Flame-assisted synthesis of nanoscale, amorphous and crystalline, spherical BiVO4 with visible-light photocatalytic activity

The synthesis of bismuth vanadate (BiVO4) nanoparticles has drawn considerable attention to their application as a visible-light-driven photocatalyst. Several techniques are addressing the enlargement of surface area, but some of them can cause impurities and lower the performance of the material. In this work, flame spray synthesis technique was used as a simple, easy upscalable technique to produce BiVO4 powders. The effect of process parameters on particle properties such as size, morphology and crystallinity were investigated by several techniques: BET, XRD, DSC, TEM, DRS and potential. Spherical BiVO4 nanoparticles with either amorphous or monoclinic phase-pure crystal structure, along with specific surface areas (SSA) between 10 and 75 m(2) g(-1) were obtained by a setup including an in situ crystallization step at T >= 270 degrees C on the powder collection site, sometimes followed by a mild or severe annealing post-treatment. Traditional synthesis routes usually require such annealing post-treatment which implies considerable loss of SSA. The photocatalytic activity of the as-prepared powders was investigated by the degradation of the cationic dye methylene blue (MB). N-demethylation of the dye was clearly identified as one of the degradation pathways, while ring cleavage was only observed with crystalline samples. Crystallinity and SSA were crucial parameters for the photocatalytic activity of different samples of BiVO4 depending on the pH of the solutions. The control of these two parameters during the synthesis of BiVO4 qualifies this method for a potential large scale production. (C) 2010 Elsevier B.V. All rights reserved.