Activation of peroxymonosulfate by Fe,N co-doped walnut shell biochar for the degradation of sulfamethoxazole:...

Fe and N co-doped walnut shell biochar (Fe,N-BC) was prepared through a one-pot pyrolysis procedure by using walnut shells as feedstocks, melamine as the N source, and iron (III) chloride as the Fe source. Moreover, pristine biochar (BC), nitrogen-doped biochar (N-BC), and α-Fe₂O₃-BC were synthesized as controls. All the prepared materials were characterized by different techniques and were used for the activation of peroxymonosulfate (PMS) for the degradation of sulfamethoxazole (SMX). A very high degradation rate for SMX (10 mg/L) was achieved with Fe,N-BC/PMS (0.5 min^-1), which was higher than those for BC/PMS (0.026 min^-1), N-BC/PMS (0.038 min^-1), and α-Fe₂O₃-BC/PMS (0.33 min^-1) under the same conditions. This is mainly due to the formation of Fe₃C and iron oxides, which are very reactive for the activation of PMS. In the next step, Fe,N-BC was employed for the formation of a composite membrane structure by a liquid-induced phase inversion process. The synthesized ultrafiltration membrane not only exhibited high separation performance for humic acid sodium salt (HA, 98%) but also exhibited improved self-cleaning properties when applied for rhodamine B (RhB) filtration combined with a PMS solution cleaning procedure. Scavenging experiments revealed that ¹O₂ was the predominant species responsible for the degradation of SMX. The transformation products of SMX and possible degradation pathways were also identified. Furthermore, the toxicity assessment revealed that the overall toxicity of the intermediate was lower than that of SMX.