Efficient removal of sulfamethoxazole by boron-doped porous biochar-activated persulfate: simultaneously enhanced adsorption and non-radical pathways

The properties of catalysts and activation pathway are crucial in persulfate-based advanced oxidation processes. In this study, boron-doped porous biochar (BPC-0.25), featuring adsorption-catalysis dual function, was successfully synthesized to activate peroxydisulfate (PDS) for sulfamethoxazole (SMX) degradation. The results showed that BPC-0.25 removed 83 % of SMX in 30 min via absorption and achieved complete degradation in 20 min through the synergistic effect with PDS oxidation. Meanwhile, the BPC-0.25/PDS system exhibited good anti-interference ability to adapt to complex water quality conditions. The quenching experiments, EPR tests, and electrochemical analyses collectively revealed that the PDS activation by BPC-0.25 was dominated by the generation of singlet oxygen (¹O₂) and supplemented by electron transfer process (ETP). Remarkably, boron doping enhanced the adsorption capacity and mass transfer of the catalysts due to the formation of mesoporous structure and improvement of surface affinity. Simultaneously, the content of carbonyl group (C=O) and boron doped species were increased, both of which possessed high reactivity, thereby significantly improving the catalytic performance and ETP efficiency. The results further identified that CO, structural defects, and BC₃ were the main active sites in the BPC-0.25/PDS system. Besides, possible degradation pathways of SMX were proposed by mass spectrometry and theoretical calculations, while the ecotoxicity of the intermediates was predicted by ECOSAR. Overall, this work offers innovative strategies for designing efficient and environmentally friendly metal-free catalysts, provides novel insights into the activation mechanism of PDS, and presents effective approaches for wastewater remediation.