Mechanistic insights into nitrogen doping effects on cobalt-loaded biochar for peroxymonosulfate Catalysis

Cow manure-derived biochar was used to synthesize a series of cobalt/nitrogen co-doped biochars with varying nitrogen contents for enhanced sulfamethoxazole (SMX) removal in a peroxymonosulfate (PMS)-based oxidation process. Their structures, catalytic activities, and mechanisms were systematically compared. Nitrogen doping significantly tuned biochar's surface area, pore structure, electronic properties, and active site distribution, showing a "rise-then-fall" trend in catalytic performance. Medium nitrogen-doped biochar (CoBC-2) exhibited optimal PMS activation and SMX degradation effects, with higher reaction rates than low- or high-doped samples. Mechanistic analysis revealed that moderate nitrogen doping synergistically enhanced the activity of Co-O, graphitic N, and oxygen-containing functional groups. Density functional theory (DFT) calculations further confirmed that medium nitrogen-doped biochar promoted electron transfer, PMS adsorption, and OO bond cleavage, thereby efficiently generating reactive species. This work provides a clear guideline for designing tunable biochar catalysts with optimized nitrogen content.