Efficient Activation of Low Concentrations of Peroxymonosulfate with Nanoconfined Co₃O₄ in Hollow Mesoporous Silica 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, kobs = 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 f0 (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.