Cobalt-Loaded Peanut Shell Biochar Enables Nonradical Peroxymonosulfate Activation for Rapid Tetracycline Degradation

Conventional peroxymonosulfate (PMS) activation systems are often dominated by nonselective radical pathways, which limit oxidation efficiency. Herein, a cobalt-loaded peanut shell biochar (Co-BC) was synthesized via a co─impregnation-pyrolysis strategy for efficient PMS activation and tetracycline (TC) degradation. The optimized Co-BC (1:2:1.5-600) achieved nearly complete TC removal within 10 min with a high rate constant (kobs = 0.4911 min-1). Characterization results show that the excellent performance is attributed to defect-rich carbon structures, well-developed porosity, and cobalt sites involving Co2+/Co3+ redox cycling. Correlation analysis indicates that carbon defects and Co loading are closely associated with catalytic activity. Mechanistic studies indicate that the reaction is dominated by a nonradical pathway. Singlet oxygen (1O2) is identified as the main reactive species, while •OH and SO4•- contribute relatively little. DFT results further reveal that cobalt incorporation enhances PMS adsorption and interfacial charge redistribution, favoring subsequent PMS activation. The catalyst also shows good magnetic recoverability and applicability under various water chemistry conditions and remains catalytically active after eight consecutive cycles. This study provides insight into designing efficient biomass-derived catalysts for predominantly nonradical PMS activation.