The activation of PMS for PFOA degradation by adjustable metal stripping Fe/Co/N@BC catalysts: Degradation performance with single-line oxygen and high-valent metal oxides as the main active substances

In this study, a modified biochar (P-Fe/Co/N@BC) catalyst was prepared with wood chips as raw material by hydrothermal method for the activation of peroxymonosulfate (PMS) and degradation of perfluorooctanoic acid (PFOA). Scanning electron microscopy (SEM), x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) characterization methods were used to demonstrate the presence of FeNx, CoNx, Fe-Co and CO active sites, which contribute to the improvement of the PMS activation capacity for single-line oxygen (1O2). Electron paramagnetic resonance spectroscopy (EPR), reactive oxygen species (ROS) scavenging experiments and methyl phenyl sulfoxide (PMSO) conversion experiments were performed to clarify the main mechanisms of PFOA degradation by reactive species. Further, 1O2, sulfate radical (SO4−), hydroxyl radical (OH), high-valent metal oxides (Fe(IV) and Co(IV)) were jointly involved in the degradation of PFOA, and nonradical were the main activation pathway of PMS. In particular, Fe3+ decomposed from Fe(IV) in the presence of Fe0 and Co2+ decomposed from Co(IV) are able to enhance iron cycling and cobalt cycling, respectively. Meanwhile, Co0 accelerates the conversion of Co3+ to Co2+. The findings suggested that the removal rate of the P-Fe/Co/N@BC-PMS system (99 %) was much higher than that of the P-Fe-N-C/PMS (68.9 %) over 180 min. It emphasized that the incorporation of PTFE (polytetrafluoroethylene) can regulate metal leaching significantly and improve the cycling stability of the catalysts. This study aimed to prepare efficient and stable modified biochar catalysts to activate PMS, which provided an effective solution to the problem of metal ion leaching from metal-modified biochar materials.