Advanced Materials Research Vols. 93-94 (2010) pp 153-156 © (2010) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.93-94.153
Chemical Synthesis and Characterization of Bismuth Vanadate Powder Pusit Pookmanee1,a, Sumintra Paosorn1,b, and Sukon Phanichphant2,c 1
Department of Chemistry, Faculty of Science, Maejo University, Chiang Mai, Thailand
2
Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai, Thailand a
[email protected],
[email protected],
[email protected]
Keywords: Bismuth vanadate, chemical co-precipitation method, XRD, SEM
Abstract. Bismuth vanadate powder was synthesized by a chemical co-precipitation method. Bismuth nitrate and ammonium vanadate were used as the starting precursors. The yellow precipitated powder was formed after adding ammonium hydroxide until the pH of final solution was 7. The powder was filtered and dried at 60 °C for 24h and calcined at 200-400 °C for 2h. The phase of bismuth vanadate powder was studied by X-ray diffraction (XRD). A single phase of monoclinic structure was obtained after calcinations at 200-400 °C for 2h. The morphology and particle size of bismuth vanadate powder were investigated by scanning electron microscopy (SEM). The particle was irregular in shape and highly agglomerated with an average particle size of 0.5 µm in width and 1.5 µm in length. Introduction Bismuth vanadate (BiVO4) has attracted significant recent attention because of its good ferroelasticity, ionic conductivity and its photocatalytic activity for degradation of organic materials and organic dyes as well as for splitting of water for hydrogen and oxygen evolution. It is known that photocatalytic properties strongly depend on the crystal structure. BiVO4 powder with a monoclinic structure shows high photocatalytic activity because of its relatively narrow band gap of 2.4 eV, as compared to BiVO4 with a tetragonal phase (3.1 eV) [1]. Three main crystal forms of BiVO4 are known; tetragonal (zircon-type structure), monoclinic (distorted scheelite structure, fergusonite structure) and tetragonal scheelite structure (high-temperature phase). The phase transition between monoclinic scheelite structure and tetragonal scheelite structure of BiVO4 reversibly occurs at about 255 oC (ferroelastic to paraelastic transition), whereas the irreversible transition from tetragonal zircon type structure to monoclinic BiVO4 occurs after heat treatment at 400–500 oC and cooling to room temperature [2]. Recently, various techniques are used to synthesize monoclinic structure BiVO4 crystallites, such as chemical bath deposition method [3], hydrothermal method [4], sonochemical method [5] and chemical co-precipitation method [6]. In this research, we present a chemical synthesis and characterization of bismuth vanadate powder. Experimental Bismuth vanadate (BiVO4) powder was synthesized by a chemical co-precipitation method. Bismuth nitrate and ammonium vanadate were used as the starting precursors. Solution I, bismuth nitrate (Bi(NO3)3·5H2O, Ajax, Australia) was dissolved in HNO3 (Merck, Germany). Solution II, ammonium vanadate (NH4VO3, Carlo, Italy) was dissolved in NH4OH (Merck, Germany). Then, both solutions were mixed together with stirring and adjusted until the final pH of solution was 7 with 4M NH4OH. The yellow precipitated powder was formed after adding ammonium hydroxide until the pH of final solution was 7. The powder was filtered and dried in oven (Gallenkamp, England) at 60 °C for 24h and calcined in muffle furnance (Carbolite, England)at 200-400 °C for 2h. The phase of BiVO4 powder was studied by X-ray diffraction (JDX-3530, JEOL, Japan) using the Ni-filtered monochromatic with CuKα radiation. The detection range was 10-60° with the step size of 0.10° (2θ°/s/s). Confirmation structure of BiVO4 powder was obtained by comparison with the Joint Committee on Powder Diffraction Standards (JCPDS) Card File No.00-014-0688 [7]. The All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 118.172.36.242-11/12/09,18:32:54)
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morphology and particle size of bismuth vanadate powder were investigated by scanning electron microscopy (S3400N, Hitachi, Japan) with the tungsten filament K type, accelerate voltage of 15.0 kV and working distance of 18 mm. Powder was dispersed with ethanol (C2H5OH, Merck, Germany) medium in an ultrasonic bath (136H, Ultrasonik, USA.) for 15 min and gold coated by fine coater (JSC1200, JEOL, Japan). Results and Discussion Figure 1 shows the XRD pattern of the BiVO4 powder synthesized by a chemical co-precipitation method after calcination at 200-400 oC for 2h. The BiVO4 powder after calcination 200 oC for 2h (Fig. 1 (a)) shows XRD pattern of single phase of monoclinic phase of BiVO4 powder corresponding to the JCPDS File Card No. 00-014-0688 [7]. At higher calcination temperatures of 300-400 oC for 2h (Fig. 1 (b,c)) show the XRD pattern of single phase of monoclinic phase of BiVO4 powder corresponding to the JCPDS File Card No. 00-014-0688 [7]. Tetragonal structure of BiVO4 powder absorbs in the ultraviolet region (band gap 2.9 eV), whereas monoclinic structure of BiVO4 powder with a 2.4 eV band gap has a characteristic visible light absorption in addition to the UV band. The photocatalytic activities of tetragonal and monoclinic BiVO4 powder differ markedly. Also, the photocatalytic activity of the monoclinic BiVO4 powder synthesized by a chemical co-precipitation method was much higher than that of monoclinic BiVO4 powder synthesized by a conventional solid-state reaction even in the same crystal structure [2]. The calcinations and reaction time were lower than previously reported [8]. As the calcination temperatures increased, the line width decreased and intensity of diffraction line increased.
Intensity (a.u.) (111)
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(042) (202) (161) (-152) (-321) (321)
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(110) (011)
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2θ Figure 1. XRD pattern of BiVO4 powder synthesized by a chemical co-precipitation method after calcination at (a) 200 °C, (b) 300 °C and (c) 400 °C for 2h
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(b)
(c) Figure 2. SEM micrograph of BiVO4 powder synthesized by a chemical co-precipitation method after calcination at (a) 200 °C, (b) 300 °C and (c) 400 °C for 2h Figure 2 shows SEM micrograph of the BiVO4 powder synthesized by a chemical coprecipitation method after calcination at 200-400 oC for 2h. The BiVO4 powder after calcination
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200 oC for 2h was agglomerated, irregular and plate sheet in shape and the average particles size of 0.1 µm in width and 1.5 µm in length.as shown in Figure 2 (a). The BiVO4 powder after calcinations at higher temperature of 300-400 oC for 2h the particles became larger with average particles size of 0.3 µm in width and 1.0 µm in length (Fig. 2 (b)); and 0.5 µm in width and 1.5 µm in length (Fig. 2 (c)), respectively. The particle sizes were smaller than previously reported [8]. The results indicate that increase of the synthesis temperature can promote the growth of the particles and have significant influence on the morphology and microstructure of the BiVO4 powder [9]. Summary Bismuth vanadate (BiVO4) powder was successfully synthesized by a chemical co-precipitation method. Single phase monoclinic structure was obtained after calcinations at 200-400 oC for 2h. The powder was agglomerated, irregular and plate sheet in shape with the particle size in the range of 0.1-0.5 µm in width and 1.0-1.5 µm in length. Acknowledgements This research was supported by the Department of Chemistry, Faculty of Science, Maejo University, Thailand and the Research Project for Undergraduate Students (IRPUS) with grant RPUS-R52D13005, the National Research Council of Thailand (NRCT) and the Commission on Higher Education, Ministry of Education. References [1] H.-Q. Jiang, H. Endo, H. Natori, M. Nagai and K. Kobayashi: J. Eur. Ceram. Soc. Vol. 28 (2008), p. 2955 [2] M. Gotić, S. Musić, M. Ivanda, M. Šoufek and S. Popović: J. Mol. Struct. Vol. 744-747 (2005), p. 535 [3] M.C. Neves and T. Trindade: Thin Solid Films Vol. 406 (2002), p. 93 [4] J.B. Liu, H. Wang, S. Wang and H. Yan: Mat. Sci. Eng. B Vol. 104 (2003), p. 36 [5] L. Zhou, W.Z. Wang, S.W. Liu, L. Zhang, H. Xu and W. Zhu: J. Mol. Catal. A-Chem. Vol. 252 (2006), p. 120 [6] A.K. Bhattacharya, K.K. Mallick and A. Hartridge: Mater. Lett. Vol. 30 (1997), p. 7 [7] Joint Committee on Powder Diffraction Standards (JCPDS). Powder Diffraction File, Card No. 00-014-0688, Swarthmore, PA. [8] K. Shantha and K.B.R. Varma: Mat. Sci. Eng. B Vol. 56 (1999), p. 66 [9] L. Ge: Mater. Chem. Phys. Vol. 107 (2008), p. 465
