Deposition and characterization of BiVO4 thin films and evaluation as photoanodes for methylene blue degradation

Thin films of bismuth vanadate (BiVO4) are deposited through the solution combustion synthesis technique coupled with the dip-coating process. Thermal gravimetric analyis shows a total mass loss of 71 % besides the formation of the monoclinic phase, about 300 A degrees C, which is also revealed by X-ray diffraction. UV-Vis optical absorption spectra show direct bandgap transition about 2.5 eV for films, in good agreement with semiconducting monoclinic phase. Scanning electron microscopic images reveal that thermal annealing time at 500 A degrees C is a very important parameter to control the thickness and shape of the particles and yields an average thickness of about 800 nm for 10 dip-coated deposited layers, with round-shaped nanometric-sized particles, homogeneously distributed on the film surface. Photoelectrochemical degradation of methylene blue by a bismuth vanadate film deposited on fluor-doped tin oxide substrate shows up as a very efficient process. The first-order rate constant for the photoinduced process is about five times the rate constant for degradation in the dark, showing the capacity of the BiVO4/fluorine-doped tin oxide film for electrochemical degradation, mainly in the presence of light.