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

Singlet oxygen (O) 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 O. Herein, the coordination and engineering architecture of the foam board-like CoSe alloy were facilely constructed through a green solvent-free method and displayed almost 100% O production selectivity. The CoSe 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 CoSe/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 CoSe alloy. Mechanism studies revealed that O was the only reactive oxygen species in the CoSe/PMS system. Theoretical calculations demonstrated that Co was the dominant adsorption site for PMS in CoSe, and the production pathway of O was PMS* → *OH → *O → O. In addition, it was proved that *OH and *O served as the rate-determining steps for the formation of O by PMS activation on CoSe 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 O production in the elimination of organic pollutants.