Ultrasonics Sonochemistry 19 (2012) 883–889

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Ultrasonics Sonochemistry

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Sonodegradation and photodegradation of methyl orange by InVO4/TiO2

nanojunction composites under ultrasonic and visible light irradiation

YuLin Min a,b,⇑, Kan Zhang c,⇑, YouCun Chen a,b, YuanGuang Zhang a,b

a School of Chemistry and Chemical Engineering, Anqing Normal University, Anqing 246011, PR Chinab Anhui Provincial Laboratory of Optoelectronic and Magnetism Functional Materials, Anqing Normal University, Anqing 246011, PR Chinac Department of Chemical Engineering, Sungkyunkwan University, Suwon, Gyeonggi-do 440-746, Republic of Korea

a r t i c l e i n f o

Article history:Received 1 April 2011Received in revised form 14 December 2011Accepted 22 December 2011Available online 29 December 2011

Keywords:InVO4/TiO2 nanojunction compositesSonocatalytic activityPhotocatalytic activityCharge transfer

1350-4177/$ - see front matter � 2011 Elsevier B.V. Adoi:10.1016/j.ultsonch.2011.12.015

⇑ Corresponding authors. Tel./fax: +86 556 5500690E-mail addresses: ahaqmylin@yahoo.com (Y.L. Min

com (K. Zhang).

a b s t r a c t

The InVO4/TiO2 nanojunction composites with different weight ratio of 1:10, 1:25, 1:50 and 1:100 weresuccessfully constructed using an ion impregnate method, followed by calcining temperature 400 �C for2 h in Ar. The sono- and photo-catalytic activities of the InVO4/TiO2 nanojunction composites were eval-uated through the degradation of methyl orange (MO) in aqueous solution under ultrasonic and visiblelight irradiation, respectively. The experimental results determined that the (1:50) InVO4/TiO2 nanojunc-tion composite has exhibited the highest sonocatalytic activity. It can be ascribed to vectorial chargetransfer at the co-excited InVO4/TiO2 interface under ultrasonic irradiation, results in the complete sep-aration of electrons and holes. Interestingly, the (1:25) InVO4/TiO2 nanojunction composite displayedsuperior photocatalytic activity for MO degradation under visible light, indicating that InVO4 as a narrowband gap sensitizer can expand photocatalytic activity of TiO2 to visible region, and the charge transfercan be formed from high energy level of InVO4 conduction band to the low energy level of TiO2 conduc-tion band in a present of excited InVO4 alone under visible light irradiation. The sono- and photo-catalyticactivities of the InVO4/TiO2 nanojunction composites were found to be dependent significantly on differ-ent InVO4 contents, which can be explained by the influence of charge transfer on the basis of the workfunctions of different catalysis mechanism.

� 2011 Elsevier B.V. All rights reserved.

1. Introduction

The excess use of various dyes in the textile, rubber and plasticindustries has led to the severe surface water and groundwatercontamination by releasing the toxic and colored effluents, whichare important for the sake of increasing amount, its variety andresistance to biological destruction [1]. So advanced oxidation pro-cesses (AOPs), including application of technologies, such as perox-one, non-thermal plasma, photo-Fenton, UV/O3, UV/H2O2, UV/semiconductor, have been developed and described by manyresearchers to degrade organic compounds in wastewater [2–6].Particularly, due to high efficiency, low cost and easiness, semicon-ductor photocatalysis has emerged as an important destructivetechnology leading to the mineralization of most of the organicpollutants. The use of TiO2 as frequent candidate for environmentalclean-up has been devoted of great interest.

However, the photocatalytic degradation must need UV light toinduce TiO2 semiconductor, which costs lot of energy and presentlow penetrating ability. Thus the sonocatalytic degradation or

ll rights reserved.

(K. Zhang).), Zhangkan112255@hotmail.

visible light-induced photocatalytic degradation to treat variouswastewaters all through was become increasingly popular. Be-cause the penetrating ability of ultrasound is very strong for anywater medium and its penetrating depth can ordinarily attain to25–30 cm. Moreover, the effects of ultrasound waves were discov-ered that heat generated from the cavity implosion degrades water(H2O) into extremely reactive hydrogen atoms (H�) and hydroxylradicals (OH�) [7]. Hence, the ultrasonic irradiation has been pro-posed as one of the techniques for degradation of hazardous organ-ic dyes. Tuziuti et al. determined that the presence of the TiO2

particles contributed to an increase in bubble cavitation whichpromotes the transfer of the generated free radicals to the liquidbulk region as the bubble collapses [8]. Wang and co-workers havereported that sonocatalytic degradation of some organic pollutantsby TiO2 system including homogenous and inhomogenous TiO2

shows a great degradation performance [9–11]. Zhang et al. alsodetermined that the sonodegradation performance of TiO2 semi-conductor depends on its surface area due to the turbulence liquidinducing fragmentation and deagglomeration of TiO2, resulting inan increase of the adsorption ability [12]. As a result, attentionhas been drawn to the fact that the ultrasound can compete withUV light, which also excite the TiO2 to act as a photocatalyst duringsonication.

884 Y. Min et al. / Ultrasonics Sonochemistry 19 (2012) 883–889

As we known, in order to improve the responding TiO2 to visiblelight and enhance the separation of electron–hole pairs, mostmethods are metal [13] or non-metal [14] doped TiO2 and couplingTiO2 by using a narrow band gap semiconductor such as CdS [15],CuBi2O4 [16], SnO2 [17] and WO3 [18], which have higher conduc-tion band (CB) than that of TiO2. Particularly, the enhanced photo-catalytic activity of coupled two semiconductors has to formheterojunction or homojunction by intimate junction of two com-pounds, which allows excellent charge transfer at the interface[19,20]. Since a new type of InVO4 semiconductor with narrowband gap (Eg = 2.0 eV) has been developed by Zou et al. and [21]and used as water splitting photocatalyst under visible irradiation,the InVO4 has been received much attention for constructing het-erojunction photocatalyst, aiming at improvement of their photo-catalytic activity. For instance, InVO4/TiO2 thin film by sol–gelmethod has been widely studied for effective degradation oforganic compounds under visible light [22,23]. In InVO4/TiO2 thinfilm, InVO4 with narrow band gap acts as a visible-light sensitizer;combined with TiO2, InVO4 is also responsible for effective chargeseparation that enables suppression of the electron/hole recombi-nation process.

In this study, the novel heterojunction catalysts of InVO4/TiO2

composites with different weight ratio were synthesized by anion impregnate method. Sono- and photo-catalytic degradation inthe presence of InVO4/TiO2 nanojunction composites to degradeMO is also investigated.

2. Experimental

2.1. Materials

Indium chloride (InCl3) and ammonium metavanadate(NH4VO3) were used as precursors of indium vanadate (InVO4),which was purchased from Aldrich. P25 was obtained from the De-gussa Company, hydrogen peroxide (H2O2, 35%) and ammoniasolution (NH3�H2O, 3 mol/L) from Junsei chemicals, Japan. Ammo-nium persulfate ((NH4)2S2O8) and HNO3 as an oxidant was pur-chased from Daejung Chemicals & Metals Co. Ltd., Korea. MethylOrange (MO) as analytical grade was purchased from Duksan PureChemical Co. Ltd., Korea.

2.2. Synthesis of InVO4/TiO2 nanojunction composites

0.5 g P25 was firstly dispersed in 100 mL 5% H2O2 solution andsonicated 30 min to obtain a homogenous mixture in a flask. InCl3

and NH4VO3 were dissolved with distilled water, respectively, theas-prepared InCl3 solution with a concentration of 0.5 mL/L wasslowly drop into a mixture of P25 with a vigorous stirring at ambi-ent temperature. After 2 h of stirring, the 0.5 mL/L NH4VO3 solutionwas added to above In3+ doped TiO2 sol formed until the mole ratioof In3+ to VO3� reached 1:1, a primrose yellow gel were formedafter the temperature up to 150 �C on oil bath. The pH value ofthe solution was then adjusted to about 7 with ammonia solution,white slurry was momentary formed, after 3 h of stirring, the ob-tained white slurry was centrifuged and washed with distilledwater for three times to remove the remained Cl� and NHþ4 . Finallythe solid obtained was vacuum-dried at 50 �C, and was then cal-cined at 400 �C under a flow of Ar for 2 h. During this thermal reac-tion, the InVO4 compound can be completed with simultaneousjunction to the TiO2 matrix, and the weight of InVO4 was calculatedto 0.05, 0.02, 0.01 and 0.005 g, respectively.

Another InVO4/TiO2 composite was synthesized to comparewith InVO4/TiO2 nanojunction composites by thermal treatmentof physical mixtures method. Firstly, the 0.5 mL/L NH4VO3 solutionwas slowly added to 0.5 mL/L InCl3 solution at 150 �C on oil bath,

pH value of the solution was adjusted to about 7 with ammoniasolution, and stirred for 2 h. the formed InVO4 slurry was centri-fuged, washed and vacuum-dried at 50 �C in succession. The0.01 g InVO4 was physically mixed with 0.5 g P25 in a mortarand was calcined at 400 �C under a flow of Ar for 2 h, and namedas TTP-InVO4/TiO2 composite.

2.3. Analysis instruments

XRD patterns were obtained with a diffractometer on Riguka,Japan, RINT 2500 V using Cu Ka radiation. UV–Vis diffuse reflec-tance spectra and adsorption spectra were recorded using a Gen-spec III (Hitachi, Japan) spectrometer. XPS analysis wasperformed with an ESCALAB-220I-XL (THERMO-ELECTRON, VGCompany) device. Scanning electron microscopy (SEM) images ofthe product were taken on a field emission scanning electronmicroscope (FESEM, JEOL, FEG-XL 30S). Transmission electronmicroscopy (TEM) observations were performed on a JEOL, JEM-2010 (Japan) electron microscope with an accelerating voltage of200 kV. Photoluminescence was recorded at room temperatureusing a fluorescence spectrometer (Shimadzu, RF-5410PC). A Con-trollable Serial-Ultrasonics apparatus (NXG-MD, Kodo TechnicalResearch Co. Ltd., Korea) was used to irradiate the reactant, operat-ing at an ultrasonic frequency of 28 kHz with a nominal outputpower through manual adjustment.

2.4. Sonocatalytic activity

Sonocatalytic degradation was tested using the bare P25 andInVO4/TiO2 nanojunction composites with ultrasonic generatorsoperated at a fixed frequency of 28 kHz. The reactions were carriedout in an open cylindrical stainless glass vessel. Photocatalytic deg-radation was tested using bare P25 and InVO4/TiO2 nanojunctioncomposites in an aqueous solution of MO in the same glass vesseland irradiated with visible light (k > 420 nm, LED lamp). The bareP25 and InVO4/TiO2 nanojunction composites (0.03 g) were sus-pended in 50 mL of a MO solution with a concentration of�1.0 � 10�5 M. The mixed solution was then placed in the darkfor at least 30 min to establish an adsorption–desorption equilib-rium, which is hereafter considered to be the initial concentration(c0) after dark adsorption. After different irradiation time of 0, 10,20, 30, 40, 50 and 60 min, 2 mL of the solution was removed andimmediately centrifuged to separate any suspended solid. Theclean transparent solution was analyzed using a UV–Visspectrophotometer.

3. Results and discussion

3.1. Textural and optical properties

XRD patterns of the P25 and InVO4/TiO2 nanojunction compos-ites are shown in Fig. 1. The X-ray diffraction peaks of InVO4 cancorrespond to the orthorhombic phase of (JCPDF 48-0898). Thebare P25 displays a mix of anatase and rutile crystals. However,in XRD patterns of the InVO4/TiO2 nanojunction composites, signif-icant diffraction peaks of anatase-phase TiO2 become broad, whilethe rutile phase is difficultly detected in high content of InVO4 case.The average crystalline size can be evaluated using the Scherrermethod based on the diffraction peak corresponding to the (101)plane [24]. The d (Å) and FWHM of plane (101) of TiO2 in theInVO4/TiO2 nanojunction composites are listed in Table 1. It clearlyindicates different crystallite size of TiO2 in the InVO4/TiO2 nano-junction composites, which can be ascribe to that the introducedInVO4 nanoparticles inhibit TiO2 grain aggregation. In addition,No obvious XRD diffraction peaks of InVO4 appear in the InVO4/

Fig. 1. XRD patterns of InVO4, P25 and InVO4/TiO2 nanojunction composites.

Table 1The d(Å) and FWHM of plane (1 0 1) of P25 and InVO4/TiO2 nanojunction composites.

Sample d (Å) FWHM

P25 7.2977 0.125(1:100) InVO4/TiO2 7.0459 0.137(1:50) InVO4/TiO2 6.8548 0.162(1:10) InVO4/TiO2 6.1679 0.773

Y. Min et al. / Ultrasonics Sonochemistry 19 (2012) 883–889 885

TiO2 nanojunction composites that may be due to the less amountsdoping of InVO4 and highly dispersed in sample InVO4/TiO2 nano-junction composites.

The morphology of the InVO4/TiO2 nanojunction composite ischaracterized by SEM and TEM as shown in Fig. 2. The SEM micro-graph of Fig. 2a and b shows the surface morphology and rough-ness of the InVO4/TiO2 with dense and composed of sphereparticles with 10–20 nm in diameter. The TEM image of InVO4/TiO2 nanojunction composite is shown in Fig. 2c,1 which clearlyshows the nanojunction of TiO2 and InVO4 (indicated by the yellowarrow). The HR-TEM image of the nanojunction region is present inFig. 2d, it can be seen that the lattice spacing of TiO2 is 0.352 nm, andthat of InVO4 is 0.28 nm. An interconnected fine particulate mor-phology observed indicates the existence of InVO4/TiO2 heterojunc-tion. The appearing of such junctions seems that the stronginteraction between InVO4 and TiO2 is formed in the degradationprocess.

Fig. 3 shows high-resolution XPS spectra of InVO4/TiO2 nano-junction composite. The peaks around 458.5 eV and 464.1 eV areassigned to Ti2p3/2 and Ti2p1/2 of TiO2, corresponding to Ti4+ ina tetragonal structure (Fig. 4(a)). The In3d5 peak is centered at444.6 eV (Fig. 4(b)), which can be assigned to In3+ of InVO4 [25].The V2p peak is observed at 515.3 eV (Fig. 4(c)), corresponding toV5+ of InVO4 [25]. The results indicate that a compound of InVO4

can be formed with simultaneous junction to the TiO2 matrix inthermal reaction process.

Fig. 4 shows the PL spectra of various samples with 300 nm ex-cited wavelength. Bare P25 exhibits a strong PL signal at the rangefrom 400 to 500 cm�1, and has five obvious PL peaks at about 450,468, 483 and 493 cm�1, respectively, possibly the former mainlyresulting from band edge free excitons, the latter mainly resultingfrom binding excitons [26,27]. It is also clear that the InVO4 exhib-its one broad and strong emission band at �520 cm�1 which iscaused by electron–hole recombination at surface traps [28]. Inaddition, the characteristic emission of InVO4 is significantly

1 For interpretation of color in Fig. 2, the reader is referred to the web version ofthis article.

reduced after introduction to the TiO2 matrix, simultaneous emis-sion from the TiO2 is reduced considerably. This behavior showsthat efficient charge or energy transfer occurs at the InVO4/TiO2

heterojunction interface. This suggests that interactions betweenthe InVO4 and TiO2 involve charge transfer of photoexcited elec-trons from the conductive band of the donor InVO4 to empty elec-tronic states of the acceptor TiO2 and photoexcited holes from thevalence band of the TiO2 to InVO4, resulting in more emissionquenching of InVO4 and TiO2. Similarly, the TTP-InVO4/TiO2 com-posite can also complete charge transfer between InVO4 and TiO2.

The corresponding UV/Vis absorption spectra for the bare P25,InVO4 and InVO4/TiO2 nanojunction composite are shown inFig. 5. Compared with the optical absorption of bare P25(�400 nm), the absorption edge of InVO4 has an intense absorptionin the visible light (�590 nm). Whereas the InVO4/TiO2 nanojunc-tion composite by ion impregnate method has two absorptionedges; the main edge due to InVO4 is located at �580 nm and sec-ond one due to TiO2 at �425 nm. The absorption edge for theInVO4/TiO2 nanojunction composites indicates that the TiO2 canbe responded to visible region by combined with InVO4.

3.2. Catalytic activities

3.2.1. Effect of InVO4 contents and synthesis method on sono- andphoto-catalytic activity of InVO4/TiO2 nanojunction composites

Fig. 6a displays the effect of ultrasonic irradiation time within60 min at 10 min intervals on the sonocatalytic degradation ofMO in the presence of bare P25 and InVO4/TiO2 nanojunction com-posites. It is clearly observed that the degradation performancesfor all cases increase gradually along with an increase of irradiationtime. It can be seen that the sonodegradation performances inpresence of catalysts are much higher than that in absence of cat-alyst under ultrasonic irradiation, while the sonolysis only reaches20% degradation for the MO dye. The reduction ratios range in adiminishing sequence of bare P25 and InVO4/TiO2 nanojunctioncomposite is (1:50) InVO4/TiO2 > (1:25) InVO4/TiO2 > (1:100)InVO4/TiO2 � TTP-InVO4/TiO2 � bare P25 > (1:10) InVO4/TiO2,which indicates that the (1:50) InVO4/TiO2 nanojunction compos-ite reveals to be much more efficient for degradation of MO underultrasonic irradiation.

The effect of visible light irradiation time within 60 min at10 min intervals on the photocatalytic degradation of MO in thepresence of bare P25 and InVO4/TiO2 nanojunction compositesare shown Fig 6b. A blank test (MO alone) under visible light exhib-its exceptionally low photodegradation efficiency, which can be al-most ignored. The photodegradation performances of MO with allcatalysts generally under visible light follows the order as below:(1:25) InVO4/TiO2 > (1:50) InVO4/TiO2 > TTP-InVO4/TiO2 > (1:100)InVO4/TiO2 � (1:10) InVO4/TiO2 > bare P25. Clearly, the (1:25)InVO4/TiO2 nanojunction composite has highest photocatalyticactivity for degradation of MO under visible light irradiation. Inparticular, it is found that the (1:50) InVO4/TiO2 nanojunction com-posite exhibits much higher catalytic activities than that of TTP-InVO4/TiO2 composite under both of ultrasonic and visible lightirradiation. It indicates that the InVO4/TiO2 nanojunction compos-ite by an ion impregnate method is not only beneficial for forma-tion of heterojunction, but also In3+ doped into TiO2 lattice inpreparation process, resulting in trapping more electrons.

3.2.2. Possible sonodegradation mechanismUntil now, there has been no ready-made mechanism and satis-

fying explanation for the sonodegradation of organic pollutants inthe presence of various catalysts. Possibly, the following two pointsof view, namely, ‘‘sonoluminescence’’ and ‘‘hot spot’’, can explainthe sonodegradation of organic dye in the presence of semiconduc-tor catalysts [29–31]. First, the ultrasonic irradiation can form light

Fig. 2. SEM (a) and TEM (b) image of InVO4/TiO2 nanojunction composite.

Fig. 3. XPS spectra of InVO4/TiO2 nanojunction composite. (a) Ti2p, (b) V2p and (c) In3d5.

886 Y. Min et al. / Ultrasonics Sonochemistry 19 (2012) 883–889

with a comparatively wide wavelength range [32]. It is well knownthat the wavelengths below 387 nm can excite the TiO2 particles to

act as a photocatalyst, hence to bring hole and electron pairs.Therefore, the sonocatalytic method also needs to retard the

Fig. 4. Photoluminescence spectra of InVO4, P25 and InVO4/TiO2 nanojunctioncomposites.

300 400 500 600 700 800

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Ab

sorb

ance

(a.

u.)

Wavelenght (nm)

P25 InVO

4

InVO4/TiO

2

Fig. 5. UV–Vis diffuse reflectance spectroscopy of P25, InVO4 and InVO4/TiO2

nanojunction composite.

Fig. 6. Catalytic degradation behaviors of MO over P25, TTP-InVO4/TiO2 and InVO4/TiO2 nanojunction composite under ultrasonic and visible light irradiation, (a)ultrasonic and (b) visible light.

Fig. 7. Effect of reuse of the (1:50) InVO4/TiO2 nanojunction composite on thedegradation efficiency of MO under ultrasonic irradiation.

Y. Min et al. / Ultrasonics Sonochemistry 19 (2012) 883–889 887

recombination of electron–hole pairs for semiconductor catalysts.Based on the energy band between InVO4 and TiO2, their Fermi en-ergy levels are supposed to affect the interfacial charge transferand thus the charge separation in the InVO4/TiO2 heterojunction.In general, the minimum energy needed to move an electron fromthe Fermi energy level into vacuum is defined as the work function[33]. Therefore, the vectorial photogenerated electrons transfer ofInVO4 ? TiO2 and photogenerated holes transfer of TiO2 ? InVO4

in nanojunction composites greatly improves the separation rateof photo-induced electron–hole pairs, resulting in higher sonocat-alytic activity. The possible process of sonocatalytic degradation isshown in Fig. 7a.

Fig. 7b depicts the valence and conduction bands for InVO4

[34,35] and TiO2 with their band gap energy. Due to two semicon-ductors in nanojunction having different redox energy levels oftheir corresponding conduction and valence bands, the energy lev-els can actually be considered as one of the most important prom-ising methods to improve charge transfer. For efficient electrontransfer between the semiconductors that is considered as sensi-tizer by narrow band gap of InVO4 and TiO2, the conduction bandof TiO2 must be anodic than the corresponding band of sensitizer.Under visible light irradiation, the photo-generated electrons inthe conduction band of excited InVO4 also easily flow into the con-duction band of TiO2, because of the lower Fermi energy levels ofTiO2 than the conduction band of InVO4. The charge transfer pro-cess in the InVO4/TiO2 nanojunction composites under visible lightirradiation is shown in Fig. 7c.

For investigating the long-term stability of the InVO4/TiO2

nanojunction composites under ultrasonic irradiation, recyclingexperiments are carried out using (1:50) InVO4/TiO2 nanojunctioncomposite. For each new cycle, the sample is collected and vac-uum-dried at 100 �C for 2 h by keeping other reaction conditions

constant. As shown in Fig. 8, it is apparent that the sonodegrada-tion performances of MO during three time cycle are stable, whichis maintained at approximate 80% of the MO. It is considered thatthe catalytic activity of the InVO4/TiO2 nanojunction composite ismaintained through the repeated cycles of MO degradation with-out showing a significant deactivation of the catalyst, weakening

Fig. 8. Electron transfer processes of InVO4/TiO2 nanojunction composites under (a)ultrasonic and (c) visible light irradiation. (b) Energetic diagrams of InVO4 and TiO2.

Fig. 9. Effect of intensities of ultrasonic irradiation over (1:50) InVO4/TiO2

nanojunction composites for sonocatalytic degradation of MO.

Fig. 10. Effect of different oxidation reagent over (1:50) InVO4/TiO2 nanojunctioncomposites for sonocatalytic degradation of MO.

888 Y. Min et al. / Ultrasonics Sonochemistry 19 (2012) 883–889

adsorbability and phase separation of InVO4/TiO2 nanojunctioncomposite.

3.2.3. Effect of intensities of ultrasonic irradiation on thesonodegradation efficiencies

As shown in Fig. 9, the intensities of ultrasonic irradiation canbring the considerable influence on the sonodegradation ratio ofMO by (1:50) InVO4/TiO2 nanojunction composite. The effect of

intensities within 60 min was studied by varying the power ofultrasonic ranging from 40 W to 60 W. It can be seen from Fig. 9that within 60 min, along with the increase in the intensities ofultrasonic irradiation, the sonodegeneration efficiency is distinctlyenhanced. Apparently, the bigger the power of irradiation lamps,the stronger is the light intensity, and therefore, the degenerationefficiency is higher.

3.2.4. Effect of different oxidation reagent on the sonodegradationefficiencies

Sonodegradation of MO in presence of (NH4)2S2O8, H2O2 andHNO3 with a same molar amount at 1 � 10�6 are shown inFig. 10. It can be seen that the sonodegradation efficiencies gradu-ally increase along with addition of the different oxidation reagentfor (1:50) InVO4/TiO2 nanojunction composite. However, themechanisms of enhancing sonodegradation ratio in presence of(NH4)2S2O8, H2O2 and HNO3 maybe are difference. As we known,the catalytic degradation of dye are generally based on point ofzero charge (pZC) of catalyst. While the solution pH value is lowerthan the pZC, the surface is positively charged. Because MO is acidazo and strong electrolyte dye, the anionic MO solution can bemore adsorbed on the surfaces of InVO4/TiO2 nanojunction com-posite in the acidic condition, hence enhancing sonodegradationefficiency of MO in present of HNO3. The addition of (NH4)2S2O8

enhancing sonodegradation efficiency is more attributed to theprevention of the recombination between electrons and holes bythe entrapment of the generated electron with simultaneous the

Y. Min et al. / Ultrasonics Sonochemistry 19 (2012) 883–889 889

production of sulfate radicals which is very strong oxidizing agent,which generated by the following equation:

InVO4=TiO2þÞÞÞÞðultrasoundÞ ! e� þ hþ ð1Þ

S2O2�8 þ e� ! SO2�

4 þ SO��4 ð2Þ

SO��4 þH2O! SO2�4 þ OH� þHþ ð3Þ

Interestingly, the sonodegradation efficiency of MO in presentof H2O2 as basic condition can also be increased. It can be pointedout that H2O2 react with hydrogen to regenerate hydroxyl radicalsby escape of free radicals from the interface under ultrasoundirradiation:

H� þH2O2þÞÞÞðultrasoundÞ ! OH� þH2O ð4Þ

4. Conclusion

The InVO4/TiO2 nanojunction composites have been success-fully constructed by an ion impregnate method, and exhibitedhigher catalytic activities for MO degradation under ultrasoundand visible light irradiation compared to P25 and thermal treat-ment of physical mixtures of InVO4/TiO2 composite. This enhance-ment was mainly due to the vectorial electrons or holes transferbetween InVO4 and TiO2, which greatly improved the separationof photo-generated charges. Moreover, the InVO4/TiO2 nanojunc-tion composites with weight ratios at 1:50 and 1:25 have highestcatalytic activities under ultrasound and visible light irradiation,respectively. It can be attributed to the influence of charge transferon the basis of the work functions of different catalysis mechanism.The reasons of enhancing sonodegradation efficiencies for differentpower of ultrasonic and addition of oxidation reagent wereexplained.

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