High performance of N-doped cobalt oxide (N-CoOx) for peroxymonosulfate activation: Unraveling the functional mechanism of Co-Nx sites at molecular level

Nitrogen (N)-doping has been reported effective to reinforce catalysis in advanced oxidation processes (AOPs) due to the formation of N-related active sites. Although several documents have reported that transition metal-nitrogen (metal-N x ) sites could work as reactive centers, the catalytic mechanism was hardly elucidated. In this study, N-doped cobalt oxide (N-CoO x ) was initiatively prepared via calcination in ammonia atmosphere to construct cobalt-nitrogen (Co-N x ) sites. The emergence of Co-N x sites effectively improved peroxymonosulfate (PMS) activation efficiency (above 5.8 times), leading to higher pollutant decomposition rate (95.8 % at 30 min) and kinetics constant (above 4.1 times). N introduction changed main facets of material and elevated adsorption energy (E ads ) (from −1.81 eV to −3.71 eV) between catalyst and PMS. Co atoms at Co-N x sites could donate larger quantity of electrons (from 1.088 e to 1.583 e) to PMS, therefore, contributed to stretching and breaking O–O bonds of PMS molecules to form reactive species. As a result, both radical and electron transfer pathway (ETP) were enhanced in the oxidation processes. Ultimately, the catalytic membrane coated with N-CoO x maintained 100 % treatment towards continuous antibiotic wastewater at environmentally relevant concentration (μg/L), realizing purification as well as separation of catalyst. This work systematically elaborates the superiority of Co-N x sites and unravels the underlying mechanism to inspire further study to metal-N x tailored catalysis.