Photoreduction and extraction of U(VI) from mining wastewater using magnetically recoverable ZnIn2S4-based Z-scheme photocatalysts

The photocatalytic reduction of highly toxic and soluble U(VI) to low toxic and insoluble U(IV) represents an environmentally friendly and efficient approach for uranium extraction. However, the application of photocatalytic U(VI) reduction is limited by low efficiency and challenges in recovering powder catalysts. In this study, we develop magnetically recyclable photocatalysts by integrating Fe 3 O 4 particles with in-situ grown ZnIn 2 S 4 /CdS Z -scheme heterojunctions (FO@ZIS/CS). Without adding any sacrificial agents, about 100 % of U(VI) in 50-mL aqueous solution (20 mg/L) is reduced by FO@ZIS/CS within 30-min visible light irradiation, which is 2.8 times higher than that of pristine ZnIn 2 S 4 (36 %). The remarkable performance is attributed to the Z -scheme heterojunction formed between ZnIn 2 S 4 and CdS, which promotes charge separation and preserves strong redox capabilities. Comprehensive experiments and theoretical simulations reveal that S and In atoms on ZnIn 2 S 4 (110) facets act as the active species for the U(VI) adsorption and reduction. Moreover, the FO@ZIS/CS photocatalyst maintains high U(VI) reduction efficiency in complex water matrices. The used FO@ZIS/CS and the adsorbed U(IV) can be easily recovered by an external magnetic field. This work offers a practical strategy for reducing and extracting U(VI) from mining wastewater, achieving both environmental remediation and resource recycling objectives.