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Chemical Engineering Journal 168 (2011) 1227–1233

Contents lists available at ScienceDirect

Chemical Engineering Journal

journa l homepage: www.e lsev ier .com/ locate /ce j

ffective degradation of acid orange 10 by catalytic ozonation in the presence ofu-Bi2O3 nanoparticles

alenthiran Pugazhenthirana,b, Panneerselvam Sathishkumara,epperumal Murugesanb, Sambandam Anandana,∗

Nanomaterials & Solar Energy Conversion Lab, Department of Chemistry, National Institute of Technology, Tiruchirappalli 620 015, IndiaSchool of Chemistry, Madurai Kamaraj University, Madurai 625 021, India

r t i c l e i n f o

rticle history:eceived 31 August 2010eceived in revised form 8 February 2011ccepted 10 February 2011

a b s t r a c t

In this study, the catalytic ozonation of acid orange 10 (AO-10) in the presence of Au-Bi2O3/Bi2O3 nanocat-alysts is investigated. The influence of various effects of the synthetic procedure is evaluated by preparingthe Bi2O3 and Au-Bi2O3 catalysts in two different routes. The nanomaterials are characterized throughvarious analytical tools like X-ray diffraction (XRD), scanning electron microscopy (SEM) and photolumi-

eywords:atalytic ozonationu-Bi2O3

onochemical synthesisydrothermal synthesis

nescence (PL) spectroscopy. Addition of sonochemically synthesized Bi2O3 and gold nanoparticles loadedsonochemically synthesized Bi2O3 catalysts on ozone assisted catalytic degradation of AO-10 show 1.8-and 3.5-fold enhancement in the degradation rate, respectively. Bi2O3 and gold loaded Bi2O3 samples pre-pared by sonochemical method provide effective environment for the degradation of AO-10. The totalorganic carbon (TOC) removal studies performed to understand the mineralization of AO-10 in the pres-ence of various catalysts show that, about 47% AO-10 can be completely abated in 30 min by ozonation

emic

in the presence of sonoch

. Introduction

Advanced Oxidation Technologies (AOTs) has provided innova-ive, highly cost-effective, catalyzed chemical oxidation processesor the environmental remediation. In recent years, extensivenvestigations have been carried out to study the adsorption andhe reaction of molecules on the catalyst surface [1–7]. Among theumerous AOTs developed so far, some of the important innova-ions readily applicable in the large scale are the AOTs involving3/H2O2, Fe2+/H2O2, UV/O3, UV/H2O2, UV/O3/H2O2 and catalyticzonation [4,7–14]. In particular, ozonation is the most promis-ng method for the removal of colour from the textile effluents

s ozone molecules rapidly and selectively attacks the unsatu-ated bonds, resulting in the rapid removal of colour [8,11]. Theroficiency of ozonation process suffers to oxidize the ozonationy-products formed from the oxidation of dye molecules [4,8–11]

Abbreviations: AO-10, acid orange 10; XRD, X-ray diffraction; SEM, scanninglectron microscopy; PL, photoluminescence; TOC, total organic carbon; AOTs,dvanced Oxidation Technologies; PVP, polyvinyl pyrrolidone; S-Bi2O3, sonochem-

cally synthesized Bi2O3; H-Bi2O3, hydrothermally synthesized Bi2O3; C-Bi2O3,ommercially available Bi2O3; Au-Bi2O3, gold doped Bi2O3; DRS, diffuse reflectancepectra; UV–vis, ultraviolet–visible; JCPDS, Joint Committee on Powder Diffractiontandards.∗ Corresponding author. Tel.: +91 431 2503639; fax: +91 431 2500133.

E-mail addresses: sanand@nitt.edu, sanand99@yahoo.com (S. Anandan).

385-8947/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.cej.2011.02.020

ally prepared Bi2O3 doped with gold nanoparticles.© 2011 Elsevier B.V. All rights reserved.

which requires the new catalytic technologies based on ozone incombination with nano-size metals or metal oxides as homoge-neous or heterogeneous catalytic materials [12,13]. However, theremediation of the contaminated water by homogeneous catalysisis not recommended since the metal ions fetch its notorious impacton the aquatic environment [14].

Heterogeneous catalytic ozonation has received increasingattention in recent years due to its potentially higher effectivenessin the degradation and the mineralization of the harmful organicpollutants with lower negative effects [15]. The major advantageof heterogeneous catalytic system is the ease of catalyst retrievaland can be reused after some pre-treatments. Further, the nanos-tructured metal/metal oxides were used to improve the generationof electron-rich species such as O−, O2

•−, HO2• and •OH during the

ozonation treatment [12,16]. The nano-sized metal or metal oxidesas catalysts exhibit exciting enhancement in the catalytic activi-ties due to the enhanced surface to volume ratio and quantum-sizeeffect which make their properties and structural ability very dif-ferent from their bulk counterparts [16,17].

On the other hand, the catalytic activities were found to beenhanced when noble metals such as Au, Ag, Cu and Pt nanopar-

ticles were deposited on the semiconductors because the metalnanoparticles store electrons within them and in turn act as asink for the interfacial charge transfer processes [18]. Since goldnanoparticles often recognized as a better catalyst for variouschemical reactions, some attempts have been made recently to

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228 N. Pugazhenthiran et al. / Chemical E

tudy the ozonation reactions in the presence of gold nanoparticles19–22]. However, it requires a solid support or stabilizing agento interact with the various substrates. Bismuth trioxide (Bi2O3) isonsidered as a good choice as solid support since bismuth triox-de (Bi2O3) is a narrow band gap (2.8 eV) semiconductor existingn �, �, � and � polymorphs possessing excellent catalytic [7],lectrical [23], optical [24], and conducting [25] properties. In addi-ion, Bi2O3 nanoparticles or thin films have proven their efficacy ashotocatalyst for the removal of Methyl Orange and Rhodamine-Brom wastewater under ultraviolet as well as visible light irradia-ion [26–28]. Further more, some of the recent investigations onhe development of various nanostructures of Bi2O3 reveal thathe synthetic procedure strongly influences the catalytic activityf Bi2O3 [17,29]. In this study, to take advantage of the aboveacts, hydrothermal and sonochemical methods were used for theynthesis of Bi2O3 and gold nanoparticles were deposited on theurface of bismuth trioxide to enhance the catalytic performance.cid orange 10 (AO-10) was selected as the target pollutant (C.I.6230). The degradation of AO-10 by catalytic ozonation in theresence of various catalysts was studied and their catalytic effi-iencies were compared.

. Experimental details

.1. Materials

Bismuth(III) nitrate pentahydrate (Bi(NO3)3·5H2O), polyvinylyrrolidone (PVP); (MW 55,000), chloroauric acid trihydrateHAuCl4·3H2O) and acid orange 10 sodium salt (C16H10N2Na2O7S2)ere purchased from Sigma–Aldrich and were used as receivedithout further purification. Unless otherwise specified, all the

eagents used were of analytical grade and the solutions were pre-ared using double distilled water.

.2. Preparation of nanoparticles

.2.1. Sonochemical synthesis of Bi2O3 (S-Bi2O3)The Bi2O3 nanoparticles were synthesized by using the proce-

ure reported in the literature [30] with slight modifications. Thats, about 0.97 g of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O)

as dissolved in 10 mL of 1.12 M HNO3 in order to avoid hydrolyza-ion of Bi3+ ions. Subsequently, 0.1 g of PVP (stabilizing agent) wasdded into the above mixture and stirred for 10–15 min. Then, thisolution was slowly added drop-wise to a 250 mL round bottomask containing 100 mL of 0.2 M aqueous NaOH solution underonstant stirring till the pH reached 11. After stirring for 5 min,he resultant suspension was sonicated (20 kHz) in ambient air for0 min. On completion of sonication the suspension turned yellow

n colour; the precipitate was centrifuged and washed with dis-illed water and ethanol for several times. The resultant productas dried under vacuum at 80 ◦C for about 2 h and the dry powder

ample obtained was used for further studies.

.2.2. Hydro thermal synthesis of Bi2O3 nanoparticles (H-Bi2O3)The above mentioned concentrations of precursors of

i(NO3)3·5H2O, HNO3 and PVP were stirred for 10–15 min.his solution was then slowly dropped into 100 mL of aqueousaOH (0.2 M) solution under constant stirring till the pH of the

uspension reached 11. After stirring for 5 min, the resultinguspension was auto-claved in a Teflon-lined autoclave at 90 ◦C for

h followed by cooling to room temperature and the suspension

urned to yellow from white. The yellow precipitate was cen-rifuged and washed with distilled water and ethanol for severalimes. The resultant product was dried under vacuum at 80 ◦C forh.

ering Journal 168 (2011) 1227–1233

2.2.3. Preparation of Au-Bi2O3 nanoparticlesAu-Bi2O3 nanoparticles were prepared by deposition precipita-

tion method [31,32] as follows: 100 mL of an aqueous solution ofHAuCl4·3H2O (0.0169 g) was heated to 80 ◦C. The pH of the solu-tion was adjusted to 7 by drop wise addition of NaOH (1 M). 1 gof S-Bi2O3 was dispersed in the above solution and the pH of thesuspension was readjusted to 7 by drop wise addition of NaOH(1 M). The suspension was then thermostated at 80 ◦C with vigor-ous stirring for 2 h and the solids were gathered by centrifugation(12,000 rpm for 10 min) and washed several times with 100 mLof distilled water under stirring for 10 min at 50 ◦C. The sampleswere dried under vacuum at 100 ◦C for 2 h in order to get pure Au-Bi2O3 nanocatalyst and named as S-Au-Bi2O3. The final yield of goldloading was 2 mol% on Bi2O3, assuming all Au atoms were loadedduring doping. Similar procedure was repeated for Au loading onthe H-Bi2O3 and the commercially available Bi2O3 (C-Bi2O3) andthe resultant gold loaded samples are named as H-Au-Bi2O3 andC-Au-Bi2O3 respectively.

2.3. Characterization techniques

Diffuse reflectance spectra (DRS) of the samples were recordedin the wavelength range 200–800 nm using a UV–vis spectropho-tometer (T90+, PG Instruments) equipped with an integratingsphere accessory employing BaSO4 as reference material. Photolu-minescence (PL) spectra were recorded using a Shimadzu RF-5301spectrofluorophotometer. Material phase analysis of the preparednanocatalysts was done by powder X-ray diffraction, XRD, (Rigakudiffractometer, Japan, Cu K� radiation, � = 1.5406 A), and, mor-phology and particle size of the samples were analyzed throughscanning electron microscopy, SEM, (HITACHI-3000 SH Model). Theextent of decolourization during catalytic ozonation was followedspectrophotometrically using a UV–vis spectrophotometer (T90+,PG Instruments). The total organic carbon (TOC) of the reactionmixture during the catalytic ozonation was analyzed by injectingthe filtered sample solutions into a Shimadzu Total Organic Car-bon Analyzer (Shimadzu TOC-VCPH model). TOC measured after theequilibrium adsorption of the dye on the surface of various catalystsis denoted as TOC0 and the TOC obtained at a certain time (t) duringreaction is denoted as TOCt.

2.4. Catalytic ozonation experiments for evaluation of catalyticactivity

A 500 mL capacity borosilicate glass reactor was used and theouter walls were covered with aluminium foil to avoid the expo-sure to ambient light. The degradation of AO-10 was carried outat 25 ◦C and at natural pH. In all the experiments the concentra-tion of AO-10 [1 mM] and catalyst [1 g/L] were fixed and the ozonewas introduced through a porous fritted diffuser that can producefairly fine bubbles with diameter less than 1 mm in the suspen-sion. Ozone was produced from pure oxygen by corona dischargeusing an ozone generator (Sim O2 plus, Italy) which produced anozone concentration of 2 g/h (calculated) in the oxygen gas stream(2 L/min). The ozone concentration of about 2 mg/L was used forthe experiment by regulating the gas flow rate. The concentra-tion of ozone was analyzed using an ozone analyzer (BMT 201,Berlin).

3. Results and discussion

3.1. XRD and SEM studies

In order to investigate the changes in the crystal structure due todifferent preparation conditions, X-ray diffraction (XRD) measure-ments have been made in the range of 2� = 10–80◦ for the prepared

N. Pugazhenthiran et al. / Chemical Engineering Journal 168 (2011) 1227–1233 1229

10 20 30 40 50 60 70 80

(d) S-Au-Bi2O

3

(c) S-Bi2O

3

(b) H-Au-Bi2O

3

(a) H-Bi2O

3

Inte

nsit

y (

a.u

)

2O

40 42 44 46 48 50

Au

(2

00)

(b)

(c)

(d)

(a)

Inte

nsit

y (

a.u

)

2

3 and

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Fig. 1. X-ray diffraction pattern of (a) H-Bi2O3, (b) H-Au-Bi2O3, (c) S-Bi2O

i2O3/Au-Bi2O3 nanocatalysts. Fig. 1 shows typical XRD patternsf pure Bi2O3 and Au-Bi2O3 nanocatalysts prepared by sonochem-cal and hydrothermal methods. On the basis of the XRD results,he crystallographic phase of the prepared Bi2O3 and Au-Bi2O3anocatalysts is confirmed as the monoclinic �-Bi2O3 form. That is,he diffraction peaks of �-Bi2O3 (JCPDS # 71-2274) were observedt 2� values 27.39 (1 2 0), 33.25 (2 0 0), 46.33 (2 2 1) as predominanteaks in all the catalysts and no other Bi2O3 phases were detected.

n addition to the strong peaks of Bi2O3, weak diffraction peaksttributed to Au (2 0 0 planes) were also observed (JCPDS # 04-784) [33,34]. No peaks belonging to other chemicals (no existencef Au2O3 impurity peak) were found [35]. Further, on viewing theRD peaks in detail, it is found that the intensity of XRD peaks getecreased together with tightening of peaks for the hydrothermallyrepared samples compared to sonochemically prepared samples.his gives a first notion to us that hydrothermally prepared sam-

les may be nanorods whereas sonochemically prepared samplesay be nanoparticles. To obtain further insight, we performed

canning electron microscopic (SEM) analysis for the preparedamples. The Bi2O3/Au-Bi2O3 prepared via hydrothermal methodossesses short rod-like morphology (100%) with 20–30 nm in

(d) S-Au-Bi2O3 nanocatalysts. Inset: 2� = 40–50◦ region of above samples.

diameter and 100–150 nm in length (Fig. 2a–c). Whereas, theBi2O3/Au-Bi2O3 prepared via sonochemical method possesses bothrod-like (80–100 nm in diameter and several microns in length)and particle-like (∼80 nm) morphologies (Fig. 2d–f). Upon clearexamination of SEM image, we noticed that the particle-like mor-phology (50–60%) appeared consists of spherical particles. This isbecause, while preparing Bi2O3 using ultrasound in the presenceof PVP as a stabilizer, the generated ultrasound may prevent theone dimensional rod growth and keep the spherical Bi2O3 particlesformed in small size. It seems that, the stabilizing polymer (PVP)may play some role in the growth controlling process. That is, thestabilising polymer (PVP) may be coordinated to the bismuth ionsbefore the formation of Bi2O3 and this interaction may provide adifferent growth pathway leading to the formation of nanorods andnanospheres.

3.2. DRS and PL studies

The optical properties of the prepared Bi2O3 and Au-Bi2O3 sam-ples were explored by UV–vis diffuse reflectance spectroscopy andphotoluminescence (PL) spectroscopy. Fig. 3 shows the UV–vis

1230 N. Pugazhenthiran et al. / Chemical Engineering Journal 168 (2011) 1227–1233

3 (c), S

dA4tptdscoAbgAd

Fig. 2. SEM images of H-Bi2O3 (a and b), H-Au-Bi2O

iffuse reflectance absorption spectra of the prepared Bi2O3 andu-Bi2O3 samples. The absorption onset is observed at about60 nm for sonochemically prepared Bi2O3 nanoparticles whereashe absorption onset is slightly red shifted for hydrothermallyrepared Bi2O3 nanorods. Such small red shift can be related tohe increase of the aspect ratio (length to diameter ratio of oneimensional nanomaterial) of the nanorods [36–39]. That is, in theonochemically synthesized Bi2O3 the absorption band has someontribution from the spherical Bi2O3 nanoparticles and it shiftsnly slightly to shorter wavelength. Similar effect was observed for

u-Bi2O3 samples prepared by above methods with an additionalroad surface plasmon resonance peak (�max = 602 nm) due to theold doping. The absorption coefficients of the prepared Bi2O3 andu-Bi2O3 samples were analyzed by Tauc approach [40], and theirect band gap of the semiconductors was calculated using the

-Bi2O3 (d and e), and S-Au-Bi2O3 (f) nanocatalysts.

following equation:

˛ = C(hv − Ebulkg )

2

hv

where ˛ is the absorption coefficient, C is a constant, h� is thephoton energy and Ebulk

g is the band gap. Extrapolation of the lin-ear region of Tauc plots (Fig. 3 Insets) gives a band gap of 2.81 eVfor sonochemically prepared Bi2O3 and 2.73 eV for hydrothermallyprepared Bi2O3 nanorods. Similarly, the observed band gap for the

Au-Bi2O3 prepared by sonochemical and hydrothermal methodsare 2.83 eV and 2.79 eV, respectively.

Fig. 4 shows the photoluminescence (PL) spectra of the pre-pared Bi2O3 and Au-Bi2O3 samples. Bulk Bi2O3 sample shows onlyone peak at 440 nm whereas excitation of the prepared nano sam-

N. Pugazhenthiran et al. / Chemical Engineering Journal 168 (2011) 1227–1233 1231

F (b) sos ts.

pm[tanpopdntgrAs

ig. 3. Diffuse reflectance UV–vis spectra of (a) hydrothermally synthesized Bi2O3,onochemically synthesized Au-Bi2O3 nanocatalysts. Inset: corresponding Tauc plo

les at 367 nm shows two emission peaks (452 and 470 nm) whichay be due to the increase in the aspect ratio of the nanorods

41,42]. Further, the observed peak positions and shapes of the pho-oluminescence (PL) spectra are almost identical for both Bi2O3nd Au-Bi2O3 samples which may be due to radiative recombi-ation process (recombination of e−/h+ pairs with emission ofhoton) and self-trapped excitations [43]. However, the intensityf the Au-Bi2O3 samples are low compared to pure Bi2O3 sam-les due to low radiative recombination process caused by goldoping (i.e., low recombination of the e−/h+ pairs). When goldanoparticles are present at the surface of the catalyst, the pho-

−

oexcited e is easily transferred from conduction band to theold nanoparticles and leads to e−/h+ charge separation whicheduces the recombination rate. Thus, the results suggest thatu-Bi2O3 could be an effective catalyst compared to pure Bi2O3ample.

nochemically synthesized Bi2O3, (c) hydrothermally synthesized Au-Bi2O3 and (d)

3.3. Catalytic ozonation studies

3.3.1. Degradation of AO-10The catalytic activities of the prepared nanocrystalline Bi2O3

and nanocrystalline Au-Bi2O3 samples were evaluated by catalyticozonation of aqueous acid orange 10 (AO-10). The decomposi-tion kinetics data of catalytic ozonation of AO-10 in the presenceand in the absence of nanocrystalline Bi2O3 and Au-Bi2O3 sam-ples are displayed in Fig. 5. Experiments are carried out at roomtemperature, and, natural pH (∼5.8) and 1 mM initial concentra-tion of AO-10 were maintained during O3 (initial concentration of

ozone 2.0 mg/L) and simultaneous O3/nanocatalysts (initial ozoneconcentration in the solution 2 mg/L per 1 g/L catalyst dosage)treatments. Experimental data fitted well with apparent first-orderkinetic rate law (Langmuir–Hinshelwood model) with respect toAO-10 concentration. That is, plot of ln(C0/C) as a function of time

1232 N. Pugazhenthiran et al. / Chemical Engineering Journal 168 (2011) 1227–1233

400 450 500 550 600 650

100

200

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400

500

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2O

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2O

3

O3 + S-Bi

2O

3

O3 + H-Bi

2O

3

O3 + C-Bi

2O

3

O3

Wavelength (nm)

ig. 4. Photoluminescence spectra (excited at 367 nm) of H-Bi2O3 (a), S-Bi2O3 (b),-Au-Bi2O3 (c) and H-Au-Bi2O3 (d) nanocatalysts.

ave straight line fits (r2 = 0.98) where C0 is the initial concentrationf AO-10 and C is the concentration of AO-10 at time ‘t’. As seen inig. 5, ozonation in the presence of nanocatalyst increased AO-10emoval rate, as compared with O3 without any catalyst. In a sep-rate experiment, it was confirmed that in the presence of catalystithout O3, the rate of the reaction is negligible. The value of the

pparent first-order rate constant increased from 2.29 × 10−3 s−1

ozonation without catalyst) to 7.82 × 10−3 s−1 (3.5-fold) whenold loaded Bi2O3 nanocatalyst was introduced in ozonation. Theighest rate constant obtained in the presence of Au-Bi2O3 sam-les may be due to the low recombination of radicals (the radicalsre scavenged by gold nanoparticles to AO-10). The other impor-ant reason is the enhanced generation of hydroxyl radicals athe catalyst surface which acts as initiators as well as promotersn the degradation of AO-10. The enhanced adsorption of AO-10n catalyst surface and high density of hydroxyl radical gener-tion depends on the number of surface active sites present in

he catalyst in addition to the crystal defects and the oxygenacancies which may mainly depend on the synthetic procedure44–46]. The increased rate of degradation of AO-10 in the pres-nce of the gold loaded sonochemically prepared nanocatalysts

0 5 10 15 20

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-1

k = 3.44x10-3 s

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O3

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3

O3+H-Bi

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3

O3+S-Bi

2O

3

O3+C-Au-Bi

2O

3

O3+H-Au-Bi

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O3+S-Au-Bi

2O

3

ln (

C0/C

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Time (min)

k = 2.29x10-3 s

-1

ig. 5. Plot of ln(C0/C) vs time for catalytic ozonation of acid orange 10 in the pres-nce of various catalysts. [AO-10] = 1 mM and [catalyst] = 1 g/L.

Time (min)

Fig. 6. Total organic carbon (TOC) removal plot for catalytic ozonation of acid orange10 in the presence of various catalysts. [AO-10] = 1 mM and [catalyst] = 1 g/L.

(1.9-fold) when compared to the sonochemically synthesized bareBi2O3 (4.09 × 10−3 s−1) can be attributed to the fact that the goldnanoparticles have very high affinity towards O3. In addition, goldnanoparticles in the Au-Bi2O3 can increase the rate of catalyticozonation by creating the local electric field in the vicinity ofnanoparticles [47–49]. Thus, the sonochemically synthesized sam-ples provide an effective environment for the enhanced catalyticdegradation of AO-10. The observed experimental results show thatthe synthetic procedure plays a major role in the resulting catalyticactivity of bismuth trioxide.

3.3.2. Mineralization of AO-10Fig. 6 shows the mineralization of AO-10 which is much slower

than the decolourization in the presence of various catalysts.Among the various catalysts used, S-Au-Bi2O3 exhibited 47% of totalorganic carbon (TOC) removal in 30 min which is 2.3 times highercompared to bare S-Bi2O3 (20.1%). Ozonation of AO-10 without anycatalyst exhibits only 11% mineralization in 30 min. The observedlow rate of mineralization (TOC removal) in the absence of cata-lysts proves that ozone alone cannot completely degrade AO-10.On the other hand, the enhanced mineralization in the presenceof catalysts proves that indirect ozonation (with catalyst) providesenhanced number of effective radicals for the degradation of AO-10 than the direct ozonation (without any catalyst). Hence, it isexpected that the active radicals dwell at the surface active sitesof the catalyst and they can interact effectively with the targetpollutant by continuously producing various radical intermediates,which in turn degrade the AO-10 effectively. The beneficial effect ofthe deposition of gold nanoparticles on the surface of Bi2O3 is theenhanced generation of active radicals (as Au has more affinity toO3) which degrade the pollutants effectively through radical chainbranching mechanism in the presence of ozone.

4. Conclusions

In this study, we have demonstrated a simple and inexpen-sive way of preparing nanocrystalline Bi2O3 and gold loaded Bi2O3possessing nanorod and nanoparticle morphologies which are in

contrast to the widely reported fact that Bi2O3 mostly forms rodshaped particles. The photoluminescence intensity of the Au-Bi2O3samples are low compared to that of Bi2O3 which suggests golddoping in Bi2O3 reduces radiative recombination process. A 3.5-foldenhancement in the rate of degradation of AO-10 upon addi-

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ion of Au-Bi2O3 during ozonation is attributed to the enhancedeneration of active radicals at the Au-Bi2O3 catalyst surface. Min-ralization studies (TOC studies) reveal that gold loaded Bi2O3repared by sonochemical method could be a better candidate forhe degradation of dyes such as AO-10.

cknowledgements

The author SA thanks CSIR, New Delhi for the sanction ofesearch fund (CSIR reference No.01 (2197)/07/EMR-II) and DST-IST, New Delhi (SR/FT/CSI-190/2008) towards development ofew facilities. Also, the author NP thank CSIR, New Delhi, for theanction of senior research fellowship and the author PS thankICTE, New Delhi for the sanction of national doctoral fellowship.he authors would like to thank Dr. Muthukumar, Bharathiar Uni-ersity for extending facilities to carryout the Ozonation studies.

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