<p>Photocatalysis is hindered by inefficient charge carrier separation and transfer, which result in poor photocatalytic performance. Herein, an interfacial Fe-S chemical-bonded Fe(III)/CdIn₂S₄ photocatalyst was designed and synthesized via a facile impregnation method. The Fe(III) species chemical-bonded on the surface of CdIn₂S₄ facilitate the electron transfer from CdIn₂S₄ to Fe(III) cluster, achieving the boosted O₂ molecule activation for ciprofloxacin (CIP) photocatalytic degradation. Under visible-light irradiation, the optimal 15%Fe(III)/CdIn₂S₄ yielded a CIP degradation rate and mineralisation degree of 98.9% and 74.5%, respectively. The apparent kinetic constant (<i>k</i>_app, min⁻¹) for CIP degradation was 3.66 times larger than that of pristine CdIn₂S₄. Notably, the degree of CIP mineralisation surpassed those of most reported photocatalysts. The regulatory effects of Fe(III) on the interfacial electronic structure of CdIn₂S₄ were further confirmed using Kelvin probe force microscopy, in -situ X-ray photoelectron spectroscopy, and density functional theory calculations. Furthermore, the boosted charge separation and transfer for O₂ molecule activation mechanisms were also elucidated. In addition, a photocatalytic degradation pathway for CIP and its potential ecotoxicological effects were proposed. The findings of this study provide a new strategy for regulating the interfacial electronic structure of catalysts to improve their photocatalytic performance.</p> Graphical Abstract <p></p>