[email protected]

8/17/2019 [email protected]

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Photocatalytic activity of undoped and Ag-doped TiO2-supported zeolite for

humic

acid

degradation and

mineralization

C. Lazau a,1, C. Ratiu a,b,1, C. Orha a,1, R. Pode c, F. Manea c,*aNational Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Condensed Matter Department, P. Andronescu no.1,

300254 Timisoara, RomaniabNational Institute for Research and Development in Microtechnologies, Erou Iancu Nicolae Street, 077190 Bucharest, Romaniac ‘‘Politehnica’’ University of Timisoara, P-ta Victoriei no.2, 300006 Timisoara, Romania

1. Introduction

Photocatalysts based on TiO2 have been intensively investigat-

ed in order to achieve better photocatalytic efficiency for different

applications such as decomposition of various organic pollutants

from water and air. Recently, studies on the doping of transition

metal and non-metal ions into TiO2 and the immobilization of TiO2on supports have become attractive in the area of photocatalysis

[1–5]. Various substrates have been used as a catalyst support for

the photocatalytic degradation of polluted water, such as glass and

stainless steel [6], alumina beds [7,8], activated carbons [9,10],

MCM-41 [11–14] and zeolites [5,11,15–19]. The results revealed

that supports possess good pollutant adsorption, diffusion

properties and absence of light absorption, which exhibited the

enhancement of photocatalytic activity of dispersed TiO2 [20,21].

Zeolites have been chosen as support since they can delocalize

band gap excited electrons of TiO2 and thereby minimize electron-

hole recombination [11]. In addition, the ability of zeolites favoring

photoinduced electron-transfer reactions and retarding undesired

back electron transfer has been reported [11]. Supporting TiO2 in

zeolite matrix depends on several factors, such as location and

migration of cations, strength of the interactions between cations,

and guest molecules dimensions of cavities and channels. The

combination of the two properties will lead to distinct and

different properties as compared to those with semiconductor

alone. The functionalization of zeolite with TiO2 can be carried out

through three ways, namely solid–solid, solid–liquid and solid–gas

reactions. Solid-state reactions between inorganic species have

been studied [22,23], however, to the best of our knowledge, no

solid-state reaction in hydrothermal conditions between TiO2powders with natural zeolite has been studied.

Recently, numerous applications towards the synthesis of

inorganic materials have gained greater importance [24]. Our

previous studies also reported the synthesis of supported TiO2 on

the natural zeolite through sol–gel, hydrothermal and solid–solid

methods [25–27]. The microwave offers several advantages over

the conventional routes. The most important are the improvement

of reaction yields and the increase in reaction rates. Microwaves

are also used in synthesis to improve the nanometer size fraction of

particles [28]. In addition, microwaves save energy and appear

today as a new technology for the development of the green

chemistry, with synthesis methods involving preparation proce-

dures based on solvent-free or reduced amount of reactant [26]. In

the late 1980s, microwave heating was introduced to the synthesis

of zeolites. Compared with conventional heating in air ovens,

microwave heating can greatly shorten synthesis time and produce

zeolites with high purity and narrow particle size distribution

Materials Research Bulletin 46 (2011) 1916–1921

A R T I C L E I N F O

Article history:

Received 7 March 2011

Received in revised form 18 June 2011

Accepted 14 July 2011

Available online 23 July 2011

Keywords:

A. Microporous materials

A. Nanostructures

B. Sol–gel chemistry

C. X-ray diffraction

D. Catalytic properties

A B S T R A C T

Thehybridmaterialsbased onnatural zeolite andundoped and Ag-dopedTiO2, i.e., Z-Na-TiO2 andZ-Na-

TiO2-Ag, were successfully synthesized by solid-state reaction in microwave-assisted hydrothermal

conditions. Undoped TiO2 and Ag-doped TiO2 nanocrystals were previously synthesized by sol–gel

method. The surface characterization of undoped TiO2/Ag-doped TiO2 and natural zeolite hybrid

materials has been investigated by X-ray diffraction, DRUV-VIS spectroscopy, FT-IR spectroscopy, BET

analysis, SEM microscopy and EDX analysis. The results indicated that anatase TiO2 is the dominant

crystalline type as spherical form onto zeolitic matrix. The presence of Ag into Z-Na-TiO2-Ag was

confirmed by EDX analysis. The DRUV-VIS spectra showed that Z-Na-TiO2-Ag exhibited absorption

within the range of 400–500 nm in comparison with Z-Na-TiO2 catalyst. The enhanced photocatalytic

activity of Z-Na-TiO2-Ag catalyst is proved through the degradation and mineralization of humic acid

under ultraviolet and visible irradiation.

2011 Elsevier Ltd. All rights reserved.

* Corresponding author. Tel.: +40 256 403069; fax: +40 256 403069.

E-mail address: [email protected] (F. Manea).1 Tel: +40 256 494413, Fax: +40 256 204693.

Contents

lists

available

at

ScienceDirect

Materials Research Bulletin

jo u rn al h omep a ge : ww w.els evier .co m/loc ate /matresb u

0025-5408/$ – see front matter 2011 Elsevier Ltd. All rights reserved.

doi:10.1016/j.materresbull.2011.07.026

http://dx.doi.org/10.1016/j.materresbull.2011.07.026http://dx.doi.org/10.1016/j.materresbull.2011.07.026http://dx.doi.org/10.1016/j.materresbull.2011.07.026http://dx.doi.org/10.1016/j.materresbull.2011.07.026http://dx.doi.org/10.1016/j.materresbull.2011.07.026http://dx.doi.org/10.1016/j.materresbull.2011.07.026http://dx.doi.org/10.1016/j.materresbull.2011.07.026http://dx.doi.org/10.1016/j.materresbull.2011.07.026http://dx.doi.org/10.1016/j.materresbull.2011.07.026http://dx.doi.org/10.1016/j.materresbull.2011.07.026http://dx.doi.org/10.1016/j.materresbull.2011.07.026mailto:[email protected]:[email protected]://www.sciencedirect.com/science/journal/00255408http://dx.doi.org/10.1016/j.materresbull.2011.07.026http://dx.doi.org/10.1016/j.materresbull.2011.07.026http://www.sciencedirect.com/science/journal/00255408mailto:[email protected]://dx.doi.org/10.1016/j.materresbull.2011.07.026


2/6

[29,30]. These advantages reveal it as a promising way to

prepare high-quality zeolite membranes in a short time. Koegler

and coworkers [31] reported that the microwave heating is very

effectively to study synthesis parameters of zeolite by showing

in relation with dependence of temperature profile of the

synthesis mixture on the conventional and microwave heating.

Other researchers have successfully prepared a film of NaA and

AlPO45 crystals on Al2O3 and gold substrates, respectively,

using a microwave heating [32–34]. They found that the

microwave conditions affect the thickness and the orientation

of zeolite crystals. All these above-presented advantages reclaim

microwaves as suitable for annealing.

Humic acid (HA) is the main constituent of natural organic

matter (NOM) from water resources responsible for water colour

and odour, and it is considered to be the precursor of carcinogenic

products like trihalomethanes (THMs) formed during water

disinfection using chlorine. Based on these considerations, the

degradation of the HA prior to disinfection step for drinking water

treatment is necessary. The effective degradation of humic acid

from water by photocatalytic oxidation based on TiO2 catalyst has

been reported [35,36].

In the present study, hybrid materials based on natural zeolite

modified with undoped TiO2/Ag-doped TiO2 were synthesized by

solid-state reaction in microwave-assisted hydrothermal condi-tions. X-ray diffraction, FT-IR spectroscopy, DRUV-VIS spectrosco-

py, BET and SEM/EDX analysis were used for the characterization of

hybrid materials. The performances of the photocatalytic activities

of the hybrid materials were determined comparatively for the

degradation of humic acid from water by photocatalysis under UV

irradiation at wavelengths of 254 nm and VIS irradiation at

wavelengths of 450 nm. Also, the photocatalytic activities for the

humic acid mineralization were assessed.

2.

Materials

and

methods

2.1. Chemicals

Romanian zeolitic mineral from Mirsid, used as support fordoped TiO2 loading, was supplied by Cemacon Company, Romania.

The mineral was powdered and sieved with a Multilab sieve

shaker.

The

diameter

of

grains

size

selected

to

carry

out

the

experiments

was

between

315

and

500

mm

with

the

mass

composition 62.20% SiO2, 11.65% Al2O3, 1.30% Fe2O3, 3.74% CaO,

0.67% MgO, 3.30% K2O, 0.72% Na2O and 0.28% TiO2.

Titanium

(IV)

isopropoxide

(TTIP,

98%),

silver

nitrate

(AgNO3),

hydrochloric

acid

(HCl),

ethanol,

sodium

nitrate

(NaNO3) and nitric

acid (HNO3) were purchased from ALDRICH Company.

2.2.

Preparation

of

photocatalyst

The hybrid materials based on natural zeolite modified with

undoped

TiO2 and

Ag-doped

TiO2 nanocrystals

were

prepared

bysolid-state

reaction

in

microwave-assisted

hydrothermal

condi-

tions.

The

hybrid

materials

synthesis

are

performed

in

two

steps,

in

the first one the undoped and doped TiO2 nanocrystals were

synthesized by sol–gel method (1) and the second step supposed

the

hybrid

material

synthesis

by

solid-state

reaction

in

micro-

wave-assisted

hydrothermal

conditions

(2).

The undoped and silver doped TiO2 (Ag-doped TiO2) nanocrys-

tals were synthesized by sol–gel method. An amount of ethanol

was

stirred

with

5

mL

TTIP

and

after

10

min,

30

mL

of

distilled

water

was

added

in

dropwise.

The

pH

of

the

initial

solution

was

5.5

and before adding the doping precursor (AgNO3) the pH was

adjusted with HNO3. The solutions were filtered, washed and dried

to

60

8C

for

5

h.

For

crystallization

the

materials

were

annealed

into

an

oven

at

the

temperature

range

between

300

and

600

8

C for

2

h.

The preparation of the chemically modified zeolite presumes

two stages to reach acid form (H form) by using 2 M HCl solution

and sodium form (Na form) with 2 M NaNO3 solution for a more

efficient ion exchange. Consequently, Na forms of clinoptilolite are

expected to remove other cations easily in ion-exchange applica-

tions. For that reason, Na forms are the forms that most frequently

prepared for research in clinoptilolite literature [37]. The hybrid

materials based on natural zeolite and undoped and doped TiO2were synthesized by solid-state reaction through microwave-

assisted hydrothermal method, in aqueous solution. The micro-

wave synthesis was performed in a microwave reaction system,

Multiwave 3000, produced by Anton Paar at 2.45 GHz for a

continuous power of 1000 W.The temperature measurements are

recorded with an IR sensor depending on autoclave solution

content. Therefore, an amount of natural zeolite as Na form was

mixed with 40 mL distilled water and undoped TiO2/Ag-doped

TiO2 nanocrystals (2 wt%) under continuous stirring for 4 h. The

obtained solutions were introduced into a Teflon autoclave with a

50% degree of fullness, for 30 min to 180 8C, under microwave

radiations. After autoclaving, the hybrid materials (Z-Na-TiO2 and

Z-Na-TiO2-Ag) were washed with distilled water and dried at 60 8C

for 5 h.

2.3. Characterization of hybrid material

The crystallinity of the prepared samples was measured by X-

Ray diffraction (XRD) using PANalytical X’PertPRO MPD Difract-

ometer with Cu tube. A scanning electron microscopy (SEM) using

Inspect S PANalytical model coupled with the energy dispersive X-

ray analysis detector (EDX) was used to characterize the external

surfaces of the hybrid materials, using catalyst powder supported

on carbon tape. The specific surface areas of the materials were

determined by BET using an ASAP 2020 Micromeritics system. The

light absorption properties of the hybrid materials were studied by

UV–vis diffuse reflectance spectroscopy (DRUV-VIS), performed

under ambient conditions using Lambda 950 Perkin Elmer in the

wavelength

range

of

200–430

nm.

The

blank

board

was

used

as

the

reference. The bond vibration of modified materials was analyzedby Fourier transform infrared spectrometry (FT-IR) using a JASCO

FT/IR-430 spectrometer.

2.4.

Photocatalytic

degradation

procedure

and

analytical

methods

The photocatalytic activities of the prepared catalyst hybrid

materials

were

assessed

through

degradation

of

50

mg

L 1 humic

acid

in

an

RS-1

photocatalytic

reactor

(Heraeus,

Germany).

The

volume of the reaction solution was 200 ml, into which 0.2 g of

photocatalyst was added. UV and VIS irradiation was provided by a

medium-pressure

Hg

lamp

(300

W).

After

irradiation

time

of

2

h,

the

suspension

was

sampled

and

filtered

through

a

0.2

mm

membrane filter. The concentration of humic acid was measured in

terms

of

absorbance

at

254

nm

( A254)

and

436

nm

( A436)

with

aCarry

100

Varian

spectrophotometer.

Also,

the

mineralization

degree

was

assessed

by

monitoring

total

organic

carbon

(TOC)

parameter using Carbon Multi N/C 2100S Analyzer, Analytik Jena.

The degradation ratio ( X ) of the reactant can be calculated as

X (%)

=

100( A0 A)/ A0, and mineralization ratio was determined

used

the

same

relation

using

TOC

parameter

instead

of

A

value.

3. Results and discussion

3.1.

XRD

analysis

The XRD patterns of TiO2 nanocrystals annealed at different

temperatures

are

illustrated

in

Fig.

1. It

is

known

that

annealing

improved

the

crystallization

of

TiO2 powders

and

accelerated

the

C. Lazau et al. / Materials Research Bulletin 46 (2011) 1916–1921 1917


3/6

transformation

from

amorphous

phase

to

anatase

or

rutile

phase.

It

can

be

seen

that

for

a

temperature

of

300

8C

the

crystalline

phase

of

undoped TiO2 nanocrystals reveals anatase form and by tempera-

ture increasing at 400 8C the phase transition from anatase to rutile

occurred

(Fig.

1i).

At

600

8C the

anatase

phase

of

undoped

TiO2 is

almost

disappeared

and

the

rutile

form

is

predominantly

(Fig.

1i).

In according with the literature [38,39], this behavior is expected

and can be explained by the effect of the annealing temperature on

the

anatase

phase,

which

become

metastable

at

higher

tempera-

ture

and

it

is

converted

into

stable

rutile

phase.

The

Ag-doped

TiO2nanocrystals exhibited a different behavior under the same

annealing

temperature

rang.

The

pure

anatase

form

was

noticeduntil

to

600

8C

temperature,

without

the

appearance

of

the

rutile

form

(Fig.

1ii).

Based

on

the

literature

data

[40]

this

behavior

is

own

to the fact that the presence of Ag ions decreased the oxygen

vacancy concentration, which inhibited the phase transition under

the

studied

temperatures

range.

Thus,

the

diffraction

peaks

of

anatase

TiO2 corresponding to 2u : 25.38, 378, 37.88, 38.68, 488, 548,

558 [41] and of rutile phase to 2u : 27.38, 35.98, 41.18, 54.18 were

noticed [42]. Crystallite size was calculated by the use of Scherrer

formula

i.e.,

D

=

kl / bcos

u .

The

average

particle

size

obtained

for

anatase

from

XRD

data

for

undoped

and

doped

nanocrystals

were

about 10 nm.

Taking into account that in general,the anatase form exhibited an

improved

photocatalytic

activity

in

comparison

with

rutile

form,

for

the

further

experiments

regarding

obtaining

zeolite-based

hybrid

materials were selected the TiO2 materials crystallized as anataseform, i.e., undoped TiO2 annealed 300 8C and Ag-doped TiO2annealed 600 8C. Anatase TiO2 exhibits higher photocatalytic

activity than rutile TiO2 due to its conduction band position which

demonstrates stronger reducing power [6].

Fig. 2 described XRD patterns of hybrid materials based on

natural zeolite and undoped/Ag-doped TiO2 nanocrystals, i.e., Z-

Na-TiO2 and Z-Na-TiO2-Ag. For comparison, the XRD pattern of

the natural zeolite in Na form is also shown in Fig. 2 (spectra a).

The presented results revealed that the natural zeolite used is

mostly clinoptilolite (2u : 108; 22.58; 308) [25]. It can be seen that

the main peak positions of natural zeolite (clinoptilolite) are

unchanged, indicating that the structure of natural zeolite has a

good

thermal stabilization, after the microwave-assisted hydro-

thermal treatment. In comparison with the XRD pattern of thenatural zeolite in Na form, the specific peaks corresponding to

anatase TiO2 form recorded at 2u : 25.38, 378 and 38.68 were

noticed for both Z-Na-TiO2 and Z-Na-TiO2-Ag hybrid materials.

3.2. DRUV-VIS spectroscopy

DRUV-VIS

patterns

are

examined

to

determine

the

light

absorption

quantification

and

absorption

wavelength

range

corre-

lated with band gap energy. Fig. 3 presents an intense absorption

maximum at 250 nm, which can be assigned to isolated titanium

with

tetrahedral

coordination.

Another

absorption

range

found

in

the

range

of

300–370

nm

indicates

that

some

titanium

is

also

in

an

octahedral environment [43].

For

the

hybrid

material

modified

with

undoped

TiO2 theabsorption

bands

intensity

is

higher

in

UV

domain,

because

the

anatase

form

of

undoped

TiO2 with the band gap energy about

3.2 eV strongly adsorbs in this domain [44]. The low doping degree

with Ag of the hybrid material led to a slight shifting of the

absorption

band

to

the

visible

range.

3.3. FT-IR analysis

Fig.

4i and

ii

show

FT-IR

spectra

obtained

for

the

hybrid

materials

in

comparison

with

Na

form

of

the

zeolite.

The

bands

at

3540 and 3360 cm1 have been attributed to the symmetric and

antisymmetric stretching modes of molecular water coordinated

to

the

magnesium

at

the

edges

of

the

channels.

The

presence

of

doped

TiO2 into

hybrid

materials

seems

to

affect

the

symmetric

Fig. 1. XRD patterns of (i) undoped and (ii) Ag-doped TiO2 nanocrystals at differentcalcination temperatures (*, anatase; *, rutile).

Fig. 2. XRD patterns for (a) Z-Na, (b) Z-Na-TiO2 and (c) Z-Na-TiO2-Ag (*, anatase

TiO2; ^, clinoptilolite).

C. Lazau et al. / Materials Research Bulletin 46 (2011) 1916–19211918


4/6

stretching modes of water coordinated to the magnesium at the

edges of channels (Fig. 4i). The band at 1630–1640 cm1(Lewis

sites) region is assigned to the zeolite water in channels of thesamples. The shoulders at 1350 cm1 noticed for the hybrid

materials (Z-Na-TiO2 and Z-Na-TiO2-Ag) can be attributed to

stretching and vibration of the Ti-O-Ti group, indicating the

formation of the inorganic matrix [45]. For the hybrid materials

synthesized by solid-state reaction in microwave-assisted

hydrothermal conditions the corresponding tetrahedral loadings

bands from 450 to 900 cm1 are not modified, so the zeolite

network is not affected (Fig. 4ii). FT-IR results clearly showed for

hybrid materials in comparison with Z-Na some modifications

specific to presence of TiO2 bounded at zeolite within absorption

band range between 945 and 860cm1. Thus, according to Liu

et al. [46] the absorption bands at 920 and 860 cm1 are

originated from the Ti-O stretching vibration and Ti-O-Ti linkage

vibration, respectively [47,48]. Also, the absorption band range

from945 to 905 cm1 corresponds to the stretching vibration of

Ti-O-Si and Ti-O-Al [48].

3.4. Scanning electron microscopy (SEM) and energy dispersive X-ray

analysis (EDX) results

The SEM images (Fig. 5a–d) present the lamellar texture of

clinoptilolite, according to the literature data [49]. The TiO2particles are distributed randomized and form cluster agglomerate

groups on the surface and in site of zeolite channels. At a larger

magnification times (mag. 12,000), it is obvious that the TiO2nanocrystals (spherical form) are non-uniformly distributed on thezeolite surface, forming the porous surface (Fig. 5b and d). EDX

microprobe provided a semiquantitative elemental analysis of the

Fig. 3. DRUV-VIS spectra of hybrid materials (a) Z-Na-TiO2, (b) Z-Na-TiO2-Ag and (c)

Z-Na.

Fig. 4. (i) FT-IR spectra of (a) Z-Na, (b) Z-Na-TiO2-Ag and (c) Z-Na-TiO2 for the wavelength range of 4000–400 cm1; (ii) FT-IR spectra of (a) Z-Na, (b) Z-Na-TiO2-Ag and (c) Z-

Na-TiO2 for

the

wavelength

range

of

1300–400

cm

1

.



5/6

surface indicating that Ti and Ag were present on the zeolite

surface.

Also,

this

natural

zeolite

contain

the

major

elements

such

as

Na,

Si,

Al,

Ca,

K

and

Mg

as

can

be

seen

from

the

EDX

spectra

(Inset

Fig. 5b and d).

BET surface area value of Z-Na-TiO2-Ag is found to be higher

(59.45

m2 g1)

compared

to

Z-Na-TiO2 (19.83 m2 g1)

indicating

the

more

porous

surface

with

the

possibility

of

application

for

efficient catalytic material.

3.5.

Photocatalytic

activity

The prepared hybrid materials, Z-Na-TiO2 and Z-Na-TiO2-Ag

were used to degrade and mineralize humic acid under ultraviolet

and

visible

light

irradiation

for

2

h,

and

the

results

are

presented

in

Fig.

6. A

slight

degradation

of

humic

acid

assessed

in

terms

of

A254and A436 occurred under VIS irradiation (11% for A254 and 14% A436)

by photolysis process, conducted under the similar conditions with

photocatalysis

in

the

absence

of

the

photocatalyst.

Applying

photolysis

under

UV

irradiation

better

results

regarding

degrada-

tion degree were achieved (27% for A254 and 41% A436), which

informed about the photo-sensitive character of humic acid, much

better

under

UV

than

VIS

irradiation.

However,

the

mineralization

degrees

evaluated

in

terms

of

TOC

parameter

(8%

under

UV

irradiation and 5% under VIS irradiation) showed a negligible effect

to

evaluate

the

mineralization

activity

of

the

photocatalyst.

Under

all

applied

irradiation

conditions,

the

best

results

were

reached

for

the degradation of humic acid expressed by A436 corresponding to

the chromophore groups that denoted the colour. This aspect was

an

expected

one

because

in

general,

during

the

photocatalytic

process

the

chromophore

groups

are

most

susceptible

for

breakage. The decrease of A254 informed about the possibility of

the

aromatic

ring

opening

during

degradation

process.

Fig.

6

showsthat

humic

acid

can

be

mineralized

up

to

21%

under

VIS

irradiation

and

32%

under

UV

irradiation

using

Z-Na-TiO2-Ag in comparison

with 12% under VIS irradiation and 25% under UV irradiation using

Z-Na-TiO2, which suggested that the presence of silver in TiO2particles

enhanced

the

mineralization

and

quite

degradation

efficiency

of

humic

acid.

These

results

can

be

explained

by

silver

acting to prevent hole and electron recombination in TiO2, thus

enhancing the photocatalytic activity [50] both under UV and

especially

under

VIS

irradiation.

Also,

the

higher

specific

surface

area

of

the

Z-Na-TiO2-Ag should improve its photocatalytic

activity. Nevertheless, the high difference between the degrada-

tion and mineralization efficiencies were noticed, which informed

about

an

incomplete

degradation

of

humic

acid,

with

possible

production

of

intermediates.

Fig. 5. SEM morphology for Z-Na-TiO2-Ag (a and b) and Z-Na-TiO2 (c and d). Inset : EDX spectra for elemental analysis of Z-Na-TiO2-Ag (inset (b)) and Z-Na-TiO2 (inset (d)).

C. Lazau et al. / Materials Research Bulletin 46 (2011) 1916–19211920


6/6

4.

Conclusions

The hybrid materials based on natural zeolite and undoped and

Ag-doped

TiO2 were successfully synthesized by solid-state

reaction in microwave-assisted hydrothermal conditions. Theoptimum annealing temperature was set up at 300 8C for undoped

TiO2 and 600 8C for Ag-doped TiO2 to obtain pure anatase TiO2form.

XRD

results

proved

the

presence

of

anatase

form

of

undoped

and

Ag-doped

TiO2 onto zeolite. Silver presence was confirmed by

EDX analysis. The FT-IR spectra evidenced the presence on TiO2bounded at the zeolite network by Ti-O-Al and Ti-O-Si, which

indicated

the

load

of

TiO2 into zeolite more durable than simple

physical

combination.

The

DRUV-VIS

spectra

indicated

that

for

Ag-

doped TiO2 nanocrystals onto natural zeolite the absorption bands

were slightly shifted to the visible range, and led to a stronger

visible

light

response

than

undoped

TiO2 onto zeolite. The Ag-

doped

TiO2 onto zeolitic matrix exhibited an enhanced photo-

catalytic activity on degradation and mineralization of humic acid

under

both

ultraviolet

and

visible

light

irradiation

in

comparisonwith

undoped

TiO2 onto zeolitic matrix.

Acknowledgements

This

study

was

supported

by

the

Sectoral

Operational

Programme

Human

resources

Development

(SOP

HRD),

financed

from the European Social Fund and by the Romanian Government

under the contract number POSDRU/89/1.5/S/63700 and by the

Romanian

National

Project

No.

72–156/2008

NANOZEOREZID.

The

authors

thank

to

the

X-ray

Diffraction

and

Electron

Microscopy

Laboratories from the Characterization Department of National

Institute for Research and Development in Electrochemistry and

Condensed Matter, Timisoara for the characterization results.

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Fig. 6. Comparison of the degradation and mineralization of 50 mg L 1 humic acid

under UV (i) and VIS (ii) irradiation by photolysis and photocatalysis using Z-Na, Z-

Na-TiO2 and Z-Na-TiO2-Ag catalyst.


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