Water-Soluble Salt-Template-Assisted Fabrication of Co4N@C for Efficient Tetracycline Destruction via Peroxymonosulfate Activation

The facile synthesis of functional materials containing Co₄N centers presents a significant challenge, particularly in achieving effective integration of Co₄N nanoparticles with porous carbons. In this study, Co₄N nanoparticles anchored on porous carbon are fabricated using a water-soluble Na₂SO₄ template through urea-assisted pyrolysis, with precise control of the calcination temperature for the Co@C precursor. The resulting Co₄N@C composite, featuring Co₄N nanoparticles as the primary active centers, exhibits high performance in peroxymonosulfate activation for tetracycline (TC) degradation, achieving a degradation rate exceeding 90% within 15 min. The magnetic properties of Co₄N@C facilitate its easy separation from the reaction medium, and the recovered catalyst demonstrates only a slight decline in removal efficiency observed over five consecutive cycles. Quenching and electron paramagnetic resonance tests reveal that the degradation pathways involve both free radicals and nonfree radicals, with the electron transfer mechanism predominantly occurring in the nonradical pathway. Three degradation pathways are proposed based on the documentation of intermediate products from TC decomposition. The toxicity assessment of these intermediates and the original TC indicates a reduction in phytotoxicity of the degraded TC solution using the Co₄N@C/PNS system.