Interface-regulated S-type core-shell PCN-224@TiO₂ heterojunction for visible-light-driven generation of singlet oxygen for selective photooxidation of 2-chloroethyl ethyl sulfide

Selective oxidation of sulfur mustard gas (HD) to non-toxic sulfoxide by the visible-light-catalyzed generation of singlet oxygen (¹O₂) is a promising degradation strategy. Although PCN-224 can absorb visible light, it suffers from rapid electron-hole recombination and low redox capacity, which limits the performance of HD degradation. Titanium dioxide (TiO₂) is an excellent photocatalyst but it lacks visible-light-activity in degrading HD. In this study, PCN-224@TiO₂ heterojunction with S-type core-shell structure was synthesized by in-situ growth method to prolong the visible light absorption capacity of TiO₂ and inhibit the rapid recombination of PCN-224. The interface formation and internal electric field were optimized by adjusting the Zr/Ti ratio to enhance the charge transfer, redox capacity, electron-hole separation, and visible light absorption. In this study, the formation of heterojunction composites based on Zr-O-Ti linkages is demonstrated by a series of characterization methods. It is demonstrated by experiments and theoretical calculations that PCN-224@TiO₂ can generate nearly 100 % ¹O₂ under visible light conditions without a sacrificial agent, resulting in efficient and selective oxidation of 2-chloroethyl ethyl sulfide (CEES), a simulant of HD, to non-toxic sulfoxide form.