Solvent-free synthesis of foam board-like CoSe₂ alloy to selectively generate singlet oxygen via peroxymonosulfate activation for sulfadiazine degradation

Singlet oxygen (¹O₂) is a highly effective reactive species in selectively oxidizing organic pollutants. However, it is still challenging to rationally design robust catalysts for the selective generation of ¹O₂. Herein, the coordination and engineering architecture of the foam board-like CoSe₂ alloy were facilely constructed through a green solvent-free method and displayed almost 100% ¹O₂ production selectivity. The CoSe₂ alloy showed excellent catalytic ability for the efficient and fast removal of organic pollutants via peroxymonosulfate (PMS) activation compared with previously reported cobalt-based catalysts. The CoSe₂/PMS system exhibited strong resistance for a broad pH range (3.0–11.0) and various coexisting inorganic ions owing to the advantage of the strong bonding of Co-Se in CoSe₂ alloy. Mechanism studies revealed that ¹O₂ was the only reactive oxygen species in the CoSe₂/PMS system. Theoretical calculations demonstrated that Co was the dominant adsorption site for PMS in CoSe₂, and the production pathway of ¹O₂ was PMS* → *OH → *O → ¹O₂. In addition, it was proved that *OH and *O served as the rate-determining steps for the formation of ¹O₂ by PMS activation on CoSe₂ alloy. These findings provide a rational strategy for preparing a series of low-cost transition metal-based alloy catalysts for PMS activation to achieve high-efficiency ¹O₂ production in the elimination of organic pollutants.