Oxygen vacancy mediated Zn3V2O8/BiVO4 type-I heterojunction: An efficient photocatalyst for the degradation of organic dye

Constructing vacancy-mediated heterojunction has proven to be a useful strategy for improving photocatalytic activity. Therefore, in this work, we have developed oxygen vacancy mediated Zn₃V₂O₈/BiVO₄ heterojunction at different molar ratios by using the hydrothermal method. The hierarchical Zn₃V₂O₈/BiVO₄ (2:1) shows well-crafted heterostructure formation with excellent photocatalytic activity under visible light and solar irradiation against congo red (CR) dye. Photoluminescence (PL) analysis confirmed the reduction of electron-hole pairs recombination of heterojunctions. X-ray Photoelectron Spectroscopy (XPS) and Electron Paramagnetic Resonance (EPR) results demonstrated the existence of oxygen vacancies in the prepared samples. The Zn₃V₂O₈/BiVO₄ (2:1) exhibited the highest efficiency, achieving 83.7 % and 95.03 % degradation of CR dye within 120 minutes under visible light and direct sunlight, respectively and the rate constant was faster than those of both pure Zn₃V₂O₈ and BiVO₄. The boosted photocatalytic activity can be the result of reduced recombination of electron-hole pairs, large surface area, and the presence of oxygen vacancies. Additionally, we investigated the effect of catalyst dosage, dye concentration, and different water matrices on the photocatalytic activity of Zn₃V₂O₈/BiVO₄ heterojunction. The radical trapping experiment confirmed that •$O_2^{-}$ played a main role in the photocatalytic degradation of CR dye. Based on the observed results and alignment of band positions, a plausible vacancy-mediated type-I charge transfer mechanism is proposed to explain the enhanced photocatalytic activity. Furthermore, the recycling experiment revealed that the synthesized heterojunction is highly stable. This work highlights the role of oxygen vacancies in enhancing photocatalytic activity.