Synthesis, characterization and evaluation of photocatalytic activity of BiVO4, TiO2 and BiVO4/TiO2 composites

The principal aim of this work was to sensitize TiO2 with BiVO4, in order to improve titania photocatalytic activity under visible light. In this contest BiVO4, TiO2 and their composites with 80:20, 50:50 and 20:80 ponderal ratio between them, were synthesized through precipitation followed by calcination and hydrothermal treatment. The crystalline phases of the products were characterized through XRD analysis, XPS was employed to obtain information on the surface composition, BET calculations provided the specific surface area of the compounds and their optical behavior was inferred through UV-Vis diffuse reflectance spectra, which provided also an evaluation of the band gap of the semiconductors. Their photocatalytic activity was evaluate following the degradation of gaseous isopropanol under indoor illumination using GC-MS. In addition the formation of hydroxyl radical on the surface of the photocatalysts was inferred observing the formation of HTPA from TPA solution. The x-ray diffractograms revealed that the photocatalitically active phases (that is anatase for TiO2 and monoclinic scheelite for BiVO4) were obtained with both the synthetic procedures. Nevertheless the sensitization did not work, and the composite resulted less active than pure TiO2 under this type of illumination toward the degradation of isopropanol. In addition XPS revealed the presence of undesired sodium and nitrogen, and the tendency of a surface enrichment of TiO2, that could explain why the sensitization did not work. The analyses on the formation of hydroxyl radical confirmed what some authors had already reported in some papers, i.e. BiVO4 does not produce hydroxyl radical.