B–N conjugated biochar enhances peroxymonosulfate activation for 1O2 generation by disrupting extended π-conjugated system

B–N doping disrupts π-conjugation and localizes electrons in biochar. • B–N sites and carbon vacancies promote axial electron transfer and PMS adsorption. • BN-Cv-Biochar enables highly selective 1 O 2 generation and rapid SMX degradation. • BN-Cv-Biochar/PMS system markedly reduces the phytotoxicity of treated water. Selective activation of peroxymonosulfate (PMS) to produce singlet oxygen ( 1 O 2 ) is desirable for efficient water purification. Graphitized biochar is a promising catalyst, but its extended π-conjugated structure favors in-plane charge delocalization and hinders axial electron transfer, leading to low 1 O 2 selectivity. Herein, we fabricated a boron-nitrogen (B–N) conjugated doped carbon-vacancy biochar (BN-Cv-Biochar) to modulate the local π-electronic system. B–N doping breaks the extended π-conjugation, creating polarized active sites and localized electrons that strengthen axial electron transfer and selective PMS adsorption. The degradation rate constant of sulfamethoxazole (SMX) of BN-Cv-Biochar is 1.68 and 4.45 times higher than that of pristine (Biochar) and nitrogen-doped carbon-vacancy biochar (N-Cv-Biochar), respectively. Experimental and theoretical results reveal that B–N sites coupled with carbon vacancies optimize the electronic environment, reduce the energy barrier for 1 O 2 generation, and preferentially promote 1 O 2 -dominated PMS activation. Product analysis clarifies the SMX degradation pathway, and toxicity assays using radish seedlings confirm the reduced toxicity of treated water. This work provides a novel strategy to tune the π-conjugated structure of biochar for high-performance carbon catalysts in advanced oxidation processes. Download: Download high-res image (201KB) Download: Download full-size image