S YNTHESIS AND CHARACTERIZATION STUDIES OF IRON … · materi als for different application [1-7]s....

SYNTHESIS AND CHARACTERIZATION STUDIES OF IRON MOLYBDENUM

MIXED METAL OXIDE (FE2(MOO4)3) NANO – PHOTOCATALYSTS

K.Seevakan

1, S.Bharanidharan

2

Assistant Professor 1 2

Department of Physics, BIST, BIHER, Bharath University, Chennai.

[email protected]

Abstract

Iron molybdate Fe2(MoO4)3 nano-photocatalyst was synthesized by simplistic one-pot

microwave combustion method using urea as fuel. The formation of crystalline orthorhombic

phase of Fe2(MoO4)3 was confirmed by powder X-ray diffraction (XRD) and the functional

group was confirmed by Fourier transform infrared (FT-IR). The morphology of the sample

consists of particle-like spherical shaped nanostructures, which was confirmed by high-

resolution scanning electron microscope (HR-SEM) with energy dispersive X-ray (EDX)

analysis and high-resolution transmission electron microscope (HR-TEM) analysis. . The

present study leads to enhance the photocatalytic (PC) activity of Fe2(MoO4)3 sample after TiO2

catalyst was added. The Fe2(MoO4)3 nanoparticles (NPs) sensitized TiO2 catalyst showed

enhanced photocatalytic degradation (PCD) of methylene blue (MB) under visible light

irradiation. The alteration of Fe2(MoO4)3-TiO2 nano-composites catalyst shows higher

adsorption with synergistic effect and enhanced towards the PCD of MB dye.

International Journal of Pure and Applied MathematicsVolume 119 No. 12 2018, 5797-5811ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

5797

1. Introduction

Nano-structured magnetic materials have attracted considerable attention due to their

unusual physical and chemical properties than that of their same bulk materials. In recent years,

transition metal oxides have attracted a much interest of research in nano technology as potential

materials for different application[1-7]s. As a family of important functional magnetic materials,

metal molybdates have been widely used in photoluminescence, microwave applications, optical

fibers, scintillator materials, humidity sensors and electro-catalysis [8-17]. The molybdates

constitute an interesting group owing to their structural electronic and catalytic properties [18-

24]. Among the many metal molybdates, iron molybdate (Fe2(MoO4)3) is a particularly efficient

catalyst for the oxidation of methanol into formaldehyde and exhibits very interesting magnetic

properties [9, 10]. Iron molybdate has important industrial application as a catalyst [25-31].

Several synthesis methods were proposed for the production of iron molybdate, including

microwave synthesis [12], precipitation [13], solvothermal [14] and hydrothermal methods [15],

etc. However, the above synthesis methods require long reaction times, and involve the use of

solution, making more costly as several steps are necessary including filtration and calcinations,

etc. The synthesis methods are expensive and more difficult to apply in an industrial application.

Among the above methods microwave combustion method have many advantages, such as high

purity product, high reaction rate and energy saving. Also, this method is very simple and low

cost technique for the preparation of functional materials in nanometer range [32-36].

Nowadays metal oxides have been used as catalysts for the degradation of organic

pollutants. Among them, magnetic iron oxides are highly used, because it can be easily removed

by external magnetic field and reused several times without any change of catalytic activity.

Manikandan et al. [17-21] reported spinel ferrites prepared by microwave combustion method

International Journal of Pure and Applied Mathematics Special Issue

5798

and are used as a photo-catalyst for the degradation of 4-chlorophenol (4-CP). Also, they

reported metal doped spinel ferrites for the catalytic oxidation of benzyl alcohol into

benzaldehyde [37-43]. Ding et al. [28] designed a template-free hydrothermal process to

selectively prepare monoclinic and orthorhombic Fe2(MoO4)3 micro-sized particles. Hassani et

al. [2] reported Fe2(MoO4)3 NPs in the reduction of nitrophenol isomers into their corresponding

aminophenol isomers. Hankare et al. [44-50] reported ZnFe2O4, TiO2-ZnFe2O4, TiO2-Al2O3-

ZnFe2O4 photo-catalysts for the degradation of methyl red and thymol blue. Routray et al. [30]

reported Fe2(MoO4)3 for the selective oxidation of methanol into formaldehyde. Zhang et al. [31]

reported magnetic and photocatalytic properties of Fe2(MoO4)3 microstructures by microwave-

assisted hydrothermal synthesis. Singh et al. [32] reported Fe2(MoO4)3 electro-catalysts prepared

by co-precipitation method for oxygen evolution reaction in alkaline solutions. Xu et al. [33]

reported visible-light-active TiO2 -ZnFe2O4 photo-catalyst. .

2. Experimental

2.1. Materials and synthesis procedure

All the chemicals used in this study were of analytical grade obtained from Merck, India

and were used as received without further purification. Iron nitrate (Fe(NO3)2·9H2O, 98%),

ammonium heptamolybdate (NH4)6Mo7O24·4H2O and urea ( CO (NH2)2) as the fuel are used for

this method. In case of Fe2(MoO4)3, the precursor mixture in urea was in a domestic microwave

oven and exposed to the microwave energy in a 2.45 GHz multimode cavity at 850 W for 10

minutes. Initially, the precursor mixture boiled and underwent evaporation followed by the

decomposition with the evolution of gases. When the solution reached the point of spontaneous

combustion, it vaporized and instantly became a solid. The obtained solid powders were washed


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well with ethanol and dried at 80ºC for 1h, and labeled as Fe2(MoO4)3 and then used for further

characterizations. The entire microwave combustion process produce Fe2(MoO4)3 powders in a

microwave-oven operated at a power of 850 W has produced Fe2(MoO4)3 within 10 min.

2.2. Characterization techniques

The characterization of the obtained Fe2(MoO4)3 powder were conducted by using

various techniques to verify the phase formation, crystallite size, distribution and to explore other

parameters of interest. The structural characterization of Fe2(MoO4)3 nanoparticles were

performed using Rigaku Ultima X-ray diffractometer equipped with Cu-Kα radiation (λ =1.5418

Å). The surface functional groups were analyzed by Perkin Elmer FT-IR spectrometer.

Morphological studies and energy dispersive X-ray analysis (EDX) of Fe2(MoO4)3 NPs have

been performed with a Jeol JSM6360 high resolution scanning electron microscopy (HR-SEM)..

2.3. Photocatalytic reactor setup and degradation procedure

Photocatalytic degradation (PCD) experiments were carried out in a self-designed

photocatalytic reactor. The cylindrical photocatalytic reactor tube was made up of

quartz/borosilicate with a dimension of 36 cm height and 1.6 cm diameter. The top portion of the

reactor tube has ports for sampling, gas purging and gas outlet. The aqueous methylene blue

(MB) solution containing appropriate quantity of Fe2(MoO4)3 nano photo-catalysts was taken in

the quartz/borosilicate tube and subjected to aeration for thorough mixing and placed inside the

reactor setup. The lamp housing has low pressure mercury lamps (8 x 8 W) emitting either 254

or 365 nm with polished anodized aluminum reflectors and black cover to prevent UV leakage.

Prior to photocatalytic experiments, the adsorption of MB on Fe2(MoO4)3 and TiO2 nano photo-

catalyst was carried out by mixing 100 ml of aqueous solution of MB with fixed weight of the


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respective photo-catalyst. This slurry was equilibrated for 30 minutes in a magnetic stirrer. The

PCD was carried out by mixing 100 ml of aqueous MB solution and fixed weight of nano photo-

catalysts. PCD of MB was also carried out with Fe2(MoO4)3-TiO2 mixed oxides.

3. Results and Discussion

3.1 Structural analysis

The structural and phase analysis of the samples were characterized by powder X-ray

diffraction (XRD) pattern and is shown in Figure 1. All the diffraction peaks could be indexed

to monoclinic Fe2(MoO4)3 structure, which is in good agreement with the literature values

(JCPDS file Card No. 35-0183) [31]. No other impurity peak was detected. The very high peak

intensity suggests that the material is highly crystalline. This indicates the complete

transformation of the precursor into Fe2(MoO4)3 phase. The average crystallite size of

Fe2(MoO4)3 sample was calculated using Debye Scherrer formula

cos

89.0L

3.2 FT-IR spectral analysis

Figure 2 shows the FT-IR spectra of Fe2(MoO4)3 powders. FT-IR spectra contain a broad

band between ~ 3200 and ~ 3400 cm-1

due to the O-H stretching mode [1]. Furthermore bands

related to C=O and C-O stretching modes that appear at ~1723 and ~1042 cm-1

respectively, due

to the ester groups formed [32]. The spectra of Fe2(MoO4)3 powders shows absorption bands

between ~1000 and 1120 cm-1

is mainly due to Mo=O stretching vibration. A peak at 827 cm-1

is

attributed to Mo(VI)-O tetrahedral stretching and peak at 656 cm-1

corresponds to Fe(III)-O

octahedral stretching vibration.

The sharpness of these bands is correlated to the high degree of

crystallinity of the Fe2(MoO4)3 phase.


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3.3. High resolution- scanning electron microscopy (HR-SEM) studies

The nanostructure and surface morphology of the as-prepared Fe2(MoO4)3 sample was

examined by high resolution scanning electron microscope (HR-SEM) analysis. Figure 3 shows

the HR-SEM images of Fe2(MoO4)3 samples, which clearly shows the spherical-like structure

consisting of agglomerated particles. The agglomeration of the particles with nanoparticles

structure may be due to the magnetic nature of the samples. In this microwave combustion

method the crystal formation is due to the stable nuclei via ion-by-ion addition and unit

replication. The formation of rods-like structure may be due the agglomeration and attachment

of the nano-crystals. Also, the layer-by-layer self-assembled nano-particles, which lead to the

formation of spherical-like Fe2(MoO4)3 nanostructure.

3.4. High resolution transition electron microscopy (HR-TEM) studies

To provide a further evidence for the formation of spherical-like nanoparticle

morphology of Fe2(MoO4)3 samples, high-resolution transmission electron microscopy (HR-

TEM) analysis was carried out and is shown in Fig. 4. Figure 4a shows the HR-TEM image of

Fe2(MoO4)3 spherical- like NPs with diameter ranging from 15-25 nm. It is obvious that the

spherical-like NPs are uniform in size, which is consistent with the average crystallite size

obtained from the peak broadening in XRD analysis. The Fig. 4b, shows the selected area

electron diffraction pattern (SAED) of spinel Fe2(MoO4)3, which implies that the as-prepared

samples are single crystalline in nature. SAED results show spotty ring characteristic of small

crystallites of Fe2(MoO4)3 nanoparticle without any additional diffraction spots.

3.5 Photocatalytic properties


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TiO2 supported Fe2(MoO4)3 NPs on the PCD efficiency is evaluated as shown in Figure 5.

The PCD efficiency of Fe2(MoO4)3 is very low when compared with TiO2. The PCD efficiency

of TiO2 supported Fe2(MoO4)3 (i.e. Fe2(MoO4)3-TiO2 NCs) is higher than pure Fe2(MoO4)3 NPs.

The photocatalytic activity of single phase Fe2(MoO4)3 is enhanced, when it is coupled with TiO2

to form a composite catalyst. Though, the band gap of Fe2(MoO4)3 is smaller than that of TiO2

and it is a visible light active catalyst, it exhibits lower photo-catalytic activity, due to its lower

valence band potential compared to TiO2 When TiO2 and Fe2(MoO4)3 are coupled and irradiated

with UV-Vis light, the photocatalytic activity is improved, though the charge carriers can

migrate to Fe2(MoO4)3, due to the higher VB potential of TiO2. Photocatalytic degradation was

occurred by hydroxyl radicals attack the MB.

4. Conclusions

Fe2(MoO4)3 nanoparticles were successfully synthesized by a simple micro wave

combustion method using urea as the fuel. Powder XRD results confirmed that the pure single

phase crystalline with monoclinic structure of Fe2(MoO4)3 nanoparticles. HR-SEM images show

that the morphology of the sample consists with well defined nanoparticles (NPs) structure with

agglomeration. VSM results showed ferromagnetic behavior. The PCD efficiency of Fe2(MoO4)3

is very lower than TiO2 catalyst. The PCD efficiency of TiO2 supported Fe2(MoO4)3 (i.e.

Fe2(MoO4)3-TiO2 NCs) is higher than pure Fe2(MoO4)3 NPs. These results indicated that the

Fe2(MoO4)3 nano-structures may find applications in water pollution control. Compared to other

synthetic methods, microwave combustion method is a facile, low-cost pathway for the

preparation of Fe2(MoO4)3 nano-structures.

Figure captions


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Figure 1. XRD patterns of Fe2(MoO4)3 NPs.

Figure 2. FT-IR spectra of Fe2(MoO4)3 NPs.

Figure 3. HR-SEM images of Fe2(MoO4)3 NPs.

Figure 4. HR-TEM images of Fe2(MoO4)3 NPs.

Figure 5. PCD efficiency of TiO2-supported Fe2(MoO4)3 photocatalyst (Experimental conditions:

MB = 100 mg/L, Photocatalyst = 30 mg/100 mL, k = 365 nm).

Figure captions

Figure 1. Powder XRD pattern of Fe2(MoO4)3 NPs.

10 20 30 40 50

Inte

nsi

ty (

a.u

)

2 Theta (degree)

(237

) (012

)

(11

2)

(120

) (1

20

) (- 214)

(- 144)

(220

) (212

) (1

22

)

(- 105)

(- 224

) (4

00

) (- 503)

(222

) (0

24

) (0

32

) (- 116)

(- 234)

(- 525)

(- 616)

(511

) (106

) (4

03

) (035

)

(225

)


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4000 3600 3200 2800 2400 2000 1600 1200 800

Inte

nsi

ty (

a.u

)

Wavenumber (cm-1

)

Figure 2. FT-IR spectra of Fe2(MoO4)3 NPs.

Figure 3. HR-SEM images of Fe2(MoO4)3 NPs.

a b


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0 50 100 150 200 250 300

0

20

40

60

80

100

PC

D e

ffic

ien

cy

(%

)

Time (minutes)

Photolysis

Fe2(MoO4)3

TiO2

Fe2(MoO4)3-TiO2

Figure 4. HR-TEM image (a) and SAED pattern (b) of Fe2(MoO4)3 NP

Figure 5. PCD efficiency of TiO2-supported Fe2(MoO4)3 photocatalyst (Experimental

conditions: MB = 100 mg/L, Photocatalyst = 30 mg/100 mL, k = 365 nm).

a b


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S YNTHESIS AND CHARACTERIZATION STUDIES OF IRON … · materi als for different application [1-7]s....

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