Fabrication of effective visible-light-driven ternary Z-scheme ZnO-Ag-BiVO4 heterostructured photocatalyst for hexavalent chromium reduction

Abstract A simple hydrothermal technique was used for the synthesis of a ternary ZnO-Ag-BiVO4 nanocomposite.The morphology, structure and optical performance of ZnO-Ag-BiVO4 were analyzed by XPS, TEM, XRD, FT-IR, FE-SEM, PL, and DRS. The sharp peaks of ZnO-Ag-BiVO4 indicated the good crystalline nature of the photocatalyst. FE-SEM images depicted the hexagonal structure of ZnO and the plate-like structure of BiVO4. The heterostructured catalyst Ag-ZnO-BiVO4 is capable of reducing 20 ppm of Cr(VI) from potassium dichromate in 100 mL aqueous solution to 97% within 70 min under visible light. The first-order rate constant value of 0.0371 min-1 and a 97% reduction for the ZnO-Ag-BiVO4 catalyst show its maximum photoreduction efficiency.The optimum pH for effective Cr(VI) reduction on ZnO-Ag-BiVO4 is 5 and it is steady and recyclable. The photo generated electron acts mainlyin the photocatalytic reduction of hexavalent chromium. The photocurrent analysis shows that the ZnO-Ag-BiVO4 composite material can enhance the photoexcited charge production, separation and migration, which improved the photocatalytic reduction of Cr(VI). Proposed Z-scheme mechanism of ternary ZnO-Ag-BiVO4 clearly explains the electron-hole separation and higher efficiency of this nanocomposite in the photoreduction.