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TiO2 branched nanoheterostructures: Facile fabrication and efficient visible light photocatalytic activity
Materials Letters 128 (2014) 358–361
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Ag0.35V2O5/TiO2 branched nanoheterostructures: Facile fabrication and efficient visible light photocatalytic activity Yuan Wang, Lixin Liu n, Yuanjie Huang, Xuhai Li, Xiuxia Cao, Liang Xu, Chuanmin Meng n, Zhigang Wang, Wenjun Zhu The National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, P.O. Box 919-111, Mianyang, Sichuan 621900, People's Republic of China
art ic l e i nf o
a b s t r a c t
Article history: Received 5 February 2014 Accepted 24 April 2014 Available online 2 May 2014
Although titanium dioxide (TiO2) is a prototypical semiconductor photocatalyst, further application is limited by its inefficient solar energy conversion because of the relative large bandgap. Herein, a novel TiO2 based photocatalyst, Ag0.35V2O5/TiO2 branched nanoheterostructures, is synthesized using a onestep electrospinning process. The nanoheterostructures exhibit enhanced visible light absorption, and the visible light photocatalytic activity of the nanoheterostructures is far exceeding than that of pure TiO2 nanofibers. Furthermore, the influence of Ag0.35V2O5/TiO2 molar ratio on the visible light photocatalysis is studied and the optimum molar ratio is found to be around 1:2, where the Ag0.35V2O5/TiO2 branched nanoheterostructures demonstrate the most excellent photocatalytic activity. & 2014 Elsevier B.V. All rights reserved.
Keywords: Ag0.35V2O5/TiO2 nanoheterostructure Photocatalysis Semiconductor Interface
1. Introduction Since Fujishima and Honda have reported for the first time on the water photochemical splitting on TiO2 surfaces [1], TiO2 has attracted tremendous scientific and technological interest due to the potentially promising applications in solving current energy and environmental problems with the use of solar light [2–4]. Unfortunately, the photocatalytic efficiency of TiO2 is substantially limited by its usually fast electron–hole recombination and large bandgap energy of 3.2 eV (i.e. only UV light can be efficiently absorbed) [5,6]. To overcome these limitations, a great deal of effort, such as ion doping of metals [7,8] or nonmetals [9,10], combination with narrow bandgap semiconductors [6,11–13], and surface modification [1,14], is ongoing to lower the bandgap energy, suppress the electron–hole recombination rate, and enhance the surface charge carrier transfer rate of TiO2. Among these techniques, coupling of TiO2 with narrow bandgap semiconductors is one of the most efficient ways to improve the visible light photocatalytic activity of TiO2, which can achieve a better solar absorption characteristics and/or efficient charge separation [6]. Recently, silver-based multimetal oxides, such as silver vanadium oxides, have attracted considerable attention for their applications in visible light photocatalysis because of the good photoabsorption ability (generally low bandgap energy) and high
n
Corresponding authors. Tel./fax: þ86 816 2485139. E-mail addresses: [email protected] (L. Liu), [email protected] (C. Meng).
http://dx.doi.org/10.1016/j.matlet.2014.04.161 0167-577X/& 2014 Elsevier B.V. All rights reserved.
carrier mobility [15,16]. Specially, it has been reported that the electrical conductivity of Ag0.35V2O5 nanowires is 0.5 S/cm, about 6–7 times higher than that of V2O5 nanowires [17]. Therefore, it may be an effective way to couple Ag0.35V2O5 to TiO2 to achieve a promising excellent visible light photocatalyst. Unfortunately, to the best of our knowledge, there have been no reports on the photocatalytic performance of Ag0.35V2O5/TiO2 composite in the public literatures. In this paper, novel Ag0.35V2O5/TiO2 branched nanoheterostructures (NHs) are prepared for the first time using a facile onestep electrospinning process. Moreover, the synthesized Ag0.35V2O5/ TiO2 branched NHs exhibit excellent visible light photocatalytic performance.
2. Experimental details First, 0.50 g tetrabutyl titanate (TBT) and 0.20 g polyvinylpyrrolidone (PVP) were dissolved in a mixture of 1.50 ml ethanol and 1.20 ml acetic acid, and stirred for 20 min to result in PVP/TBT composite. Then, 0.60 g PVP, 0.20 g VO(acac)2, and 0.035 g Ag (NO)3 were added into 3.7 g dimethylformamide (DMF), after stirring for 20 min, the resulting solution was mixed with the PVP/TBT composite and stirred for 1 h to prepare PVP/TBT/Ag (NO)3/VO(acac)2 composite. Finally, the PVP/TBT and PVP/TBT/Ag (NO)3/VO(acac)2 composites were electrospun and annealed at 500 1C to form TiO2 nanofibers (NFs) and Ag0.35V2O5/TiO2 NHs,
Y. Wang et al. / Materials Letters 128 (2014) 358–361
respectively. The amount of Ag0.35V2O5 in NHs could be determined by adjusting the molar ratio of Ag(NO)3/VO(acac)2 to TBT in the composite solution, and the samples with Ag0.35V2O5/TiO2 molar ratios of 1:4, 1:2, 3:4, and 1:1 were named as S1, S2, S3, and S4, respectively. The morphologies of the samples were characterized by field emission scanning electron microscopy (FESEM, Hitachi S-4800) and transmission electron microscopy (TEM, FEI Tecnai F30). X-ray diffraction (XRD, CuKα, λ ¼1.5406 Å) and high-resolution TEM (HRTEM) were employed to characterize the crystal structure and elemental analysis of the samples, respectively. UV–vis absorption spectra were recorded using a TU-1901 spectrophotometer to evaluate the visible light response and the photocatalytic performance.
Fig. 1. XRD patterns of TiO2 NFs (a) and Ag0.35V2O5/TiO2 NHs with different Ag0.35V2O5/TiO2 molar ratios of 1:4 (b), 1:2 (c), 3:4 (d), and 1:1 (e).
359
Photocatalytic decomposition of RhB was carried out in a beaker containing a suspension of 30 mg catalysts in 30 ml RhB solution (initial concentration of RhB was 10 mg/L) under visible light irradiation (Xe lamp: λ 4420 nm). At given time intervals, 3 ml aliquots were sampled and filtrated to remove the catalysts. The filtrates were analyzed by recording the variations of the absorption band maximum (554 nm).
3. Results and discussion XRD patterns have been employed to identify the phase composition and crystal structure of the samples (Fig. 1). The diffraction peaks of pure TiO2 NFs match the standard patterns of the anatase phase TiO2 (PDF#21-1272) and rutile phase TiO2 (PDF#21-1276) (Fig. 1(a)). As for Ag0.35V2O5/TiO2 NHs, the XRD patterns reveal that anatase TiO2, rutile TiO2, and monoclinic Ag0.35V2O5 (PDF #28-1027) phases coexist in the NHs (Fig. 1(b)–(e)). Furthermore, the incorporation of Ag0.35V2O5 leads to an increase of the phase transition of TiO2 from anatase to rutile; this effect can also be observed in other materials, such as V2O5 [5]. The microstructures of the samples are investigated by SEM images. As shown in Fig. 2(a), pure TiO2 NFs with smooth surface and uniform morphology can be observed. After introducing Ag0.35V2O5, some nanorods with smooth surfaces are located on the fiber surface (Fig. 2(b)–(e)). Moreover, thickness of the nanorods increases monotonically with the increase of the Ag0.35V2O5 amount, which can be attributed to the enhanced secondary growth of Ag0.35V2O5. From the typical enlarged SEM image of Ag0.35V2O5/TiO2 NHs (Fig 2(f)), it is obvious that the nanorods are about 50–200 nm in length and 5–20 nm in diameter when the Ag0.35V2O5/TiO2 molar ratio is 1:2. To further study the microscopic morphology and structure information of Ag0.35V2O5/TiO2 NHs, TEM analysis has been
Fig. 2. SEM images of pure TiO2 NFs (a) and Ag0.35V2O5/TiO2 NHs with different Ag0.35V2O5/TiO2 molar ratios: (b) 1:4, (c) 1:2, (d) 3:4, and (e) 1:1; scale bars are 500 nm. (f) Enlarged view of the NHs from (c); scale bar is 100 nm.
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Y. Wang et al. / Materials Letters 128 (2014) 358–361
Fig. 3. (a) Low-magnification TEM image of Ag0.35V2O5/TiO2 NHs with Ag0.35V2O5/TiO2 molar ratio of 1:2. (b) TEM image of a single Ag0.35V2O5/TiO2 NH. (c) EDS patterns taken from the backbone and branch. (d, e) Typical HRTEM images taken from different locations in (b).
Fig. 4. (a) UV–vis absorption spectra of TiO2 NFs and Ag0.35V2O5/TiO2 NHs with different Ag0.35V2O5/TiO2 molar ratios. (b) Concentration change of RhB in the presence of the different photocatalysts.
performed, as shown in Fig. 3. The branched structure of Ag0.35V2O5/TiO2 NHs is clearly evidenced in Fig. 3(a) and (b), where the nanorods of 5–20 nm in diameter are well dispersed on the surface of NFs backbones. The EDS analysis (Fig. 3(c)) shows that the backbone is mainly composed of O, Ag, Ti and V elements, whereas the branch only consists of O, Ag, and V elements (Cu signal in the EDS spectra is due to the sample holder). Moreover, three lattice fringe spacings of 3.5 Å, 3.3 Å, and 7.2 Å (Fig. 3(d)) are clearly observed in the HRTEM image of the backbone, consistent with the lattice parameters of (101) plane of anatase TiO2, (110) plane of rutile TiO2, and (002) plane of monoclinic Ag0.35V2O5, respectively, indicating that the backbone is composed of TiO2 and Ag0.35V2O5. On the other hand, only one lattice fringe spacing of the monoclinic Ag0.35V2O5 is
observed in the HRTEM image of the branch (Fig. 3(e)), revealing that the branch is composed of Ag0.35V2O5. UV–vis absorption spectra of the samples are shown in Fig. 4 (a). For the pure TiO2 NFs, the strong absorption peak at 255 nm can be assigned to the intrinsic bandgap absorption of TiO2. After coupling Ag0.35V2O5, Ag0.35V2O5/TiO2 NHs exhibit additional broad absorption band at visible light range; furthermore, the visible light absorption capability is constantly enhanced by increasing the Ag0.35V2O5 amount, indicating that Ag0.35V2O5/TiO2 NHs have an outstanding visible light response and thus can be efficient visible light photocatalysts. The visible light photocatalytic activity of Ag0.35V2O5/TiO2 NHs is measured by monitoring the photocatalytic decomposition
Y. Wang et al. / Materials Letters 128 (2014) 358–361
process of RhB solution. Fig. 4(b) shows the corresponding concentration change of RhB as a function of visible light exposure time for the different photocatalysts; and the black curve presents the data without adding any catalyst in the solution in order to exclude the photolysis effect of RhB. It is obvious that all Ag0.35V2O5/TiO2 NHs display prominent photocatalytic performance due to the coupling of TiO2 with Ag0.35V2O5, which has a good visible light response. After 150 min of irradiation, at least 57% RhB molecules are decomposed by Ag0.35V2O5/TiO2 NHs, but only 40% RhB molecules are decomposed by pure TiO2 NFs. Moreover, the photocatalytic activity of Ag0.35V2O5/TiO2 NHs increases first and then decreases with increasing amount of Ag0.35V2O5. The best photocatalytic activity is achieved at the Ag0.35V2O5/TiO2 molar ratio of around 1:2 (sample S2), where at least 95% RhB molecules are decomposed in 150 min. This can be explained by the fact that although more Ag0.35V2O5 lead to a much improved visible light response, the active sites on the TiO2 surface may be covered too much when excessive Ag0.35V2O5 is coupled to TiO2. These two competing factors determine what should be the ideal Ag0.35V2O5/TiO2 molar ratio yielding the most efficient photocatalytic performance in Ag0.35V2O5/TiO2 NHs. 4. Conclusions In summary, Ag0.35V2O5/TiO2 branched NHs have been successfully fabricated for the first time via a facile one-step electrospinning process. The coupling of TiO2 with Ag0.35V2O5 makes the photocatalysts have excellent visible light absorption, and thus the visible light photocatalytic performance is significantly enhanced. Furthermore, the best photocatalytic activity is achieved at the
361
Ag0.35V2O5/TiO2 molar ratio of 1:2, where at least 95% RhB molecules are decomposed in 150 min. It is obvious that such branched heterostructure may bring new insight into the designing of highly efficient photocatalyst for organic compounds.
Acknowledgment We greatly acknowledge the financial support obtained from the Science and Technology Development Foundation of Chinese Academy of Engineering Physics (Grant no. 2012B0101002). References [1] Fujishima A, Honda K. Nature 197237–8. [2] Chen X, Liu L, Yu PY, Mao SS. Science 2011746–50. [3] Zhou W, Liu H, Wang J, Liu D, Du G, Cui J. ACS Appl Mater Interfaces 2010;2:2385–8. [4] Qiu X, Miyauchi M, Sunada K, Minoshima M, Liu M, Lu Y, et al. ACS Nano 2012;6:1609–10. [5] Wang Y, Zhang J, Liu L, Zhu C, Liu X, Su Q. Mater Lett 201295–8. [6] Tada H, Mitsui T, Kiyonaga T, Akita T, Tanaka K. Nat Mater 2006;5:782–5. [7] Parida K M, Sahu NJ. Mol Catal A Chem 2008;287:151–8. [8] Fisher MB, Keane DA, Fernández-Ibánez P, Colreavy J, Hinder SJ, McGuigan KG, et al. Appl Catal B: Environ 20138–13. [9] Naik B, Parida KM, Gopinath CS. J Phys Chem C 201019473–82. [10] Pany S, Parida K M, Naik B. RSC Adv 2013;3:4976–9. [11] Wang Y, Su YR, Qiao L, Liu LX, Su Q, Zhu CQ, et al. Nanotechnology 2011;22:225702–8. [12] Cao T, Li Y, Wang C, Shao C, Liu Y. Langmuir 2011;27:2946–7. [13] Liu Z, Sun DD, Guo P, Leckie JO. Nano Lett 2007;7:1081–5. [14] Pan X, Yang MQ, Fu X, Zhang N, Xu Y-J. Nanoscale 2013;5:3601–14. [15] Maruyama Y, Irie H, Hashimoto KJ. Phys Chem B 2006;110:23274–5. [16] Li X, Ouyang S, Kikugawa N, Ye J. Appl Catal A 2008;334:51–8. [17] Xiong C, Aliev AE, Gnade B, Balkus Jr KJ. ACS Nano 2008;2:293–9.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Ag0.35V2O5/TiO2 branched nanoheterostructures: Facile fabrication and efficient visible light photocatalytic activity Yuan Wang, Lixin Liu n, Yuanjie Huang, Xuhai Li, Xiuxia Cao, Liang Xu, Chuanmin Meng n, Zhigang Wang, Wenjun Zhu The National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, P.O. Box 919-111, Mianyang, Sichuan 621900, People's Republic of China
art ic l e i nf o
a b s t r a c t
Article history: Received 5 February 2014 Accepted 24 April 2014 Available online 2 May 2014
Although titanium dioxide (TiO2) is a prototypical semiconductor photocatalyst, further application is limited by its inefficient solar energy conversion because of the relative large bandgap. Herein, a novel TiO2 based photocatalyst, Ag0.35V2O5/TiO2 branched nanoheterostructures, is synthesized using a onestep electrospinning process. The nanoheterostructures exhibit enhanced visible light absorption, and the visible light photocatalytic activity of the nanoheterostructures is far exceeding than that of pure TiO2 nanofibers. Furthermore, the influence of Ag0.35V2O5/TiO2 molar ratio on the visible light photocatalysis is studied and the optimum molar ratio is found to be around 1:2, where the Ag0.35V2O5/TiO2 branched nanoheterostructures demonstrate the most excellent photocatalytic activity. & 2014 Elsevier B.V. All rights reserved.
Keywords: Ag0.35V2O5/TiO2 nanoheterostructure Photocatalysis Semiconductor Interface
1. Introduction Since Fujishima and Honda have reported for the first time on the water photochemical splitting on TiO2 surfaces [1], TiO2 has attracted tremendous scientific and technological interest due to the potentially promising applications in solving current energy and environmental problems with the use of solar light [2–4]. Unfortunately, the photocatalytic efficiency of TiO2 is substantially limited by its usually fast electron–hole recombination and large bandgap energy of 3.2 eV (i.e. only UV light can be efficiently absorbed) [5,6]. To overcome these limitations, a great deal of effort, such as ion doping of metals [7,8] or nonmetals [9,10], combination with narrow bandgap semiconductors [6,11–13], and surface modification [1,14], is ongoing to lower the bandgap energy, suppress the electron–hole recombination rate, and enhance the surface charge carrier transfer rate of TiO2. Among these techniques, coupling of TiO2 with narrow bandgap semiconductors is one of the most efficient ways to improve the visible light photocatalytic activity of TiO2, which can achieve a better solar absorption characteristics and/or efficient charge separation [6]. Recently, silver-based multimetal oxides, such as silver vanadium oxides, have attracted considerable attention for their applications in visible light photocatalysis because of the good photoabsorption ability (generally low bandgap energy) and high
n
Corresponding authors. Tel./fax: þ86 816 2485139. E-mail addresses: [email protected] (L. Liu), [email protected] (C. Meng).
http://dx.doi.org/10.1016/j.matlet.2014.04.161 0167-577X/& 2014 Elsevier B.V. All rights reserved.
carrier mobility [15,16]. Specially, it has been reported that the electrical conductivity of Ag0.35V2O5 nanowires is 0.5 S/cm, about 6–7 times higher than that of V2O5 nanowires [17]. Therefore, it may be an effective way to couple Ag0.35V2O5 to TiO2 to achieve a promising excellent visible light photocatalyst. Unfortunately, to the best of our knowledge, there have been no reports on the photocatalytic performance of Ag0.35V2O5/TiO2 composite in the public literatures. In this paper, novel Ag0.35V2O5/TiO2 branched nanoheterostructures (NHs) are prepared for the first time using a facile onestep electrospinning process. Moreover, the synthesized Ag0.35V2O5/ TiO2 branched NHs exhibit excellent visible light photocatalytic performance.
2. Experimental details First, 0.50 g tetrabutyl titanate (TBT) and 0.20 g polyvinylpyrrolidone (PVP) were dissolved in a mixture of 1.50 ml ethanol and 1.20 ml acetic acid, and stirred for 20 min to result in PVP/TBT composite. Then, 0.60 g PVP, 0.20 g VO(acac)2, and 0.035 g Ag (NO)3 were added into 3.7 g dimethylformamide (DMF), after stirring for 20 min, the resulting solution was mixed with the PVP/TBT composite and stirred for 1 h to prepare PVP/TBT/Ag (NO)3/VO(acac)2 composite. Finally, the PVP/TBT and PVP/TBT/Ag (NO)3/VO(acac)2 composites were electrospun and annealed at 500 1C to form TiO2 nanofibers (NFs) and Ag0.35V2O5/TiO2 NHs,
Y. Wang et al. / Materials Letters 128 (2014) 358–361
respectively. The amount of Ag0.35V2O5 in NHs could be determined by adjusting the molar ratio of Ag(NO)3/VO(acac)2 to TBT in the composite solution, and the samples with Ag0.35V2O5/TiO2 molar ratios of 1:4, 1:2, 3:4, and 1:1 were named as S1, S2, S3, and S4, respectively. The morphologies of the samples were characterized by field emission scanning electron microscopy (FESEM, Hitachi S-4800) and transmission electron microscopy (TEM, FEI Tecnai F30). X-ray diffraction (XRD, CuKα, λ ¼1.5406 Å) and high-resolution TEM (HRTEM) were employed to characterize the crystal structure and elemental analysis of the samples, respectively. UV–vis absorption spectra were recorded using a TU-1901 spectrophotometer to evaluate the visible light response and the photocatalytic performance.
Fig. 1. XRD patterns of TiO2 NFs (a) and Ag0.35V2O5/TiO2 NHs with different Ag0.35V2O5/TiO2 molar ratios of 1:4 (b), 1:2 (c), 3:4 (d), and 1:1 (e).
359
Photocatalytic decomposition of RhB was carried out in a beaker containing a suspension of 30 mg catalysts in 30 ml RhB solution (initial concentration of RhB was 10 mg/L) under visible light irradiation (Xe lamp: λ 4420 nm). At given time intervals, 3 ml aliquots were sampled and filtrated to remove the catalysts. The filtrates were analyzed by recording the variations of the absorption band maximum (554 nm).
3. Results and discussion XRD patterns have been employed to identify the phase composition and crystal structure of the samples (Fig. 1). The diffraction peaks of pure TiO2 NFs match the standard patterns of the anatase phase TiO2 (PDF#21-1272) and rutile phase TiO2 (PDF#21-1276) (Fig. 1(a)). As for Ag0.35V2O5/TiO2 NHs, the XRD patterns reveal that anatase TiO2, rutile TiO2, and monoclinic Ag0.35V2O5 (PDF #28-1027) phases coexist in the NHs (Fig. 1(b)–(e)). Furthermore, the incorporation of Ag0.35V2O5 leads to an increase of the phase transition of TiO2 from anatase to rutile; this effect can also be observed in other materials, such as V2O5 [5]. The microstructures of the samples are investigated by SEM images. As shown in Fig. 2(a), pure TiO2 NFs with smooth surface and uniform morphology can be observed. After introducing Ag0.35V2O5, some nanorods with smooth surfaces are located on the fiber surface (Fig. 2(b)–(e)). Moreover, thickness of the nanorods increases monotonically with the increase of the Ag0.35V2O5 amount, which can be attributed to the enhanced secondary growth of Ag0.35V2O5. From the typical enlarged SEM image of Ag0.35V2O5/TiO2 NHs (Fig 2(f)), it is obvious that the nanorods are about 50–200 nm in length and 5–20 nm in diameter when the Ag0.35V2O5/TiO2 molar ratio is 1:2. To further study the microscopic morphology and structure information of Ag0.35V2O5/TiO2 NHs, TEM analysis has been
Fig. 2. SEM images of pure TiO2 NFs (a) and Ag0.35V2O5/TiO2 NHs with different Ag0.35V2O5/TiO2 molar ratios: (b) 1:4, (c) 1:2, (d) 3:4, and (e) 1:1; scale bars are 500 nm. (f) Enlarged view of the NHs from (c); scale bar is 100 nm.
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Y. Wang et al. / Materials Letters 128 (2014) 358–361
Fig. 3. (a) Low-magnification TEM image of Ag0.35V2O5/TiO2 NHs with Ag0.35V2O5/TiO2 molar ratio of 1:2. (b) TEM image of a single Ag0.35V2O5/TiO2 NH. (c) EDS patterns taken from the backbone and branch. (d, e) Typical HRTEM images taken from different locations in (b).
Fig. 4. (a) UV–vis absorption spectra of TiO2 NFs and Ag0.35V2O5/TiO2 NHs with different Ag0.35V2O5/TiO2 molar ratios. (b) Concentration change of RhB in the presence of the different photocatalysts.
performed, as shown in Fig. 3. The branched structure of Ag0.35V2O5/TiO2 NHs is clearly evidenced in Fig. 3(a) and (b), where the nanorods of 5–20 nm in diameter are well dispersed on the surface of NFs backbones. The EDS analysis (Fig. 3(c)) shows that the backbone is mainly composed of O, Ag, Ti and V elements, whereas the branch only consists of O, Ag, and V elements (Cu signal in the EDS spectra is due to the sample holder). Moreover, three lattice fringe spacings of 3.5 Å, 3.3 Å, and 7.2 Å (Fig. 3(d)) are clearly observed in the HRTEM image of the backbone, consistent with the lattice parameters of (101) plane of anatase TiO2, (110) plane of rutile TiO2, and (002) plane of monoclinic Ag0.35V2O5, respectively, indicating that the backbone is composed of TiO2 and Ag0.35V2O5. On the other hand, only one lattice fringe spacing of the monoclinic Ag0.35V2O5 is
observed in the HRTEM image of the branch (Fig. 3(e)), revealing that the branch is composed of Ag0.35V2O5. UV–vis absorption spectra of the samples are shown in Fig. 4 (a). For the pure TiO2 NFs, the strong absorption peak at 255 nm can be assigned to the intrinsic bandgap absorption of TiO2. After coupling Ag0.35V2O5, Ag0.35V2O5/TiO2 NHs exhibit additional broad absorption band at visible light range; furthermore, the visible light absorption capability is constantly enhanced by increasing the Ag0.35V2O5 amount, indicating that Ag0.35V2O5/TiO2 NHs have an outstanding visible light response and thus can be efficient visible light photocatalysts. The visible light photocatalytic activity of Ag0.35V2O5/TiO2 NHs is measured by monitoring the photocatalytic decomposition
Y. Wang et al. / Materials Letters 128 (2014) 358–361
process of RhB solution. Fig. 4(b) shows the corresponding concentration change of RhB as a function of visible light exposure time for the different photocatalysts; and the black curve presents the data without adding any catalyst in the solution in order to exclude the photolysis effect of RhB. It is obvious that all Ag0.35V2O5/TiO2 NHs display prominent photocatalytic performance due to the coupling of TiO2 with Ag0.35V2O5, which has a good visible light response. After 150 min of irradiation, at least 57% RhB molecules are decomposed by Ag0.35V2O5/TiO2 NHs, but only 40% RhB molecules are decomposed by pure TiO2 NFs. Moreover, the photocatalytic activity of Ag0.35V2O5/TiO2 NHs increases first and then decreases with increasing amount of Ag0.35V2O5. The best photocatalytic activity is achieved at the Ag0.35V2O5/TiO2 molar ratio of around 1:2 (sample S2), where at least 95% RhB molecules are decomposed in 150 min. This can be explained by the fact that although more Ag0.35V2O5 lead to a much improved visible light response, the active sites on the TiO2 surface may be covered too much when excessive Ag0.35V2O5 is coupled to TiO2. These two competing factors determine what should be the ideal Ag0.35V2O5/TiO2 molar ratio yielding the most efficient photocatalytic performance in Ag0.35V2O5/TiO2 NHs. 4. Conclusions In summary, Ag0.35V2O5/TiO2 branched NHs have been successfully fabricated for the first time via a facile one-step electrospinning process. The coupling of TiO2 with Ag0.35V2O5 makes the photocatalysts have excellent visible light absorption, and thus the visible light photocatalytic performance is significantly enhanced. Furthermore, the best photocatalytic activity is achieved at the
361
Ag0.35V2O5/TiO2 molar ratio of 1:2, where at least 95% RhB molecules are decomposed in 150 min. It is obvious that such branched heterostructure may bring new insight into the designing of highly efficient photocatalyst for organic compounds.
Acknowledgment We greatly acknowledge the financial support obtained from the Science and Technology Development Foundation of Chinese Academy of Engineering Physics (Grant no. 2012B0101002). References [1] Fujishima A, Honda K. Nature 197237–8. [2] Chen X, Liu L, Yu PY, Mao SS. Science 2011746–50. [3] Zhou W, Liu H, Wang J, Liu D, Du G, Cui J. ACS Appl Mater Interfaces 2010;2:2385–8. [4] Qiu X, Miyauchi M, Sunada K, Minoshima M, Liu M, Lu Y, et al. ACS Nano 2012;6:1609–10. [5] Wang Y, Zhang J, Liu L, Zhu C, Liu X, Su Q. Mater Lett 201295–8. [6] Tada H, Mitsui T, Kiyonaga T, Akita T, Tanaka K. Nat Mater 2006;5:782–5. [7] Parida K M, Sahu NJ. Mol Catal A Chem 2008;287:151–8. [8] Fisher MB, Keane DA, Fernández-Ibánez P, Colreavy J, Hinder SJ, McGuigan KG, et al. Appl Catal B: Environ 20138–13. [9] Naik B, Parida KM, Gopinath CS. J Phys Chem C 201019473–82. [10] Pany S, Parida K M, Naik B. RSC Adv 2013;3:4976–9. [11] Wang Y, Su YR, Qiao L, Liu LX, Su Q, Zhu CQ, et al. Nanotechnology 2011;22:225702–8. [12] Cao T, Li Y, Wang C, Shao C, Liu Y. Langmuir 2011;27:2946–7. [13] Liu Z, Sun DD, Guo P, Leckie JO. Nano Lett 2007;7:1081–5. [14] Pan X, Yang MQ, Fu X, Zhang N, Xu Y-J. Nanoscale 2013;5:3601–14. [15] Maruyama Y, Irie H, Hashimoto KJ. Phys Chem B 2006;110:23274–5. [16] Li X, Ouyang S, Kikugawa N, Ye J. Appl Catal A 2008;334:51–8. [17] Xiong C, Aliev AE, Gnade B, Balkus Jr KJ. ACS Nano 2008;2:293–9.