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One-step preparation of bismuth tungstate nanodisks with visible-light photocatalytic activity
Materials Letters 68 (2012) 171–173
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
One-step preparation of bismuth tungstate nanodisks with visible-light photocatalytic activity Peisong Tang ⁎, Haifeng Chen, Feng Cao Department of Chemistry, Huzhou Teachers College, Huzhou 313000, PR China
a r t i c l e
i n f o
Article history: Received 8 July 2011 Accepted 22 October 2011 Available online 29 October 2011 Keywords: Semiconductors Nanocrystalline materials Bismuth Tungstate Photocatalysis Nanodisk
a b s t r a c t Bismuth Tungstate (Bi2WO6) nanodisks were synthesized using Bi (NO3)3·5H2O and Na2WO4·2H2O as starting materials by a one-step hydrothermal process in the presence of ethylene glycol. The prepared sample was characterized by powder X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), Brunauer–Emmett–Teller (BET) measurement, Fourier transform infrared spectroscopy (FTIR) and UV–visible diffuse reflectance spectrum (DRS). The prepared Bi2WO6 nanodisks consist of fine particles and possess an optical band gap of 2.76 eV. The photocatalytic experiment demonstrates that the prepared Bi2WO6 nanodisks exhibit high photocatalytic activity for decomposition of Rhodamine B under visiblelight, which is ascribed to the unique shaped structures as well as narrow optical band gap. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Visible-light photocatalysis is a promising route for harnessing of solar energy to perform useful reactions and to convert light to chemical energy in a “green” manner. Intensive efforts have been devoted to realizing visible-light photocatalysis, including cation- or anion-doping, organic dye-sensitizing, composition with a semiconductor of narrow band gap [1–5]. In addition, the search for suitable semiconductors as visible-light active photocatalysts for photochemical purification of organic contaminants, bacterial detoxification, hydrogen production via photochemical water splitting and conversion of CO2 to hydrocarbon fuel has been paid extensive attentions as well [6–11]. Recently, bismuth tungstate (Bi2WO6) has been found to be visible-light active for degradation of organic contaminants. Ye et al. reported that Bi2WO6 has high visible-light photocatalytic activity for not only O2 evolution but also the degradation of organic contaminants CHCl3 and CH3CHO [12]. Zhu et al. found that Bi2WO6 exhibits efficient removal of bisphenol A under simulated solar light [13]. The superior visible-light photocatalytic activity is mainly attributed to the narrow band gap of around 2.7 eV and unique electric structures. It is well-known that the photocatalytic activity closely relates with the particle size, specific surface areas and the geometric shapes, etc. [14–16] Synthesis of visible-light active Bi2WO6 photocatalysts with well-defined geometric shapes and investigation of their photocatalytic activities are of fundamental importance, which offers opportunity to understand the correlation between photocatalytic properties and
⁎ Corresponding author. Tel./fax: + 86 572 2321166. E-mail address: [email protected] (P. Tang). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.10.080
geometric shapes, and also benefits to develop new photocatalytic materials. Zhu et al. and Wang et al. synthesized the Bi2WO6 nanoplates, and found that these nanoplates exhibit enhanced visible-light photocatalytic activities for degradation of Rhodamine B in comparison with those obtain in the solid-state reaction route [17,18]. Furthermore, nano- or micro-superstructures, for example, hierarchical microspheres, nanocages, and nest-like structures, are obtained via various wetting chemistry routes, which show distinct photocatalytic activities [19–22]. Herein, we report the preparation of Bi2WO6 nanodisks by a onestep hydrothermal process, and investigated the photocatalytic activity by decomposition of Rhodamine B (RhB) under visible-light (λ > 400 nm). It is demonstrated that the prepared Bi2WO6 nanodisks exhibit excellent visible-light photocatalytic activity. 2. Experimental section 2.1. Synthesis of Bi2WO6 nanodisks All reagents are of analytical purity, and were used as received from Aladdin Reagent Database Inc.(Shanghai, China). In a typical synthetic process, 1.5 mmol Bi(NO3)3·5H2O dissolved in a 1.35 mL 20% nitric acid and 1.5 mmol Na2WO4·2H2O dissolved in 12.0 mL deionized water were added to 30 mL ethylene glycol. The mixture was magnetically stirred at room temperature for 1 h, and the pH value was adjusted to 7.5 by addition of 1 M KOH solution. Finally, the resulting precursor suspension was transferred to a 50 mL Teflon-line autoclave, and held at 180 °C for 2 h. After cooled down to room temperature, the resulting samples were washed by deionized water and ethanol, and then dried at 100 °C in air for further use.
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P. Tang et al. / Materials Letters 68 (2012) 171–173
2.2. Photocatalytic activity testing Photocatalytic activities of the prepared samples were evaluated by the photocatalytic decomposition of RhB under visible-light. A 150 W metal halogen lamp was used as the light source with a 400 nm cutoff filter to provide visible-light irradiation (λ ≥ 400 nm). The distance between the light source and the liquid surface is about 8 cm. In a typical photocatalysis measurement, 20 mg of photocatalysts was added to 10 mL of RhB aqueous solution (10 mg/L). Before exposed to the visible-light, the suspensions were magnetically stirred for 30 min in the dark to get the adsorption–desorption equilibrium. Then the solution was exposed to the visible-light under magnetic stirring. After a given time, the solution was centrifuged, and the upper transparent solution was subjected to the UV–visible absorption spectra measurement. The concentration of the residual RhB was evaluated by the absorbance at 554 nm. The commercial photocatalyst P25 (Degussa, Germany), which is the photocatalyst model, was used for control experiment. 2.3. Characterization The X-ray diffraction (XRD) of the samples was performed on a C-98 X-ray diffractometer (Beijing Purkinje General Intstrument Co., Ltd.) operated at 40 kV and 35 mA with Cu Kα radiation (λ = 0.15418 nm). Morphologies of the prepared samples were observed with a Hitachi S-4800 field emission scanning electron microscope (FE-SEM) at 5 kV. UV–visible diffuse reflectance spectra (DRS) were recorded on a Hitachi-4100 UV–visible spectrophotometer in the range of 200–800 nm with BaSO4 as the reference. The Brunauer–Emmett–Teller (BET) specific surface areas were evaluated on the basis of nitrogen adsorption isotherms at 77 K on an ASAP analyzer (Micromeritics, USA). The Fourier transform infrared spectra (FTIR) were recorded using a Nicolet 5700 FTIR spectrometer. 3. Results and discussion 3.1. Structure and morphology of Bi2WO6 nanodisks The crystalline structure and composition of the prepared product were examined by the XRD measurement. Fig. 1a shows the XRD pattern of the Bi2WO6 sample. All peaks can be indexed to the orthorhombic Bi2WO6 according to the JCPDS card No. 79–2382. No additional crystalline phase was observed in the XRD pattern, which indicates synthesis of the single phase Bi2WO6 product. The morphology of the prepared Bi2WO6 sample was further investigated with FE-SEM, and the SEM image is shown in Fig. 1b. It is found that the prepared Bi2WO6 product consists almost entirely of hierarchical disk-like structures with a diameter of ca. 500 nm and a thickness of 80 nm. The inset of Fig. 1b shows the high magnification SEM image, and it can be clearly seen that the prepared Bi2WO6 nanodisks are composed of fine particles. As a result, XRD and SEM demonstrate that single phase Bi2WO6 nanodisks are synthesized by a one-step hydrothermal process. It is suggested that ethylene glycol plays an important role in shaping the geometric structure and determining the disk dimension since disklike structure and (or) nanoscale dimension cannot be achieved when the ethylene glycol was replaced with water or other solvents. In previous work, solid state reaction and microwave-assisted synthesis were carried out for preparation of various shaped Bi2WO6 [23–25]. Herein, the present developed methodology and use of ethylene glycol facilitate the assembly of hierarchical nanodisks. 3.2. Surface area and surface chemistry of Bi2WO6 nanodisks As mentioned above, Bi2WO6 with different morphologies should have different photocatalytic activities, which originates from the different band gaps and the BET specific surface area. The pore-size distribution
Fig. 1. (a) XRD pattern and (b) FE-SEM image of the prepared Bi2WO6 product. Inset is the high magnification SEM image.
and the BET specific surface area of the prepared Bi2WO6 were investigated. As shown in Fig. 2, the adsorption–desorption isotherm of the prepared Bi2WO6 nanodisks displays a significant hysteresis. The BET specific surface area is estimated to be 6.2 m2/g, which is much larger than the Bi2WO6 nanospheres prepared by the solid state reaction [24]. The pore-size distribution was calculated from the desorption data using the Barrett–Joyner–Halenda method, and is centralized on 2 nm along with a minor distribution around 8 nm, which will benefit to favorable adsorption of organic molecules in the photocatalysis. Fig. 2c shows the FTIR spectrum of the prepared Bi2WO6 nanodisks. Peaks at 730 cm− 1 and 580 cm− 1 are assigned to the stretching vibration modes of Bi–O and W–O, respectively [26]. The 1384 cm− 1 and 1640 cm− 1 peaks are attributed to the deformation vibration modes of C–H and O–H of adsorbed H2O molecule. The weak 1384 cm− 1 peak intensity indicates the low adsorption of organic molecules from the synthetic procedure and the clean surface of the prepared Bi2WO6 nanodisks. 3.3. Optical properties and photocatalytic activity The optical absorption property of the prepared Bi2WO6 nanodisks was investigated by the UV–visible diffuse reflectance spectroscopy (DRS) (Fig. 3a). It can be seen that the prepared Bi2WO6 nanodisks have an absorption edge of 450 nm, indicating that the optical band gap of Bi2WO6 nanodisks is 2.76 eV. The optical band gap of 2.76 eV is comparable with the previous reports [23]. RhB, a widely used dye, was selected as a representative pollutant to evaluate the photocatalytic activity of the prepared Bi2WO6 nanodisks. Fig. 3b shows the photocatalytic decomposition efficiencies of RhB in the presence of the prepared Bi2WO6 nanodisks and commercial P25 photocatalysts under visible-light (λ>400 nm). The blank experiment revealed that RhB is very stable under visible-light, and no significant decomposition of RhB was observed in the absence of photocatalysts even after exposed to the visible-light for 180 min. RhB was completely decomposed after 90 min exposure to the visible-light in the presence of Bi2WO6 nanodisks while in the commercial P25 photocatalyst, only 30% of RhB was decomposed after 180 min exposure to the visible-light. The photocatalytic test demonstrates that Bi2WO6 nanodisks display higher
P. Tang et al. / Materials Letters 68 (2012) 171–173
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Fig. 3. (a) UV–visible diffuse reflectance spectrum of the prepared Bi2WO6 nanodisks, and (b) photocatalytic decomposition curves of RhB under visible-light in the presence and absence of P25 and the prepared Bi2WO6 nanodisks.
Acknowledgments The authors acknowledge the financial support from Zhejiang Province Natural Science Foundation of China (No.Y4100471 and Y4110641), Zhejiang Province Education Department Project of China (No.Y200903866), and Science and Technology Planning Project of Zhejiang Province (2008 F70042). Fig. 2. (a) Pore-size distribution, (b) nitrogen adsorption–desorption isotherm and (c) FTIR spectrum of the prepared Bi2WO6 nanodisks.
photocatalytic activity under visible-light than the commercial P25 photocatalysts. This kind of hierarchical nanodisk has easy accessible reactive sites to the RhB molecule and large surface area, compared to the traditional nanostructures and bulk phase. We attribute the high visiblelight photocatalytic activity to not only the intrinsic band gap structure but also the unique geometric morphology. The disk-like shape provides favorable transport paths for RhB molecules to the active sites, and facilitates the fast transport of photogenerated electrons. Thus, the prepared Bi2WO6 nanodisks exhibit high visible-light photocatalytic activity. 4. Conclusions In summary, the Bi2WO6 nanodisks were synthesized using Bi (NO3)3·5H2O and Na2WO4·2H2O as starting materials by a one-step hydrothermal process in the presence of ethylene glycol. The hierarchical nanodisks were found to be constructed with fine particles. The poresize distribution measurements indicate the favorable pore structure for adsorption of small molecules in despite of the small BET specific surface area. The prepared Bi2WO6 nanodisks possess an optical band gap of 2.76 eV. The photocatalytic experiment demonstrates that the prepared Bi2WO6 nanodisks exhibit superior photocatalytic activity for decomposition of RhB under visible-light, which is ascribed to the unique structural characteristics as well as the narrow optical band gap.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26]
Xu J, Yang B, Wu M, Fu Z, Lv Y, Zhao Y. J Phys Chem C 2010;114:5251–15259. Takata T, Domen K. J Phys Chem C 2009;113:19386–8. Zhang Y, Tang ZR, Fu X, Xu YJ. ACS Nano 2010;4:7303–14. Graciani J, Nambu A, Evans J, Rodriguez JA, Sanz JF. J Am Chem Soc 2008;130: 12056–63. Harris C, Kamat PV. ACS Nano 2009;3:682–90. Paul T, Miller PL, Strathmann TJ. Environ Sci Technol 2007;41:4720–7. Yin L, Shen Z, Niu J, Chen J, Duan Y. Environ Sci Technol 2010;44:9117–22. Xu T, Kamat PV, O'Shea KE. J Phys Chem A 2005;109:9070–5. Utschig LM, Dimitrijevic NM, Poluektov OG, Chemerisov SD, Mulfort KL, Tiede DM. J Phys Chem Lett 2011;2:236–41. Wang C, Thompson R, Baltrus LJ, Matranga C. J Phys Chem Lett 2010;1:48–53. Fujiwara H, Hosokawa H, Murakoshi K, Wada Y, Yanagida S. Langmuir 1998;14:5154–9. Tang J, Zou Z, Ye J. Catal Lett 2004;92:53–6. Wang C, Zhang H, Li F, Zhu L. Environ Sci Technol 2010;44:6843–8. Xue H, Li Z, Ding Z, Wu L, Wang X, Fu X. Cryst Growth Des 2008;8:4511–6. Dinh CT, Nguyen TD, Kleitz F, Do TO. ACS Nano 2009;3:3737–43. Mclaren A, Valdes-Solis T, Li G, Tsang SC. J Am Chem Soc 2009;131:12540–1. Zhang C, Zhu Y. Chem Mater 2005;17:3537–45. Shang M, Wang W, Sun S, Zhou L, Zhang L. J Phys Chem C 2008;112:10407–11. Ge M, Li Y, Liu L, Zhou Z, Chen W. J Phys Chem C 2011;115:5220–5. Huang Y, Ai Z, Ho W, Chen M, Lee S. J Phys Chem C 2010;114:6342–9. Shang M, Wang W, Xu H. Cryst Growth Des 2009;9:991–6. Wu J, Duan F, Zheng Y, Xie Y. J Phys Chem C 2007;111:12866–71. Alfaro SO, Martínez-de la Cruz A. Appl Catal A 2010;383:128–33. Li G, Zhang D, Yu J, Leung MH. Environ Sci Technol 2010;44:4276–81. Ge L, Zhang X, Liu J. Adv Mater Res 2010;105–106:837–40. Yu J, Xiong J, Cheng B, Yu Y, Wang J. J Solid Stat Chem 2005;178:1968–72.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
One-step preparation of bismuth tungstate nanodisks with visible-light photocatalytic activity Peisong Tang ⁎, Haifeng Chen, Feng Cao Department of Chemistry, Huzhou Teachers College, Huzhou 313000, PR China
a r t i c l e
i n f o
Article history: Received 8 July 2011 Accepted 22 October 2011 Available online 29 October 2011 Keywords: Semiconductors Nanocrystalline materials Bismuth Tungstate Photocatalysis Nanodisk
a b s t r a c t Bismuth Tungstate (Bi2WO6) nanodisks were synthesized using Bi (NO3)3·5H2O and Na2WO4·2H2O as starting materials by a one-step hydrothermal process in the presence of ethylene glycol. The prepared sample was characterized by powder X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), Brunauer–Emmett–Teller (BET) measurement, Fourier transform infrared spectroscopy (FTIR) and UV–visible diffuse reflectance spectrum (DRS). The prepared Bi2WO6 nanodisks consist of fine particles and possess an optical band gap of 2.76 eV. The photocatalytic experiment demonstrates that the prepared Bi2WO6 nanodisks exhibit high photocatalytic activity for decomposition of Rhodamine B under visiblelight, which is ascribed to the unique shaped structures as well as narrow optical band gap. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Visible-light photocatalysis is a promising route for harnessing of solar energy to perform useful reactions and to convert light to chemical energy in a “green” manner. Intensive efforts have been devoted to realizing visible-light photocatalysis, including cation- or anion-doping, organic dye-sensitizing, composition with a semiconductor of narrow band gap [1–5]. In addition, the search for suitable semiconductors as visible-light active photocatalysts for photochemical purification of organic contaminants, bacterial detoxification, hydrogen production via photochemical water splitting and conversion of CO2 to hydrocarbon fuel has been paid extensive attentions as well [6–11]. Recently, bismuth tungstate (Bi2WO6) has been found to be visible-light active for degradation of organic contaminants. Ye et al. reported that Bi2WO6 has high visible-light photocatalytic activity for not only O2 evolution but also the degradation of organic contaminants CHCl3 and CH3CHO [12]. Zhu et al. found that Bi2WO6 exhibits efficient removal of bisphenol A under simulated solar light [13]. The superior visible-light photocatalytic activity is mainly attributed to the narrow band gap of around 2.7 eV and unique electric structures. It is well-known that the photocatalytic activity closely relates with the particle size, specific surface areas and the geometric shapes, etc. [14–16] Synthesis of visible-light active Bi2WO6 photocatalysts with well-defined geometric shapes and investigation of their photocatalytic activities are of fundamental importance, which offers opportunity to understand the correlation between photocatalytic properties and
⁎ Corresponding author. Tel./fax: + 86 572 2321166. E-mail address: [email protected] (P. Tang). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.10.080
geometric shapes, and also benefits to develop new photocatalytic materials. Zhu et al. and Wang et al. synthesized the Bi2WO6 nanoplates, and found that these nanoplates exhibit enhanced visible-light photocatalytic activities for degradation of Rhodamine B in comparison with those obtain in the solid-state reaction route [17,18]. Furthermore, nano- or micro-superstructures, for example, hierarchical microspheres, nanocages, and nest-like structures, are obtained via various wetting chemistry routes, which show distinct photocatalytic activities [19–22]. Herein, we report the preparation of Bi2WO6 nanodisks by a onestep hydrothermal process, and investigated the photocatalytic activity by decomposition of Rhodamine B (RhB) under visible-light (λ > 400 nm). It is demonstrated that the prepared Bi2WO6 nanodisks exhibit excellent visible-light photocatalytic activity. 2. Experimental section 2.1. Synthesis of Bi2WO6 nanodisks All reagents are of analytical purity, and were used as received from Aladdin Reagent Database Inc.(Shanghai, China). In a typical synthetic process, 1.5 mmol Bi(NO3)3·5H2O dissolved in a 1.35 mL 20% nitric acid and 1.5 mmol Na2WO4·2H2O dissolved in 12.0 mL deionized water were added to 30 mL ethylene glycol. The mixture was magnetically stirred at room temperature for 1 h, and the pH value was adjusted to 7.5 by addition of 1 M KOH solution. Finally, the resulting precursor suspension was transferred to a 50 mL Teflon-line autoclave, and held at 180 °C for 2 h. After cooled down to room temperature, the resulting samples were washed by deionized water and ethanol, and then dried at 100 °C in air for further use.
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P. Tang et al. / Materials Letters 68 (2012) 171–173
2.2. Photocatalytic activity testing Photocatalytic activities of the prepared samples were evaluated by the photocatalytic decomposition of RhB under visible-light. A 150 W metal halogen lamp was used as the light source with a 400 nm cutoff filter to provide visible-light irradiation (λ ≥ 400 nm). The distance between the light source and the liquid surface is about 8 cm. In a typical photocatalysis measurement, 20 mg of photocatalysts was added to 10 mL of RhB aqueous solution (10 mg/L). Before exposed to the visible-light, the suspensions were magnetically stirred for 30 min in the dark to get the adsorption–desorption equilibrium. Then the solution was exposed to the visible-light under magnetic stirring. After a given time, the solution was centrifuged, and the upper transparent solution was subjected to the UV–visible absorption spectra measurement. The concentration of the residual RhB was evaluated by the absorbance at 554 nm. The commercial photocatalyst P25 (Degussa, Germany), which is the photocatalyst model, was used for control experiment. 2.3. Characterization The X-ray diffraction (XRD) of the samples was performed on a C-98 X-ray diffractometer (Beijing Purkinje General Intstrument Co., Ltd.) operated at 40 kV and 35 mA with Cu Kα radiation (λ = 0.15418 nm). Morphologies of the prepared samples were observed with a Hitachi S-4800 field emission scanning electron microscope (FE-SEM) at 5 kV. UV–visible diffuse reflectance spectra (DRS) were recorded on a Hitachi-4100 UV–visible spectrophotometer in the range of 200–800 nm with BaSO4 as the reference. The Brunauer–Emmett–Teller (BET) specific surface areas were evaluated on the basis of nitrogen adsorption isotherms at 77 K on an ASAP analyzer (Micromeritics, USA). The Fourier transform infrared spectra (FTIR) were recorded using a Nicolet 5700 FTIR spectrometer. 3. Results and discussion 3.1. Structure and morphology of Bi2WO6 nanodisks The crystalline structure and composition of the prepared product were examined by the XRD measurement. Fig. 1a shows the XRD pattern of the Bi2WO6 sample. All peaks can be indexed to the orthorhombic Bi2WO6 according to the JCPDS card No. 79–2382. No additional crystalline phase was observed in the XRD pattern, which indicates synthesis of the single phase Bi2WO6 product. The morphology of the prepared Bi2WO6 sample was further investigated with FE-SEM, and the SEM image is shown in Fig. 1b. It is found that the prepared Bi2WO6 product consists almost entirely of hierarchical disk-like structures with a diameter of ca. 500 nm and a thickness of 80 nm. The inset of Fig. 1b shows the high magnification SEM image, and it can be clearly seen that the prepared Bi2WO6 nanodisks are composed of fine particles. As a result, XRD and SEM demonstrate that single phase Bi2WO6 nanodisks are synthesized by a one-step hydrothermal process. It is suggested that ethylene glycol plays an important role in shaping the geometric structure and determining the disk dimension since disklike structure and (or) nanoscale dimension cannot be achieved when the ethylene glycol was replaced with water or other solvents. In previous work, solid state reaction and microwave-assisted synthesis were carried out for preparation of various shaped Bi2WO6 [23–25]. Herein, the present developed methodology and use of ethylene glycol facilitate the assembly of hierarchical nanodisks. 3.2. Surface area and surface chemistry of Bi2WO6 nanodisks As mentioned above, Bi2WO6 with different morphologies should have different photocatalytic activities, which originates from the different band gaps and the BET specific surface area. The pore-size distribution
Fig. 1. (a) XRD pattern and (b) FE-SEM image of the prepared Bi2WO6 product. Inset is the high magnification SEM image.
and the BET specific surface area of the prepared Bi2WO6 were investigated. As shown in Fig. 2, the adsorption–desorption isotherm of the prepared Bi2WO6 nanodisks displays a significant hysteresis. The BET specific surface area is estimated to be 6.2 m2/g, which is much larger than the Bi2WO6 nanospheres prepared by the solid state reaction [24]. The pore-size distribution was calculated from the desorption data using the Barrett–Joyner–Halenda method, and is centralized on 2 nm along with a minor distribution around 8 nm, which will benefit to favorable adsorption of organic molecules in the photocatalysis. Fig. 2c shows the FTIR spectrum of the prepared Bi2WO6 nanodisks. Peaks at 730 cm− 1 and 580 cm− 1 are assigned to the stretching vibration modes of Bi–O and W–O, respectively [26]. The 1384 cm− 1 and 1640 cm− 1 peaks are attributed to the deformation vibration modes of C–H and O–H of adsorbed H2O molecule. The weak 1384 cm− 1 peak intensity indicates the low adsorption of organic molecules from the synthetic procedure and the clean surface of the prepared Bi2WO6 nanodisks. 3.3. Optical properties and photocatalytic activity The optical absorption property of the prepared Bi2WO6 nanodisks was investigated by the UV–visible diffuse reflectance spectroscopy (DRS) (Fig. 3a). It can be seen that the prepared Bi2WO6 nanodisks have an absorption edge of 450 nm, indicating that the optical band gap of Bi2WO6 nanodisks is 2.76 eV. The optical band gap of 2.76 eV is comparable with the previous reports [23]. RhB, a widely used dye, was selected as a representative pollutant to evaluate the photocatalytic activity of the prepared Bi2WO6 nanodisks. Fig. 3b shows the photocatalytic decomposition efficiencies of RhB in the presence of the prepared Bi2WO6 nanodisks and commercial P25 photocatalysts under visible-light (λ>400 nm). The blank experiment revealed that RhB is very stable under visible-light, and no significant decomposition of RhB was observed in the absence of photocatalysts even after exposed to the visible-light for 180 min. RhB was completely decomposed after 90 min exposure to the visible-light in the presence of Bi2WO6 nanodisks while in the commercial P25 photocatalyst, only 30% of RhB was decomposed after 180 min exposure to the visible-light. The photocatalytic test demonstrates that Bi2WO6 nanodisks display higher
P. Tang et al. / Materials Letters 68 (2012) 171–173
173
Fig. 3. (a) UV–visible diffuse reflectance spectrum of the prepared Bi2WO6 nanodisks, and (b) photocatalytic decomposition curves of RhB under visible-light in the presence and absence of P25 and the prepared Bi2WO6 nanodisks.
Acknowledgments The authors acknowledge the financial support from Zhejiang Province Natural Science Foundation of China (No.Y4100471 and Y4110641), Zhejiang Province Education Department Project of China (No.Y200903866), and Science and Technology Planning Project of Zhejiang Province (2008 F70042). Fig. 2. (a) Pore-size distribution, (b) nitrogen adsorption–desorption isotherm and (c) FTIR spectrum of the prepared Bi2WO6 nanodisks.
photocatalytic activity under visible-light than the commercial P25 photocatalysts. This kind of hierarchical nanodisk has easy accessible reactive sites to the RhB molecule and large surface area, compared to the traditional nanostructures and bulk phase. We attribute the high visiblelight photocatalytic activity to not only the intrinsic band gap structure but also the unique geometric morphology. The disk-like shape provides favorable transport paths for RhB molecules to the active sites, and facilitates the fast transport of photogenerated electrons. Thus, the prepared Bi2WO6 nanodisks exhibit high visible-light photocatalytic activity. 4. Conclusions In summary, the Bi2WO6 nanodisks were synthesized using Bi (NO3)3·5H2O and Na2WO4·2H2O as starting materials by a one-step hydrothermal process in the presence of ethylene glycol. The hierarchical nanodisks were found to be constructed with fine particles. The poresize distribution measurements indicate the favorable pore structure for adsorption of small molecules in despite of the small BET specific surface area. The prepared Bi2WO6 nanodisks possess an optical band gap of 2.76 eV. The photocatalytic experiment demonstrates that the prepared Bi2WO6 nanodisks exhibit superior photocatalytic activity for decomposition of RhB under visible-light, which is ascribed to the unique structural characteristics as well as the narrow optical band gap.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26]
Xu J, Yang B, Wu M, Fu Z, Lv Y, Zhao Y. J Phys Chem C 2010;114:5251–15259. Takata T, Domen K. J Phys Chem C 2009;113:19386–8. Zhang Y, Tang ZR, Fu X, Xu YJ. ACS Nano 2010;4:7303–14. Graciani J, Nambu A, Evans J, Rodriguez JA, Sanz JF. J Am Chem Soc 2008;130: 12056–63. Harris C, Kamat PV. ACS Nano 2009;3:682–90. Paul T, Miller PL, Strathmann TJ. Environ Sci Technol 2007;41:4720–7. Yin L, Shen Z, Niu J, Chen J, Duan Y. Environ Sci Technol 2010;44:9117–22. Xu T, Kamat PV, O'Shea KE. J Phys Chem A 2005;109:9070–5. Utschig LM, Dimitrijevic NM, Poluektov OG, Chemerisov SD, Mulfort KL, Tiede DM. J Phys Chem Lett 2011;2:236–41. Wang C, Thompson R, Baltrus LJ, Matranga C. J Phys Chem Lett 2010;1:48–53. Fujiwara H, Hosokawa H, Murakoshi K, Wada Y, Yanagida S. Langmuir 1998;14:5154–9. Tang J, Zou Z, Ye J. Catal Lett 2004;92:53–6. Wang C, Zhang H, Li F, Zhu L. Environ Sci Technol 2010;44:6843–8. Xue H, Li Z, Ding Z, Wu L, Wang X, Fu X. Cryst Growth Des 2008;8:4511–6. Dinh CT, Nguyen TD, Kleitz F, Do TO. ACS Nano 2009;3:3737–43. Mclaren A, Valdes-Solis T, Li G, Tsang SC. J Am Chem Soc 2009;131:12540–1. Zhang C, Zhu Y. Chem Mater 2005;17:3537–45. Shang M, Wang W, Sun S, Zhou L, Zhang L. J Phys Chem C 2008;112:10407–11. Ge M, Li Y, Liu L, Zhou Z, Chen W. J Phys Chem C 2011;115:5220–5. Huang Y, Ai Z, Ho W, Chen M, Lee S. J Phys Chem C 2010;114:6342–9. Shang M, Wang W, Xu H. Cryst Growth Des 2009;9:991–6. Wu J, Duan F, Zheng Y, Xie Y. J Phys Chem C 2007;111:12866–71. Alfaro SO, Martínez-de la Cruz A. Appl Catal A 2010;383:128–33. Li G, Zhang D, Yu J, Leung MH. Environ Sci Technol 2010;44:4276–81. Ge L, Zhang X, Liu J. Adv Mater Res 2010;105–106:837–40. Yu J, Xiong J, Cheng B, Yu Y, Wang J. J Solid Stat Chem 2005;178:1968–72.