ISSN 1203-8407 © 2011 Science & Technology Network, Inc. J. Adv. Oxid. Technol. Vol. 14, No. 1, 2011 93 Solution Combustion Synthesis of BiVO 4 Nanoparticles: Effect of Combustion Precursors on the Photocatalytic Activity H. K. Timmaji 1, 2 , W. Chanmanee 1 , N. R. de Tacconi 1 , and K. Rajeshwar* ,1 1 Center for Renewable Energy Science & Technology, University of Texas at Arlington, Arlington, TX 76019- 0065, USA 2 Environmental and Earth Sciences, University of Texas at Arlington, Arlington, TX 76019 – 0065 USA Abstract: This paper describes the solution combustion synthesis, solid-state characterization, photoelectrochemical behavior, and photocatalytic properties of bismuth vanadate (BiVO 4 ). In particular, the influence of combustion precursor was addressed in this study. Bismuth nitrate pentahydrate was used as the bismuth precursor and either vanadium chloride or vanadium oxysulfate was used as the vanadium precursor. Urea, glycine, or citric acid was used as the fuel. Stoichiometric mixtures (1:1) of the fuels and oxidants (with the Bi:V mole ratio also maintained at 1:1) were subjected to solution combustion synthesis. The resultant samples were characterized by X-ray diffraction, high- resolution transmission electron microscopy, diffuse reflectance spectrophotometry, thermal analyses, and laser Raman spectroscopy. Methyl orange was used as a probe to test the photocatalytic attributes of the combustion- synthesized (CS) samples, and benchmarked against a commercial bismuth vanadate sample. The CS samples were superior to the commercial benchmark sample, and samples derived from vanadium chloride were superior to vanadium oxysulfate counterparts. The photoelectrochemical properties of the various CS samples were also studied and these samples were shown to be useful both for environmental photocatalytic remediation and water photooxidation applications. Keywords: Semiconductor; Photocatalyst; Monoclinic Introduction Bismuth vanadate (BiVO 4 ) is interesting from a variety of perspectives, including ferroelastic behavior, acousto-optical and ion conductive properties. Yellow pigments based on BiVO 4 are also environmentally- attractive “green” substitutes for lead, chromium, and cadmium based paints especially from a ecotoxi- cological perspective and high performance (good gloss and hiding power) (1). More relevant and important to this study, however, are the excellent photoelectro- chemical and photocatalytic performance for applica- tions in solar water splitting (2) and environmental remediation (3). Bismuth vanadate exists in three polymorphic forms, monoclinic phase (distorted scheelite, clino- bisvanite), tetragonal phase (tetragonal scheelite, dreyerite) and orthorhombic phase (tetragonal zircon, pucherite) (4, 5). The orthorhombic phase occurs naturally as the pucherite mineral. The tetragonal zircon type structure can be formed by low temperature laboratory synthesis, while high temperature synthesis produces the monoclinic form. The monoclinic form undergoes a reversible transition to the tetragonal *Corresponding author; E-mail address: rajeshwar@uta.edu scheelite form on heating above 255 °C. The tetragonal form also transforms irreversibly to the monoclinic form on mechanical treatment (e.g., grinding with an agate mortar and pestle) (6). Among the three polymorphic forms, the mono- clinic form is known to exhibit the best photocatalytic activity. The reason for this is explained from the electronic band structure of BiVO 4 . Metal oxide semi- conductors typically have valence and conduction bands derived from O 2p and metal s or d orbitals respectively. The valence band in monoclinic BiVO 4 comprises of hybrid Bi 6s and O 2p orbitals, resulting in an upward dispersion of the valence band at the zone boundary (7). However, a direct energy bandgap is maintained via coupling between V 3d, O 2p and Bi 6s lowering the conduction band minimum and resulting in symmetric hole and electron masses (7). In view of the above, BiVO 4 has been extensively studied, especially in the last decade, and a wide range of methods have been developed for preparing it (6- 53). These methods include solution co-precipitation (8), solid-state calcinations (8), various solution-phase preparation strategies (9), hydrothermal synthesis (with or without surfactant) (13), metallo-organic deposition (23), sol–gel synthesis (16), flame pyrolysis (31),