Bi-functional S-scheme S-Bi2WO6/NiO heterojunction for photocatalytic ciprofloxacin degradation and CO2 reduction: Mechanisms and pathways

Designing bi-functional photocatalysts for contaminants removal and carbon dioxide (CO2) reduction has important practical significance for solving pollution and energy issues. In this paper, the S-scheme layered nanochain S-Bi2WO6/NiO heterojunction was fabricated for efficient ciprofloxacin (CIP) degradation and CO2 reduction. The layer chain structure and functional groups of the S-Bi2WO6/NiO provided abundant active sites and facilitated carriers’ separation and transfer, as well as reactants adsorption. The 0.35 S-Bi2WO6/NiO heterojunction exhibited CIP removal of 92.5 %, and yields of CO and CH4 of 46.9 and 12.1 μmol/g/h, respectively, within 90 min of visible light illumination. X-ray photoelectron spectroscopy (XPS), Ultraviolet photoelectron spectroscopy (UPS) and Density functional theory (DFT) work function calculation together demonstrated that carriers transfer over the S-Bi2WO6/NiO conformed to S-scheme heterojunction mechanism. Both h+ and ·OH were dominant contributors toward CIP degradation, and most of degradation intermediates showed lower ecotoxicity. Three possible pathways of CIP degradation were proposed. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results demonstrated that CO* was the most important intermediate mediated generation of CO and CH4. This study could advance the development of bi-functional heterojunctions for pollutants elimination and CO2 conversion.