Structural tuning of multishelled hollow microspheres for boosted peroxymonosulfate activation and selectivity: Role of surface superoxide radical

Herein, a multi-shelled hollow micro-reactor with tunable shell number, thickness and porosity is constructed by nanosized Co₃O₄ to catalyze peroxymonosulfate (PMS) for the first time. Triple-shelled hollow microspheres (TS-HM) exhibit superior catalytic activity with the degradation rate of 0.4158 min⁻¹, which is 22, 5.8, 1.9 times of that of solid nanoparticles, quadruple-shelled hollow microspheres (QS-HM), and double-shelled hollow microspheres (DS-HM), respectively. Such an outstanding performance of TS-HM is attributed to more exposed active sites, strong capacity of Co^II regeneration and desired structure stability. Furthermore, the selectivity of 2-cholorophenol (2-CP) over humic acid (HA) is optimized by tuning shell thickness and porosity. The thick shell and narrow pore size are recognized as the dominant contributors based on size exclusion effects. Significantly, mechanistic studies reveal that O₂^·− is generated on the catalyst surface via O₂ adsorption and reduction by oxygen vacancies, and plays an important role for Co^II regeneration.