Unlocking robust antibiotics oxidation in nanosphere-confined Fe2O3 via size-exclusion effect and inner-surface-bound radicals

Nanoconfined peroxymonosulfate (PMS) activation provides a promising strategy for the robust degradation of emerging organics in complex water matrices. However, the resistance to size-dependent natural organic matter (NOM) and the behavior of confined oxidative radicals remain unclear. Herein, we precisely confine Fe 2 O 3 nanoparticles within the mesoporous hollow carbon nanospheres (MHCN) via an encapsulation strategy, constructing a nanoreactor (Fe 2 O 3 -in-MHCN) for PMS activation. This unique size-exclusion and electrostatic repulsion architecture effectively blocks diverse macromolecular NOM and inorganic anions from entering the cavity, while allowing the small-molecule antibiotic levofloxacin (LVFX) to freely diffuse and enrich inward, achieving 99.5% degradation within 10 min, with a 6.3-fold higher k obs than the non-confined system. Finite element analysis reveals that the shorter pore channels (20 ± 2 nm) accelerate the mass transfer of LVFX molecules toward the inner nanosphere. Moreover, the confined microenvironment shifts the dominant reaction pathway from free radicals to surface-bound radicals (SO 4 •− * and •OH*), significantly improving reactive species utilization. Fe 2 O 3 -in-MHCN gel beads further exhibit excellent long-term stability and environmental safety over 100 h of continuous operation. This study offers a new strategy for designing confined PMS activation systems that synergize pollutant enrichment, enhanced radical utilization, and strong anti-interference capability.