Theoretical and experimental insight into the construction of FTO/NiSe₂/BiVO₄ photoanode towards an efficient charge separation for the degradation of pharmaceuticals in water

The increasing contamination of water bodies by pharmaceuticals has become a major environmental concern, with traditional treatment methods often proving ineffective. In this manuscript, we present a theoretical and experimental investigation into the construction of an S-scheme FTO/NiSe₂/BiVO₄ (NSB) photoanode toward the photoelectrocatalytic degradation of pharmaceutical pollutants in water. The study focuses on the optimization of the photoanode structure to significantly restrain charge recombination and maximize photoelectrocatalytic performance. The photoanode achieves higher efficiency (76%) in comparison with the pristine FTO/BiVO₄ (BVO) (43%) and FTO/NiSe₂ (NS) (17%) for the PEC degradation of ciprofloxacin. This can be attributed to the improved band gap (1.92 eV), low charge transfer resistance (9.6 Ω), reduced flat band potential (0.24 V) and higher charge density (4.86 × 10¹⁷ cm^–1) resulting from synergic interaction at the interface of the semiconductor resulting to fast transition of the charge and restraining of recombination of the charge carriers. The accumulation of the electrons majorly takes place at the NS layer as displayed by the theoretical modeling of the charge density difference. This suggests a transition of electrons from BVO to NS. The band offset as well as the built-in electric field across the NSB interface limit the recombination of the photoinduced carriers. The mechanism including the functions of different reactive species is studied, which reveals that the holes mostly dominate the degradation process. Based on density functional theory, active species capture experiment, and photoelectrochemical detection, the synthesized NSB photocatalyst conforms to an S-scheme heterojunction charge transfer mechanism. We consider the composite suitable for the treatment of water contaminated with pharmaceutical waste.