Different peroxymonosulfate activation and utilization pathways of typical cobalt oxides, cobalt-carbon and carbonaceous composites derived from metal-organic frameworks for pollutant oxidation in wastewater

Cobalt-based persulfate activation system has attracted increasing interests in recent years. However, few studies have focused on the corresponding relationship between different types of catalysts and peroxymonosulfate (PMS) utilization pathway in PMS activation process. To unravel this, three typical cobalt-based catalysts derived from ZIF materials (metal oxides ZMs, metal–carbon composite ZMCs, and etching metal–carbon composite ZCs) were applied in PMS activation system, and acetaminophen (APAP) was used as target contaminant. Quenching experiments and electron paramagnetic resonance (EPR) investigation testified that SO4·− were considered as the dominant reactive oxygen species (ROS) in the ZMs/PMS system, whereas non-radical pathway was dominant in the ZMCs/PMS and ZCs/PMS system. More Co-N species in ZMCs promoted the adsorption of PMS molecules and the formation of metastable PMS-catalyst complex. Electrochemical analysis proved that the improved intrinsic redox potential of metastable PMS-catalyst complex was due to the strong combination of PMS with positively charged Co-N species, resulting in the mass consumption of PMS. In addition, the CoⅣ=O species were mainly generated from single atomic Co or encapsulated Co sites in ZMCs and ZCs. Major degradation intermediates of APAP were detected by liquid chromatograph mass spectrometer (LC-MS) and differences in degradation pathway in three reaction systems were proposed. This study provides new insight into the PMS utilization mechanism during PMS activation process and offered environmentally friendly catalytic process for the degradation of pharmaceutical contaminants in wastewater.