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Hydrothermal processing for obtaining of BiVO4 nanoparticles
Materials Letters 63 (2009) 1939–1942
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Hydrothermal processing for obtaining of BiVO4 nanoparticles Aiping Zhang ⁎, Jinzhi Zhang College of Sciences, North China University of Technology, Beijing 100144, PR China
a r t i c l e
i n f o
Article history: Received 24 February 2009 Accepted 4 June 2009 Available online 12 June 2009 Keywords: Nanomaterials Solar energy materials Characterization methods
a b s t r a c t Nano-sized monoclinic BiVO4 particles were effectively obtained by hydrothermal processing and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible absorption spectroscopy, micro-Raman scattering spectroscopy and Fourier transform infrared spectroscopy. The XRD patterns revealed that the hydrothermal conditions (180 °C over a wide range of processing time) are favorable for the formation of monophasic monoclinic BiVO4 nanoparticles. The TEM results represented that samples as-prepared in this route had a decrease of grain size with the processing time increased from 10 to 20 h. It also indicated that a relationship between its local structures and the hydrothermal time exists based upon the spectral characterization. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Bismuth vanadate (BiVO4) has recently attracted considerable attention not only for its interesting technological properties [1,2] but also for its strong photocatalytic effect on water splitting and organic pollutant decomposing under visible light irradiation [3–6]. There are three crystalline phases (the monoclinic wolframite-type [7], the tetragonal scheelite-type [8] and the tetragonal zircon-type [9]) reported for synthetic BiVO4, and according which its photocatalytic properties are strongly related to its crystal phase [10–12]. For the preparation of BiVO4 powder, several common methods have been reported, including solid-state reaction [13–15], aqueous solution [16], solution combustion [17], sol–gel [18], coprecipitation [19], hydrothermal method [20,21] and metalorganic decomposition [22], etc. Among these methods, hydrothermal treatment has been developed for preparing powder of nano-sized functional inorganic materials for a variety of applications [23] due to its notable advantages: firstly, size distribution and particle morphology of products can be controlled by adjusting the hydrothermal prescription; secondly, only one step of hydrothermal treatment without any other complicated post-preparation process makes the preparation fast and easy repetition. This study reported an efficiency hydrothermal processing for obtaining highly crystalline monoclinic BiVO4 nanoparticles; and different processing times were controlled for comparison. 2. Experimental In a typical preparation, 0.02 mol Bi(NO3)3·5H2O and 0.02 mol NH4VO3 were dissolved in 20 mL of 65% (w/w) HNO3 and 20 mL
⁎ Corresponding author. Tel./fax: +86 10 88803271. E-mail address: [email protected] (A. Zhang). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.06.013
6 mol/L NaOH solutions separately; and mixed these two solutions together in 1:1 molar ratio to get a stable mixture. Then, the mixture was sealed in a 50 mL Teflon-lined stainless autoclave and allowed to heat at 180 °C for hydrothermal times ranging from 10 to 20 h under autogenous pressure in an oven. After that, the precipitate was filtered, washed with distilled water for three times each, and dried in vacuum at RT for 12 h. X-ray powder diffraction patterns (XRD, Puxi Co. LTD, model XD-3) were recorded in the region of 2θ = 17–55° using Cu Kα radiation (λ = 0.15418 nm) with a step scan of 2.0°/min. The morphologies of samples were examined with transmission electron microscopy (TEM, Hitachi Model H-7500N). Ultraviolet– visible (UV–vis) absorption spectroscopy in diffuse reflectance mode was recorded on a doubled-beam UV–vis spectrophotometer (Puxi Co. LTD, model TU-1901) using BaSO4 as a reference and was converted from reflection to absorbance by Kubelka–Munk method [24]. Fourier transform infrared (FTIR) spectroscopy was recorded using a PerkinElmer spectrometer (model Gx); and the Raman spectra were recorded by a microprobe Raman (Renishaw, model H13325) system; the excitation wavelength was 514.5 nm from an Ar ion laser. 3. Results and discussion Fig. 1 shows the XRD patterns of samples prepared at 180 °C as a function of different hydrothermal time. It is clear that all the XRD patterns are in good agreement with the standard Joint Committee on Powder Diffraction Standards (JCPDS) card No. 14-0688, which is assigned to monoclinic BiVO4 (space group I2/a, unit-cell parameters a = 5.195 Å, b = 11.701 Å, c = 5.092 Å, β = 90.38°, mineral name: clinobisvanite). No impurity peaks were observed, indicating that 180 °C is sufficient for the formation of phase-pure monoclinic BiVO4 hydrothermally. The morphology and microstructure of samples were revealed by TEM in the inset of Fig. 2a to f. It showed that all primary particles with nano-sized diameter were nearly the same in size and were almost
1940
A. Zhang, J. Zhang / Materials Letters 63 (2009) 1939–1942
Fig. 1. XRD patterns of BiVO4 prepared from different hydrothermal time: (a) 10 h, (b) 12 h, (c) 14 h, (d) 16 h, (e) 18 h, and (f) 20 h.
near spherical. Particle sizes were measured according to the statistical analysis of large number of particles, and the average diameters of particles were measured as 53, 52, 48, 46, 44 and 45 nm for samples prepared at 10, 12, 14, 16, 18 and 20 h, respectively. It indicates a reduction in the size of particles with the increase of processing time, which may be caused by the nucleation–dissolution–recrystallization effect as other report [25]. The Raman spectra of these time series samples listed above in the 150–1000 cm− 1 region are shown in Fig. 3A; the modes component analysis [3,22] of both Raman and IR spectra of samples is listed in Table 1. All samples showed the same feature that each Raman
spectrum was dominated by an intense mode at 827 cm− 1 assigned to the symmetric V–O stretching mode, and with a weak shoulder at about 718 cm− 1 assigned to the antisymmetric V–O stretching mode. The symmetric and antisymmetric bending modes of vanadate anion are at 367 and 324 cm− 1 respectively, and external modes occur at 210 cm− 1. A functional relationship between the Raman stretching frequencies and the metal–oxygen bond length in the local structure has been established [2,23], in which the lower frequencies of the Raman stretching band correspond to the longer bond lengths in the local structures. Seen from Fig. 3A and Table 1, it is clear that a continuum shift of the Raman band to the lower wave numbers, from 718 to 702 cm− 1 assigned to antisymmetric longer V–O bond stretching mode, reveals that the average lone-range symmetry of the VO4 tetrahedral becomes less regular when hydrothermal processing time increased from 10 to 20 h. Furthermore, a distinct reversion of relative intensity of the symmetric (367 cm− 1) and antisymmetric (324 cm− 1) deformational vibrations of the VO4 tetrahedron was observed between spectra (a) and (b) in Fig. 3A, which may be also caused by the increase of symmetry defaults in the VO4 tetrahedral. Fig. 3B shows FTIR spectra of synthesized samples, recorded ranging from 400 to 2000 cm− 1 at room temperature. All the samples show a characteristic broad and strong IR band near 736 cm− 1 with shoulders at 892, 828, 684 and 623 cm− 1. One sharp CO− 3 derived band is observed at 1386 cm− 1, which might be due to the adsorption of atmospheric carbon dioxide during the experiments as other report [22]. The tiny band near 1600 cm− 1 can be assigned to the presence of residual trace water in the structure. A similar lower-wavenumber shift of the V–O asymmetric stretching vibration from 736 to 720 cm− 1 was also observed, it might due to the same reason as that deduced from Raman, that is to say, samples prepared at longer hydrothermal processing time may be consisted of longer V–O bond than those at shorter time in the local structure of samples. The UV–vis diffuse reflectance spectra of samples are shown in Fig. 4. All the samples showed the similar absorption character with a steep sharp band shape, which always considered being from the band gap transition [2,12] of semiconductors. As a crystalline
Fig. 2. TEM images of BiVO4 and their relative abundance of grain size prepared from different hydrothermal time: (a) 10 h, (b) 12 h, (c) 14 h, (d) 16 h, (e) 18 h, and (f) 20 h.
A. Zhang, J. Zhang / Materials Letters 63 (2009) 1939–1942
1941
Fig. 4. UV–vis reflectance diffuses spectra of BiVO 4 prepared from different hydrothermal time: (a) 10 h, (b) 12 h, (c) 14 h, (d) 16 h, (e) 18 h, and (f) 20 h.
Fig. 3. Raman (A) and FTIR (B) spectra of BiVO4 prepared from different hydrothermal time: (a) 10 h, (b) 12 h, (c) 14 h, (d) 16 h, (e) 18 h, and (f) 20 h.
semiconductor, the band gaps can be calculated from the following equation [26,27], n 2 αhυ = A hυ− Eg
Fig. 5. Plots of the (αhυ)2 versus photo energy (hυ) for BiVO4 powders prepared at different hydrothermal time: (a) 10 h, (b) 12 h, (c) 14 h, (d) 16 h, (e) 18 h, and (f) 20 h.
ð1Þ
Where α, υ, Eg and A are the absorption coefficient, incident light frequency, band gap and constant, respectively. Among them, n depends on the characteristics of the transition in a semiconductor, i.e.,
direct transition (n = 1) or indirect transition (n = 4). For BiVO4, n is always taken as 1 [23,26]. The band gap energy for the BiVO4 can be thus estimated from a plot (αhυ)2 versus photon energy (hυ), as can be seen from Fig. 5. The intercept of the tangent to the x-axis will give
Table 1 Assignations of Raman and FTIR wavenumbers observed for samples (a) to (f) in Fig. 3. (a) 10 h
(b) 12 h
(c) 14 h
(d) 16 h
(e) 18 h
(f) 20 h
Suggested assignments
Raman
IR
Raman
IR
Raman
IR
Raman
IR
Raman
IR
Raman
IR
827
892 822 736 684 632 474 410
827
892 822 734 684 632 474 410
827
892 822 731 684 632 474 410
827
892 822 727 684 632 474 410
827
892 822 724 684 632 474 410
827
892 822 720 684 632 474 410
718
367 324 210
712
367 324 210
710
367 324 210
707
367 324 210
705
367 324 210
702
367 324 210
v1 symmetric stretching mode of VO4 v3 antisymmetric stretching of VO4 Bi–O stretching vibration v4 bending mode of VO4 units v2 bending mode of VO4 units External mode
1942
A. Zhang, J. Zhang / Materials Letters 63 (2009) 1939–1942
a good approximation of the band gap for as-prepared BiVO4. Thus the Eg of BiVO4 can be estimated about 2.28, 2.21, 2.19, 2.15, 2.14 and 2.12 eV for samples prepared at 10, 12, 14, 16, 18 and 20 h respectively, showing a decreasing trend shown in the inset of Fig. 5. These data agrees with its components (monoclinic type BiVO4) and clearly demonstrate that a good visible-light-driven photocatalyst can be synthesized by this hydrothermal processing. 4. Conclusions Highly crystallized monoclinic BiVO4 nanoparticles were obtained by hydrothermal processing and characterized by XRD, TEM, UV–vis, Raman and FTIR techniques. The results revealed that a decrease trend of particle size and a gradual increase of band gap were observed when hydrothermal time increased from 10 to 20 h. Its spectra indicated that samples prepared for longer hydrothermal time may be consisted of more antisymmetric VO4 tetrahedral in its local structures, and thus changed the electronic structures of products. Acknowledgement We acknowledge the financial support from the General Program of Beijing Municipal Education Committee (No. KM200910009011). References [1] Xiao GC, Wang XC, Li DZ, Fu XZ. J Photoch Photobio A: Chem 2008;193:213–21. [2] Yu JQ, Kudo A. Adv Funct Mater 2006;16:2163–9. [3] Kohtani S, Koshiko M, Kudo A, Tokumura K, Ishigaki Y, Toriba A, et al. Appl Catal B: Environ 2003;46:573–86.
[4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27]
Tücks A, Beck HP. Dyes Pigments 2007;72:163–77. Ge L. Mater Lett 2008;62:926–8. Zhou L, Wang WZ, Xu HL. Cryst Growth Des 2008;8:728–33. Thongtem S, Wannapop S, Thongtem T. Ceram Int 2009;35:2087–91. Cavalcante LS, Sczancoski JC, Lima LF, Espinosa JWM, Pizani PS, Varela JA, et al. Crys Growth Des 2009;9:1002–12. Tahir MN, Gorgishvili L, Li J, Gorelik T, Kolb U, Nasdala L, et al. Solid State Sci 2007;9:1105–9. Kudo A, Omori K, Kato H. J Am Chem Soc 1999;121:11459–67. Tokunaga S, Kato H, Kudo A. Chem Mater 2001;13:4624–8. Walsh A, Yan YF, Huda MN, Al-Jassim MM, Wei SH. Chem Mater 2009;21:547–51. Lim AR, Choh SH, Jang MS. J Phys: Condens Mater 1995;7:7309–23. Yao WF, Iwai H, Ye JH. Dalton Trans 2008:1426–30. Yu JQ, Zhang Y, Kudo A. J Solid State Chem 2009;182:223–8. Xu H, Li HM, Wu CD, Chu JY, Yan YS, Shu HM. Mater Sci Eng B 2008;147:52–6. Jiang HQ, Endo H, Natori H, Nagai M, Kobayashi K. J Eur Ceram Soc 2008;28:2955–62. Bhattacharya AK, Mallick KK, Hartridage A. Mater Lett 1997;30:7–13. Long M, Cai WM, Kisch H. J Phys Chem C 2008;112:548–54. Yang T, Xia DG, Chen G, Chen Y. Mater Chem Phys 2009;114:69–72. Li HB, Liu GC, Duan XC. Mater Chem Phys 2009;115:9–13. Galembeck A, Alves OL. J Mater Sci 2002;37:1923–7. Liu JB, Wang H, Wang S, Yan H. Mater Sci Eng B 2003;104:36–9. Kubelka P, Munk F. Tech Z Phys 1931;12:593–601. Sczancoski JC, Bomio MDR, Cavalcante LS, Joya MR, Pizani PS, Varela JA, et al. J Phys Chem C 2009;113:5812–22. Zhang X, Ai ZH, Jia FL, Zhang L, et al. Mater Chem Phys 2007;103:162–6. Oliveira RC, Cavalcante LS, Sczancoski JC, Aguiar EC, Espinosa JWM, Varela JA, et al. J Alloys Compd 2009;478:661–70.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Hydrothermal processing for obtaining of BiVO4 nanoparticles Aiping Zhang ⁎, Jinzhi Zhang College of Sciences, North China University of Technology, Beijing 100144, PR China
a r t i c l e
i n f o
Article history: Received 24 February 2009 Accepted 4 June 2009 Available online 12 June 2009 Keywords: Nanomaterials Solar energy materials Characterization methods
a b s t r a c t Nano-sized monoclinic BiVO4 particles were effectively obtained by hydrothermal processing and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible absorption spectroscopy, micro-Raman scattering spectroscopy and Fourier transform infrared spectroscopy. The XRD patterns revealed that the hydrothermal conditions (180 °C over a wide range of processing time) are favorable for the formation of monophasic monoclinic BiVO4 nanoparticles. The TEM results represented that samples as-prepared in this route had a decrease of grain size with the processing time increased from 10 to 20 h. It also indicated that a relationship between its local structures and the hydrothermal time exists based upon the spectral characterization. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Bismuth vanadate (BiVO4) has recently attracted considerable attention not only for its interesting technological properties [1,2] but also for its strong photocatalytic effect on water splitting and organic pollutant decomposing under visible light irradiation [3–6]. There are three crystalline phases (the monoclinic wolframite-type [7], the tetragonal scheelite-type [8] and the tetragonal zircon-type [9]) reported for synthetic BiVO4, and according which its photocatalytic properties are strongly related to its crystal phase [10–12]. For the preparation of BiVO4 powder, several common methods have been reported, including solid-state reaction [13–15], aqueous solution [16], solution combustion [17], sol–gel [18], coprecipitation [19], hydrothermal method [20,21] and metalorganic decomposition [22], etc. Among these methods, hydrothermal treatment has been developed for preparing powder of nano-sized functional inorganic materials for a variety of applications [23] due to its notable advantages: firstly, size distribution and particle morphology of products can be controlled by adjusting the hydrothermal prescription; secondly, only one step of hydrothermal treatment without any other complicated post-preparation process makes the preparation fast and easy repetition. This study reported an efficiency hydrothermal processing for obtaining highly crystalline monoclinic BiVO4 nanoparticles; and different processing times were controlled for comparison. 2. Experimental In a typical preparation, 0.02 mol Bi(NO3)3·5H2O and 0.02 mol NH4VO3 were dissolved in 20 mL of 65% (w/w) HNO3 and 20 mL
⁎ Corresponding author. Tel./fax: +86 10 88803271. E-mail address: [email protected] (A. Zhang). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.06.013
6 mol/L NaOH solutions separately; and mixed these two solutions together in 1:1 molar ratio to get a stable mixture. Then, the mixture was sealed in a 50 mL Teflon-lined stainless autoclave and allowed to heat at 180 °C for hydrothermal times ranging from 10 to 20 h under autogenous pressure in an oven. After that, the precipitate was filtered, washed with distilled water for three times each, and dried in vacuum at RT for 12 h. X-ray powder diffraction patterns (XRD, Puxi Co. LTD, model XD-3) were recorded in the region of 2θ = 17–55° using Cu Kα radiation (λ = 0.15418 nm) with a step scan of 2.0°/min. The morphologies of samples were examined with transmission electron microscopy (TEM, Hitachi Model H-7500N). Ultraviolet– visible (UV–vis) absorption spectroscopy in diffuse reflectance mode was recorded on a doubled-beam UV–vis spectrophotometer (Puxi Co. LTD, model TU-1901) using BaSO4 as a reference and was converted from reflection to absorbance by Kubelka–Munk method [24]. Fourier transform infrared (FTIR) spectroscopy was recorded using a PerkinElmer spectrometer (model Gx); and the Raman spectra were recorded by a microprobe Raman (Renishaw, model H13325) system; the excitation wavelength was 514.5 nm from an Ar ion laser. 3. Results and discussion Fig. 1 shows the XRD patterns of samples prepared at 180 °C as a function of different hydrothermal time. It is clear that all the XRD patterns are in good agreement with the standard Joint Committee on Powder Diffraction Standards (JCPDS) card No. 14-0688, which is assigned to monoclinic BiVO4 (space group I2/a, unit-cell parameters a = 5.195 Å, b = 11.701 Å, c = 5.092 Å, β = 90.38°, mineral name: clinobisvanite). No impurity peaks were observed, indicating that 180 °C is sufficient for the formation of phase-pure monoclinic BiVO4 hydrothermally. The morphology and microstructure of samples were revealed by TEM in the inset of Fig. 2a to f. It showed that all primary particles with nano-sized diameter were nearly the same in size and were almost
1940
A. Zhang, J. Zhang / Materials Letters 63 (2009) 1939–1942
Fig. 1. XRD patterns of BiVO4 prepared from different hydrothermal time: (a) 10 h, (b) 12 h, (c) 14 h, (d) 16 h, (e) 18 h, and (f) 20 h.
near spherical. Particle sizes were measured according to the statistical analysis of large number of particles, and the average diameters of particles were measured as 53, 52, 48, 46, 44 and 45 nm for samples prepared at 10, 12, 14, 16, 18 and 20 h, respectively. It indicates a reduction in the size of particles with the increase of processing time, which may be caused by the nucleation–dissolution–recrystallization effect as other report [25]. The Raman spectra of these time series samples listed above in the 150–1000 cm− 1 region are shown in Fig. 3A; the modes component analysis [3,22] of both Raman and IR spectra of samples is listed in Table 1. All samples showed the same feature that each Raman
spectrum was dominated by an intense mode at 827 cm− 1 assigned to the symmetric V–O stretching mode, and with a weak shoulder at about 718 cm− 1 assigned to the antisymmetric V–O stretching mode. The symmetric and antisymmetric bending modes of vanadate anion are at 367 and 324 cm− 1 respectively, and external modes occur at 210 cm− 1. A functional relationship between the Raman stretching frequencies and the metal–oxygen bond length in the local structure has been established [2,23], in which the lower frequencies of the Raman stretching band correspond to the longer bond lengths in the local structures. Seen from Fig. 3A and Table 1, it is clear that a continuum shift of the Raman band to the lower wave numbers, from 718 to 702 cm− 1 assigned to antisymmetric longer V–O bond stretching mode, reveals that the average lone-range symmetry of the VO4 tetrahedral becomes less regular when hydrothermal processing time increased from 10 to 20 h. Furthermore, a distinct reversion of relative intensity of the symmetric (367 cm− 1) and antisymmetric (324 cm− 1) deformational vibrations of the VO4 tetrahedron was observed between spectra (a) and (b) in Fig. 3A, which may be also caused by the increase of symmetry defaults in the VO4 tetrahedral. Fig. 3B shows FTIR spectra of synthesized samples, recorded ranging from 400 to 2000 cm− 1 at room temperature. All the samples show a characteristic broad and strong IR band near 736 cm− 1 with shoulders at 892, 828, 684 and 623 cm− 1. One sharp CO− 3 derived band is observed at 1386 cm− 1, which might be due to the adsorption of atmospheric carbon dioxide during the experiments as other report [22]. The tiny band near 1600 cm− 1 can be assigned to the presence of residual trace water in the structure. A similar lower-wavenumber shift of the V–O asymmetric stretching vibration from 736 to 720 cm− 1 was also observed, it might due to the same reason as that deduced from Raman, that is to say, samples prepared at longer hydrothermal processing time may be consisted of longer V–O bond than those at shorter time in the local structure of samples. The UV–vis diffuse reflectance spectra of samples are shown in Fig. 4. All the samples showed the similar absorption character with a steep sharp band shape, which always considered being from the band gap transition [2,12] of semiconductors. As a crystalline
Fig. 2. TEM images of BiVO4 and their relative abundance of grain size prepared from different hydrothermal time: (a) 10 h, (b) 12 h, (c) 14 h, (d) 16 h, (e) 18 h, and (f) 20 h.
A. Zhang, J. Zhang / Materials Letters 63 (2009) 1939–1942
1941
Fig. 4. UV–vis reflectance diffuses spectra of BiVO 4 prepared from different hydrothermal time: (a) 10 h, (b) 12 h, (c) 14 h, (d) 16 h, (e) 18 h, and (f) 20 h.
Fig. 3. Raman (A) and FTIR (B) spectra of BiVO4 prepared from different hydrothermal time: (a) 10 h, (b) 12 h, (c) 14 h, (d) 16 h, (e) 18 h, and (f) 20 h.
semiconductor, the band gaps can be calculated from the following equation [26,27], n 2 αhυ = A hυ− Eg
Fig. 5. Plots of the (αhυ)2 versus photo energy (hυ) for BiVO4 powders prepared at different hydrothermal time: (a) 10 h, (b) 12 h, (c) 14 h, (d) 16 h, (e) 18 h, and (f) 20 h.
ð1Þ
Where α, υ, Eg and A are the absorption coefficient, incident light frequency, band gap and constant, respectively. Among them, n depends on the characteristics of the transition in a semiconductor, i.e.,
direct transition (n = 1) or indirect transition (n = 4). For BiVO4, n is always taken as 1 [23,26]. The band gap energy for the BiVO4 can be thus estimated from a plot (αhυ)2 versus photon energy (hυ), as can be seen from Fig. 5. The intercept of the tangent to the x-axis will give
Table 1 Assignations of Raman and FTIR wavenumbers observed for samples (a) to (f) in Fig. 3. (a) 10 h
(b) 12 h
(c) 14 h
(d) 16 h
(e) 18 h
(f) 20 h
Suggested assignments
Raman
IR
Raman
IR
Raman
IR
Raman
IR
Raman
IR
Raman
IR
827
892 822 736 684 632 474 410
827
892 822 734 684 632 474 410
827
892 822 731 684 632 474 410
827
892 822 727 684 632 474 410
827
892 822 724 684 632 474 410
827
892 822 720 684 632 474 410
718
367 324 210
712
367 324 210
710
367 324 210
707
367 324 210
705
367 324 210
702
367 324 210
v1 symmetric stretching mode of VO4 v3 antisymmetric stretching of VO4 Bi–O stretching vibration v4 bending mode of VO4 units v2 bending mode of VO4 units External mode
1942
A. Zhang, J. Zhang / Materials Letters 63 (2009) 1939–1942
a good approximation of the band gap for as-prepared BiVO4. Thus the Eg of BiVO4 can be estimated about 2.28, 2.21, 2.19, 2.15, 2.14 and 2.12 eV for samples prepared at 10, 12, 14, 16, 18 and 20 h respectively, showing a decreasing trend shown in the inset of Fig. 5. These data agrees with its components (monoclinic type BiVO4) and clearly demonstrate that a good visible-light-driven photocatalyst can be synthesized by this hydrothermal processing. 4. Conclusions Highly crystallized monoclinic BiVO4 nanoparticles were obtained by hydrothermal processing and characterized by XRD, TEM, UV–vis, Raman and FTIR techniques. The results revealed that a decrease trend of particle size and a gradual increase of band gap were observed when hydrothermal time increased from 10 to 20 h. Its spectra indicated that samples prepared for longer hydrothermal time may be consisted of more antisymmetric VO4 tetrahedral in its local structures, and thus changed the electronic structures of products. Acknowledgement We acknowledge the financial support from the General Program of Beijing Municipal Education Committee (No. KM200910009011). References [1] Xiao GC, Wang XC, Li DZ, Fu XZ. J Photoch Photobio A: Chem 2008;193:213–21. [2] Yu JQ, Kudo A. Adv Funct Mater 2006;16:2163–9. [3] Kohtani S, Koshiko M, Kudo A, Tokumura K, Ishigaki Y, Toriba A, et al. Appl Catal B: Environ 2003;46:573–86.
[4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27]
Tücks A, Beck HP. Dyes Pigments 2007;72:163–77. Ge L. Mater Lett 2008;62:926–8. Zhou L, Wang WZ, Xu HL. Cryst Growth Des 2008;8:728–33. Thongtem S, Wannapop S, Thongtem T. Ceram Int 2009;35:2087–91. Cavalcante LS, Sczancoski JC, Lima LF, Espinosa JWM, Pizani PS, Varela JA, et al. Crys Growth Des 2009;9:1002–12. Tahir MN, Gorgishvili L, Li J, Gorelik T, Kolb U, Nasdala L, et al. Solid State Sci 2007;9:1105–9. Kudo A, Omori K, Kato H. J Am Chem Soc 1999;121:11459–67. Tokunaga S, Kato H, Kudo A. Chem Mater 2001;13:4624–8. Walsh A, Yan YF, Huda MN, Al-Jassim MM, Wei SH. Chem Mater 2009;21:547–51. Lim AR, Choh SH, Jang MS. J Phys: Condens Mater 1995;7:7309–23. Yao WF, Iwai H, Ye JH. Dalton Trans 2008:1426–30. Yu JQ, Zhang Y, Kudo A. J Solid State Chem 2009;182:223–8. Xu H, Li HM, Wu CD, Chu JY, Yan YS, Shu HM. Mater Sci Eng B 2008;147:52–6. Jiang HQ, Endo H, Natori H, Nagai M, Kobayashi K. J Eur Ceram Soc 2008;28:2955–62. Bhattacharya AK, Mallick KK, Hartridage A. Mater Lett 1997;30:7–13. Long M, Cai WM, Kisch H. J Phys Chem C 2008;112:548–54. Yang T, Xia DG, Chen G, Chen Y. Mater Chem Phys 2009;114:69–72. Li HB, Liu GC, Duan XC. Mater Chem Phys 2009;115:9–13. Galembeck A, Alves OL. J Mater Sci 2002;37:1923–7. Liu JB, Wang H, Wang S, Yan H. Mater Sci Eng B 2003;104:36–9. Kubelka P, Munk F. Tech Z Phys 1931;12:593–601. Sczancoski JC, Bomio MDR, Cavalcante LS, Joya MR, Pizani PS, Varela JA, et al. J Phys Chem C 2009;113:5812–22. Zhang X, Ai ZH, Jia FL, Zhang L, et al. Mater Chem Phys 2007;103:162–6. Oliveira RC, Cavalcante LS, Sczancoski JC, Aguiar EC, Espinosa JWM, Varela JA, et al. J Alloys Compd 2009;478:661–70.