Constructing electron-rich metal sites in M0.5Co0.5O through N substitution for efficient peroxymonosulfate activation to degrade organic pollutants

Transition metal oxides are promising heterogeneous catalysts for peroxymonosulfate (PMS) activation. However, the catalytic degradation performance was unsatisfactory. Herein, nitrogen doping was applied to construct electron-rich metal sites in bimetallic oxides (Mn_0.5Co_0.5O, Fe_0.5Co_0.5O, Cu_0.5Co_0.5O) to boost their PMS activation performance for sulfamethoxazole (SMX) degradation. The N-doped bimetallic oxides (Mn_0.5Co_0.5O-N, Fe_0.5Co_0.5O-N, Cu_0.5Co_0.5O-N), obtaining through a facile ammonia-assisted medium-temperature heat treatment method, displayed enhanced PMS activation performance for SMX degradation compared with the pristine bimetallic oxides. Especially, Mn_0.5Co_0.5O-N is the optimal option with 100% SMX degradation efficiency within 2 min, wide pH application range (3.5-11.5), and excellent cycling performance. The density functional theory (DFT) calculations confirmed that Mn_0.5Co_0.5O-N with more negative adsorption energy (E_ads) and higher electron transfer number was more beneficial for PMS adsorption and activation. Quenching experiments, electron paramagnetic resonance (EPR), and solvent exchange (H₂O to D₂O) indicated that ¹O₂ contributed predominantly to SMX degradation. This research offers an economical strategy for boosting the PMS activation activity to degrade pollutants of transition metal oxides through constructing electron-rich metal sites in bimetallic oxides by N substitution.