Bifunctional2D K‑SnS for One-Pot PhotocatalyticReduction of Cr(VI) and <i>In Situ</i> Ion-Exchange Recycleof Product Cr(III)

Remediating industrial wastewater containing Cr­(VI) is crucial to addressing environmental and health challenges posed by heavy-metal pollution. However, the product Cr­(III) may cause secondary pollution and even photocatalyst poisoning. In this study, we developed a two-dimensional bifunctional photocatalyst, K_2<i>n</i>[Sn₃S₇]_<i>n</i> (2D K-SnS), to achieve Cr­(VI) reduction and Cr­(III) sequestration simultaneously via photocatalysis under visible-light irradiation and ion-exchange conditions, respectively. A reduction efficiency of 30 ppm Cr­(VI) could reach up to 99.3%. The product Cr­(III) could potentially be stored inside the [Sn₃S₇]_<i>n</i>^2<i>n</i>– framework by in situ ion exchange with the filled K⁺; this was followed by recycling through reversible ion exchange in KCl solution with the total Cr recycling rate reaching nearly 90%. Furthermore, the photocatalyst demonstrated excellent stability, retaining high activity (as measured by a total Cr removal efficiency above 95%) after reversible ion-exchange. The structural and functional attributes of 2D K-SnS ensure efficient Cr­(VI) detoxification while minimizing secondary pollution. Ultimately, this study presents a sustainable strategy for treating industrial wastewater via combining heavy-metal ion removal with resource recovery. The study’s findings highlight the potential uses of photocatalytic materials in practical environmental applications.