Ultrafast reductive dehalogenation of hexachlorobenzene and 2,2′,4,4′-tetrabromodiphenyl ether over Ag/Ag₂S/ZnIn₂S₄ photocatalyst under visible light

This research details the synthesis of an Ag/Ag₂S/ZnIn₂S₄ composite photocatalyst via the in-situ reduction of Ag/Ag₂S onto a flower-like ZnIn₂S₄ structure. The optimized 2%Ag/Ag₂S/ZnIn₂S₄ material displays augmented visible-light absorption spanning 500–800 nm, a photocurrent density 3.9-fold higher than pristine ZnIn₂S₄, and a more negative flat-band potential of −1.04 V versus Ag/AgCl. This composite achieves over 99% degradation of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) within 15 min (k = 0.2629 min −1 ) and 98.9% degradation of hexachlorobenzene (HCB) within 100 min (k = 0.0408 min −1 ), representing a degradation rate approximately 40 times faster than pure ZnIn₂S₄. To our knowledge, this is the fastest reported case to date of a visible-light-driven reductive dehalogenation reaction involving BDE-47 under similarly mild conditions, and its performance significantly outperforms that of ZnIn₂S₄ modified with Pd, Au, or Cu. Photogenerated electron-mediated mechanisms are confirmed through trapping experiments, and the catalyst exhibits robust stability across five reaction cycles. The accelerated degradation of BDE-47 is ascribed to its lower C Br bond energy (285 kJ/mol) compared to C Cl (327 kJ/mol) and enhanced hydrophobic adsorption. This study introduces a triple-synergy heterojunction approach for achieving ultrafast visible-light-driven reductive dehalogenation of halogenated persistent organic pollutants.