Transforming radical to non-radical pathway in peroxymonosulfate activation on nitrogen doped carbon sphere for enhanced removal of organic pollutants: Combined effect of nitrogen species and carbon structure

Carbon induced non-radical based peroxymonosulfate (PMS) activation has exhibited several advantages over radical process for eliminating organic pollutants in complicated water matrices. However, the relationship between configuration and composition of carbon and non-radical mechanism, which is important for designing high-efficiency carbon catalysts, remains elusive. In this work, the nitrogen doped carbon spheres (NCSs) with superior PMS activation ability were prepared from low-cost chitosan via two-step hydrothermal carbonization-pyrolysis method for organic pollutants removal. The carbon structure and nitrogen species of NCSs were tuned via changing hydrothermal temperature to explore their correlation with their PMS catalytic mechanism. Results showed hydrothermal carbonization boosted the content of pyridinic N, graphitic N and sp2-hybrided carbon (CC) in NCS, which significantly enhanced its catalytic performance and collaboratively promoted the catalytic mechanism switch from radical-dominant (SO4•- and •OH) to non-radical-dominant (surface-mediated electron transfer (SMET) and 1O2) process. The NCS with most pyridinic N and CC performed best, whose catalytic activity was 10.4 times higher than that without hydrothermal carbonization. The pyridinic N and CC enhanced the SMET process through strengthening PMS adsorption capacity and facilitating the electron migration from pollutant to PMS, respectively, while graphitic N triggered PMS oxidation on its neighboring electron-deficient C to produce 1O2.