Construction of a novel dual S-scheme CdS@Si-α-Fe2O3/ZnO heterojunction for visible-light-driven photo-Fenton degradation of ciprofloxacin.

Visible-light-driven heterogeneous photo-Fenton processes have emerged as one of the most promising technologies for wastewater decontamination. In this study, a novel CdS@Si-α-Fe2O3/ZnO dual S-scheme heterojunction photocatalyst was successfully constructed and applied to the visible-light-driven photo-Fenton degradation of ciprofloxacin. The relationship between the heterojunction structure and its charge-separation efficiency under visible-light irradiation was comprehensively investigated using various physicochemical characterizations, femtosecond transient absorption spectroscopy (fs-TAS), and Kelvin probe force microscopy. Owing to the synergistic effect of the accelerated Fe2+/Fe3+ redox cycle and efficient separation of photoexcited carriers, the CdS@Si-α-Fe2O3/ZnO photocatalyst demonstrated a higher degradation efficiency of 95 % within 60 min in the presence of H2O2. Free radical quenching experiments combined with EPR analysis confirmed the coexistence of multiple reactive species in the photo-Fenton reaction system, including ·OH, ·O2‒, 1O2, and h+/e‒. Furthermore, based on the detected degradation intermediates of ciprofloxacin using liquid chromatography-mass spectrometry (LC-MS), plausible degradation pathways were proposed. A comprehensive toxicity assessment of the intermediate products was conducted with the Toxicity Estimation Software Tool and ECOSAR program.