Regulating the peroxymonosulfate activation on N doped δ-MnO₂ nanosheets for tetracycline degradation: N species as the degradation pathways switcher to convert radical to nonradical

Although the free radical pathway can obtain high organic degradation efficiency during advanced oxidation processes, it is difficult to cater the diverse degradation environment due to the coexistence of various interference. Here, the δ-MnO₂ nanosheets are prepared to regulate the reactive oxidation species converting from radical-dominated to nonradical-dominated through the nitrogen doped operation in a gentle mechanical stirring method. The optimal 0.5 N-MnO₂ materials present 91.2 % TC degradation efficiency in the presence of peroxymonosulfate (PMS) with the apparent rate constant is 0.63 min⁻¹, which is 1.66 and 4.2 times higher than that of in δ-MnO₂/PMS (0.38 min⁻¹) and alone PMS (0.15 min⁻¹) systems, respectively. Radicals quenching experiments, electron paramagnetic resonance spectra and competing kinetics experiments indicate that the δ-MnO₂ nanosheets promote PMS decomposition with attaining a high radical (SO₄·^-, ·OH and ·O₂^–) oxidation path contribution (74.5 %) for TC degradation. Meanwhile, the doping of N species and electrons contribute to the generation of ¹O₂, allowing the whole reactive system dominated by a nonradical species (e^- and ¹O₂) pathway (80.3 %). Importantly, electrochemical tests verify the participation of electrons and the electrons transfer from TC to the 0.5 N-MnO₂ surface for PMS activation via 0.5 N-MnO₂-PMS* surface complex. Overall, it is practical to cater the specific application of advanced oxidation processes through N as the degradation pathways switcher.