Balanced adsorption and catalysis in nitrogen-doped biochar for efficient peroxymonosulfate activation and 4-chlorophenol removal via electron transfer pathways

Nitrogen-doping is an effective strategy for enhancing peroxymonosulfate (PMS) activation efficiency by carbon-based catalysts, yet its impact on pollutant adsorption remains largely unexplored. Here, N-doped biochar (CNC) was synthesized via pyrolysis of sodium lignosulfonate, melamine, and activated carbon. The CNC/PMS system exhibited excellent efficiency for 4-chlorophenol (4-CP) removal, following a pseudo-second-order kinetic model with an observed rate constant of 0.0134 L·mg –1 ·min –1 . This process relied on synergistic adsorption and catalytic degradation processes. N-doping improved the graphitization of the carbon skeleton and introduced defects that facilitated PMS activation via non-radical pathways. However, excessive pyridinic N reduced 4-CP adsorption due to increased hydrophilicity, emphasizing the need for balanced doping. Mechanistic analysis of the CNC/PMS/4-CP system revealed that electron transfer pathways dominated the degradation process, with C=O groups and pyrrolic N on the CNC surface serving as primary active sites. Degradation pathways of 4-CP involved hydroxylation, dechlorination, and polymerization, with many intermediates adsorbed onto CNC, thereby minimizing ecological risks. The system achieved over 95 % removal efficiency both in tap and river water and maintained effectiveness over seven cycles, demonstrating robust anti-interference capability and stability. These findings advance understanding of electron transfer pathway control and broaden N-doped biochar applications in water treatment.