Efficient Activationof Low Concentrations of Peroxymonosulfatewith Nanoconfined Co₃O₄ in Hollow MesoporousSilica Microspheres for Diclofenac Degradation

This study demonstrated that the core–shell structure plays a critical role in promoting the redox reactions of peroxymonosulfate (PMS) with nanoconfined Co₃O₄, facilitating the generation of O₂^•– as reactive oxygen species (ROS) for diclofenac (DCF) elimination, and thereby the first-order rate constant of the nanoconfined Co₃O₄ within hollow mesoporous silica microspheres (Co@C-HMSMs, <i>k</i>_obs = 0.1813 min^–1) outperformed that of the aggregated Co₃O₄ supported on carbon (Co@C, without the core–shell structure) by a factor of 27.47. The electron paramagnetic resonance (EPR) spectra, probe quantifications, and molecular dynamics simulations demonstrated that Co@C-HMSMs induced the nanoconfinement effect and thus increased the efficient utilization of low concentrations of PMS (84.5% for 0.1 mM) for O₂^•– production by enriching the DCF and PMS molecules, reducing mass transfer distance, and enhancing the probability of molecular collisions, which effectively promoted DCF degradation. Meanwhile, Fukui function and toxicity analysis revealed that the higher <i>f</i>⁰ (0.0567) value of the Cl atomic site on DCF was vulnerable to be attacked by O₂^•–, generating the dechlorination products with less toxicity. Therefore, the O₂^•–-dominated dechlorination pathway for DCF oxidation presented a lower risk compared to the ^•OH-dominated hydroxylation pathway (hydroxylated products with higher toxicity), increasing the potential of Co@C-HMSMs for practical applications in antibiotic elimination.