In-situ formation of surface reactive oxygen species on defective sites over N-doped biochar in catalytic ozonation

Adsorption is the first step of the interface mechanism, but the adsorption behaviors of ozone (O3) and pollutants on the catalyst during catalytic ozonation have always been overlooked in previous works. In this study, a promising strategy for the in-situ decomposition of O3 to trigger surface reactive oxygen species (ROS) by nitrogen (N)-doped biochar was proposed, which greatly improved the efficiency of O3 utilization. Specifically, Ndoped biochar (NBC700) with a high defect level (ID/IG = 1.165) was achieved by a one-pot method. It showed good adsorption on O3 and atrazine (ATZ), which promoted the in-situ formation of surface ROS, as well as resists the interferences of multiple coexisting anions (NO3-, Cl-, PO43-, SO42- and HCO3- ) on ATZ removal. In-situ Raman spectra revealed the interface catalytic mechanism of O3 decomposition into adsorbed peroxide species (*O2) and adsorbed atomic oxygen (*O). Additionally, center dot OH was the dominant ROS and surface-O3 further strengthened direct ozonation via intramolecular electron transfer. In this process, sp2-hybridized system with delocalized pi electrons, electron-rich oxygen-containing functional groups, and conjugated heteroatoms were identified as the active sites, but defective sites with free electrons played the most important part according to the lowest adsorption energy (-13.12 eV) calculated by density functional theory (DFT). The degradation of ATZ included dechlorination and non-dechlorination pathways, which made the acute and chronic toxicity of most intermediate products both decrease to not be harmful to fish and green algae. This work provides a new perspective on the interface mechanism in catalytic ozonation for ATZ removal.