Persistent free radicals and oxygen functionalities in biochar via lignin valorization for high-capacity pollutant polymerization

Biochar-enabled catalytic polymerization in advanced oxidation processes (AOPs) offers a sustainable route for pollutant removal. However, the mechanistic link between lignocellulosic biopolymer composition (lignin, cellulose, hemicellulose) and polymerization capacity of biochar remains unexplored. Herein, five biochars with distinct structures and surface chemistries were synthesized from representative biomass (walnut shell, corn stalks, reed straw, pine wood chips, bamboo powder). These biochars predominantly activated peroxymonosulfate (PMS) through non-radical pathways, specifically electron-transfer pathway (ETP) and singlet oxygen ( 1 O 2 ) mechanisms, to drive pollutant polymerization into oligomeric dimers and trimers. Crucially, clear correlations emerged between the biomass composition and the resulting biochar functionality. Pearson analysis confirmed that precursors rich in lignin yielded biochars enriched with persistent free radicals (PFRs) and oxygen functional groups (OFGs), which were key to promoting the generation of active species and facilitating their direct participation in phenol C-C/C-O coupling reactions. Consequently, biochars derived from lignin-rich precursors achieved a polymerization capacity of 16.23 mg/g, surpassing that of lignin-poor biochars (2.42 mg/g) by 6.7-fold. This work reveals lignin content as a critical design parameter for developing highly efficient polymerization-based decontamination systems.