Unraveling the Co(IV)-Mediated Oxidation Mechanism in a Co3O4/PMS-Based Hierarchical Reactor: Toward Efficient Catalytic Degradation of Aromatic Pollutants

A metal (oxide)/peroxymonosulfate (PMS)-based hierarchical reactor has recently been developed as an emerging technology involving a heterogeneous advanced oxidation process for wastewater treatment. HO•, SO4•–, and 1O2 were regarded as predominant reactive oxidants that contributed to the degradation of pollutants in these reactors. However, the possible contribution of potentially generated high-valent metal to pollutant degradation in the reactor was rarely studied. Herein, we unraveled the Co(IV)-mediated oxidation mechanism in a Co3O4/PMS-based hierarchical reactor for the degradation of aromatic pollutants. The Co3O4/PMS-based hierarchical reactor demonstrated an efficient degradation of aromatic organic pollutants (>90%). Electron paramagnetic resonance characterization, radical quenching, and probe oxidation experiments confirmed that Co(IV) was the dominant reactive species in the Co3O4/PMS-based hierarchical reactor. Further scavenger experiments validated that Co(IV) played the most crucial role in the removal of the aromatic pollutant. The majority of Co(IV) originated from the immobilized Co3O4 rather than the leaching of Cox+ ions in the Co3O4/PMS-based hierarchical reactor. Our study revealed the critical role of high-valent metal species in the reactor for the degradation of aromatic pollutants, which will facilitate the understanding of mechanisms involved in heterogeneous metal (oxide)/PMS-based systems.