Fp

Ma

Sb

a

ARRA

KPSE

1

irdcciribtsdtpfacasetm

0d

Materials Chemistry and Physics 124 (2010) 619–622

Contents lists available at ScienceDirect

Materials Chemistry and Physics

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

acile synthesis of core–shell SnO2/V2O5 nanowires and their efficienthotocatalytic property

uhammad Shahida, Imran Shakira, Seok-Jo Yangb,∗, Dae Joon Kanga,∗

BK 21 Physics Research Division, Department of Energy Science, Institute of Basic Sciences, SKKU Advanced institute of Nanotechnology,ungkyunkwan University, Suwon 440-746, Republic of KoreaDepartment of Mechatronics Engineering, Chungnam National University, Daehang-no, Yusung-gu, Daejeon 305-764, Republic of Korea

r t i c l e i n f o

rticle history:

a b s t r a c t

One-dimensional SnO2/V2O5 core–shell nanowires were synthesized by a combination of hydrothermal

eceived 16 March 2010eceived in revised form 2 July 2010ccepted 10 July 2010

eywords:hotocatalysis

and wet chemical routes at room temperature. The photocatalytic behavior of the SnO2/V2O5 nanowiresfor the photodegradation of toluidine blue “O” dye (TBO) under UV exposure was examined. SnO2/V2O5

showed better photocatalytic activity than V2O5 nanowires and bulk. The significant enhancement of thephotocatalytic activity of the core–shell SnO2/V2O5 nanowires was attributed mainly to its large specificsurface area and efficient charge separation at the SnO2/V2O5 photocatalyst interface.

© 2010 Elsevier B.V. All rights reserved.

nO2/V2O5 nanowireslectron–hole separation

. Introduction

Over the last few decades, there has been considerable interestn the synthesis of semiconductor photocatalysts for potential envi-onmental applications which include air purification and waterisinfection [1–3]. Among the many semiconductor oxide photo-atalysts available, V2O5 has been studied extensively owing to itshemical inertness, strong oxidizing power and long-term stabil-ty against photo and chemical decay [4–6]. However, the rapidecombination of photogenerated electron–hole pairs has limitedts practical utility. The photonic efficiency of a photocatalyst cane increased by decreasing the rate of charge carrier recombina-ion relative to that of interfacial charge transfer [7,8]. Previoustudies have reported that the specific surface area increases withecreasing average particle size of a photocatalyst in the nanome-er regime. This in turn increases the number of active sites forhotogenerated charge carriers to undergo interfacial charge trans-er [9,10]. There are many reports showing that the photocatalyticctivity can be increased effectively by combining different semi-onductor nanomaterials with different band energies [11,12]. Thispproach has been applied successfully in a variety of particulate

ystems which include CdS–TiO2 [13] and CdS–CNT [14]. This studyxamined the potential of a combination of SnO2 and V2O5 for effec-ive photocatalytic applications. Tin oxide (SnO2) is an important

aterial on account of its unique electronic and optical properties

∗ Corresponding authors. Tel.: +82 31 290 5906; fax: +82 31 290 5947.E-mail addresses: sjyang@cnu.ac.kr (S.-J. Yang), djkang@skku.edu (D.J. Kang).

254-0584/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.matchemphys.2010.07.023

[15,16]. SnO2 can readily donate holes with high oxidation abilitywith no absorption of light more than 330 nm. It has been reportedthat a combination of SnO2 with TiO2 [17], ZnO [18] and Fe2O3[19] can effectively increase the photocatalytic activity. This studyexamined the optimized conditions for the formation of SnO2/V2O5core–shell nanostructure along with its photocatalytic behavior.

2. Experimental

Vanadium oxytripropoxide (98%), ammonium metavanadate (99%) HCl (38%),sulphuric acid (95%), toluidine blue O (85% dye content) and tin(II) chloride (99%)were purchased from Sigma–Aldrich and used as received. V2O5 nanowires weresynthesized by dissolving 1 mmol vanadium oxytripropoxide in 10 mL of deion-ized water and stirred with a magnetic stirrer for 30 min until the mixture becamehomogeneous. The pH of the solution was adjusted to 1–2 by adding dilute sul-phuric acid (H2SO4/H2O = 1:4, v/v) drop-wise with constant stirring. The resultingorange solution was transferred to a teflon-lined stainless autoclave (25 mL capac-ity) which was kept at 180 ◦C for 48 h and then cooled to room temperature. Theprecipitates were filtered, washed several times with distilled water and ethanol,and dried on a hot plate at 100 ◦C for 12 h. The as-prepared sample was calcinedat 550 ◦C for 2 h in air to produce high quality V2O5 nanowires. To functionalizethe V2O5 nanowires with SnO2 nanoparticles, initially 1 g of tin(II) chloride wasdissolved in 100 mL of distilled H2O. Subsequently, 1 mL of HCl was added to thesolution followed by V2O5 nanowires (15 mg). The resulting mixture was sonicatedfor 2 min and stirred for 1 h at room temperature. The SnO2 treated nanowire sam-ple was rinsed with distilled H2O and dried on a hot plate at 80 ◦C for 2 h. Themorphological and structural properties were examined by field emission scan-ning electron microscopy (FE-SEM, JEOL JSM–7401F) and X-ray diffraction (XRD, D8FOCUS 2200V, Bruker AXS, Cu K� radiation (�) 1.5418 Å), respectively. The formation

of SnO2–V2O5 core–shell structure was observed by high-resolution transmissionelectron microscopy (HRTEM, field emission-TEM, JEM2100F). The presence of SnO2

and the chemical composition of the core–shell nanowires were investigated byX-ray photoelectron spectroscopy (XPS, Perkin-Elmer PHI 660) and energy disper-sive x-ray analysis (EDXA) (Oxford Instruments Inca-FET-3). The surface area of theV2O5 nanowires, SnO2/V2O5 core–shell structure and bulk V2O5 was estimated from

620 M. Shahid et al. / Materials Chemistry a

tAp

3

otrVatVn(iVnt(n

icSnF

Fig. 1. FE-SEM image of the V2O5 nanowires.

he surface area (Digisorb 2006) and pore volume analysis (Nova Quanta Chrome).UV-3600 Shimadzu spectrophotometer was used to examine the photocatalytic

roperty.

. Results and discussion

Good quality V2O5 nanowires with a well defined morphol-gy were observed by FE-SEM (Fig. 1). The diameter and length ofhe V2O5 nanowires ranged from 100 to 150 ± 10 nm and 1–5 �m,espectively. The inset in Fig. 3(b) shows the EDXA spectrum of2O5 nanowires which shows that the nanowires contain only Vnd O with no detectable impurities. Fig. 2(a) and (b) presentshe XRD patterns of the SnO2/V2O5 core–shell structure and pure2O5 nanowires, respectively. There were XRD peaks for tetrago-al SnO2 (JCPDS, No. 02-1340) and orthorhombic V2O5 nanowiresJCPDS, No. 41-1426) in the SnO2/V2O5 core–shell (Fig. 2a). The XRDntensities of the SnO2/V2O5 peaks were lower than those of the2O5 nanowires which indicate the presence of SnO2 in the V2O5anowires. The EDXA spectrum (inset Fig. 2) of SnO2/V2O5 showshat the core–shell structure contained only tin (Sn), vanadiumV) and oxygen (O) without impurities. The distance between theeighboring planes in the orthorhombic V2O5 nanowire (HRTEM

´

mage in Fig. 3) was approximately 0.429 nm A (Fig. 3b) which isonsistent with that of the orthorhombic (0 0 1) plane of V2O5. TheAED pattern (inset Fig. 3a) clearly shows the single crystallineature of V2O5 nanowires. Fig. 3(c) and Supporting informationig. S3 show a TEM image of SnO2/V2O5 of the core–shell struc-

Fig. 2. XRD spectra of V2O5 (a) and SnO2/V2O5 core–shell nanowires (b).

nd Physics 124 (2010) 619–622

ture nanowire which confirms that the V2O5 nanowires are coatedwith 4–6 nm diameter SnO2 nanoparticles. The corresponding elec-tron diffraction pattern in Fig. 3(c) is composed of two sets ofSAED patterns. The bright diffraction pattern spots confirm theorthorhombic single crystalline nature of the V2O5 nanowires. Anadditional weak ring pattern is attributed to the amorphous SnO2nanoparticles layer on the surface of the V2O5 nanowire. The TEMresults are in good agreement with the XRD and SEM results.Fig. 4(a) shows high-resolution XPS spectra of the SnO2/V2O5nanowires, and the inset in Fig. 4(a) presents the Sn 3d5/2 high-resolution XPS spectra acquired for the nanowires. The V 2p3/2and V 2p1/2 binding energy for the SnO2/V2O5 was observed at517.2 and 524.17 eV which fits well with the characteristic peaks ofV5+ [20,21]. The Sn 3d5/2 regions show distinct signals at 487.4 eV.Deconvolution of the O 1s peak of pure V2O5 (Fig. 4d) shows thatoxygen on the sample surface exists in two forms with a bindingenergy of 530.28 eV corresponding to oxygen in the V2O5 lattice.The peak at 532.03 eV was assigned to oxygen in the V2O5 surfaceadsorption of (–OH). The deconvolution of O 1s peaks SnO2/V2O5nanowires in Fig. 4(c) shows that oxygen on the sample surfaceexists in three forms at a binding energies of 530.4 eV, 532.25 eV and533.88 eV which corresponds to oxygen in the V2O5 lattice, oxygenin SnO2 and oxygen in the SnO2/V2O5 surface adsorption of H2Orespectively. The quantity of •OH radicals generated during photo-catalysis is proportional to the metal–OH/metal–O ratios in the O 1speaks which represents surface hydroxyl groups [22,23]. Fig. 4(c)shows that surface area ratios of •OH/metal–O in the O 1s peaks isenhanced by the SnO2 coating on the V2O5 (0.34) nanowires com-pared to that of the uncoated V2O5 nanowires (0.16). These resultsclearly show that the nanowires become more hydrophilic with theSnO2 coating, which increases the number of •OH radicals duringthe photocatalytic reaction that result in enhanced photocatalyticactivity of the core–shell nanowires.

3.1. Photocatalytic measurement

Before examining the photocatalytic activity it is important tostudy the optical absorption of the as-prepared nanowires becausethe UV–vis absorption edge is relevant to the energy band of thesemiconductor catalyst [24,25]. The UV–vis spectra of SnO2/V2O5core–shell nanowires in Fig. 3(d) show a broad absorbance from410 to 550 nm and a shift in the absorption edge to the UV regioncompared to the pure V2O5 nanowires. TBO dye solutions in waterwere used as a test reaction to examine the photocatalytic behaviorof the SnO2/V2O5 nanowires. The reaction solution was preparedby adding SnO2/V2O5 nanowires (15 mg) into 50 mL of TBO solu-tion (0.5 mmol). Prior to irradiation, the solutions were stirred inthe dark for 30 min to establish adsorption/degradation equilib-rium. After the adsorption–desorption process, 3 mL of the solutionwas removed, and the toluidine blue O concentration was ana-lyzed by measuring the absorbance at 633 nm using a UV–visspectrophotometer (UV-3600 Shimadzu). A sample of a toluidineblue O (3 mL) solution was removed at regular intervals and cen-trifuged at 6000 rpm for 2 min to separate the catalyst particlesfrom the solution. For comparison, analogous photodegradationexperiments were performed on two other samples: bulk V2O5powder prepared by annealing ammonium metavanadate at 500 ◦Cfor 2 h in air and V2O5 nanowires prepared by the abovementionedhydrothermal and calcination procedure.

3.2. Photocatalytic activity for the decomposition of toluidine

blue “O” (TBO)

Fig. 5 shows the photocatalytic activity of the V2O5 nanowires,core–shell SnO2/V2O5 nanowires and bulk V2O5 powder for thedecomposition of “TBO” under UV irradiation. The core–shell

M. Shahid et al. / Materials Chemistry and Physics 124 (2010) 619–622 621

F e (b)t orptio

nVtiaw

Fo

ig. 3. TEM image of V2O5 nanowires (a) inset shows the SAED pattern. HRTEM imaghe HRTEM image on the top right and SAED pattern on the lower right. Optical abs

anowires showed higher photocatalytic activity than the bulkO and nanowires. This increase in the photocatalytic activity of

2 5

he core–shell SnO2/V2O5 nanowires was attributed mainly to anncrease in the specific surface area (supporting information Fig. S1nd Table T1). This also increases the number of surface active sites,hich improves the oxidation degradation rate of TBO consider-

ig. 4. XPS spectra of the SnO2/V2O5 core–shell nanowires (a) inset show the XPS spectrf V2O5 (d).

inset shows the EDXA spectrum, TEM image of SnO2/V2O5 nanowire (c) inset showsn of V2O5 and SnO2/V2O5 nanowires (d).

ably. It is believed that when light hits the SnO2/V2O5 nanowires,electrons photogenerated from the conduction band of SnO are

2injected into the lower lying conduction band of V2O5. The pho-togenerated holes in the V2O5 valence band are transferred to thevalence band of SnO2, which increases the spatial separation of thecharge carriers as shown in Fig. 6, thereby reduces the probability of

a of Sn 3d5/2, V 2p1/2 and V 2p3/2 (b). XPS spectra of O 1s of SnO2/V2O5 (c) and O 1s

622 M. Shahid et al. / Materials Chemistry a

Fig. 5. Photocatalytic properties of SnO2/V2O5 nanowires. (a) Degradation profile ofTBO under UV–vis light irradiation. (b) Photocatalytic activity of the TBO degradationcurves (a) SnO2/V2O5 core–shell nanowires (b) V2O5 nanowires. (c) Bulk V2O5 (d)without catalyst under UV irradiation.

Ft

rTassemp

[

[[[[

[

[

[[[[

[[

[

[

ig. 6. Schematic diagram of the overall band structures, charge excitation, separa-ion and transportation charts in the core–shell SnO2/V2O5 nanowires.

ecombination relative to that of interfacial charge transfer [26,27].he synthesized high quality SnO2/V2O5 nanowires can be used asphotocatalyst that can possibly purify water. It is hoped that this

tudy will represent a new material in the field of photocataly-is, particularly as a photocatalyst for industrial applications. It isxpected that the SnO2 nanoparticle coating produced in this studyight also show other interesting physical properties relevant to

otential applications.

[

[

[

nd Physics 124 (2010) 619–622

4. Conclusion

SnO2/V2O5 core–shell nanowires were synthesized and char-acterized. The nanowires exhibited significantly higher photocat-alytic activity for the degradation of TBO under UV light than bulkor V2O5 nanowires. This enhanced photocatalytic performance wasattributed to the higher surface area of the SnO2/V2O5 core–shellstructure and the effective charge separation of SnO2 and V2O5.

Acknowledgement

This work was supported by the Korean Ministry of Education,Science and Technology under grants NRF-20090094026 (PriorityResearch Centers Program), 2009-00591 (KICOS Global PartnershipProgram) and R31-2008-000-10029-0 (World Class University Pro-gram).

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.matchemphys.2010.07.023.

References

[1] X. Guangcan, W. Xinchen, Li. Danzhen, Fu Xianzhi, J. Photochem. Photobiol. A193 (2008) 213.

[2] Li. Qilin, M. Shaily, Y.L. Delina, B. Lena, V.L. Michael, Li. Dong, J.J.A. Pedro, WaterRes. 42 (2008) 4591.

[3] B. Detlef, Sol. Energy 77 (2004) 445.[4] G. Victor, L. Ovadia, J. Am. Chem. Soc. 115 (1993) 2533.[5] D.M. Smith, M.P. Neu, E. Garcia, V.R. Dole, J. Alloys Compd. 319 (2001) 258.[6] A. Fumiaki, T. Tsunehiro, Chem. Lett. 35 (2006) 468.[7] S. Chen, L. Chen, S. Gao, G. Cao, Mater. Chem. Phys. 98 (2006) 116.[8] C. Wen-Ku, W. Yu-Shiang, T. Chih-Yao, Y.L. Austin, J. Alloys Compd. 478 (2009)

341.[9] L. KunWei, W. Yan, W. Hao, Z. Mankang, Y. Hui, Nanotechnology 17 (2006)

4863.10] T. Yao-Hsuan, K. Chien-Sheng, H. Chia-Hung, L. Yuan-Yao, C. Po-Wen, C. Chia-

Liang, W. Ming-Show, Nanotechnology 17 (2006) 2490.11] L. Haimei, N. Ryuhei, N. Yoshihiro, Electrochem. Solid-State Lett. 9 (2006) 187.12] H. Tsutomu, V.K. Prashant, J. Am. Chem. Soc. 127 (2005) 3928.13] C. Wang, H. Shang, Y. Tao, T. Yuan, G. Zhang, Sep. Purif. Technol. 32 (2003) 357.14] L.L. Ma1, Z.S. Hai, G.Z. Yong, L.L. Yu, L.L. Jia, W. Enke, Y. Ying, T. Ming, W. Jian-Bo,

Nanotechnology 19 (2008) 115709.15] Z. Qingrui, L. Zhengquan, W. Changzheng, B. Xue, X. Yi, J. Nanopart. Res. 8 (2006)

1065.16] J.A. Aguilar-Martinez, M.B. Hernandez, A.B. Glot, M.I. Pech-Canul, J. Phys. D:

Appl. Phys. 40 (2007) 7097.17] E.Y. Kim, C.M. Whang, W.I. Lee, Y.H. Kim, J. Electroceram. 17 (2006) 899.18] A. Dodd, A. McKinley, M. Saunders, T. Tsuzuki, Nanotechnology 17 (2006) 692.19] M. Niu, F. Huang, L. Cui, P. Huang, Y. Yu, Y. Wang, ACS Nano 4 (2010) 681.20] J. Mendialdua, R. Casanova, Y. Barbaux, J. Electron. Spectrosc. Relat. Phenom.

71 (1995) 249.21] Y. Chen, K. Xie, Z. Liu, Appl. Surf. Sci. 126 (1998) 347.22] D. Hui, L. Zhaohui, X. Ximing, D. Zhengxin, W. Ling, W. Xuxu, F. Xianzhi, Appl.

Catal. B 89 (2009) 551.23] C. Jinho, L. Juhyun, J. Jong Hwa, K. Misook, Bull. Korean Chem. Soc. 30 (2009)

302.24] L. Ren, L. Jin, W. Jian-B, Y. Fan, Q.Q. Ming, Y. Ying, Nanotechnology 20 (2009)

115603.

25] G. Feng, C. Xinyi, Y. Kuibo, D. Shuai, R. Zhifeng, Y. Fang Tao, Y. Zhigang, L. Jun-

Ming, Adv. Mater. 19 (2007) 2889.26] N. Mutong, H. Feng, C. Lifeng, H. Ping, Y. Yunlong, W. Yuansheng, ACS Nano 4

(2010) 681.27] A.L. Stroyuk, V.V. Shvalagin, A.E. Raevskaya, A.I. Kryukov, S.Y. Kuchmii, Theor.

Exp. Chem. 44 (2008) 205.