A comprehensive study on the mechanism pathways and scavenging agents in the photocatalytic activity of BiVO4/WO3 nano-composite

The BiVO4-WO3 nano-composite (NC) was synthesized, characterized by the x-ray diffraction (XRD), scanning electron microscope (SEM), diffuse reflectance spectroscopy (DRS), and the photoluminescence spectroscopy (PL), Transmission electron microscope (TEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and N-2 adsorption-desorption (for the BET surface area determination) and used in the photodegradation of sulfasalazine (SFSZ) aqueous solution. Band gap energy and potential positions of the conduction and valence bands of the semiconductors were estimated. The composite with a mole ratio of 1:4 of BiVO4:WO3 showed the best photodegradation efficiency under visible light irradiation. The results confirmed a relatively smaller mineralization extent for SFSZ molecules than its photodegradation extent. The kinetic results showed k-values of 0.041 min(-1) and 0.022 min(-1) for the degradation and mineralization extents of SFSZ molecules that correspond to t(1/2) values of 17.1 and 31.5 min, respectively, confirming that photodegradation extent of SFSZ is about 1.85 times greater than its mineralization extent. Effects of the scavenging agents were studied and the results showed superoxide radicals, the photogenerated holes, OH radicals, and the photogenerated electrons have the important roles in SFSZ photodegradation, respectively. Among the type II-heterojunction and Z-scheme mechanisms, the latter case had the most important role in the photodegradation of SFSZ.