 2.5 using 0.1 mol/L HCl. The adsorbent samples were recovered by

magnetic separation. The Langmuir adsorption isotherm (Santhi et al., 2010) was used to correlate the adsorption data:

ee

e m m

1 1C Cq q q b

[4]

where Ce is the aqueous concentration at equilibrium (mg/L), qe is the adsorbed amount at equilibrium (mg/g), and qm and b are constants related to the adsorption capacity and the affinity coefficient, respectively.

The fundamental characteristics of the Langmuir equation can be interpreted in terms of a dimensionless constant separation factor (RL), defined by Hall et al. (1966) and others (Al-Rub et al., 2002; Ho and McKay, 1999; Hu et al., 2007; Lo et al., 2009) as

Lo

11

RbC

[5]

where b is the Langmuir constant and C0 is the highest initial concentration of metal.

The dimensionless separation factor, RL, can predict the affinity between the sorbate and sorbent (Hu et al., 2007). The value of RL indicated the type of Langmuir isotherm (Table 1).

Results and DiscussionAdsorbent Characterization

The crystalline structure of the Fe3O4 powder was identified with XRD, as can be seen in Fig. 1a, with maximum intensity of peak diffraction at 35.44 for 2 . The XRD pattern shows a spinel structure for Fe3O4, according to ICDD File 75-1610 (International Centre for Diffraction Data).

Stability of the crystalline phase of Fe3O4 during polymer coating can be observed in Fig. 1b, where characteristic peaks for Fe3O4 are maintained. Also, the influence of the amorphous phase from sodium alginate on the diffraction patterns can be seen between 10 and 50 as a specific increase of the background reading. By applying Eq. [1] to the two synthesized adsorbents, the average crystallite size was found to be similar. For uncoated

Fe3O4, the average size was 79.34 nm, and for Fe3O4–PAA it was 76.35 nm. This is because Eq. [1] provides information only for the crystalline phase and the amorphous phase of sodium alginate is not calculated.

The TEM image of Fe3O4 nanoparticles in Fig. 2a indicates good dispersion. The selected area electron diffraction image from Fig. 2b confirmed that Fe3O4 was single phase. The rings of diffraction spots in Fig. 2b correspond to the crystalline planes with characteristic Miller indexes (h–k–l) for the Fe3O4 compound (according to ICDD File 75-1610). The average size of the particles was found to be 85.5 nm (Fig. 3).

The SEM analysis for Fe3O4–PAA showed spherical particles of magnetite wrapped into the polymer with a dimension of about 200 nm, as shown in Fig. 4a. The mapping of the elements and an EDS spectrum are shown in Fig. 4b.

Also, the EDS spectrum from Fig. 4b for Na, O, and Fe elements from the analyzed composite indicate a uniform distribution of the elements. The differences found between the Debye–Scherrer equation by XRD (Eq. [1]) and SEM analysis for Fe3O4–PAA are possibly due to the amorphous structure of the polymer (sodium alginate).

Batch Adsorption StudiesThe theoretical Langmuir isotherm is used for adsorption

of a solute from a liquid solution as monolayer adsorption onto a surface containing a finite number of identical sites. The Langmuir isotherm model assumes uniform energies of adsorption onto the surface without transmigration of adsorbate in the plane of the surface. The Langmuir isotherm model was chosen to allow an estimation of the maximum adsorption

Table 1. Characteristics of adsorption Langmuir isotherms as described

Hall et al. (1966) indicating affinity between the sorbate and sorbent

depending on the separation factor, RL.

Separation factor Characteristics of adsorption

RL > 1 unfavorableRL = 1 linear0 < RL < 1 favorableRL = 0 irreversible

Fig. 1. X-ray diffraction patterns (Cu–K radiation) for (a) uncoated Fe3O

4 and (b) Fe

3O

4 covered with sodium alginate (PAA), with crystalline plane

(h–l–k) indicating the presence of magnetite and polymer as an amorphous phase.


capacity corresponding to complete monolayer coverage on the adsorbent surface (Santhi et al., 2010).

The adsorption isotherms for Zn, Cd, Cu, Cr, and Ni onto 0.05, 0.1, and 0.2 g of Fe3O4 and Fe3O4–PAA were calculated using Eq. [4] and [5]. The efficiency of removal of Cr(VI), Cu(II), Zn(II), Ni(II), Cd(II) at various concentrations (20, 50, and 100 mg/L) by adsorption onto different adsorbent quantities (0.05, 0.1, and 0.2 mg/L) between 10 and 100 min was evaluated according to Eq. [2]. The percentages of metal removal decreased with an increase in the initial concentration of metals for both Fe3O4 and Fe3O4–PAA (Table 2).

It can be seen that the maximum efficiency was up to about 80% for Cr(VI) and between 74 and 79% for the other metals. For uncoated Fe3O4, the removal efficiency decreased in the order: Cr(VI) > Cu(II) > Zn(II) > Ni(II) > Cd(II). Adsorption can be explained by the point of zero net charge (PZNC) of magnetite being 6.5 (Pang et al., 2007). Below this value, the adsorbent surface is more positively charged, and anions are adsorbed by electrostatic attraction. Above this PZNC value, the adsorbent surface is more negatively charged, and the metal ions are adsorbed on the magnetite. The uptake of Cr(VI) ions will decrease with an increase in pH because, in the aqueous phase, the surface of the metal oxides is covered with hydroxyl groups

that vary at different pH values (Hu et al., 2005; van Loon and Duffy, 2005). According to Lo et al. (2009) and Hu et al. (2005), the available sites for nanoparticles are mostly present on the surface and, based on this assumption, a larger surface area will provide more sites for adsorption.

With respect to the Fe3O4–PAA nanocomposite (45% w/w Fe in a mass of polymer) the adsorption phenomena appears as follows: Cr(VI) > Cd(II) > Cu(II) ? Zn(II) > Ni(II) (Table 2). Adsorption can also be due to ionic exchange between Na ions from the polymer structure and metal ions from solution, according to their ionic radius: Cr (0.185 nm) > Cd (0.097 nm) > Cu (0.073 nm) ? Zn (0.074 nm) > Ni (0.069 nm). It was observed that the tendency of binding increased with increasing ionic radius and, for the adsorption process, the heavy metal ions appear to have exchanged with Na ions from the sodium alginate to form a metal alginate. The results indicate that Fe3O4–PAA maintained the removal efficiency for metal ions at approximately the same values as for the uncoated Fe3O4. The values indicate that the nanocomposite Fe3O4–PAA as a good adsorbent for the studied metal ions.

Data regarding the removal of heavy metal ions (Cd, Hg, Pb, and Cr) on alginate have been reported (Al-Rub et al., 2004; Aksu et al., 1999; Tam et al., 1998), but a model of the adsorption of metal from aqueous solution onto various polymeric matrices

Fig. 2. (a) Transmission electron microscopy image and (b) associated

selected area electron diffraction image with crystalline plane for

uncoated Fe3O

4 as agglomerates.

Fig. 3. Dimension distribution for Fe3O

4 (average size: 85.5 nm)

determined from the transmission electron microscopy image.

Fig. 4. (a) Scanning electron microscopy image and (b) element mapping by X-ray energy dispersive spectra for magnetite covered with sodium

alginate (Fe3O

4–PAA) with enhancement of Na and O specific for sodium alginate and Fe from magnetite.

is not yet fully developed. It is presumed that the adsorption process is controlled by transfer of the metal ion from the surface to the active sites by internal diffusion, followed by metal ion uptake on the active sites of the adsorbent (Niţă et al., 2007).

The adsorption equilibrium was achieved within 10 min for both Fe3O4 and Fe3O4–PAA. After this time, the rate of metal uptake was the same, being independent of the adsorbate concentration (results not shown). This phenomenon appears to be a result of the monolayer adsorption model, where the total available adsorption sites of adsorbents are saturated with the metal ions. Another important consideration is the quantity of adsorbent used, as presented in Fig. 5. The increasing quantity of the adsorbent, for both Fe3O4 and Fe3O4–PAA, from 0.05 to 0.2 g, did not lead to a significant increase in the adsorption efficiency. It can be seen that the optimum quantity was 0.05 g for the two adsorbents (Fe3O4 and Fe3O4–PAA). This can be explained by the agglomeration of the nanoparticles, in the case of higher quantities of adsorbents (0.1 and 0.2 g), reducing the available surface for metal ion adsorption.

The obtained results were subjected to a statistical analysis between different quantities of adsorbents: 0.05 , 0.1, and 0.2 g of Fe3O4 and Fe3O4–PAA (Table 3). It can be observed from the statistical data that there are similarities between the average qe for Fe3O4 and Fe3O4–PAA at a confidence level of 95%. The presented results are expressed only for 20 mg/L concentrations of each metal according to the data from Table 2, which indicated this concentration as the optimum concentration used for the adsorption tests. This phenomenon indicates a good adsorption capacity of Fe3O4–PAA for metal ions as well as uncoated Fe3O4. Even the results are very similar.

The use of uncoated Fe3O4 can lead to the dissolution of Fe under acidic conditions, especially under industrial conditions where the wastewaters usually have acidic pH values. Under these conditions, the use of a core–shell nanocomposite consisting of Fe3O4 as the core and a polymer such as sodium alginate as the shell can protect the Fe3O4, thus maintaining the magnetic properties of this compound for separation of the nanocomposite. The advantage of using Fe3O4–PAA in the adsorption process under acidic conditions is that dissolution of uncoated Fe3O4 could otherwise occur (Matei et al., 2011b).

Table 2. Removal efficiency (%) of metal ions (Cr, Cu, Zn, Ni, Cd) at different initial concentrations (C0) in mixed solutions by their adsorption onto 0.05,

0.1 and 0.2 g of Fe3O

4 and Fe

3O

4 covered with sodium alginate (PAA).

Metal ion C0

Removal efficiency

Fe3O

4Fe

3O

4–PAA

0.05 g 0.1 g 0.2 g 0.05 g 0.1 g 0.2 g

mg/L ——————————————————————— % ———————————————————————Cr(VI) 20 80.00 79.00 78.00 82.00 80.60 80.40

50 78.12 77.34 76.15 78.10 71.20 72.53100 79.21 75.12 70.26 75.39 69.51 68.91

Cu(II) 20 77.81 76.34 72.10 75.23 72.98 70.5450 75.12 74.14 70.00 72.01 70.23 68.09

100 75.20 73.21 68.01 70.81 67.92 65.03Zn(II) 20 76.20 74.12 71.96 75.87 72.56 69.87

50 75.00 73.00 70.65 72.67 70.11 68.12100 74.98 71.29 67.88 70.45 66.87 64.98

Ni(II) 20 74.10 70.15 69.23 70.12 68.95 65.2350 72.78 68.55 67.12 68.97 66.34 64.20

100 69.13 65.12 64.97 67.23 65.98 64.02Cd(II) 20 70.12 68.34 65.12 76.12 75.34 73.98

50 67.00 65.38 62.86 75.23 74.23 72.10100 65.10 63.28 60.84 74.21 72.87 70.09

Fig. 5. Quantity of metal ions adsorbed onto 0.05, 0.1, and 0.2 g of (a) Fe3O

4 and (b) Fe

3O

4 covered with sodium alginate (PAA) adsorbents.


The values of the coefficient of determination (R2) indicate a good reproducibility of data for different values of the two adsorbents. Stability of the two magnetic nanomaterials was studied under acidic conditions. Different quantities (0.05, 0.1, and 0.2 g) of Fe3O4 and Fe3O4–PAA were added to a solution of 0.1 mol/L HCl (Table 4). It was observed that there was a higher Fe dissolution capacity for the Fe3O4 nanoparticles compared with same quantities of Fe3O4–PAA nanoparticles. The sodium alginate can offer good stability of the nanocomposite.

The fundamental characteristics of the Langmuir equation can be interpreted in terms of a dimensionless constant separation factor RL, according to Eq. [5]. A comparison between the qe and RL parameters (Table 5) suggests a monolayer adsorption that follows the Langmuir model. The RL values indicate a favorable adsorption process, all values being between 0 and 1. The quantity of metal ions adsorbed at equilibrium, according to Eq. [3], qe, was higher in comparison with another nanoscale

magnetic adsorbent studied, -Fe2O3, under the same conditions, for which the qe values were 15 mg/g for Cu (II), 12.75 mg/g for Zn (II), 10.9 mg/g for Ni (II), and 19.16 mg/g for Cr(VI) (Matei et al., 2011b).

Langmuir isotherms for adsorption of metal ions are presented in Fig. 6. The plot of Ce/qe vs. Ce, according to Eq. [4], at different concentrations is linear, indicating the possibility of application of this classical adsorption isotherm to this adsorbate–adsorbent system. The calculated R2 values from Fig. 6 are all >0.99, suggesting a strong linear relationship between Ce/qe and Ce. The high values for RL indicate the greater affinity of metal ions for nanoparticles and a favorable adsorption of these metals.

Table 3. Statistical analysis comparing 0.05, 0.1, and 0.2 g of adsorbent (Fe3O

4 and Fe

3O

4 covered with sodium alginate [PAA]) in mixed solutions

containing 20 mg/L of each metal ion (Cr, Cu, Zn, Ni, and Cd).

Parameter

Data analysis for adsorption process at different quantities of adsorbent

0.05 g 0.1 g 0.2 g

Fe3O

4Fe

3O

4–PAA Fe

3O

4Fe

3O

4–PAA Fe

3O

4Fe

3O

4–PAA

Cr(VI)

Avg. qe†, mg/g 31.072800 31.511400 15.986900 15.652900 7.858300 7.778850SD 1.302505 1.189946 0.633694 0.579208 0.280872 0.283567Confidence level (95.0%) 0.931756 0.851236 0.453318 0.414340 0.200923 0.202852R2 0.997100 0.997200 0.998300 0.998100 0.997600 0.998500

Cu(II)

Avg. qe, mg/g 31.346250 30.874800 15.661875 15.501900 7.852875 7.758800SD 1.286563 1.174601 0.603969 0.561482 0.371228 0.282073Confidence level (95.0%) 1.075593 0.840259 0.504931 0.401660 0.310354 0.201783R2 0.999100 0.998700 0.998400 0.998600 0.998600 0.998200

Zn(II)


Ni(II)


Cd(II)


† qe is the adsorbed metal amount at equilibrium, given by the ratio between adsorbed metal (mg) and adsorbent mass (g).

Table 4. Dissolved Fe content from 0.05, 0.1, and 0.2 g of Fe3O

4 and

Fe3O

4 covered with sodium alginate (PAA) nanoparticles under acidic

conditions in the presence of 0.1 mol/L HCl to evaluate the stability of

the nanoparticles.

Magnetic

nanomaterial

Dissolved Fe content

0.05 g 0.1 g 0.2 g

————————— % —————————Fe3O4 1.96 5.24 8.59Fe3O4–PAA 0.09 0.85 3.05

Table 5. Langmuir parameters, the adsorbed amount at equilibrium

(qe) and the dimensionless separation factor R

L, for adsorbed metals

onto Fe3O

4 and Fe

3O

4 covered with sodium alginate (PAA) to evaluate

monolayer adsorption processes.

Metal

Langmuir parameters

Fe3O

4Fe

3O

4–PAA

qe

RL

qe

RL

mg/g mg/gZn 29.80 0.062 30.12 0.060Cd 31.00 0.046 30.80 0.041Cu 30.97 0.040 30.06 0.037Cr 31.99 0.041 29.50 0.040Ni 29.97 0.051 29.03 0.055

ConclusionsMagnetite (Fe3O4) with an average size of 85.5 nm and a

composite (Fe3O4–PAA) with approximately 200-nm size were synthesized to be used as nanoadsorbents. The removal efficiency for Zn(II), Cd(II), Cu(II), Cr(VI), and Ni(II) was higher for lower concentrations (20 mg/L), and the quantity adsorbed at equilibrium (qe) indicates a higher efficiency in comparison with another nanoscale magnetic adsorbent,

-Fe2O3. Adsorption equilibrium was achieved within 10 min and remained the same after 100 min. Langmuir parameters indicated a favorable monolayer adsorption at pH 2.5. The tendency of Fe to dissolve from uncoated Fe3O4 is reduced by using a nanocomposite such as Fe3O4–PAA. The removal efficiency for metal ions remained at the same values, approximately 80%. The nanocomposite Fe3O4–PAA can be used as an adsorbent with the same performance as uncoated

Fe3O4 but with the advantage of its stability under conditions where industrial wastewaters have an acidic pH.

AcknowledgmentsWe recognize financial support from the European Social Fund through the POSDRU/89/1.5/S/54785 Project “Postdoctoral Program for Advanced Research in the field of nanomaterials.”

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Applied Surface Science 285P (2013) 86– 95

Contents lists available at ScienceDirect

Applied Surface Science

jou rn al h omepa g e: www.elsev ier .com/ locate /apsusc

Maghemite and poly-dl-alanine based core–shell multifunctional

nanohybrids for environmental protection and biomedicine

applications

Cristina Ileana Covaliua,∗, Gigel Paraschiva, Sorin-S tefan Biris a, Ioana Jitarub,Eugeniu Vasileb, Lucian Diamandescuc, Tanja Cirkovic Velickovicd, Maja Krsticd,Valentin Ionitae, Horia Iovub, Ecaterina Matei f

a University Politehnica of Bucharest, Faculty of Biotechnical Systems Engineering, Bucharest, Romaniab University Politehnica of Bucharest, Faculty of Applied Chemistry and Materials Science, Bucharest, Romaniac National Institute of Materials Physics, Bucharest, Romaniad University of Belgrade, Faculty of Chemistry, Belgrade, Serbiae University Politehnica of Bucharest, Faculty of Electrical Engineering, Bucharest, Romaniaf University Politehnica of Bucharest, Faculty of Materials Science and Engineering, Bucharest, Romania

a r t i c l e i n f o

Article history:

Received 2 May 2013

Received in revised form 2 August 2013

Accepted 15 August 2013

Available online 23 August 2013

Keywords:

Core–shell nanohybrid materials

Maghemite

Poly-dl-alanine

HeLa cells

Removal efficiency of Cd (II) ions from

wastewater

a b s t r a c t

This paper deals with the synthesis of two nanohybrid materials based on maghemite (�-Fe2O3)

and poly-dl-alanine using a two-step procedure consisting of maghemite nanoparticles synthesis

by microemulsion method and nanohybrids obtaining by coating of maghemite nanoparticles with

poly-dl-alanine biopolymer in two different molar ratios (H1:5 and H1:15). The maghemite and

their corresponding nanohybrids were characterized by X-ray diffraction, Fourier transform infrared

spectroscopy, X-ray photoemission spectroscopy, Mössbauer spectroscopy, Transmission electron

microscopy, High resolution transmission electron microscopy with selected area electron diffraction and

Atomic absorption spectroscopy. The two nanohybrids under the investigation have the average particle

sizes of 22 nm and 23 nm. The Fourier transform infrared spectroscopy spectra and X-ray photoemission

spectroscopy data indicate the existence of some interactions between the maghemite nanoparticles

and poly-dl-alanine shell. The saturation magnetization values for maghemite and the two nanohybrids

determined by a Vibrating Sample Magnetometer correspond to a typical superparamagnetic behavior

suitable for applying in biomedical field. Also, with respect of biomedical application the biological activ-

ity of maghemite and its corresponding nanohybrids was investigated on healthy human cells (PBMC)

and cancerous cells (HeLa). Furthermore, in order to support the multifunctionality of the �-Fe2O3 sample

and nanohybrids we also investigated their wastewater treatment properties by measuring the removal

efficiency of heavy metal Cd (II) ions.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

Magnetic core–shell nanohybrids consisting of inorganic and

organic components are very interesting due to the combination

of several important properties which gives them the possibility

of applying in many fields. An example of this type of magnetic

hybrids is represented by magnetic oxide core nanoparticles coated

by polymeric shells which have the potential to be used in fields

as: environmental protection and biomedicine [1–3]. Magnetic

nanohybrids may exhibit special magnetic properties, such as

∗ Corresponding author. Tel.: +40 722791791.

E-mail addresses: cristina [email protected], [email protected]

(C.I. Covaliu).

superparamagnetism, suitable for various biomedical applications

that involve the use of an external magnetic field, such as magnetic

resonance imaging (MRI), magnetically controlled transport of

pharmaceuticals and localized hyperthermia. As regarding de

environmental protection applications of the magnetic materials

are currently investigated the priority pollutants removal from

wastewater such as heavy metals which have as major source of

pollution the disposal of effluents from the industries like battery

manufactures, painting, paper, electroplating, metal finishing [4].

The required characteristic for using magnetic nanoparticles as

adsorbents for removal heavy metals removal from wastewater is

the diameter <50 nm [5].

Various chemical methods can be used to synthesize maghemite

nanoparticles with the required characteristics for use in the

biomedical field, but these have to provide the following main

0169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.apsusc.2013.08.059

C.I. Covaliu et al. / Applied Surface Science 285P (2013) 86– 95 87

N

O

n

H

CH3

Fig. 1. Structural formula of poly-dl-alanine.

challenges: the selection of the optimum preparation condition for

obtaining nanometric and monodisperse magnetic oxide particles,

finding a reproducible procedure which can be applied in the

pharmaceutical industry and using of a cost-efficient method

[6–8]. From various synthesis methods microemulsion has proved

to be a very efficient route to prepare nanosized and monodisperse

nanoparticles [9].

The coating of the magnetic oxide nanoparticles with biopoly-

mers brings many advantages such as: it prevents the agglomer-

ation by providing a steric barrier, it avoids the opsonization and

their clearance by reticuloendothelial system (RES) from the human

organism before the therapeutic action is achieved. In addition, the

polymeric coatings compared with inorganic coatings provide bio-

compatibility to magnetic oxide nanoparticles, the possibility to

link on the target zone within the human body and attachment on

the nanoparticles surface of various drugs. A variety of natural and

synthetic polymers have been evaluated for using as coatings of the

magnetic nanoparticles such as: dextran, sodium alginate, chitosan

[10,11].

Polyaminoacids, including poly-dl-alanine, are biodegradable

polyanionic materials having very low toxicity and immuno-

genicity and a wide range of applications from release agents

in agriculture to water treatments, paint additives, cosmetics,

metal adsorbents, and surfactants. Polyaminoacids have clin-

ical applications being used as components for diagnostics,

dialysis membrane, artificial skin, orthopedic implants, drug

delivery systems and carriers for therapeutic protein conjugates

[12].

Until now poly-dl-alanine polymer has not been used for

inorganic nanoparticles biocompatibilization (Fig. 1). This articles

reports a simple and economical synthesis procedure of core–shell

multifunctional nanohybrids based on �-Fe2O3 nanoparticles and

poly-dl-alanine: synthesis of the maghemite nanoparticles by

microemulsion method in the presence of a soft template fol-

lowed by their coating with poly-dl-alanine. These hybrids were

primarily characterized by X-ray diffraction (XRD) and Möss-

bauer spectroscopy providing information about the crystalline

and polymeric phases. The morphological characterization reveals

the core–shell nanostructure and the nanometric sizes of the two

synthesized nanohybrids. The magnetic properties were provided

from the experimental measurements of the first magnetization

curve and the major hysteresis cycles. The results show the super-

paramagnetic behavior of the maghemite and its corresponding

hybrid nanoparticles, which is different from the ferrimagnetic-

type magnetization of the “bulk” sample. The biological activity

was evaluated on human cervical carcinoma cells (HeLa) and

peripheral blood mononuclear cells (PMBC) of a healthy donor.

The results of the magnetic properties along with those of bio-

logic activity are very important characteristics for the purpose of

application in the biomedical field. The influence of the amounts

of maghemite and poly-dl-alanine used in synthesis upon the

characteristics of the core–shell nanohybrids finally obtained

(core and shell sizes, magnetic properties) was also studied. For

sustaining the multifunctionality of prepared nanopowders was

done the investigation of environmental protection application in

terms the heavy metal ion Cd (II) removal efficiency was investi-

gated.

2. Experimental

2.1. Synthesis of core–shell magnetic nanohybrids based on

�-Fe2O3 and poly-dl-alanine

All chemicals were supplied from commercial suppliers (Sigma-

Aldrich Co.) and were used without any further purification.

The synthesis of maghemite was done by microemulsion

method using ferric chloride (FeCl2·6H2O), sodium dodecyl sulfate

(SDS), n-butanol, ammonia solution (NH3) 25% as raw materials. A

transparent mixture was obtained from SDS, water and n-butanol

starting from a molar ratio of 1:2:5. Prior adding NH3 solution to

achieve the pH value of 10, the FeCl2·6H2O 0.5 M solution was added

into the mixture. The precipitate obtained after 2 h of stirring the

reaction mixture at room temperature was separated by centrifu-

gation and washed several times with water and ethanol and finally

kept at 105 ◦C for 3 h. The two nanohybrids were obtained starting

from two molar ratios (1:5 or 1:15) between maghemite nanopow-

der and poly-dl-alanine biopolymer. The maghemite powder was

added gradually to 15 mL of poly-dl-alanine 0.5 M solution to

prepare nanohybrid noted H1:5 or 50 mL of poly-dl-alanine 0.5 M

solution for obtaining nanohybrid noted H1:15 and stirred at room

temperature for 6 h. The hybrid particles were separated by cen-

trifugation and dried at 90 ◦C for 2 h.

2.2. Core–shell magnetic nanohybrids based on �-Fe2O3 and

poly-dl-alanine characterization

X-ray diffraction was done in order to characterize the crys-

talline structure, using a X- ray analytical diffractometer, X’PERT

PRO MPD with Cu-K� radiation (� = 0.15418 nm). The maghemite

content in the two nanohybrids was determined by using ANA-

LYTIK JENA Atomic Absorption Spectrophotometer Contra AA7. The57Fe Mössbauer spectra were recorded at room temperature using a57Co(Rh) source and a standard spectrometer in constant accelera-

tion mode. �-iron foil was utilized for the spectrometer calibration.

The computer fit was performed in the hypothesis of Lorenzian

shape of the absorption lines. X-ray photoemission spectroscopy

(FTIR) spectra were registered on a Bruker Tensor 27 spectrom-

eter using 32 scans at 4 cm−1 resolution in the 400–4000 cm−1

range. The X-ray Photoelectron Spectroscopy (XPS) was done on a

K-Alpha instrument from Thermo Scientific, monochromated AlK�

source (1486.6 eV) at a bass pressure of 2 × 10−9 mbar. The pass

energy for the survey spectra was 200 eV and 20 eV for high reso-

lution. The transmission electron microscopy images (TEM) were

obtained on FEI Tecnai TMG2F30 S-TWIN with energy dispersive X-

ray spectrometer. The magnetic curves (first magnetization curve

and hysteresis loop) at 24 ◦C (297 K) for the maghemite and hybrids

samples were measured by a vibrating sample magnetometer (VSM

7304 LakeShore USA).

2.2.1. Cell culture

Peripheral blood mononuclear cells (PBMC) were separated

from the whole heparinized blood of a healthy volunteer and cul-

tured as described previously [13]. Briefly, blood was diluted with

PBS (1:1) and layered on Histopaque solution. After centrifuga-

tion, interface cells were collected and washed three times with

PBS. After counting, cells were resuspended in nutrient medium.

Nutrient medium was RPMI medium supplemented with 10% fetal

calf serum (FCS), glutamine (2 mM), �-mercaptoethanol (50 �M),

penicillin (100 IU mL−1) and streptomycin (100 �g mL−1). Cells

were seeded (200,000 cells per well) in 96-well plates in nutrient

medium with phytohemagglutinin (PHA) (5 �g mL−1) and differ-

ent concentrations of nanoparticles. Cells were incubated for 72 h

at 37 ◦C in a humidified atmosphere with 5% CO2.

88 C.I. Covaliu et al. / Applied Surface Science 285P (2013) 86– 95

Fig. 2. XRD patterns of �-Fe2O3 powder (a), H1:15 hybrid (b), poly-dl-alanine (c) and H1:5 hybrid (d).

Human cervix adenocarcinoma cells (HeLa) were grown in RPMI

medium supplemented with 10% fetal calf serum (FCS), glutamine,

�-mercaptoethanol and antibiotics. After trypsinization, cells were

seeded (10,000 cells per well) in 96-well plates for 24 h at 37 ◦C

in a humidified atmosphere with 5% CO2. After this period, differ-

ent dilutions of nanoparticles in complete medium were added to

the wells and incubated for 24 h under identical conditions. Only

medium was added to the cells in the control wells.

All experiments were performed in triplicate. Final concentra-

tions of the tested nanoparticles (maghemite and the two hybrids)

were 1 mg/mL.

2.2.2. Cell sensitivity analysis

Cytotoxicity of tested compounds was evaluated by MTT (3-(4,5-

dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide) assay.

After the incubation period, 100 �L of MTT solution (0.5 mg mL−1)

was added to each well. Samples were further incubated for 2 h at

37 ◦C under 5% CO2. Formazan (the color that was formed during

MTT metabolism) was resuspended in DMSO and the absorbance

was red at 540 nm and 670 nm (background absorbance). The

absorbance, which represents the number of viable cells, was cal-

culated as A540-A670. The absorbance of the control wells, cell

suspensions without the inhibitor added, represented 100% cell

vitality. The percentage of cells vitality in the presence of inhibitor

was calculated as percentage of absorbance in control wells.

2.3. Cd (II) ions removal efficiency tests

Cadmium solutions were prepared from Merck reagent-grade

solutions by dissolving into ultrapure water. The stock solution had

an initial concentration of 1000 mg/L and pH value was adjusted by

adding NaOH (0.1 mol/L) in order to obtain a proper value close to

the industrial effluents, namely pH 5.6. The adsorption studies were

carried out by measuring of the initial and final concentration of the

cadmium by flame atomic absorption spectrometry (FAAS).

The adsorbed cadmium amount at equilibrium is given by

ratio between adsorbed cadmium (mg) onto adsorbent mass (g)

expressed as qe, according to the Eq. (1):

qe = (C0 − Ce) V

m(1)

where C0 – Cd (II) ions initial concentration, mg/L; Ce – equilibrium

Cd (II) ions concentration, mg/L; V – volume of solution, L; m –

adsorbent quantity, g.

Adsorption studies were performed by mixing of adsorbents

(�-Fe2O3, H1:5 and H1:15, respectively) with 100 mL solution con-

sists of 10, 20, 50, 80 and 100 mg/L of Cd(II) ions in a glass vial

at room temperature (21.5 ◦C). The used quantity for adsorbents

was 0.1 g from each compound. For adsorption kinetic studies, solu-

tions prepared were kept into contact with each type of adsorbent

nanoparticles from 10 to 120 min. The adsorbent samples were

recovered by magnetic separation. The metal contents were mea-

sured by FAAS with a GBC 932 AB Plus spectrometer with spectral

domain between 185 and 900 nm in order to establish the quantity

of adsorbed metal.

The adsorption isotherm for cadmium ions onto 0.1 g �-Fe2O3

powder, H1:5 and H1:15 hybrid materials were fitted to the Lang-

muir model expressed as Eq. (2):

Ce

qe= 1

qmCe + 1

qmb(2)

where Ce – is the aqueous concentration of cadmium ions at equi-

librium, mg/L; qe – is adsorbed amount of cadmium at equilibrium,

mg/g; qm and b – are the constants related to the adsorption capacity

and the affinity coefficient.

For adsorption studies only 100 mL of each mentioned con-

centration of Cd was added to 0.1 g �-Fe2O3 powder. The same

procedure was applied using as adsorbents the two hybrids H1:5

and H1:15. After mixing, the supernatant layer from all samples

was analyzed by AAS in order evaluate the quantity of the adsorbed

metal. The effect of the contact time for the adsorption of cadmium

ions onto the three adsorbents was evaluated. It is assumed that the

equilibrium was achieved within 10 min, according to active sites

of nanoparticles placed in the exterior of the adsorbent for �-Fe2O3.

3. Results and discussion

3.1. X-ray diffraction (XRD)

The XRD data show that uncoated oxide powder is mono-phase

and it exhibits the crystalline structure of maghemite (�-Fe2O3),

with cubic symmetry (Fig. 2a). The average crystallite size


calculated by Scherrer formula is 21 nm. For both nanohybrids

based on maghemite and poly-dl-alanine (H1:5 and H1:15), XRD

patterns present beside characteristic peaks of the maghemite crys-

talline structure, peaks assigned to poly-dl-alanine compound of

the nanohybrids (Fig. 2b and d).

3.2. Atomic Absorption Analysis (AAS)

The percentage of maghemite from the two prepared nanohy-

brids determined by Atomic absorption analysis was 85% for H1:5

and 90% for H1:15 hybrids.

3.3. Mössbauer spectroscopy

Before referring to the Mössbauer spectra of the analyzed

hybrids, we have to outline some structural peculiarities of

maghemite. It is well known that maghemite has the composition

of hematite but it exhibits the structure of magnetite (Fe3O4). In

the cubic structure of both maghemite and magnetite, 1/3 of the

interstices are tetrahedrally coordinated with oxygen and 2/3 are

octahedrally coordinated. In maghemite structure, only 5/6 of the

total available positions are filled by Fe3+, the rest are vacant (�):

Fe2.67�0.33O4. Maghemite may have different structures depend-

ing on the degree of ordering of the vacancies. Completely ordered

maghemite has a tetragonal symmetry, otherwise it is cubic.

At room temperature maghemite is ferrimagnetic and the Möss-

bauer spectrum displays an unresolved hyperfine magnetic pattern

with large line widths. This pattern can be deconvoluted in two

magnetic sextets corresponding to iron ions in the tetrahedral (A)

and octahedral (B) positions [14].

In the maghemite lattice there are 8 Fe3+ in tetrahedral sites

and 13.33 Fe3+ ions in octahedral sites. The magnetic field values

are 488 KOe for the tetrahedral sites and 499 KOe for the octahedral

ones [15]. The room temperature Mössbauer spectra of the initial

maghemite and the corresponding nanohybrids (H1:5 and H1:15)

are displayed together with the computer fit (continuous lines) in

Fig. 3a–c. All spectra consist mainly in a six line magnetic hyperfine

pattern accompanied by a very small central doublet. The central

doublet with a quadrupole splitting of ∼0.45 mm/s and isomer shift

of ∼0.15 mm/s comes from the very small amount of Fe in the Beryl-

lium detector windows; this doublet is observed only at very high

statistics on the recorded spectra, as in the case of our spectra. The

magnetic patterns were deconvoluted in two sextets correspond-

ing to Fe3+ in A and respectively B site of maghemite. The magnetic

hyperfine fields of 484 KOe for A sites and 495 KOe for the B sites,

respectively, are close to the standard values of maghemite values.

No significant differences can be reported between the Mössbauer

spectra of the initial maghemite sample and the hybrids.

3.4. FTIR spectroscopy

The interaction between �-Fe2O3 powder and poly-dl-alanine

was proved by FTIR analysis. The �-Fe2O3 is a deficient magnetite

having inverse spinel structure and is represented as Fe3+[Fe3+X]O3,

where X is the vacancy site from the lattice, Fe3+ inside the square

bracket represents tetrahedral position and Fe3+outside the square

Fig. 3. Mössbauer spectra of the uncoated maghemite (a) together with the spec-

tra of maghemite-based nanohybrids with poly-dl-alanine in different molar ratio:

H1:5 (b) and H1:15 (c).

bracket represents the octahedral position. The comparison study

of the maghemite and poly-dl-alanine spectra with that of the

corresponding hybrids reveals the following characteristics:

the shifting of Fe O vibration bands placed in octahedral and

tetrahedral sites frequencies located at 467 cm−1 and 615 cm−1

in maghemite spectrum to higher vibration frequencies for H1-5

Table 1Binding Energy (eV) of �-Fe2O3, poly-dl-alanine, H1:5 and H1:15 nanohybrids.

Samples Nanopowder�-Fe2O3 Nanohybrid H1:5 Nanohybrid H1:15 Poly-dl-alanine

Fe 2p3/2 712.81 714.74 714 –

Fe 2p1/2 727 725 726 –

O1s 531.33 533.62 531.14 530.8

C1s – 290.89 286.3 285.47

N1s – 403.32 401.18 400.35


Fig. 4. FTIR spectra of H1:5 hybrid (a), poly-dl-alanine (b), H1:15 (c), �-Fe2O3 (d).

(478 cm−1 and 640 cm−1) and H1-15 (487 cm−1 and 637 cm−1)

nanohybrids spectra, the shifting of vibration bands assigned to

amino (NH) and carbonyl (C O) groups located at 3210 cm−1 and

1637 cm−1 in poly-dl-alanine spectrum to higher wavenumbers

for H1:5 (3225 cm−1 and 1661 cm−1) and H1:15 (3227 cm−1 and

1661 cm−1) hybrids spectra (Fig. 4).

Hence, it can be concluded that the binding sites of the poly-

dl-alanine biopolymer are the amino and carbonyl groups which

interact with the Fe3+ ions from the maghemite like in Fig. 5a and b.

3.5. XPS analysis

The existence of the interactions between the poly-dl-alanine

biopolymer and maghemite powder was further investigated by

Fig. 5. Expected interactions between Fe3+ ions of maghemite nanoparticles and

poly-dl-alanine polymer by amino group (a) and carbonyl group (b).

XPS spectroscopy. The main signals in XPS spectra at 712.8 and

727 eV are assigned to Fe 2p3/2 and Fe 2p1/2 both occurring in

maghemite and nanohybrids spectra. The binding energies cor-

responding to the main species from maghemite, polymer and

nanohybrids are presented in Table 1. We may notice, especially

in the case of C1s, a significant shift of the corresponding bind-

ing energy from 285.4 eV in the poly-dl-alanine to 286.3 eV and

290.8 eV in the nanohybrids which is a strong argument for the

interactions between Fe3+ and oxygen atoms from the polymer

chain like we previously assumed (Fig. 5).

Considering that for the two obtained hybrids the poly-dl-alanine shell thickness is less than 2 nm (Figs. 6a and 9b) and the

X-ray photoemission depth of surface examination is 3–5 nm, we

did not expect to demonstrate the well defined poly-dl-alanine

shell around the maghemite core by XPS, but only the existence of

the polymeric layer around the maghemite nanoparticles and the

interactions that exist between the two components of the H1:5

and H1:15 hybrids.

3.6. Morphological characterization

TEM images and high resolution transmission electron

microscopy (HRTEM) show the core–shell nanostructure of the pre-

pared �-Fe2O3-poly-dl-alanine hybrids nanoparticles. The SAED

images of uncoated maghemite and corresponding nanohybrids

confirm the Miller indices of crystalline structures first identified by

XRD (insets of Figs. 6d 7b and 9c). Fig. 6a and b clearly show the well

defined nanostructure of H1:5 composed of 21 nm maghemite core

and a poly-dl-alanine shell of 1.5 nm. The H1:5 hybrid nanoparti-

cles exhibit polyhedral shape. Additional information supporting

the structure of H1:5 hybrid nanoparticles was obtained through

the detailed analysis of HRTEM images which reveal the interplanar

distances of 2.52 A and 2.10 A assigned to crystallographic planes

of Miller indices (311) and (400) characteristic to cubic �-Fe2O3

structure (Fig. 6b and c).

For the H1:5 nanohybrid, an average particle size of 22 nm

was calculated from the size distribution of 150 particles

(Fig. 8b).


Fig. 6. HRTEM images at different magnitudes (a), (b) and (c); TEM inset SAED (d) of H1:5 nanohybrid, beam direction: B = [001].

HRTEM image of the uncoated maghemite nanoparticles shows

2.52 A and 2.95 A interplanar distances assigned to crystallographic

planes of Miller index (3 1 1) and (2 2 0), respectively (Fig. 7a). In

the absence of the polymeric coat, the agglomeration tendency of

maghemite nanoparticles is higher because of the magnetic inter-

action and the absence of a steric barrier. The average particle size

of uncoated maghemite determined by counting 150 particles is

21 nm (Fig. 8a) and their shape is polyhedral (Fig. 7b).

Fig. 7. HRTEM (a) and TEM inset SAED (b) images of �-Fe2O3 nanopowder, beam direction: B = [112].


252015

0

5

10

15

20

25

30

35

40

D= 21 nm

Nan

op

art

icle

s c

ou

nts

Size (nm)

(a)

2520150

5

10

15

20

25

30

35

40

D= 22 nm

Nan

op

art

icle

s c

ou

nts

Size (nm)

(b)

252015

0

5

10

15

20

25

30

35

40

D= 23 nm

Nan

op

art

icle

s c

ou

nts

Size (nm)

(c)

Fig. 8. Size distribution for �-Fe2O3 (a), H1-5 nanohybrid (b) and H1:15 nanohybrid.

HRTEM image of H1:15 hybrid shows a 2.52 A interplanar dis-

tance assigned to crystallographic plane of Miller index (3 1 1)

(Fig. 9b).

For three different HRTEM images of H1:15, the core is smaller

(9 nm and 11 nm Fig. 9a with inset) or equal (21 nm Fig. 9b)

with that measured for H1:5, but the poly-dl-alanine shell size is

higher (1.7 nm in Fig. 9a and 2 nm in Fig. 9b) indicating that an

increased amount of polymer used for maghemite coating con-

ducted to an increased amount of poly-dl-alanine retained on

maghemite nanoparticles and, consequently, to an increase of the

average particle size of the hybrid (23 nm, Fig. 8c). In addition, by

comparing Fig. 6d with Fig. 9c, it may be clearly observed that a

higher value of the polymeric coat thickness of the maghemite

nanoparticles resulted in a decrease of the agglomeration tendency

of the hybrid nanoparticles. This fact allows us to conclude that

as the amount of poly-dl-alanine biopolymer used for maghemite

coating increases, the steric barrier increases and therefore the

magnetic agglomeration particles of the hybrid decrease. Even if

an agglomeration tendency of the maghemite nanoparticles exists

because of the magnetic properties, the polymeric shell appears

to be a uniform coat and is preserved for each individual hybrid

particle (Figs. 6a and 9a). The polymeric shell is composed of

three-four polymeric layers (observed on the central particles from

Figs. 6a, b and 9 b) observed in XRD pattern at a value of 2� equal

to 20.

The results of the TEM investigation show that maghemite

and hybrid particle samples are nearly monodispersed

(Figs. 6d, 7 b and 9c).

Even if an agglomeration tendency of the maghemite nanopar-

ticles exists because of the magnetic properties, the polymeric shell

appears to be a uniform coat and is preserved for each individual

hybrid particle (Figs. 6a and 9a).

3.7. Magnetic properties

The special magnetic property provides the use of the obtained

nanohybrids in medicine for targeting the desired areas within the

human body during the diagnosis or treatment of cancer. The mag-

netic properties allow the adequate hybrid nanoparticle control in

a weak magnetic field and its reversible magnetization. The iron

oxide nanoparticles are appropriate for biomedical applications

such as cancer diagnosis to magnetic resonance imagining (MRI)

and cancer treatment by hyperthermia because their coercivity and

the remanence are very low, so the hysteresis losses are negligible.

However, the coupling between the maghemite nanoparticle and

poly-dl-alanine biopolymer may produce changes to the obtained

nanohybrids structure and also the magnetic properties could be

altered. Our study shows some of these effects. The most impor-

tant magnetic parameters are presented in Table 2 for all the

investigated samples. Fig. 10 shows the hysteresis cycles of �-

Fe2O3 and the corresponding nanohybrids. The maghemite and

hybrid nanoparticles exhibit a superparamagnetic behavior with

Table 2Magnetic properties of the �-Fe2O3 and corresponding H1:5 and H1:15 hybrids.

Material Coercivity (kA/m) Remanence (Am2/kg) Saturation (Am2/kg)

�-Fe2O3

H1:5 11.8 8.1 38.2

H1:15 7.8 1.32 7.95


Fig. 9. HRTEM images (a) and (b) at different magnitudes, TEM inset SAED (c) of H1:15, beam direction: B = [130].

negligible hysteresis cycles, which confirm the reduced size of par-

ticles that allows the presence of a single magnetic domain. The

density of the nanohybrid materials being unknown, the compari-

son is presented using the specific (mass) magnetization. The two

nanohybrids exhibit different superparamagnetic behavior, but the

saturation magnetization is diminished for the hybrid containing

an increased amount of polymer, due to the reduced composition

of magnetic component and, nevertheless, to the superparamag-

netic property. The hybrid particle diameters can be computed as

an average size corresponding to an average susceptibility (e.g. for a

half of the maximum susceptibility [16] or it can be detailed for each

measured value. The magnetization at small magnetic fields corre-

sponds to the large nanoparticles, when the domain wall motion

is possible; the smaller particles (monodomain) act especially for

Fig. 10. Hysteresis loops of �-Fe2O3 (a), H1:5 nanohybrid (b), H1:15 nanohybrid (c).

high fields [17]. But the exact values of the magnetic susceptibility

could be known only if the measured magnitudes can be corrected

taking into account the demagnetization phenomenon inside the

sample. This correction is possible for bulk materials [18], but the

sample composed by nanoparticles and clusters requires special

techniques of numerical homogenization. Finally, the diameter D

can be estimated using Eq. (3):

D = 3

√18�KT

��0M2s

(3)

where � is the magnetic susceptibility.

Our estimation, based on Eq. (3), gives particle diameters in the

range of 5–10 nm for all the investigated samples. These values

explain the superparamagnetic behavior of the samples, but are

lower than those obtained from other measurements (e.g. trans-

mission electronic microscopy–TEM), which give the size range of

21–23 nm. This difference was reported in scientific papers [19,20]

and it is normal because the magnetic field is diminished inside

the sample by the demagnetization field; the real magnetic sus-

ceptibility � is higher than the measured one and the computed

diameter will be higher, according to Eq. (1). Also, based on the

magnetic measurement we determine only the magnetic phase

size, while the data obtained from the TEM images also includes

the so-called “dead layer” represented by the polymer, which is

not otherwise registered by the magnetic measurements. So, the

explanation regarding the particles size discrepancy between TEM


Fig. 11. (A) Graphs of the inhibition action of PBMC (healthy human cells) in the

presence of different concentrations of inhibitors: (a) �-Fe2O3 nanopowder, (b) H1:5

and (c) H1:15 nanohybrids; (B) Graphs of the vitality of HeLa (tumoral cells) in the

presence of different concentrations of inhibitors: (a) �-Fe2O3 nanopowder, (b) H1:5

and (c) H1:15 nanohybrids.

measurements and magnetic measurements is explainable and it

was expected.

The magnetic properties of the maghemite give the magnetic

behavior of the two hybrid materials. This study shows that the

experimental magnetization curves could be used for the entire

characterization of tested magnetic nanoparticles even for coated

ones like in nanohybrid materials. The superparamagnetism of

nanoparticles is essential for medical application and this property

requires particle sizes in the range of nanometers.

3.8. The biological activity tests (viability tests)

For the application in the biomedical field, low cytotoxicity

of the obtained hybrids that can be potential carriers of many

drugs is essential. Thereby, the biologic activity of H1:5 and H1:15

nanohybrids was determined by testing on human peripheral blood

mononuclear cells of a healthy donor (normal cells) and tumoral

cells (HeLa) along with a comparison study of cytotoxic activities

of maghemite �-Fe2O3 and corresponding hybrids on both HeLa

and PBMC cells.

Fig. 11 shows the graphs of cytotoxic activity of nanohybrids on

lymphocytes (PBMCs) and on HeLa cells. Even at the highest con-

centration of �- Fe2O3 and nanohybrid samples used in the testing

(1 mg/mL), 50% inhibition of vitality of HeLa and PBMC cells could

not be obtained. The �- Fe2O3 and nanohybrid samples exhibited

very low cytotoxicity in the tested cell cultures. Fig. 11B shows that

the cytotoxicity in HeLa cultures increases along with the increase

of the nanohybrid concentration. The highest hybrid cytotoxic

action (about 35%) has been obtained for 1 mg mL−1 nanohybrid

H1:15. Similar to that obtained for HeLa cells, the inhibitory action

of nanoparticles on PBMC cells vitality increases slowly with the

increase of the hybrid concentration up to 1 mg mL−1 (Fig. 11A). The

highest inhibitory action (about 45%) was obtained for 1 mg mL−1

nanohybrid H1:15.

0

10

20

30

40

50

60

70

80

120603010

Time, minutes

Eff

icie

ncy

, %

γ-Fe2O3

H 1 : 5

H 1 : 15

Fig. 12. Removal efficiency in time for 10 mg Cd (II)/L onto the three types of adsor-

bents (�-Fe2O3, H1:5 and H1:15).

As expected, the inhibitory activity of prepared samples is

higher on PBMC cells than on HeLa cells because it is known that the

resistance of cancer cells at any potential drug remains an obstacle

in achieving high rates of curative cancer therapy.

From the point of view of biomedical applications, any concen-

trations of the nanohybrids below 0.5 mg mL−1 could be considered

safe as they did not influence the vitality of normal cells.

3.9. Cd (II) ions removal efficiency tests

The removal efficiency of Cd (II) ions after 10 min (after this

period of time, the removal remain almost unchanged) for all pre-

pared samples is shown in Fig. 12.

In case of using H1:5 as adsorbent, the removal efficiency was

over 50% after 10 min, and the efficiency was higher than that of

�-Fe2O3. A high removal rate for Cd ions was obtained using the

nanohybrid H1:15, almost 70% after 10 min.

The rate of removal for Cd(II) decrease in the following order:

H1:15 > H1:5 > �-Fe2O3. It can be seen that the efficiency was

between 30% for uncoated �-Fe2O3 and 80% for H1:15, after 10 min

and it remains almost the same after 120 min. The same tendency

it was observed also for the others concentrations of Cd (II) ions:

20, 50, 80 and 100 mg/L. Regarding the tendency of Cd (II) ions

removal onto the three adsorbents, as comparison, for concentra-

tions between 10 and 100 mg/L of Cd (II) ions, the most efficient

adsorbent, as it can be seen into Fig. 13, is H1:15 nanohybrid. The

decreasing of removal efficiency is: H1:15 > H1:5 > �-Fe2O3.

This can be explained by the adsorption capacity of the poly-dl-alanine polymer used.

Langmuir model parameters for adsorption of Cd (II) onto 0.1 g

adsorbents can be observed into Fig. 14.

It can be observed that the adsorption parameters, regarding the

maximum adsorbed quantity (qe, mg/g) and regression coefficient

R2 (almost 0.99) are fitted well with the Langmuir requirements.

0

10

20

30

40

50

60

70

80

10080502010

mg/L

Eff

icie

ncy

, %

γ-Fe2O3

H 1: 5

H 1 : 15

Fig. 13. Removal efficiency (%) of Cd (II) for the three adsorbents (�-Fe2O3, H1:5 and

H1:15).


y = -0.0194x + 2.4598

RγFe2O32 = 0.9675

y = 0.6988x + 2.6196

RH 1 : 52 = 0.9941

y = 1.3189x + 4.5261

R H 1: 152 = 0.9928

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

0 10 20 30 40 50 60 70Ce, mg/L

Ce/

qe,

mg/g

γ-Fe2O3

H 1 : 5

H 1 : 15

Fig. 14. Langmuir parameters for Cd (II) adsorption onto �-Fe2O3, H1:5 and H1:15.

The highest value of R2 is for H1:15. In case of uncoated �-Fe2O3,

the values indicate also a good adsorption but the model can be

improved, according to the R2 value.

4. Conclusions

Core–shell hybrids based on �- Fe2O3 and poly-dl-alanine were

prepared by a two-step procedure starting from two different molar

ratios between the two components. TEM images with selected

area diffraction patterns (SAED), high resolution TEM (HRTEM)

reveal the core–shell nanostructure of the two H1:5 and H1:15

hybrids nearly monodispersed particles and confirm the crystalline

structures first identified by XRD. The Mössbauer spectra show

for both hybrids the superparamagnetic behavior at room tem-

perature and confirm the existence of the crystalline structure of

maghemite. The interactions between maghemite (�-Fe2O3) and

poly-dl-alanine were proved by FTIR spectroscopy through the

shifts of amino and carbonyl vibration bands to higher frequencies

than those of poly-dl-alanine spectra. Also, the XPS data confirm

the existence of the interaction between the two components of

the prepared nanohybrids. The magnetic property measurement

reveals the superparamagnetic behavior useful for many in vivo

biomedical applications especially for those referring to cancer

therapy which imply the use of an external magnetic field. The bio-

logic activity tests on HeLa and PBMCs cells show that the highest

inhibitory action (about 35% for tumoral cells and 45% for normal

cells) was obtained for 1 mg mL−1 of the H1-15 nanohybrid sustain-

ing the significant potential for applying in the biomedical field, in

cancer therapy. Moreover, from the biomedical application point of

view, the concentrations of nanohybrids below 0.5 mg mL−1 could

be considered suitable for testing in vivo as they did not influence

the vitality of normal cells in in vitro testing.

The novel nanostructures have the potential to be used as low-

cost and efficient multifunctional materials showing also their

potential of applying as adsorbent for removal of cadmium ions

for wastewater. The adsorption studies indicated a good correla-

tion between Cd(II) concentrations and adsorbent quantity at pH

5.6, the adsorption data fitting well with Langmuir isotherm model.

Between the three tested adsorbents, the nanohybrid (H1:15) had

the highest affinity for Cd (II).

Acknowledgements

Authors recognize financial support from the European Social

Fund through POSDRU/89/1.5/S/54785 project: “Postdoctoral

Program for Advanced Research in the field of nanomaterials” and

to grant No 172024 of the Ministry of Education and Science of the

Republic of Serbia.

References

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[2] Y.W. Jun, Y.M. Huh, J.S. Choi, J.H. Lee, H.T. Song, S. Kim, S. Yoon, H.S. Kim, J.S.Shim, J.S. Suh, J. Cheon, Nanoscale size effect of magnetic nanocrystals and theirutilization for cancer diagnosis via magnetic resonance imaging, Journal of theAmerican Chemical Society 127 (2005) 5732–5733.

[3] K.B. Lee, S. Park, C.A. Mirkin, Multicomponent magnetic nanorods forbiomolecular separations, Angewandte Chemie International Edition 43 (2004)3048–3050.

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[5] E. Matei, A. Predescu, E. Vasile, A. Predescu, Properties of magnetic iron oxidesused as materials for wastewater treatment, Journal of Physics: ConferenceSeries 304 (2011) 1–9.

[6] Y.S. Kang, S. Risbud, J.F. Rabolt, P. Stroeve, Synthesis and characterization ofnanometer size Fe3O4 and Fe2O3 particles, Chemistry of Materials 8 (1996)2209–2211.

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[8] X. Wang, J. Zhuang, Q. Peng, Y. Li, A general strategy for nanocrystals synthesis,Nature 437 (2005) 121–124.

[9] V. Chhabra, P. Ayyub, S. Chattopadhyay, A.N. Maitra, Preparation of acicular �-Fe2O3 particles from a microemulsion-mediated reaction, Materials Letters 26(1996) 21–26.

[10] A.K. Gupta, M. Gupta, Synthesis and surface engineering of iron oxide nanopar-ticles for biomedical applications, Biomaterials 26 (2005) 3995–4021.

[11] A.K. Gupta, R.R. Naregalkar, V.D. Vaidya, M. Gupta, Recent advanced on sur-face engineering of magnetic iron oxide nanoparticles and their biomedicalapplications, Nanomedicine 2 (2007) 23–39.

[12] S. Roweton, S.J. Huang, G. Swift, Poly(aspartic acid): Synthesis, biodegradation,and current applications, Journal of Polymers and the Environment 5 (1997)3175–3181.

[13] I. Perovic, M. Milovanovic, D. Stanic, L. Burazer, D. Petrovic, N. Milcic-Matic,G. Gafvelin, M. Van Hage, R. Jankov, T. Cirkovic Velickovic, Allergenicity andimmunogenicity of the major mugwort pollen allergen Art v 1 chemicallymodified by acetylation, Clinical & Experimental Allergy 39 (2009) 435–446.

[14] N.N. Greenwood, T.C. Gibb, Mössbauer Spectroscopy, Chapman and Hall Ltd.,London, 1971.

[15] X. Teng, D. Black, N.J. Watkins, Y. Gao, H. Yang, Platinum-maghemite core-shellnanoparticles using a sequential synthesis, Nano Letters 3 (2003) 261–264.

[16] G. Gnanaprakash, S. Ayyappan, T. Jayakumar, J. Philip, B. Raj, Magnetic nanopar-ticles with enhanced �-Fe2O3 to �-Fe2O3 phase transition temperature,Nanotechnology 17 (2006) 5851–5857.

[17] A. Skumiel, M. Labowski, The heating effect of the biocompatible ferrofluidin an alternating magnetic field, Molecular and Quantum Acoustics 27 (2006)233–238.

[18] M. Di Marco, C. Sadun, M. Port, I. Guilbert, P. Couvreur, C. Dubernet, Physico-chemical characterization of ultrasmall superparamagnetic iron oxide particles(USPIO) for biomedical application as MRI contrast agents, International Journalof Nanomedicine 2 (2007) 609–622.

[19] V. Ionita, E. Cazacu, Correction of measured magnetization curves using finiteelement method, IEEE Transactions on Magnetics 45 (2009) 1174–1177.

[20] C.I. Covaliu, I. Jitaru, G. Paraschiv, E. Vasile, Biris S-S t, L. Diamandescu, V. Ionita,H. Iovu, Core–shell hybrid nanomaterials based on CoFe2O4 particles coatedwith PVP or PEG biopolymers for applications in biomedicine, Powder Tech-nology 237 (2013) 415–426.

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CHROMIUM REMOVAL FROM WASTEWATER USING CARBON NANOTUBES

Cristina Ileana Covaliu1, Gigel Paraschiv1, Biri Sorin tefan1, Cristina Cîrtoaje3, Ilie Filip2,

Emil Petrescu3

1University Politehnica of Bucharest, Faculty of Biotechnical Systems Engineering 2University Politehnica of Bucharest, Faculty of Mechanical Engineering and Mechatronics

3University Politehnica of Bucharest, Faculty of Applied Science

ABSTRACT

Heavy metals contained by wastewaters from various industrial activities tend to accumulate in the organisms causing different diseases. A representative example is chromium which has two stable oxidation states: (III) and (IV). Common chromium compounds containing chromium (III) are currently used in tanning industry. Chromium (IV) is highly toxic and it is contained by wastewater resulted from metallurgic industry. Generally conventional methods applied for heavy metals removal from wastewater have various disadvantages such as: incomplete metal removal, high amount of reagent, high energy requirements and generation of toxic sludge. Alternative technologies to conventional methods are essential for the removal of heavy metals (such as: Chromium) from industrial effluent. For these reasons, our study is focused on chromium (III) and (VI) removal from wastewater using carbon nanotubes. The effect of testing time on the removal of chromium pollutants was investigated accordingly.

1. INTRODUCTION Between the two forms of chromium, naturally occurring chromium is usually present as Cr (III), while Cr (VI) in the environment is almost totally derived from human activities. Metallic chromium is used mainly for making steel and other alloys. Chromium compounds in either (III) or (IV) forms are generally used for dyes, pigments, chrome plating, leather and wood preservation [1,2,3,4]. In 1997, U.S. reported various information regarding environment pollution with chromium, some of them been presented in Table 1 [5,6,7].

Chromium (VI) is much more toxic than chromium (III), for both acute and chronic exposures. The human body contains around 0.03 ppm of chromium. The highest chromium amount is contained by placenta. Chromium (III) is an essential element for humans: it removes glucose from blood, has a important role in metabolism of fat, its deficit may increase diabetes symptoms, it is found in ribonucleic acid, it may improve health and cure neuropathy and encephalopathy. The studies on animals have shown that chromium (III) have a moderate toxicity from oral exposure. Chromium (IV) is known for its negative health and environmental impact, having a very high toxicity. It causes allergic and asthmatic reactions, liver damage, causes diarrhea, stomach and intestinal bleedings, cramps, kidney damage, is carcinogenic and is 1000 times toxic in comparison with chromium (III). Other effects observed for acute inhalation exposure to very high concentrations of chromium (VI) include gastrointestinal and neurological effects, whereas dermal exposure causes skin burns. After inhalation of chromium (VI) the respiratory tract is the major target organ. Ingestion of high amounts of Cr (VI) causes hemorrhage, abdominal pain and vomiting.

1313 Splaiul Independentei Street, Bucuresti, 060042, Romania, +40722791791, [email protected]

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Table 1: Environment pollution with chromium Environment pollution with chromium

AIR WATER SOIL - a study referring to chromium pollution reported that in 1997 the chromium releases to the air were 706,204 pounds and represented approximately 2.2% of total environmental releases. - in some areas such as: Los Angeles, California, Houston and Texas during 1976 and 1980 period, the atmospheric chromium emissions derived from stationary fuel combustion were approximately 46-47% of the total emissions. - 1,723 metric tons of chromium annually resulted from coal and oil combustion. 0.2% from this amount of chromium was Cr (VI). - the emissions from the metal industry were between 26 to 45% of the total. - chrome-plating activities contributed to atmospheric pollution with 700 metric tons of Cr /year and consist exclusively be Cr(VI). - between the two forms of chromium, once riches the atmosphere, Cr(VI) may reacts with other types of pollutants or dust particles forming Cr(III), whereas Cr (III) does not undergo any reaction.

-in 1997 the estimated releases of chromium referring to water pollution was 111,384 pounds which represented for about 0.3% of the total environmental water pollution. -the larger sources of chromium in surface water were: electroplating, leather tanning and textile industries. The natural source of chromium from surface and underground waters is considered the leaching from rocks and topsoil. - a source of chromium pollution of the groundwater, in which the residence time might be several years is represented be the improperly disposed in landfills of the solid wastes from chromate-processing industry.

-according to the Toxics Release Inventory, in 1997 the releases of chromium to soil were 30,862,235 pounds representing approximately 94.1% of total environmental releases. - chromium waste slag containing Cr(VI) was used as fill material for many residential, industrial and recreational areas and for this reason many persons living in the vicinity of the sites were exposed to pollution through inhalation, ingestion and skin contact.

After entering the body chromium (VI) oxide suffer a dissolution process after which

is formed chromium acid which has the ability to corrode the organs, causing cramps and paralysis. Generally, the lethal dose is around 1-2 g.

The inhalation of very high concentrations of chromium trioxide leads to various negative effects on humans such as: shortness of breath, coughing and wheezing. The uptake of dust containing chromium trioxide in the workplace can cause cancer.

Most countries require for drinking water a legal limit of 50 ppb chromium. Taking into account the major concern regarding chromium toxicity and

carcinogenicity and the stringent requirements for its removal from industrial wastewater is necessary to development efficient, cost-effective and innovative ways of wastewater treatment. We propose for this study the using of carbon nanotubes for removing chromium (III) and (IV) from wastewater.

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As a new member of the carbon class, carbon nanotubes have already exhibited potential for various applications such as: field emitters for flat panel display, composite reinforcements, energy storage and energy conversion devices, sensors and catalysts support. These applications are sustained by some special properties such as: special mechanical, electrical, thermal and structural properties. Referring to environmental engineering field, their high chemical and thermal stabilities, as well as the, the large specific surface area make carbon nanotubes suitable adsorbents for wastewater treatment. In this study, carbon nanotubes were used as environmentally friendly adsorbants for removing Chromium (III) and (IV) from industrial wastewater.

2. METHODOLOGY Carbon nanotubes were used as adsorbent material. An amount of adsorbant was

contacted with the wastewater containing either Cr (III) or Cr (IV). During the investigation was measured the concentration of chromium using UV/Vis Spectrophotometer Specord 200 Plus. The chromium removal efficiency was calculated using the following formula:

Efficiency (%) = Ci-Cf, t/Ci * 100 where:

Ci- intital concentration of the chromium (III) or chromium (IV); Cf, t- final concentration of chromium (III) or chromium (IV) measured in time. As it can be seen from Figure 1, which represents the variation of concentration of

chromium from synthetic wastewater in time, the adsorbant used (carbon nanotubes) had a retention effect of chromium from wastewater.

Figure 1: Variation of Cr (III) concentration from wastewater in time, as a result of the

adsorbant efficiency In addition, as contacting time between adsorbant and wastewater increases, the

concentration of chromium (III) decreases. The efficiency of chromium (III) removal from wastewater was 87% (Fig.2). The evolution of chromium (IV) concentration from wastewater under the influence of carbon nanotubes during the performance of the investigation is shown in Figure 3. It can be

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seen that there is an increase in the treatment efficiency of the adsorbant used as the time of conducting the experiment increased.

Figure 2: Variation of Cr (III) removal efficiency from wastewater in time as a result of the

retention on adsorbant

Figure 3: Variation of the concentration of chromium (IV) from synthetic wastewater in time, as a result of the carbon nanotubes efficiency

As it can be seen from the Figure 4 which represents the variation of efficiency removal of Cr (IV) during experiment investigation, the carbon nanotubes adsorbant used is efficient for the depollution of synthetic wastewater.

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After 20 minutes of wastewater treatment with carbon nanotubes, the efficiency of Cr (IV) removal was 6.25% (Fig.4), whereas the Cr (IV) efficiency removal after 140 min of investigation reached at 91.21%.

Figure 4: Variation of Cr (IV) removal efficiency from wastewater in time as a result of the retention on adsorbant

Carbon nanotubes showed a higher efficiency for Cr (IV) removal from wastewater although even for Cr (III), the efficiency was higher than 80%.

3. CONCLUSIONS The adsorption properties of the carbon nanotubes for hexavalent and trivalent chromium have been studied and the results show that carbon nanotubes are excellent and proved to be effective adsorbants for eliminating these two harmful forms of chromium from wastewater. This study may sustain the development of a new alternative based carbon nanotubes to conventional wastewater treatment methods. References [1] Sayari A., Hamoudi S.,Yang Y., “Applications of pore-expanded mesoporous silica, Removal of heavy metal cations and organic pollutants from waste water”, Chemistry of Materials, 17(1), pp 212-216, 2005. [2] S. Gupta and B. V. Babu, “Removal of toxic metal Cr(VI) from aqueous solutions using sawdust as adsorbent: Equilibrium, kinetics and regeneration studies”, Chemical Engineering Journal, 150, 2009, pp. 352-365,2009.

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[3]. U. Förstner, and G.T.W.Wittmann, “Metal Pollution in the Aquatic Environment, 2nd rev. ed., Springer-Verlag, Berlin/New York”, 1981. [4]. Palmer, C.D. and Puls, R.W., “Natural Attenuation of Hexavalent Chromium in Ground Water and Soils. Chapter 4, EPA Environmental Assessment Source book”, EPA/540/S-94/505 pp. 57-72, 1994. [5] http://water.epa.gov/drink/contaminants/basicinformation/chromium.cfm. [6] http://www.atsdr.cdc.gov/csem/csem.asp?csem=10&po=5 [7] Li Y.H., Zhao Y. M., Hu W.B., Ahmad I., Zhu Y.Q., Peng X. J., Luan Z. K., Li Y.H., Carbon nanotubes - the promising adsorbent in wastewater treatment, Journal of Physics: Conference Series Volume 61 Volume 61

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MTiO3 (M=Cu,Ni) as Catalysts in Toluene Oxidation

GINA ALINA TRAISTARU1, CRISTINA ILEANA COVALIU1*, OVIDIU OPREA1, VASILE MATEI2, DORINA MATEI2,DIANA LUCIANA CURSARU2, IOANA JITARU1

1Politehnica University of Bucharest, Faculty of Applied Chemistry and Materials Science, 1-5 Polizu Str, 011061, Bucharest,Romania, 2 Petroleum-Gas University of Ploiesti, Faculty of Petroleum and Petrochemistry, 30 Bucuresti Bdl.,100680, Ploiesti, Romania

This study deals with the synthesis of MTiO3 (M=Ni,Cu) powders by a sol-gel method using titaniumisopropoxide – metallic acetates - isopropyl alcohol systems. The mixed oxides obtained have been structurallyand morphologically characterized by X-ray diffraction, scanning electron microscopy (SEM) andthermogravimetric analysis (TG-DTG-DSC). The catalytic activities of the prepared MTiO3 were determinedfor toluene oxidation in air. More experiments were made at different temperatures to establish the minimumtemperature when the toluene combustion appears.

Keywords: nickel titanium mixed oxide, copper titanium mixed oxide, catalytic activity, toluene oxidation

Metal mixed oxides show a great potential to be used incatalysis, electrocatalysis and electronic ceramics, being thebase of a new industrial policy for environmental technologies[1]. The use of these oxides for the purification of the volatileorganic compounds (VOCs), total combustion of hydrocarbonsfor energetic conversion and reduction of nitrogen oxides (NOx)and automotive emission make them the catalysts of thefuture [2-8]. These systems are potential substitutes of platinicmetals containing catalysts deposited on different supportedmaterials, like alumina or silica in the total oxidation reactionof the hydrocarbons. Catalysts based on transition metal(Ni, Cu, Co, Cr, Mn, and Fe) oxides have been extensivelystudied and their combustion activity was generally lowerthan that of noble metal catalysts [9-14].

In this work we have prepared MTiO3 (M=Ni,Cu)powders by a sol-gel procedure.The precurors and binarymixed oxides were investigated by means of TG-DTG-DSCanalysis, X-ray diffraction and scanning electronmicroscopy, SEM. Their catalytic activity for tolueneoxidation was also reported.

Experimental partStarting materials

Ti[OCH(CH3)2]4,Ni(CH3COO)2•4H2O, Cu(CH3COO)2) .4H2O were purchased from Sigma Aldrich. Isopropylalcohol (C3H7OH) and toluene (C6H5CH3) were purchasedfrom S.C. Chimexin S.A. All reagents were used withoutfurther purification.

Apparatus and procedureMTiO3 ultrafine powders have been prepared by a sol-

gel method.

CuTiO3The precursor of CuTiO3 was prepared by mixing a

solution of 0.5 mmol Cu(CH3COO)2•4H2O in 10 mL alcoholwith 0.5 mmol Ti[OCH(CH3)2]4 (in Cu: Ti = 1:1 molar ratio)and adding of 40 mL of isopropyl alcohol. The solutionobtained was heated under reflux at 800C for four hours,until a gel was formed. This gel was separated, filteredand dried in a capsule at 1000C.

The solid precursor was calcinated at 6000C/ 3 hoursand the powder obtained was analysed by XRD and SEM/EDAX.

* email: [email protected]

NiTiO3The precursor of NiTiO3 was obtained by the same sol-

gel method using a mixture of Ni(CH3COO)2•4H2O andTi[OCH(CH3)2]4 (in Ni:Ti = 1:1 molar ratio) in 40 mL ofisopropyl alcohol. After stirring and refluxing at 800C for 2 h,the formed gel was separated, filtered and dried in acapsule, in air at 1000C in an oven.

The precursor thus obtained was calcinated at 6000Cfor 3 h and the powder obtained was analysed by XRD andSEM/EDAX.

The thermal decomposition was investigated bythermogravimetric analysis (TG-DTA) and differentialscanning calorimetry (DSC) in STA 449C, with a NetzchJupiter apparatus. Samples were placed in open aluminacrucible and heated with 100C/min from room temperatureto 9000C, under the flow of 10 mL/min in air.

The binary oxide powders were analyzed by using X-raydiffraction (XRD) on D8 Discovery Bruker diffractometer,using Cu Kα (1.5406 Å) radiation operating with 30 mAand 40 kV in the 2θ range 10–700.

Morphological characterization was performed byscanning electron microscopy (SEM) in a HITACHI S2600Ncoupled with EDAX.

The specific surface area was measured in Carlo ErbaSopty 1750 apparatus by using Brunauer-Emmet-Teller(BET) method with nitrogen at 77 K.

Results and discussionsThermodifferential analysis

The temperature of oxides phase formation fromprecursors (CuTiO3 and NiTiO3 precursors, respectively) wasdeterminated by TG-DTG-DSC analysis (fig.1. and 2).

The decomposition of CuTiO3 was a complex processin steps. The first step, up to 1730C, corresponding to 10.4%weight loss and accompanied by an endothermic effectwas probably due to the elimination of water and partialdecomposition of titanium isopropoxide.

There are at least two separate processes in the secondstep with weight loss of 9.28% and 10.03% respectively,both of them presenting exothermic effects on DSC curve.

First process that occur in 173–270°C temperature range,may be assigned to Cu(CH3COO)2 decomposition to CuCO3and also to futher decomposition of Ti(OC3H7)4. The secondprocess (between 270-490oC) was attributed to theformation of CuTiO3 phase. No apparent peak and

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significant weight loss was observed over 490°C. Probably,over this temperature, CuTiO3 crystalline lattice was formedby this method. (fig.1).

The thermodifferential curves of NiTiO3 precursorindicated that at about 120-137oC appeared the loss ofwater and partial decomposition of titanium isopropoxideand at up to 350oC, both Ni(CH3COO)2 and Ti(OC3H7)4 ,suffered decomposition reaction to NiO and TiO2 (fig.2).NiTiO3 become stabile at about 460oC. Finally, a smallexothermic peak at about 600oC evidence the formationof ordered or crystalline NiTiO3 phase as will bedemonstrated later by X-ray diffraction.

X-ray diffraction analysisThe X-ray diffraction patterns of MTiO3(M=Cu,Ni)

obtained from precursors calcinated at 6000C/3h arepresented in figure 3 and 4.

Fig.1. TG-DSC-DTA of CuTiO3 precursor obtained by the sol-gelmethod

Fig. 2. TG-DSC-DTG of NiTiO3 precursor obtained by the sol-gelmethod

Fig.3. X-ray diffraction pattern of NiTiO3

Fig. 4. X-ray diffraction patterns of CuTiO3

Fig.5 SEM micrographs for CuTiO3, calcined at6000C/3h

Fig.6. SEM micrographs for NiTiO3, calcined at6000C/3h

The XRD pattern of NiTiO3 presents characteristicdiffraction peaks of crystalline structure suggesting theilmenite structure of NiTiO3 with rhombohedral symmetry(fig.3). At this temperature, it was also observed that thepresence of anatase phases traces. The crystallite size ofpowders calculated by Scherrer formula can be determinedfrom the XRD and d= kΛ/βcosθ where d is the crystallitesize, assuming particles are spherical, k=0.9, Λ is thewavelength of radiation, β is the full width at half maximum(FWHM) of the diffracted peak and θ is the angle ofdiffraction. The average crystallites size value of NiTiO3 is104 nm. The lattice constants calculated by programPowder X for NiTiO3 are a = 5.03210 Å, b = 5.03210 Å, c= 13.79240 Å (JCPDS 75-3757).

The X-ray diffraction pattern of CuTiO3 reveals the highlycrystalline nature of the as-prepared powder. The CuTiO3powder obtained has cubic structure with monoclinicsymmetry (fig.4). The average crystallites size valuecalculated by Scherrer formula is 79nm. and the latticeconstants are a = 4,68370 Å, b= 3,42260 ´Å, c= 5.12880Å (JCPDS 73-6023). As in the NiTiO3 case, in XRD patternof CuTiO3 obtained in this work, the characteristic peaks ofanatase were also observed.

SEM analysisThe morphologies of NiTiO3 and CuTiO3 powders were

evaluated by scanning electron microscopy (SEM) and areillustrated in figures 5 and 6.

Both samples present particles with spherical shapeand form agglomerates with polihedral shapes. Theaverage aglomerates sizes are 110 nm for CuTiO3 and 170nm for the NiTiO3 respectively.

It was observed a higher tendency of the particles toform agglomerates in the case of NiTiO3 in comparisonwith CuTiO3.

EDAX analysisFurther evidence for the formation of CuTiO3 by the

proposed method in this work came from EDAX spectrum(fig.7).

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The specific surface area for CuTiO3 is 42m2/g and forthe NiTiO3 is 19m2/g.

Catalytic activity measurementsDescription of the micropilot plant laboratory

The catalysts activity was assessed by conductingcomplete oxidation tests for toluene in a fixed-bed quartztubular reactor with an inner diameter of 10mm. For eachexperiment 0.5 g of catalyst was used, mixed with 1g ofpowdered alumina to disperse the catalyst. Prior to thereaction, the catalyst was activated in-situ under air flowat 600°C for 2 h. After the catalyst bed was cooled to 100°C,a reactant mixture consisting of 0.062cm3/min toluene and160cm3/min O2 was fed to the reactor by bubbling air at arate of 800cm3/min. The temperature ramp of 5°C/min wasconsidered to be sufficiently slow to reach a pseudo-steadystate at every point.

The reactions were investigated in 235-6200Ctemperature range. At the exit of condenser-separator, abubbler with Ba(OH)2 saturated solution was attached andcatalytic activity efficiency (CO2 conversion) wasdetermined.

Oxidation reaction of the toluene involves a very simpleexperimental technique.

The catalysts performance was evaluated bydetermining the amount of carbon dioxide formed.

The oxidation reaction are:

C7H8 + 9O2 → 7CO2 + 4H2O (1)

The yield of CO2 was calculated using the followingequation:

(2)

where: ηCO2 = the obtained CO2 yield

ηCO2(p) = CO2 yield practical;ηCO2(t) = CO2 yield theoretically

Five experiences were made on NiTiO3 catalyst obtainedby sol-gel method at five different temperatures to establishthe minimum temperature when the total combustionappears (table1). The maximum feed flows at ambientcondition were 0.047 cm3/min toluene and 800 cm3/minair. The reactions were investigated in 280-6000Ctemperature range. A temperature slope was calculatedseparately for each experiment. The NiTiO3 temperatureslope was 15,360C/min.The catalytic activity of CuTiO3 fortoluene oxidation was measured in similar conditions withthat of NiTiO3 (table 2). The maximum feed flow at ambientcondition was 0.0625cm3/min toluene and 800 cm3/minair. The reactions were investigated in 245-6200Ctemperature range. Using CO2 practical and theoreticalvalues we calculated the conversion yields of tolueneoxidation reaction for both tested titanates. The CuTiO3temperature slope calculated was 53.810C/min.

The experiments reveal that CuTiO3 powder had the bestcatalytic activity (90%) on toluene oxidation. From thevariation of temperature versus reaction time werecalculated the slopes value: 53.810 C/min for CuTiO3 (fig.8a)

Fig.7. EDAX analysis of CuTiO3

Table 1OPERATION DATA AND

MATERIAL BALANCE FORTOLUENE OXIDATION ON

NICKEL TITANATE CATALYST

Table 2OPERATION DATA AND

MATERIAL BALANCE FORTOLUENE OXIDATION ON

COPPER TITANATE CATALYST

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Fig.8. Results of catalytic tests on toluene oxidation with CuTiO3 (a) and NiTiO3 (b) catalysts

and 15.360C/min for NiTiO3 (fig.8b) which represent veryimportant items of catalytic activities. To emphasize thetextural properties of these systems have been measuredthe specific surface area. The catalysts presents selectivityfor the oxidation reactions.

Also, the solvent used in catalyst synthesis plays animportant role upon the selectivity of tested catalysts.Based on the literature date the mixed oxide obtained inalcoholic medium have higher specific surface areas thanthose obtained in aqueous medium. Larger specific surfaceareas lead implicitly to higher catalytic activities values [3-5].

Depending on working conditions were establishedbenchmarks for the catalytic oxidation of toluene as:

- setting minimum firing temperature for oxidationreaction of toluene with air for each type of catalyst;

- temperature variation of the catalytic layer dependingon the duration of each experiment;

- CO2 yield in each experiment.

ConclusionsMTiO3 (M=Ni,Cu) powders have been prepared by a sol-

gel method using titanium isopropoxide – metallic acetates- isopropyl alcohol systems.

XRD pattern of NiTiO3 indicates an ilmenite crystallinestructure with rhombohedral symmetry (with averagecrystallites size 104 nm) and that of CuTiO3 indicates acubic structure with monoclinic symmetry (with averagecrystallites size 76 nm).

Both MTiO3 samples present particles with sphericalshape and form agglomerates with polyhedral shapes (thetendency to form agglomerates is higher in the case ofNiTiO3 in comparison with CuTiO3).

The catalytic activity of MTiO3 was tested on the toluenecombustion. Thermal combustion of toluene begins atrelatively low temperatures, 2450C for CuTiO3 and 2800Cfor NiTiO3. The higher efficiencies were obtained at 3000Cfor CuTiO3 (90%) and 4080C for NiTiO3 (43%). The highercatalytic value of CuTiO3 in comparison with that of NiTiO3is probably due to the smaller size of the particles and thehigh specific surface area values.

Acknowledgements: The work has been funded by the SectoralOperational Programme Human Resources Development 2007-2013of the Romanian Ministry of Labour, Family and Social Protectionthrough the Financial Agreement POSDRU/6/1.5/S/19.

References1. CHUANG S. H., HSIEH M. L., WU S. C., LIN H. C., CHAO T. S. andHOUY T. H., in Fabrication and Characterization of High-k DielectricNickel Titanate Thin Films Using a Modified Sol–Gel Method, J. Am.Ceram. Soc.,1–5, 20102. MOHAMMADI M.R., FRAY D.J., in Mesoporous and nanocrystallinesol-gel derived NiTiO3 at the low temperature: Controlling thestructure, size and surface area by Ni:Ti molar ratio, Solid StateSciences 12, 2010, 1629-16403. LOPES K.P., CAVALCANTE L.S., SIMOES A.Z., VARELA J.A., LONGOE., LEITE E.R., in NiTiO3 powders obtained by polymeric precursormethod: Synthesis and characterization, Journal of Alloys andCompounds 468, 2009, 327–332 4. EPIFANI M., MELISSANO E., PACE G., SCHIOPPA M., in Precursorsfor the combustion synthesis of metal oxides from the sol–gelprocessing of metal complexes, Journal of the European CeramicSociety 27, 2007, 115–1235. MURUGAN A.V., SAMUEL V., NAVALE S.C., RAVI V., in Phase evolutionof NiTiO3 prepared by coprecipitation method, Materials Letters 60,2006, 1791–17926. JIANG J., GAO Q., CHEN Z., HU J., WU C., in Syntheses,characterization and properties of novel nanostructures consistingof Ni/titanate and Ni/titania, Materials Letters 60, 2006, 3803–38087. HUANG J., WANG S., ZHAO Y., WANG X., WANG S., WU S., ZHANG S.,HUANG W., in Synthesis and characterization of CuO/TiO2 catalysts forlow-temperature CO oxidation, Catalysis Communications 7, 2006,1029–1034 8. LIN Y.J., CHANG Y. H., YANG W. D., TSAI B. S., in Synthesis andcharacterization of ilmenite NiTiO3 and CoTiO3 prepared by a modifiedPechini method, Journal of Non-Crystalline Solids 352, 2006, 789–794;9. LIFEROVICH R. P., MITCHELL R. H., in Rhombohedral ilmenitegroup nickel titanates with Zn, Mg, and Mn: synthesis and crystalstructures, Phys Chem Minerals, 2005, 32: 442–44910. JACOB K.T., SAJI V.S., REDDY S.N.S., in Thermodynamic evidencefor order–disorder transition in NiTiO3, J. Chem. Thermodynamics39, 2007, 230–23511. JITARU I., OPREA O., MANDEA F., ALEXANDRU M. G., STANESCUM. D. and STÃNICÃ N., in Titanates from oxime-containing complexprecursors, Revue Roumaine de Chimie, 2007, 52(10), 941–948;12. LIN Y. J., CHANG Y. H., CHEN G. J., CHANG Y. S., CHANG Y. C., inEffects of Ag-doped NiTiO3 on photoreduction of methylene blue underUV and visible light irradiation, Journal of Alloys and Compounds479, 2009, 785–79013. NI Y., WANG X., HONG J., in Nickel titanate microtubes constructedby nearly spherical nanoparticles: Preparation, characterization andproperties, Materials Research Bulletin 44, 2009, 1797–180114. MORALES-RODRIGUEY A., JIMENEZ-MELENDO M., DOMINGUEZ-RODRIGUEZ A., BRAVO-LEON A., in High-temperature plastic behaviorof reaction-bonded CuO and TiO2 co-doped alumina–zirconia,Materials Science and Engineering A 387–389 2004, 618

Manuscript received: 23.12.2010

a b

REV. CHIM. (Bucharest) 63 No.3 2012http://www.revistadechimie.ro268

Removal of Nitrate from Water by Two Types of SorbentsCharacterization and sorption studies

GINA ALINA TRAISTARU1, CRISTINA IOANA COVALIU1*, G.P. GALLIOS2, DIANA LUCIANA CURSARU3, IOANA JITARU1

1Politehnica University of Bucharest, Faculty of Applied Chemistry and Material Science, 1-5 Polizu Str, 11061,Bucharest, Romania2Aristotle University of Thessaloniki, Department of Chemistry, GR-54124 Thessaloniki, Greece3 Petroleum-Gas University of Ploiesti, Faculty of Petroleum and Petrochemistry, Department of Petroleum Engineering andPetrochemistry, 30 Bucharest Blv., 100680, Ploiesti, Romania

The sorption of nitrate using different sorbents is an important process for water treatment. This studypresents the removal of nitrate from water by two types of sorbents: CuTiO3 and CuFe2O4. CuTiO3 wassuccessfully prepared by a sol-gel method and CuFe2O4 by a co-precipitation method. The sorbents obtainedhave been structural, morphological and textural characterized by X-ray diffraction, scanning electronmicroscopy (SEM), specific surface area (BET) and sorption studies for nitrate in water. Batch experimentswere conducted under specific operating conditions and the excellent adsorption ability for nitrate resulted atpH = 4. The effects of co-anions (SO4

2-) in water at different nitrate concentration was also studied todemonstrate the influence of ionic strength on the nitrate adsorption.

Keywords: copper titanate, copper ferrite, nitrate anion, sorption studies

In recent years, nitrate concentration is increasing ingroundwater, grow in many parts of the world due toincreased usage of nitrogenous fertilizers and discharge ofdomestic and industrial wastewater [1-10]. Nitrate anionis potentially harmful because it can be transformed intonitrite in the human body, which can cause blue babysyndrome and it is also a precursor of the carcinogenicnitrosamines [11-17]. Various environmental regulatoryagencies including the U.S. Environmental ProtectionAgency (U.S. EPA) have set a maximum contaminant level(MCL) of 10 mg/L of NO3

- in drinking water [2].The metal titanates are universally known as inorganic

functional materials with wild applications in surroundingprotection [18].

The aim of this study is to evaluate the adsorptioncapacity of nitrate from water with sorbents like CuFe2O4or CuTiO3.The effects of the presence in water of otheranions (like SO4

2-) have also investigated on the syntheticnitrate solutions. The copper titanate was prepared by sol-gel method and copper ferrite was prepared by co-precipitation method. A laboratory study was conductedto investigate the ability of different sorbents to the removalof nitrate from synthetic nitrate solution.

Experimental partMaterials and equipment

Ti(OCH(CH3)2)4, Cu(CH3COO)2)•4H2O, Ni(NO3)2·6H2O,Fe(NO3)3

. 9H2O were purchased from Sigma Aldrich. NH3and C3H7OH were purchased from S.C. Chimexin S.A.NaNO3 was purchased from Alfa Aesar, and has 99% purity.K2SO4 and HCl were purchased from Merck. All reagentswere used without further purification.

The morphology of the sorbents was determined byscanning electron microscopy (SEM) using HITACHIS2600N scanning electron microscope. The powders wereanalyzed by using X-ray diffraction (XRD) on D8 DiscoveryBruker diffractometer, using Cu K (1.5406 A) radiationoperating with 30 mA and 40 kV in 10–700 2 range.

* email: [email protected]

The specific surface areas were measured in ASAP 2020V3.04 H apparatus by using Brunauer-Emmet-Teller (BET)method with nitrogen at 77K.

The concentration of nitrate in the solutions wasdetermined by spectrophotometrically method at 220nmusing as reagent 1N HCl [18]. UV-VIS spectra wererecorded on Jasco V 560 spectrophotometer.

The pH of solution was determined with a TOAElectronics Ltd., HM-35 V digital pH meter.

pH studiesIn order to investigate the effect of pH on nitrate

adsorption, the pH of the nitrate solutions (0-300mg/L) wasadjusted from 4 to 6. The initial pH of the solution wasadjusted by using 0.1M HCl or 0.1M NaOH and sorbent(0.015 g) was added to 30mL solution. The mixture wasshaken using a temperature-controlled orbital shaker. Afteradsorption, the final pH of all solutions was measured andthe value providing the maximum nitrate removal wasdetermined.

Sorption pH is one of the factors that have been found toaffect significatively the sorption process. Maximum nitrateremoval occurred at pH= 4, because the predominant formof nitrate is at this pH.

Sorbents preparationThe precursor of CuTiO3 was prepared by mixing a

solution of 0.5 mmol Cu(CH3COO)2•4H2O in 50 mL ethanoland 0.5 mmol Ti[OCH(CH3)2]4 (in Cu: Ti = 1:1 molar ratio)in 50 mL of isopropanol. The solution obtained was heatedunder reflux at 800C, four hours, until a gel was formed.This gel was separated, filtered and dried in a capsule at1500C. The solid precursor was calcined at 7000C for 5hours and the powder obtained was analysed by scanningelectron microscopy (SEM) and X-ray diffraction analysis.

CuFe2O4 was obtained by co-precipitation method, fromFe(NO3)3 . 9H2O-Cu(NO3)2

. 2H2O in a 2:1 molar ratio at pH= 12 obtained by adding ammonia 25% as precipitation

o

REV. CHIM. (Bucharest) 63 No. 3 2012 http://www.revistadechimie.ro 269

agent. The reaction mixture was kept under reflux at 700Cfor 3h, until a black precipitate was formed. After thepurification process which implies washing ten times withwater and ethanol (10:1), the precursor was calcined at4000C for 3h in order to obtain a single phase CuFe2O4powder.

Copper titanate and copper ferrite powders obtained bythe precursors calcinations at 7000C for 5h and 5000C for2h respectively, were characterized by SEM, BET and XRDanalysis.

Nitrate adsorption studiesA stock nitrate solution (200-500 mg/L) was used in

adsorption experiments. The required concentration of thenitrate solution was prepared by serial dilution of stocksolution. We have worked at the different concentration 0to 300 mg/L nitrate and different pH between 4 and 6, toobserve the evolution of sorbents at different concentrationand pH. A fixed amount of the adsorbent was added tonitrate solution taken in 50mL Erlenmeyer flask, whichwere placed in a orbital control shaker. The solutions werestirred continuously at constant temperature to achieveequilibrium. After equilibrium, the solid was separated bycentrifugation. The adsorbent was removed bycentrifugation (6000 rpm) and the concentration of thecorresponding anion remaining in the supernatant wasdetermined spectrophotometricaly at =220 nm.

Results and discussionsX-ray diffraction

The copper titanate obtained has cubic structure withmonoclinic symmetry (fig.1). The average crystallites sizevalue calculated by Scherrer formula is 30 nm. The XRDpattern presented in figure 2 corresponds to CuFe2O4 withspinel structure and cubic symmetry. The averagecrystallites size was estimated at 40 nm, with Scherrerformula.

CuFe2O4 (fig.6). Both samples present spherical shapeparticles. The average particles size is 70 nm for CuTiO3and 90 nm for CuFe2O4 and the average aglomerates sizeis 100 nm for CuTiO3 and 150 nm for CuFe2O4.

Fig.1. XRD patern of CuTiO3,calcined at 7000C, 5h

Fig.2. XRD patern of CuFe2O4,calcined at 5000C, 2h

SEM analysisThe morphology of CuTiO3 and CuFe2O4 powders,

calcined at 7000C/5h and 5000C/2h respectively, wasevaluated by scanning electron microscopy (SEM) and wasillustrated in figs.3 and 4. A higher tendency of the particlesto form agglomerates it was observed in the case of

Fig. 3. SEM micrography for CuTiO3

Fig.4. SEM micrography for CuFe2O4

Specific surface area and BJH adsorption/desorptionanalysis

Fig.5.Adsorption isotherm for CuTiO3

Fig.6.BJH adsorption dV/Dd pore volume for CuTiO3

The BET surface area for the CuTiO3 is 15.95m2/g (fig.5).The BJH adsorption cumulative surface area of pores is20.07m2/g and BJH desorption cumulative surface area ofpores is 21.11m2/g (fig.6). The BJH is the method of Barret,Joyner and Halenda for the pores distribution. The singlepoint adsorption total pore volume of pores less than 271.22nm diameter at p/p° = 0.99 is 0.10cm3/g.

REV. CHIM. (Bucharest) 63 No.3 2012http://www.revistadechimie.ro270

The BET surface area for the CuFe2O4 is 9.15 m2/ (fig.7).The BJH adsorption cumulative surface area of pores is10.0 m2/g and BJH desorption cumulative surface area ofpores is 9.91 m2/g (fig.8). Single point adsorption total porevolume of pores less than 443.5148 nm diameter at p/p° =0.99 is 0.02 cm3/g.

Adsorption isothermsExperiments were carried out in Erlenmeyer flasks

placed in a temperature controlled orbital shaker (stirringspeed of 150 min-1) for 24 h as it had been establishedpreviously that thus is equilibrium time. Fifteen miligramsof the sorbent were equilibrated to 30 mL of nitrate solutionat 22 ± 2oC using the background electrolyte 0.1M K2SO4.Sorbents were dried at 1000C three hours before startingthe experiments.

Batch adsorptions studies were performed as a functionof contact time, initial nitrate concentration, pH andinfluence of other interfering anion.

In the equilibrium sorption were determined:- the influence of equilibrium concentration on the

sorption capacity (uptake);- the comparative study of the sorption isotherms with

Langmuir isotherms type;In figures 9a and 9b it was presented the plot of sorbtion

for copper titanate and copper ferrite used as sorbents.Good sorbtion results were obtained both in the absenceof electrolyte and also in the presence of electrolyte.Maximal sorption capacity of nitrate was obtained at pH 4,at which this is the predominant form of the anion. In thecase of copper titanate the maximal sorption capacity was2.069 mg/L and in the case of copper ferrite was 0.951mg/L. The sorption equilibrium was obtained at pH = 4.

The impact of sulphate (SO42) anion, on nitrate removal

by the studied sorbents was investigated at 200mgL-1 ofinitial nitrate concentration. The concentration of sulphateanion was 0,1M. It was observed that nitrate adsorptionwas mainly influenced by the presence of sulphate anion.At ionic strength 0.1M, the concentration of nitrate

decresed. The percentage removal was found to decreasegradually with increase in pH and the optimum pH wasfound to be 4.

The Langmuir isotherm for the nitrate anionLangmuir isotherm characteristic equation is:

(1)

where: a = adsorption capacity at equilibrium, mg/g;1 = maximum adsorption capacity for a given set of

conditions to balance the entire monomolecular layer isoccupied, mg/g; Ce = concentration of solute in the systemat equilibrium, mg/L; b = equilibrium constant that dependson the nature of the adsorption system.

Langmuir equation can be written as a linearized asfollows:

(2)

The “b” constant and the maxim adsorption capacity“am”, can be determined from experimental data if theplot 1/A by 1/Ce. Graphical representation is a line thatintersects with the point Oy (0.1 / am) where you candetermine the “am”. Knowing am we determined the “b”of the value of tangent right angle that makes with the axisOx. Langmuir equation representation by the 1/a = f (1/Ce) for nitrate anion is shown in figure 10.

The caracteristics equation of experimental data is:

(3)

R2 = 0.9960 regression coefficientThe Langmuir equation characterizes well the

experimental data for nitrate ion. Since R2 has values over

Fig.7.Adsorption isotherm for CuFe2O4

Fig.8.BJH adsorption dV/Dd pore volume for CuFe2O4

Fig.9a) Plot sorption of NO3-, versus equilibrium

concentration obtained with CuTiO3 as sorbent

Fig.9b) Plot sorption of NO3-, versus

equilibrium concentration obtained withCuFe2O4 as sorbent

REV. CHIM. (Bucharest) 63 No. 3 2012 http://www.revistadechimie.ro 271

Fig.10. Langmuir equation representation for CuTiO3

0.95 can be considered that Langmuir equationcharacterizes the nitrate anion adsorption very well.

ConclusionsThe preliminary results of this study presents the

behaviours of copper titanate and copper ferrite for nitrateremoval from aqueous solutions. The results show thatthe adsorption effectiveness of copper titanate for nitratewas higher in comparison with copper ferrite regardless ofthe concentration of nitrate in the range of 0–300mg/L. Inthis study the particle dimension, the specific surface areaand the pH have influenced the adsorbtion capacity. Wehave obtained maximal adsorption capacity at pH=4 forcopper titanate (2.069 mg/L). The pH affects the adsorptionprocess, when the pH increased, the sorption capacitydecreased. Better results for nitrate sorption were obtainedwhen the experiments were carried out in the absence ofan electrolyte (SO4

2-). The Langmuir equation hascharacterized very well the sorption for nitrate anion.

Acknowledgements: The work has been funded by the SectoralOperational Programme Human Resources Development 2007-2013of the Romanian Ministry of Labour, Family and Social Protectionthrough the Financial Agreement POSDRU/6/1.5/S/19.

References1. A. BHATNAGARA, M. SILLANPA, A review of emerging adsorbentsfor nitrate removal from water, Chemical Engineering Journal 168(2011) 493–5042. Y. H. LIOU, S. L. LO, C.J. LIN, W. H. KUAN, S. C. WENG, Effects ofiron surface pretreatment on kinetics of aqueous nitrate reduction,Journal of Hazardous Materials B126 (2005) 189–1943. N. KIM NGA, D. KIM CHI, Synthesis, Characterizations and Catalyticactivity of CoAl2O4 and NiAl2O4 spinel- Types Oxides for NOx SelectiveReduction, Advances in Technology of Materials and MaterialsProcessing”, 6(2), (2004) 336-3434. N.I. CHUBAR, V.F. SAMANIDOU, V.S. KOUTS, G.P. GALLIOS, V.A.KANIBOLOTSKI, V.V. STRELKO, I.Z. ZHURAVLEV, Adsorption of fluoride,

chloride, bromide, and bromate ions on a novel ion exchanger, inJournal of Colloid and Interface Science 291 (2005) 67–745. T. PRADEEP, ANSHUP, Noble metal nanoparticles for waterpurification: A critical review, in Thin Solid Films 517 (2009) 64416. M. KARIMI, M. H. ENTEZARI, M. CHAMSAZ, Sorption studies ofnitrate ion by a modified beet residue in the presence and absenceof ultrasound, in Ultrasonics Sonochemistry 17 (2010) 711–717;7. N. ÖZTURK, T. E. BEKTAS, Nitrate removal from aqueous solutionby adsorption onto various materials, Journal of Hazardous MaterialsB112, (2004) 155–1628. M. CHABANI, A. AMRANE, A. BENSMAILI, Equilibrium sorptionisotherms for nitrate on resin Amberlite IRA 400, Journal of HazardousMaterials 165 (2009) 27–339. K. MAAZ, S. KARIM, A. MUMTAZ, S. K. HASANAIN, J. LIU, J. L. DUAN,Synthesis and magnetic characterization of nickel ferrite nanoparticlesprepared by co-precipitation route, Journal of Magnetism and MagneticMaterials 321 (2009) 1838–184210. Y. K. SHARMA, M. KHARKWAL, S. UMA, R. NAGARAJAN, Synthesisand characterization of titanates of the formula MTiO3 (M = Mn, Fe,Co, Ni and Cd) by co-precipitation of mixed metal oxalates, Polyhedron28 (2009) 579–58511. K. A. MATIAS, A. I. ZOUBOULIS, G. P. GALLIOS, T. ERWE, C.BLCOCHER, Application of flotation for the separation of metal-loadedzeolites, Chemosphere 55 (2004) 65–7212. C. H. GUO, V. STABNIKOV, V. IVANOV, The removal of nitrogen andphosphorus from reject water of municipal wastewater treatmentplant using ferric and nitrate bioreductions, Bioresource Technology101 (2010) 3992–399913. K. MIZUTA, T. MATSUMOTO, Y. HATATE, K. NISHIHARA, T.NAKANISHI, Removal of nitrate-nitrogen from drinking water usingbamboo powder charcoal, Bioresource Technology 95 (2004) 25514. A. AFKHAMI, T. MADRAKIAN, Z. KARIMI, The effect of acid treatmentof carbon cloth on the adsorption of nitrite and nitrate ions, Journalof Hazardous Materials 144 (2007) 427–431;15. T. NISHIKAMA, K. TARUTANI, T. YAMAMOTO, Nitrate and phosphateuptake kinetics of the harmful diatom Eucampia zodiacus Ehrenberg,a causative organism in the bleaching of aquacultured Porphyra thalli,Harmful Algae 8 (2009) 513–51716. D. WAN, H. LIUA, X. ZHAO, J. QU, S. XIAO, Y. HOU, Role of the Mg/Al atomic ratio in hydrotalcite-supported Pd/Sn catalysts for nitrateadsorption and hydrogenation reduction, Journal of Colloid andInterface Science 332 (2009) 151–15717. L. S. CLESCERI, A. E. GREENBERG, R. R. TRUSSELL, StandardsMethods- For examination of water and wastewater (1989), 17th Edition,Nitrites 4-128, Nitrates 4-14018. G. A. TRAISTARU, C. I. COVALIU, V. MATEI, D. CURSARU, I. JITARU,Synthesis and characterization of NiTiO3 and NiFe2O4 as catalysts fortoluene oxidation, Digest Journal of Nanomaterials and Biostructures,Vol. 6, No 3, July-September (2011), 1257-1263

Manuscript received: 25.08.2011

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CERCET RI PRIVIND ÎNDEP RTAREA IONILOR DE CUPRU DIN APA UZAT INDUSTRIALUTILIZÂND NANOMATERIALE NEPOLUANTE

Tel: 0722791791; E-mail: [email protected]

Abstract: In the context of heavy metals pollution, environmental friendly adsorbants having nanometer size represent an important alternative to conventional wastewater treatment methods from both economical and efficiency points of view. Thus, was evaluated the potential of two nanomaterials (maghemite, -Fe2O3and its corresponding hybrid, -Fe2O3- poli-DL-alanine) for copper ions removal from wastewater, at room temperature.

Keywords: wastewater treatment, nanomaterials, heavy metals, copper ions

Rezumat: În contextul polu rii cu metale grele, adsorban ii nepoluan i având dimensiuni nanometrice reprezint o alternativ important fa de metodele conven ionale de epurare a apelor, atât din punct de vedere economic, cât i din punctul de vedere al eficien ei. În acest sens, a fost evaluat poten ialul a dounanomateriale (maghemit , -Fe2O3 i hibridul corespunz tor, -Fe2O3- poli-DL-alanin ) de îndep rtare a ionilor de cupru dintr-o ap uzat , la temperatura camerei.

Cuvinte cheie: epurarea apei, nanomateriale, metale grele, ioni de cupru

vs

vs

Handbook of Industrial Pollution Control in Chemical Process and Allied Industries

Maghemite and Poly-dl-alanine Based Core–shell Multifunctional Nanohybrids for Environmental Protection and Biomedicine Applications

Water Research Symposium

Electrochemical procedures of copper recovery from residual waters and solid wastes

Interaction of Heavy Metals and Biological Sewage Treatment Process,

Cementation Treatment of Copper in Wastewater

Studies on the Pollution of Water by Lead and Other Heavy Metals Being Studies of River Ganga and Varuna River. Water Quality and Special Emphasis on Lead and Other Heavy Metals

Lead Removal with Adsorbing Colloidal Floatation

317Starch Based Products in

Heavy Metal Removal

Manual de control al polu rii industriale în procesului chimic i ale industriilor conexe

Nanohibrizi multifunc ionali pe baz de maghemit i poli-dl-alaninpentru aplica ii în protec ia mediului i biomedicin

Simpozionul cercet rii apei

Procedee electrochimice de recuperare a cuprului din ape reziduale i din de euri solide

Interaction of Heavy Metals and Biological Sewage Treatment Process,

Tratarea cuprului din apele uzate prin cementare,

Studii privind poluarea apei cu plumb i alte metale grele investigate in râurile Ganga i Varuna. Calitatea apei cu cercetari axate pe plumbului i alte metale grele

Lead Removal with Adsorbing Colloidal Floatation

317Produsele pe baz de

amidon utilizate pentru îndep rtarea metalelor grele,

ORGANIZING COMMITTEE SECRETARY

Prof. Ph.D. Eng. PIRN Ion

Assoc. Prof. Ph.D. Eng. BIRI Sorin Ph.D. Eng. VL DU Valentin

CIOCÂRDIA Cr i a

Ph.D. Eng. POPA Lucre ia PhD. Stud. Eng. TEFAN Vasilica Lect. PhD. Eng. DU U

PROGRAM COMMITTEE

Prof. Ph.D. Eng. BIRI Sorin tefan

–

–

Prof. PhD. Eng. Heri anu Nicolae P.U. Timi oara (RO)

Prof. PhD. Eng. C S NDROIU Tudor Prof. PhD. Eng. ENU Ion USAMV Ia i (RO);Prof. PhD. JOVANOVI Larisa –

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Prof. PhD. Eng. BRKI Miladin

Prof. PhD. Eng. B DESCU Mircea Prof. PhD. Eng. S R CIN Ion

Prof. PhD. Sc. Eng. BARAC S sa

st. PhD SELV Kemal Ondokuz May s Üniversity (TR)PhD. KABA Önder Bat Akdeniz Agricultural Research Institute

PhD. Eng. VL DU Valentin PhD. Eng. P UN Ani oara

Vasile Goldi ” Western

PhD. Eng. elazi ski T. Lect. PhD. Eng. H RM NESCU Monica

Lect. PhD. Eng. DU U Mihaela

Ph.D. Eng. Tomasz ELAZI SKI

HONORARY COMMITTEE

NATIONAL INSTITUTE OF RESEARCH-DEVELOPMENT FOR MACHINES AND INSTALLATIONS DESIGNED TO

AGRICULTURE AND FOOD INDUSTRY

BIOTECHNICAL SYSTEMS ENGINEERING

290 Splaiul Independen ei Str., sector 6, Bucharest

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CONTENTS No. Article Pg.

ŽEM S DIRBIMO PROCESO VERTINIMAS S KLOS GUOLIAVIET S PARUOŠIMUI IR PAS LIO TANKUMUI PAGERINTI

Kriau i nien Z., Veli ka R., ekanauskas S., Butkevi ien L.M., Masilionyt L, Šarauskis E.,

ŽEM S DIRBIMO TECHNOLOGIJ KUKUR ZAMS ENERGIJOS IR ŠESD RODIKLI ANALIZŠarauskis E., Buragien S., Romaneckas K., Kriau i nien Z., Jasinskas A., Adamavi ien A.,

Naujokien V.

TÜRK YE TARIM SEKTÖRÜNDE ENERJ KULLANIMI

METODA INTENSIMETRIEI STUCTURALE APLICAT LA IUL AMORTIZ RII VIBRA IILOR Ciocârdia D.C., Maghe i

INFLUEN A HIDROGENULUI ASUPRA VITEZEI DE ARDERE A BIOMASEI SOLIDE

Mih escu L., L z roiu Gh., Negreanu G.P., Pî I.

MODELARE MATEMATICA SI SIMULAREA COMPARATIVA A VIBRATIILOR COMBINATOARELOR SI CULTIVATOARELOR AGRICOLE

SIMULAREA ELEMENTARA SI COMPLEXA A POLUARII UNUI RAU PENTRU INSTRUIRE SI CONSTIENTIZARE DE MEDIU

MODELAREA PARAMETRIC A CUTIEI DE VITEZE CU IMPULSURI ÎN BAIE DE ULEI DE LA MA INA DE REGENERAT PAJI TI

P un A., Cheptea C., Manea D., David A., Neac u F.

/ MODELAREA MATEMATIC A PROCESULUI DE TREIER REALIZAT DE APARATELE DE TREIER CU ROTOARE

MULTIPLE

STUDIUL VIBRA IILOR UNEI LAME DE PLUGOr anu N.,

INFLUEN A I STEMULUI DE CONDI IONARE ASUPRA VALORII CULTURALE A SEMIN EI

CONSIDERA II TEORETICE PRIVIND PROIECTAREA INSTALA IEI PNEUMATICE DE TRANSPORT UTILIZAT DE UN ECHIPAMENT

PNEUMATIC DE SEMANAT ALVEOLAR A SEMINTELOR MICI SI FOARTE MICI Vi an A.L., Milea D.

VINDROVER TRACTAT PENTRU RECOLTAREA COMBINAT CU CONDI IONAREA PLANTELOR COSITE I L SAREA ÎN BRAZDE

Ciuperc R. Dumitra cu A., tefan V.

CERCETARI EXPERIMENTALE PRIVIND TOCAREA PLANTELOR MEDICINALE

METOD NUMERIC PENTRU DETERMINAREA PROPRIET ILORINER IALE ALE UNEI PL CI DE FORM ARBITRAR

CERCET RI TEORETICE CU PRIVIRE LA VALORILE PROPRII ALE DISCURILOR ÎN MI CARE DE ROTA IE, SUPUSE LA TEMPERATURI VARIABILE PE RAZ I GROSIME

Com nescu I.S., Radu Gh.

O ANALIZ PRIVIND RECUPERAREA C LDURII DE JOAS TEMPERATUR FOLOSIND CICLUL RANKINE ORGANIC

CERCET RI EXPERIMENTALE CU UTILAJUL MULTIFUNC IONAL MOTOCULTOR M7,5 SI PLUG REVERSIBIL PR

VALORIFICAREA SUPERIOARA A LAVANDEI PRIN OBTINEREA DE ULEIURI VOLATILE APLICAND METODA DISTILARII CU VAPORI DE APA

ANALIZA STATIC STRUCTURAL A ORGANELOR DE LUCRU ALE

CULTIVATOARELOR AGRICOLE Biri S. t., Maican E., Marin E., Bungescu S., Vl du V., Ungureanu N., Vl du D.I., Atanasov At.

MANAGEMENTUL INDUSTRIEI O ELULUI ÎN CONTEXTUL DEZVOLT RII DURABILE

S r cin I., Dobrot G., Ganea

TEHNOLOGIE INOVATIV PENTRU MECANIZAREA LUCR RILOR DE MODELAT I SEM NAT DIRECT ÎN CÂMP A CULTURII DE CEAP

P un A., Neac u F.

-

CONSIDERA II PRIVIND UTILIZAREA UNOR ELEMENTE DE ECODESIGN ÎN CONSTRUC IA MA INILOR AGRICOLE

Christu I, Br c cescu C., Gheorghe G., Ganea Christu I., Neac u F., Marian M., Selvi K.C.

PROPUNERI PENTRU ÎMBUN T IREA PROCESULUI DE DISTRIBU IE A SEMIN ELORS r cin I., Pandia O., Gheorghe M, Iordache V., Ganea , S r cin I.A, PhD.Popa L.

ANALIZ NUMERIC I EXPERIMENTAL A VIBRA IILOR SISTEMULUI DE SUSPENSIE AL UNEI MA INI AGRICOLE

HIDRÓLISIS Y SEPARACIÓN DE BIOMASA LIGNOCELULÓSICA EN UN PROCESO AL SULFITO CON EL OBJETO DE VALORIZAR LAS PRINCIPALES FRACCIONES DENTRO DEL CONCEPTO DE BIO-REFINERÍA

PIANIFICAZIONE DI SISTEMI INTEGRATI PER L’ APPROVVIGIONAMENTO DI ACQUE NATURALI E RISORSE IDRICHE NON CONVENZIONALI IN AGRICOLTURA: LA FATTIBILITA’ DEL RIUSO DI EFFLUENTI SECONDARI

URBANI IN DISTRETTI IRRIGUI DELLA PUGLIA

–FOTOCATALIZATORUL TiO2 UTILIZAT IN EPURAREA APELOR –

Biri S. t., Paraschiv G., Fodorean ,Ghi escu C., Matei E.

YULAF YET T R C L NDE ATIK B YOKÜTLEN N ENERJ OLARAK DE ERLEND R LMES., Selvi K.Ç., Kaba Ö., Vladu

STUDIU COMPARATIV PRIVIND BIOSINTEZA DE PIGMENTI IN 4 TULPINI MUTANTE DE MONASCUS IN CULTURA SUBMERSA PE MEDIU MINIMAL

Ferde M., Dinca M., Stefan M.

DETERMINAREA INTERDEPENDEN EI DINTRE CANTITATEA DE CLOR REZIDUAL LIBER I CON INUTUL DE

COMPU I AMONIACALI LA DEZINFECTAREA UNEI APE UZATE CONTAMINAT MICROBIOLOGIC

Safta V.V., Ciuc V

ANALIZA ENERGETIC A PROCESULUI DE FABRICA IE A FOLIILOR AGRICOLE BIODEGRADABILE

ASPECTE ECONOMICE ALE COMBATERII FITOSANITARE CU SUBSTANTE NEPOLUANTE IN LIVEZI

Dumitra cu A., Platon V.

/ MONITORIZAREA VITEZEI VANTULUI LA DIFERITE INALTIMI FATA DE SOL

IN ORASUL BUCURESTI Rus nescu C.O., Biri Rus nescu

UTILIZAREA PROCEDEULUI DE OSMOZA INVERSA PENTRU OBTINEREA DE APA POTABILA DIN SURSE POLUATE CU NITRATI PENTRU COMUNITATI RURALE Ciocânea A., Lep datu I.,

STUDII PRIVIND PRODUCEREA BIOGAZULUI DIN CULTURI ENERGETICE Dinc M., Voicu Gh., Paraschiv G., Ungureanu N., Toma L. , Moiceanu G. , Vl du V., Z bav B. .

SISTEM OPEN-SOURCE CU COSTURI REDUSE PENTRU MONITORIZAREA I CONTROLUL FACTORILOR DE MEDIU ÎN SERE

INFLUEN A TEMPERATURII ASUPRA PRODUC IEI DE BIOGAZ ÎNTR-O INSTALA IE DE CAPACITATE MICToma M.L., Voicu Gh., Paraschiv G., Vl du V., Dinc M., Voicea I., Ungureanu N.

PRETRATAREA BIOMASEI (CULTURILOR ENERGETICE) PENTRU ÎMBUN T IREA PROCESULUI DE DIGESTIE ANAEROBIC – REVIEW

EVALUAREA IMPACTULUI CONTAMIN RII CU MOTORIN A SOLULUI - O ABORDARE ECOLOGIC

CONSIDERA II PRIVIND IMPORTAN A CULTURII DE PAULOWNIA anciu A., Vl du V., Grigore I., Soric C., Cristea (Danciu) M.A., Muscalu A., Pruteanu A., Marin E., Usenko M.

CARACTERIZAREA FIZICO- CHIMIC I MICROBIOLOGIC A APEI DE LAVAND OB INUT CA PRODUSSECUNDAR, DIN ULEIUL VOLATIL DE LAVAND (Lavandula angustifolia L)

, Vl du V., Marin E., Popescu C.

CONSIDERA II PRIVIND OB INEREA ULEIULUI VOLATIL DE LAVAND (LAVANDULA ANGUSTIFOLIA MILL.), ÎNTR-OINSTALA IE DE EXTRAC IE PRIN ANTRENARE CU ABURI

G geanu G., Marin E., G geanu I., G geanu P., Popescu C.

ECHIPAMENTE DE BAZ PENTRU TRATAREA MECANIC A APEI UZATEZ bav B. ., Voicu Gh., Ungureanu N., Dinc M., Safta V.V.

OPTIMIZAREA FUNC ION RII ECHIPAMENTELOR DE FILTRARE MECANIC PRIN SEPARAREA PAR IAL A SOLIDELOR UTILIZÂND UN DECANTOR DE N MOL

SWAP ——

TRACTORIZARE DE AUTOMOBILE, CONCEPT AMERICAN APLICABIL AGRICULTURII DIN ESTUL EUROPEI

/

:

METODE DE M SURARE A CONCENTRA IILOR DE GAZE UTILIZATE ÎN EVALUAREA CALIT II MEDIULUIC l mar A., G man G.A.,. Pup zan D., Simion S.

MODELAREA MATEMATIC A PROCESULUI DE FR MÂNTARE LA UN MALAXOR ORIZONTAL

TEHNOLOGII EFICIENTE ENERGETIC PENTRU PRODUCEREA ETANOLULUI DIN BIOMAS LIGNOCELULOZICMaican E., Teixeira J.A., Ferde M.,

SOYA SAPININ TASARIM PARAMETRES LE LG L BAZI MEKAN K ÖZELL KLER N N BELIRLENMESIKaba Ö., Selvi K.Ç., Vl du V., Gürdil G.A.K., Demirel B.

DETERMINAREA UNOR CARACTERISTICI MECANICE ALE SEMIN ELOR OLEAGINOASE UTILIZÂND TESTELE DE COMPRESIUNE UNIAXIAL

Ionescu M., Voicu Gh., Biri S. t., tefan E.M., Ungureanu N., Dinc M.N.

INDICELE DE C DERE VS. INDICELE DE LICHEFIERE ÎN ESTIMAREA ACTIVIT II ALFA-AMILAZICE DIN F INURILE DE PANIFICA IE

tefan E.M., Voicu Gh., Constantin G.A., Ferde M., Ionescu M.

INTERDEPENDEN A DINTRE MASA I DIAMETRU MAXIM ÎN CAZUL A TREI SOIURI DE MERE I CORELAREA DINTRE PARAMETRII DE V T MARE I CIOCNIREA ACESTORA

CONTRIBU II TEORETICE LA STUDIUL DINAMICII SEPARATOARELOR VIBRATOARE ACTIONATE ELECTROMAGNETIC IN SCOPUL PRELUCRARII PRIMARE A SEMINTELOR DE CEREALE Br c cescu C.,

G geanu I.,

TEHNOLOGII DE PRELUCRARE A FRUCTELOR APARTINAND GRUPEI DRUPACEELOR SI POMACEELOR IN CADRUL FERMELOR POMICOLE FAMILIALE

P un A., Marin E., Ionit Gh., tefan V., Epure M.

STUDII I CERCET RI REFERITOARE LA PROCEDEUL TEHNOLOGIC DE USCARE A PLANTELOR MEDICINALE

MONITORIZAREA ELECTROMAGNETIC A CRE TERII I FRUCTIFIC RII UNOR SOIURI DE M R ÎN LIVADChristu I., Velcea M., Laz r G., Br c cescu C.

OPTIMIZAREA CONSUMULUI ENERGETIC LA MALAXAREA UNOR LICHIDE UTILIZATE IN INDUSTRIA ALIMENTAR

,

Hyssopus officinalis l.) CERCET RI EXPERIMENTALE PRIVIND PROCESUL DE SORTARE LA HERBA DE ISOP (Hyssopus officinalis l.)

DETERMINAREA DURATEI DE RELAXARE LA SOLICITARI STATICE DE COMPRESIUNE A MERELOR DIN SOIUL IDARED

ering D., Vintil M., Popa L., tefan V., Petcu A.

(MAURITIANA LAM CV. TUFAHI)

–

OCENA WDRO ENIA PROGRAMU KAIZEN W OPINII PRACOWNIKÓW ZAK ADU PRZEMYS OWEGO -REZULTATY BADA EMPIRYCZNYCH

Kara E., mieta ski R., Cilan T.

APLICAREA METODEI DRUMULUI CRITIC (CPM) ÎN PLANIFICAREA REPAR RII MOTOARELOR DE TRACTOR

EVALUAREA GRADULUI DE COMPACTARE A SOLULUI PRIN TESTE DE PENETROMETRIEVl du V., Voicu Gh., Biri S. t., Dinc M., Cujbescu D., Persu C., Laz r G.

METODA DE RECUNOASTERE A IMAGINILOR IN AGRICULTURA PENTRU CONTROLUL UNUI ECHIPAMENT INTELIGENT DE PRASIT

Marin E., Vl du V., Voicu Gh., Br c cescu C.

INFLUEN A ELASTICIT II TIJELOR DE SUSPENDARE ASUPRA MI C RII CIRCULARE A SITEI PLANE PENTRU CERNEREA PRODUSELOR DE M CINI

CONSIDERA II PRIVIND STADIUL ACTUAL AL DISPOZITIVELOR DE CUPLARE EXISTENTE PE TRACTOARELE AGRICOLE

Mircea I.D., David L., Dumitru I., Vl du V., Marin E., Popa L., tefan V.,

STUDIUL UNOR CARACTERISTICI DEFINITORII PENTRU FENOMENE SPECIFICE PROCESULUI DE UNGERE DIN MOTOARELE CU APRINDERE PRIN COMPRIMARE ALE TRACTOARELOR

Cri an M. A., B ldean D.

PUTEREA CALORICA - O PROPRIETATE IMPORTANTA A BIOMASEI LEMNOASE

DESIGN ECOLOGIC AL APARATULUI ELECTROCASNIC 3 îN 1: CUPTOR CU MICROUNDE, PR JITOR DE PÂINE I SANDWICH MAKER

–DESIGN INTELIGENT AL APARATULUI ELECTROCASNIC – FIER DE C LCAT

TENDIN E NOI PRIVIND ÎNTRE INEREA CULTURILOR AGRICOLE PRIN METODE NECONVENTIONALE heorghe G., Mateescu M., P un A., Marin E., Matache M., Br c cescu C.

CONSIDERATII PRIVIND IMPORTANTA CULTURII DE SOIAIN HRANA OAMENILOR SI ANIMALELOR\ Ciuperc R., tefan V.

MPORTAN A UTILIZ RII ENERGIEI REGENERABILE SUB FORM DE BIOMASG geanu I., Voicu Gh., Br c cescu C., tefan V., elazi ski T

CARACTERISTICI FARINOGRAFICE ALE ALUATULUI DIN F IN ALB DE GRÂU I F IN DE SECAR

Munteanu M., Voicu Gh., tefan E.M., Constantin G.A., Popa L., Mihailov

CONSIDERA II PRIVIND STADIUL ACTUAL AL MA INILOR CU COMAND PROGRAM DIN INDUSTRIA PRELUCR TOARE

stu I., Br c cescu C.

REDUCEREA EFECTELOR POLUANTE LA EXECUTAREA MECANIZAT A LUCR RILOR ÎN AGRICULTUR

Epure M., P un A., Br c cescu C., G geanu I.

ASPECTE TEORETICE PRIVIN PROCESUL DE USCARE CONVECTIVGirleanu I.C., C s ndroiu T., Petcu A.S.

CERCET RI EXPERIMENTALE ASUPRA PROCESELOR DE LUCRU ALE MA INII DE DISTRIBUIT FURAJE Nedelcu A., Ciuperc R., Popa L., tefan V., Dumitra cu A Petcu A., Laz r G.

CERCET RI PRIVIND DEZVOLTAREA UNOR ECHIPAMENTE INOVATIVE DE FERTIRIGA IE

ov ial Gh T n sescu N.VELOCITYS AND PRESSURE DISTRIBUTION ANALYSIS IN THE CICLON /

ANALIZA DISTRIBU IEI VITEZELOR I PRESIUNILOR ÎN CICLONtefan V., Ciuperc R., Nedelcu A., M., Veringa D., Laz r G., Zaica A.

CONSIDERATIONS ON THE CONSTRUCTION OF THE DISTRIBUTING EQUIPMENT OF SOLID ORGANIC FERTILIZERS/

CONSIDERATII PRIVIND CONSTRUC IA APARATELOR DE DISTRIBU IE A ÎNGR MINTELOR ORGANICE SOLIDE

tefan (Popa) V., Popa L., Ciuperc R., Nedelcu A., Veringa D.EXPERIMENTAL RESEARCH OF AGRICULTURAL EQUIPMENT TYRES DESIGNED TO THEIR RATIONAL USE / CERCETAREA EXPERIMENTALA A PNEURILOR DE PE ECHIPAMENTELE AGRICOLE ÎN VEDEREA UTILIZ RII

RA IONALE ALE ACESTORA

METODOLOGIE DE EXPERIMENTARE LA UN ECHIPAMENT DE TRATAT SEMINTE CU TRANSPORTOR ELICOIDAL CU PERII

DETERMINAREA PERIOADEI DE RELAXARE LA COMPRESIUNEA STATIC A MERELOR DIN SOIUL GOLDEN DELICIOS

Vering D., Vintil M., Popa L., tefan V., Petcu A.S.

CERCET RI PRIVIND INFLUEN A PARAMETRILOR MEDIULUI ASUPRA PROCESULUI DE USCARE A FURAJELOR DE VOLUM Ciuperc R., Popa L., Laz r G, Stefan V.,

MODELAREA AGREGATULUI TRACTOR - MASINA SEMIPURTATA

OPTIMIZAREA UNUI ECHIPAMENT PNEUMATIC DE SEM NAT SEMIN E LEGUMICOLE ÎN T VI ALVEOLARE I STRAT NUTRITIV

Vi an A.L.,

CONSIDERA II ASUPRA COMPONENTELOR SISTEMULUI DE SUSPENSIE AL TRACTOARELOR AGRICOLEDu u I.C., Du u M.Fl., Biri Sorin tefan, Ganatsios S.

FOTOCATALIZATORUL TiO2 UTILIZAT IN EPURAREA APELOR -

Prof. Ph.D. Eng. Biri S. t.Stud. Ghi escu C.

Phone: +40722791791; E-mail: [email protected]

Abstract: Recently semiconductor photocatalytic processes have shown a huge potential for using within the wastewater treatment technologies, being considered as clean “zero” waste technologies. The review focuses on presenting the background and principles of using TiO2 semiconductor as photocatalyst in advanced oxidation process applied for treatment of wastewater containing organic pollutants.

Keywords: TiO2, photocatalysis, wastewater treatment

water, the technology is called “clean and green” [3].

Rezumat: Recent, procesele fotocatalitice pe baz desemiconductori au ar tat un poten ial crescut de utilizare în cadrul tehnologiilor de epurare a apei, fiind considerate tehnologii curate din care nu rezult de euri. Lucrare se axeaz pe prezentarea principiilor care stau la baza utiliz rii semiconductorului TiO2 ca fotocatalizator în procesul de oxidare avansat aplicat în scopul epur riiapei uzate care con ine poluan i de natur organic .

Cuvinte cheie: TiO2, fotocataliz , epurarea apelor.

limitat la sursele de ap ii din ap ;

b) urbanizarea rapid

d) modific rile cantitative se g sesc în ap ;d) existen a în ap a unor compu i chimici noi cu ac iune poluant , cunoscându se c mai mult de 300 de noi

i a diversific rii industriei,necesit noi tehnologii de epuare a apelor uzate cu eficien ridicat i far împact asupra mediului înconjur tor [9,

Una dintre noile tehnologii se bazeaz pe procesul doxidare avansat , care implic utilizarea semiconductorului

Oxidarea fotocatalitic folosind nanoparticulele de i const în mineralizarea

otal sau în descompunerea poluan ilor organici din ap ,

i ap , Hsolar în scopul tratamentului prin fotocataliz a apei, tehnologia se nume te „ecologic i verde”

În practic , pân în prezent, tor [10]. Multiplele sale

se cristalizeaz în mod naturtrei forme: rutil, anatas i brookit. Rutilul este cel mai r spândit

excitat atât de lumina vizibil cat i de lumina ultraviolet (cu lungimi de und mai mici de 390 nm) [7,6].

ea cristalin tetragonal , dar au unit i spa iale de re ea diferite. Brookitul nu este excitat de

ristalin octorombic poate fi transformat în rutil prin aplicarea tratamentului termic

Crt. No. Advantages Disadvantages

E

poate fi descris ca fiind o reac ie fotoindus care este accelerat de prezen a unui catalizator i este ini iat de un foton cu energie egal sau mai mare dec t energia benzii interzise a

Semiconductor au banda de valen (VB) ocupat cuelectroni ce au energie stabil i o banda de conduc ie de energie înalt (CB

În cazul utiliz rii TiO2 în fotocataliz , procesul ar putea fi explicat dup cum urmeaz : când este iradiat cu energie corespunz toare E

ctronul se mut din banda de valen în banda de conduc ie (CB) i in acela i timp se creaz goluri (vacan e l sate de electroni) în banda de valen (VB). Aceste perechi de electroni/goluri migreaz spre suprafa , unde particip la reac ii redox cu substan ele adsorbite (poluan i organici) pe suprafa aTiO

interzise este 3.2 eV pentru anatas i 3 eV pentru rutil, iar lungimile de und corespunz toare sunt 388 nm, i

nm. Acest lucru înseamn c la iradierea cu lumin UV, cu lungime de und mai mic decât cea corespunz toare benzii interzise, se ini iaz fotoreac ia.Electronul este fotoexcitat spre banda de conduc ie (CB)

–

este iradiat cu lumin UV sub 400 nm, atinge temperaturi extrem de ridicat , având valori mai

0 °C care oxideaz tose ap si

–

suspendate în ap au loc dou procese în urma c rora rezult dou specii active

electromii fotoindu i în CB care reac ionez cu oxigenul

difuzeaz la suprafaioneaz cu moleculele de ap absorbite,

este de obicei descries dup cum urmeaz [2].

carrier trapping of e :

H O

where:

a cum este prezentat în literatura de specialitate

succes în prototipuri de sta ii de epurare [1, 15, 5]. Câteva exemple de poluan iii de natur organic care se pot îndep rta i cu succes din ap sunt

ezenta i in Tabelul 2.

CH3CHO Acetaldehyde C6H4 (CH3)OH Cresol CH3COOH Acetic acid Cl2C6H3OH Dichlorophenol CH3COCH3 Acetone C12H10Cl2N2 Dichlorobenzidine

C3H4O Acrolein (CH3)2NNO Dimethylnitrosamine C3H4O2 Acrylic acid C12H4Cl4O2 Dioxin C6H6 Benzene CCl4 Carbon tetrachloride

C6H5COOH Benzoic acid CHCl3 Chloroform CH3CH2CH2COOH Butyric acid CH3CI Chloromethane

C6H4(CH3)2 Xylene C10H7Cl Chloronaphthalene C6H5CH3 Toluene C10H8 Naphthalene

Tetrachloroethylene CH2Cl2 Methylene Chloride C6H5OH Phenol C8H6O4 Isophthalic acid C14H10 Phenanthrene N2H4 Hydrazine

C6H5NO2 Nitrobenzene C6Cl6 Hexachlorobenzene C3H5(NO3)3 Nitroglycerine HCOOH Formic acid

H2NNO2 Nitroamine HCHO Formaldehyde C12ClxH10-x Polychlorinated biphenyl

(PCBs) (HO2CCH2)2NCH2CH2N(CH2CO2H)2 Ethylenediaminetetraacetic

acid (EDTA)

oxidare avansata aplicat epur rii apelor este foarte promi toare datorit costului redus, netoxicit

ii fotocatalitice ridicate etc.. În plus fat de

fotocatalitic a TiOmicroorganismelor prezente în ap .

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Descoperiri recente în tehnologia epur rii apei prin ataliz :

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– Cre terea hidrotermal a nanofirelor în membrane utilizate pentru ultrafiltrare i

degradarea fotocatalitic a medicamentelor–

Monografia evalu rii riscului cancerigen provocat de compu ii chimici oamenilor

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Detec ia speciilor active oxidative în folosind tehnica fluorescent ,

–iza sub ac iunea luminii

privire de ansamblu i tendin e–

–filme sub iri de dioxid de titan,

– Spectrometrie de maspoluan i emergen i i probleme actuale

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– Cum sunt îndep rtate medicamentele i produsele de igien personal din apa uzat menajer

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cantitativ a radicalilor hidroxil produ i de diver i

– Poluan i emergen i i op iuni de reutilizare a apei–

Combinarea oxid rii fotocatalitice utilizând

scopul epur rii apei, –– Prepararea i

baz de deriva i poliolici din ulei vegetal,

EVALUATION OF POWDERED ACTIVATED CARBON … · Evaluation of powdered activated carbon performance...

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