Activity Trends and Mechanisms in Peroxymonosulfate-Assisted Catalytic Production of Singlet Oxygen over Atomic Metal-N-C Catalysts

The peroxymonosulfate (PMS)-assisted advanced oxidation processes catalyzed by transition metal compounds have become state-of-the-art technologies for water treatment, especially the atomic metal-N-C catalysts. In contrast, less attention has been paid to carbon-supported atomic metal-N-C catalysts with different transition metal centers to understand the transition metals' nature on the PMS-assisted catalytic activities and trends toward reactive oxygen species production. Here we synthesized a series of carbon-supported atomic metal-N-C catalysts (named as M-SACs, M = Mn, Fe, Co, Ni, Cu) with similar structural and physicochemical properties to experimentally and theoretically uncover their catalytic activity trends and mechanisms. The PMS catalytic activity trends are Fe-SAC>Co-SAC>Mn-SAC>Ni-SAC>Cu-SAC, and Fe-SAC displays the best single-site kinetic value (1.65*105 min-1 mol-1 ) compared to the other metal-N-C species. Our first-principles calculations indicate that the most reasonable reaction pathway for 1O2 production is PMS→OH*→O*→ 1O2 ; meanwhile, M-SACs that exhibit the moderate and near-average Gibbs free energies in each reaction step own a better catalytic activity, which is the key for the outstanding performance of Fe-SACs. This study gives the atomic-scale understanding of fundamental catalytic trends and mechanisms of PMS-assisted reactive oxygen species production via M-SACs, thus providing new guidance for developing M-SACs for future catalytic organic pollutant degradation.