Mechanical chemical pretreatment boosts K-N self-templating doping in lignocellulosic biomass pyrolysis biochar for efficient tetracycline removal

Converting biomass resources into highly-active non-metallic biochar catalysts for efficient catalytic degradation of antibiotics provides a sustainable approach to biomass high-value utilization and organic pollution treatment. During biochar pyrolysis, endogenous minerals and nitrogen-rich components disperse uniformly. This promotes the formation of high-activity sites, thus enhancing the catalytic performance for persulfate (PS). However, the inherent properties and limitations of these two components pose obstacles to the precise synthesis of biochar. Herein, N-doped biochar catalysts were prepared using peanut-hull as a lignocellulosic carbon source with KHCO₃ and melamine as external modifiers. Interestingly, through an easy and green mechanochemical milling pretreatment, exogenous modifiers are uniformly grafted into the inner layers of lignocellulose. This pretreatment enables potassium and nitrogen to exhibit self-templating and self-doping synergies during pyrolysis, and leads to an effect similar to annealing. As a result, the produced biochar has abundant disordered edge defects of graphene layers (DEG), graphitic-N, and a high surface area (2223.9 m²·g^-1). In the PS system, the prepared biochar (PBC-KN) can remove up to 99% of 100 mg·L^-1 tetracycline (TC) within 3 min, and it is endowed with good environmental adaptability and potential for practical application. Electrochemical experiments and density functional theory (DFT) calculations show that DEG and graphite-N polarize the electron distribution on biochar surface. This promotes the formation of metastable complexes and enables efficient degradation of TC via electron transfer pathways. This finding presents a novel green synthetic strategy for high-value conversion of biomass into antibiotic remediation materials with high active uniform nitrogen-doped sites.