In Situ Electrochemically Generating High-Valent Iron Species Activated by Nitrogen-Doped Biochar for Efficient...

Background: Traditional methods exhibit an extremely low removal efficiency for antibiotics in water, making an efficient and energy-saving approach urgently needed. Methods and Results: In this study, a novel catalytic approach based on the in situ generation of high-valent iron (Fe(IV)/Fe(V)) has been developed by adding biochar instead of modifying the electrode materials (in previous studies) for the efficient removal of sulfamethoxazole (SMX) from water. Fe(IV)/Fe(V) was produced by the anodic oxidation of low concentrations of Fe(III) and subsequently activated by nitrogen-doped corn stalk biochar (NBC). The results showed that the degradation efficiency increased from 50.83% to 90.67% within 60 min after the addition of nitrogen-modified biochar. The abundant defect structures, graphitic N and oxygen-containing functional groups in NBC endowed the catalyst with excellent activation capability. Quenching experiments and methyl phenyl sulfoxide (PMSO) probe experiments revealed that singlet oxygen (¹O₂) and Fe(IV)/Fe(V) were the main contributors to SMX degradation. Degradation pathways were inferred based on transformation products (TPs) and density functional theory (DFT) calculations. Ecotoxicity prediction using the ECOSAR program indicated that the TPs formed in the E/Fe(III)/NBC system exhibited markedly lower toxicity to aquatic organisms than the parent SMX. Furthermore, the E/Fe(III)/NBC system maintained a high degradation efficiency for SMX in real aquatic environments. Additionally, the E/Fe(III)/NBC system showed high removal rates for other sulfonamides such as sulfadiazine (SDZ), sulfamethoxypyridazine (SMP), sulfathiazole (STZ) and sulfadoxine (SDX). Conclusions: Overall, the E/Fe(III)/NBC system was demonstrated to be a highly efficient and sustainable technology for removing various antibiotics from water.