Turning support of MnO-N/C catalysts enhances generation of nonradicals in peroxymonosulfate activation

Peroxymonosulfate-based advanced oxidation processes (PMS-based AOPs) via nonradical pathways have attracted close attention due to their excellent anti-interference properties and high selectivity in degrading organic pollutants from wastewater. However, the highly efficient production of nonradicals for PMS activation remains challenging, especially for recalcitrant organic pollutants such as tetracycline (TC) in complex aqueous matrices. Here, MnO and nitrogen-doped carbon catalysts were synthesized using NH₄Cl modified strategy. The performances and mechanisms of TC degradation were evaluated, and toxicity of the system was also assessed. Results showed that the system achieved 86.7 % removal of TC within 30 min with a rate constant of 0.1713 min⁻¹. This system demonstrated effective TC degradation across a broad pH range (3.0–10.5) while exhibiting resistance to diverse anionic interferences in aqueous matrices. Characterization data showed that NH₄Cl calcination led to a hierarchical porous structure with optimized MnO dispersion and nitrogen functionality in the carbon support, further significantly enhancing nonradicals generation through PMS activation. The key active sites were identified as Mn-N_X sites, graphitic nitrogen, and C-O/C-N groups. Quenching experiments and ESR tests indicated that electron transfer and Mn(V) played the major role in TC degradation, followed by singlet oxygen (¹O₂). Based on LC-MS analysis of intermediates, three primary TC degradation pathways were identified: hydroxylation-driven ring-opening, oxidative demethylation/deamination, and oxidative ketonization. Toxicity assessment via the Toxicity Estimation Software Tool confirmed a significant reduction in ecotoxicity throughout these pathways. These data could be referred for the optimization of PMS-based AOPs in wastewater treatment.