Pyrolysis-tuned apple branch-derived carbon catalysts for persulfate activation: dominance of 1O2 non-radical pathways

Tetracycline (TC), a pervasive antibiotic contaminant in aquatic systems, presents critical ecological and human health threats. This study pioneers a sustainable remediation strategy by fabricating a metal-free biochar catalyst (PAC) from waste apple tree branches for persulfate (PDS) activation toward TC degradation. Among PACs pyrolyzed at 500–700°C, PAC-700 demonstrated exceptional catalytic activity, attributable to its maximized defect density and enriched surface carbonyl groups. Strong linear correlations between the rate constant (log( k )) and both I D / I G ratio ( R 2  = 0.823) and C O content ( R 2  = 0.998) suggest their potential influence on PDS activation. Mechanistic investigations elucidated a dual radical/non-radical pathway: radical species (SO 4 − , OH, and O 2 − ) and non-radical processes ( 1 O 2 , electron transfer), with 1 O 2 playing the dominant role to TC degradation. Crucially, C O groups were identified as pivotal active sites for 1 O 2 generation ( R 2  = 0.866 between C O and 1 O 2 contribution). Electrochemical analyses demonstrated that PAC materials prepared at higher pyrolysis temperatures exhibit enhanced electron transfer behavior, while LC-MS and Fukui index calculations mapped degradation pathways and reactive sites. Post-treatment toxicity assays validated significant ecological risk mitigation. This work advances green antibiotic remediation by synergizing biomass valorization with non-radical catalysis.