A novel dual S-scheme heterojunction photocatalyst KBCN/t-BiVO4/m-BiVO4 induced by phase-transformed bismuth vanadate for highly efficient degradation of ciprofloxacin in full-spectrum: Degradation pathway, DFT calculation and mechanism insight

A novel KBr-g-C3N4/t-BiVO4/m-BiVO4 (15KBCN/mtBVO-P, P means PVP) heterojunction photocatalyst is synthesized using a hydrothermal method with the assistance of surfactant polyvinylpyrrolidone (PVP). Field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), and X-ray powder diffraction (XRD) confirm the formation of the heterostructure and changes in the crystal structure. Under sunlight illumination, 15KBCN/mtBVO-P exhibits the strongest photocatalytic degradation performance for ciprofloxacin (CIP), reaching 95.3 % within 240 min, the apparent kinetic constant is approximately 3.4, 2.4, and 3.3 times higher than CN, t-BVO, and m-BVO. The outstanding CIP degradation rate is observed under simulated solar and visible light, with over 93.0 % and 85.8 % in 60 and 120 min. The enhanced photocatalytic performance is attributed to the in-situ generation of the mixed-phase BiVO4 by precise crystal phase regulation. Furthermore, the charge transport and photocatalytic degradation mechanism of 15KBCN/mtBVO-P is revealed. Degradation pathways and ecotoxicity of CIP and its degradation products were elucidated through LC-MS/MS technology, DFT calculations, and QSAR models. This study presents a pioneering perspective on the fabrication and development of g-C3N4-based dual S-scheme heterojunction photocatalysts for practical application.