Selective generation of Co(IV)=O in-situ on cobalt-doping MoS₂@CC photoanode through photoelectrochemical activation of peroxymonosulfate for efficient antibiotic degradation

The frequent occurrence of antibiotics in wastewater poses a serious threat to human health and ecosystem safety. High-valent cobalt-oxo (Co(IV)=O) is a promising reactive species for antibiotic degradation, however, the selective and highly efficient generation of Co(IV)=O in advanced oxidation processes (AOPs) remains challenging. Herein, we develop a photoelectrochemical peroxymonosulfate activation (PEC/PMS) system using a cobalt-doping MoS₂@CC (Co-MoS₂@CC) photoanode to generate Co(IV)=O for efficient antibiotic degradation. The Co doping significantly improves the PEC properties of Co-MoS₂@CC and increases its active sites, achieving a high sulfamethoxazole (SMX) degradation rate constant (0.497 min⁻¹) in the PEC/PMS system. Mechanistic investigations reveal that the PEC system activates PMS through a non-radical pathway to selectively form Co(IV)=O (with a high steady-state concentration of 1.95 × 10⁻⁹ M) in-situ on Co-MoS₂@CC as the dominant reactive species for SMX degradation (93.4% contribution). The photogenerated holes are a critical driving force for Co(IV)=O formation, while the photogenerated electrons accelerate the valence cycling of Co species to facilitate Co(IV)=O generation. Additionally, the PEC/PMS treatment significantly reduces SMX toxicity by efficiently disrupting its molecular structure. Furthermore, the PEC/PMS system demonstrates excellent practicality, evidenced by stably producing Co(IV)=O under pH 5 ∼ 9 and effectively degrading five frequently detected antibiotics in real wastewater over five cycles. The study provides in-depth insight into the rational design of the PEC/PMS system for the selective formation of Co(IV)=O.