Nanoconfinement-enhanced peroxymonosulfate activation by Co single atoms in hollow mesoporous carbon: Roles of active-site chemistry and mesoscale confinement.

Peroxymonosulfate (PMS)-based advanced oxidation processes have attracted considerable attention for the removal of refractory organic pollutants, yet their practical efficiency is still limited by the insufficient coupling between intrinsic active-site reactivity and interfacial mass transport. Here, the Co single-atom catalysts (Co-SACs) confined within hollow mesoporous carbon are constructed, and the effects of the nanoconfined environment on catalytic performance and reaction mechanism are systematically investigated. Compared with its unconfined counterpart, the nanoconfined catalyst exhibits accelerated pollutant degradation kinetics and improved PMS utilization efficiency (PUE). Combined quenching experiments, electrochemical analysis, and probe tests indicate that pollutant oxidation predominantly proceeds through a nonradical pathway involving singlet oxygen (1O2) and electron transfer process (ETP). Density functional theory calculations suggest that the confined structure strengthens PMS adsorption on the Co-N4 sites and promotes interfacial charge transfer as well as the formation of the surface-bound PMS complexes (PMS*). COMSOL simulations further show that the mesoporous channels and hollow cavity could collectively enhance PMS activation by promoting reactant enrichment, accelerating fluid transport, and regulating the local microenvironment. From a multiscale perspective, this work elucidates how nanoconfinement influences PMS activation and suggests that the enhanced catalytic performance of hollow mesoporous architectures is more closely associated with confinement-induced mass-transfer regulation and microenvironment effects than with macroscopic curvature alone. This work provides mechanistic insight into PMS activation in nanoconfined Co-SACs systems and offers guidance for the rational design of highly efficient catalysts for nonradical oxidation processes.