Mn-MOF derived N-doped MnOx@carbon heterogeneous catalysts for Vis-light, S2O82, HSO5, Vis/S2O82, and Vis/HSO5-induced degradation of metronidazole: Kinetics and mechanistic study

Manganese oxide-based nanostructures have demonstrated remarkable potential for reactive radical generation to treat wastewater by activating persulfate (PS) and peroxymonosulfate (PMS) in the presence of visible-light irradiation. Herein, we report a facile strategy to synthesize nitrogen-doped porous MnOx@Carbon nanostructures by annealing Mn-based MOF at different temperatures and employed for the degradation of MTZ under Vis-light, PS, PMS, Vis/PS, and Vis/PMS systems. A significant catalytic synergy was found in the MnO-I/Vis/PMS system. Owing to the rational coordination of nitrogen-enriched porous manganese oxide embedded carbon, high surface area (179.6 m2/g), and surface-exposed abundant active sites, the composite named MnO-I exhibited excellent catalytic performance in all the studied processes. The carbonization process induces a polarization difference between Mn-N co-ordination, resulting in the carbon becoming an electron-deficient core and manganese an electron-rich center, thus providing more Mn (II/III) for PMS activation. The degradation study showed that 99% removal of MTZ was achieved within 40min, with a rate constant of 0.099min-1, in the MnO-I/Vis/PMS system. Trapping experiments and EPR detection demonstrated that SO4•−, OH• and 1O2 radicals were the major species involved in the degradation process. Besides, the degradation pathway and impact of operational parameters, i.e., catalyst dosage, PMS concentration, initial pH, MTZ concentration, co-existing anions, and humic acid, on the removal of MTZ were also explored.