Efficient Peroxymonosulfate Activation over Cobalt-Encapsulated Nitrogen-Doped Carbon Hollow Nanospheres toward Tetracycline Degradation: Performance and Catalytic Mechanism

In this study, cobalt-encapsulated nitrogen-doped carbon hollow nanospheres (Co@NCs) were synthesized for peroxymonosulfate (PMS) activation and tetracycline (TC) degradation. Co@NCs synthesized at a high pyrolysis temperature exhibited relatively higher graphitic N and C═C contents, which effectively regulated the electron density of Co sites, enhancing the PMS activation efficiency. In the Co@NCs-900/PMS system, remarkable TC removal efficiency (97.14%, kobs = 0.179 min–1) and TOC removal (63.62%) were achieved within 60 min. Based on the quenching tests, EPR technology, and electrochemical measurements, a synergistic radical and nonradical pathway was unveiled, with SO4•–, 1O2, and ETP dominated. Co@NCs-900/PMS showed efficient catalytic performance and practical application potentials without interference from organic and inorganic compounds under the experimental background. Additionally, over 80% TC removal could be achieved after the seven-cycle catalytic reaction and showed negligible Co2+ leaching, indicating superior recyclability. Chemical analysis and DFT calculation revealed that PMS adsorption and activation could be strengthened by modulating the electron density with Co and N serving as the active sites. Overall, this study provides valuable insights into the incorporation of metal sites on N-doped carbonaceous catalysts for Fenton-like reactions in water purification applications.