Porous pie-like nitrogen-doped biochar as a metal-free peroxymonosulfate activator for sulfamethoxazole degradation: Performance, DFT calculation and mechanism

Design and development of low-cost, high-efficient, metal-free persulfate heterogeneous catalysts was a hot research topic. Herein, porous pie-like nitrogen-doped biochar (NBC) was prepared by one step high temperature pyrolysis of rape straw, urea and ZnCl2 mixture, and applied for peroxymonosulfate (PMS) activation toward sulfamethoxazole (SMX) degradation. Among these as-prepared catalysts, the NBC2.0 sample presented the best catalytic activity, with the 99.8 % SMX degradation efficiency in 5 mins and the 81.7 % total organic carbon (TOC) removal rate in 30 mins. Additionally, it could realize an excellent SMX degradation in the wide pH range of 3.0 to 9.0, and possessed the high degradation efficiency in presence of various organic pollutants or in real water environments, indicating its good pH adaptability, universality and practicality. Mechanistic investigations disclosed that the NBC2.0/PMS/SMX system involved both radical and non-radical degradation pathways, with singlet oxygen (1O2) and the direct electron transfer mechanism being the main contributors. The main active reaction sites of NBC were graphitic N, pyridinic N and C = O group, as corroborated by density functional theory (DFT) calculation and X-ray photoelectron spectroscopy (XPS) measurement. The possible SMX breakdown routes were determined by intermediate identification. This work provides a promising metal-free persulfate catalyst for environment remediation.