Nitrogen-doped carbon modified with boron atoms activating peroxydisulfate for sulfamethoxazole degradation: The electron transfer-dominated pathway

The non-radical pathway has attracted extensive interest due to its unique advantages in persulfate activation . However, the conversion between non-radical pathways remains elusive. In this study, the nitrogen and boron co-doped carbon (NB-C) was synthesized from agroforestry waste by a simple co-pyrolysis method for activating peroxydisulfate (PDS) to degrade sulfamethoxazole (SMX). The results showed that nearly 100 % removal of SMX (20 mg/L) was achieved at a low catalyst dose (0.15 g L −1 ). Combining the results of quenching experiments, electron paramagnetic resonance , in situ Raman spectroscopy , premixing experiments, and electrochemical analyses , a non-radical activation mechanism dominated by the electron transfer pathway (ETP) was identified. More importantly, we have quantified the oxidation contribution of various reactive oxygen species (ROS) to SMX degradation by steady-state concentration calculations. The experimental and characterization data indicated that the carbon structure of nitrogen-doped carbon (N-C) was altered with the introduction of boron (B), and the main active sites were replaced by pyrrolic N, sp 2 -C, and the new BC 3 site, thereby transforming the reaction pathway from 1 O 2 oxidation (44.43 %) into an almost complete ETP (92.34 %). Benefitting from the advantages of the ETP, the NB-C/PDS system maintains excellent adaptability in complex background water matrices and over a wide pH range (3−11). Moreover, unlike the N-C/PDS system based on 1 O 2 oxidation, the reusability of the NB-C/PDS system was significantly improved, which further emphasizes its practical application potential. Finally, three possible degradation pathways of SMX were proposed by liquid chromatography-mass spectrometry and the toxicity of the intermediates was evaluated.