Carbonization of camphor sulfonic acid and melamine to N,S-co-doped carbon for sulfamethoxazole degradation via persulfate activation: Nonradical dominant pathway

Abstract

• ·NSC-750 outperformed the nitrogen-free SC-750 in persulfate activation. • ·96% removal, 69% mineralization, and 98% PS utilization rate were achieved. • ·Hybridized EPR spectra, coupling 1 O 2 and unpaired electron signal, was found. • ·Pyridinic N, thiophene-S, and structural defects were the active sites. • ·Nonradical 1 O 2 dominated the oxidization of SMX. A nonradical dominant degradation process via N,S-co-doped carbon-catalyzed persulfate (PS) activation was reported. The camphor sulfonic acid acted as both carbon and sulfur source, and melamine served as nitrogen source. The introduction of N atom into S-doped carbon created new defective sites and N active species. Accordingly, the resulting NSC-750 showed an enhanced catalytic activity (0.0348 min −1 ), with 5.8-folds higher SMX removal efficiency than that of SC-650 (0.006 min −1 ). 96% removal, 69% mineralization, and 98% PS decomposition rate were achieved. The NSC-750/PS system could work effectively over a wide pH range of 3–9. While carbonate (CO 3 2– ) played an opposite role in degrading SMX. Both radical and nonradical pathway were involved in SMX degradation. Therein, 1 O 2 played a critical role while . OH, SO 4 .- , and electron transfer exerted a minor contribution. It was assumed that pyridine N and thiophene S are responsible for the production of SO 4 .- ; structural defect and C = O contributed to the formation of 1 O 2 and electron-transfer process, respectively; partial 1 O 2 was originated from the conversation of O 2 .- . In addition, NSC-750/PS system was capable of degrading other contaminants (bisphenol A, ciprofloxacin, and rhodamine B et al). The obtained hybrid EPR spectra, coupling with 1 O 2 and unpaired electron signal of catalyst, broadens our horizon to better distinguish the reactive species. This work facilitates the application of N,S-co-doped carbon in nonradical-dominated antibiotics remediation, and deepens the understanding of catalytic mechanism and active sites.