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

• Synergistic effect of adsorption (24.5%) and catalytic ozonation (74.4%) by NBC700 promoted ATZ removal. • O 3 was in-situ decomposed into *O 2 and *O. • • OH was the dominant ROS and surface-O 3 further strengthened ozonation. • Defects were the major active sites verified by DFT calculation. Adsorption is the first step of the interface mechanism, but the adsorption behaviors of ozone (O 3 ) 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 O 3 to trigger surface reactive oxygen species (ROS) by nitrogen (N)-doped biochar was proposed, which greatly improved the efficiency of O 3 utilization. Specifically, N-doped biochar (NBC700) with a high defect level ( I D /I G = 1.165) was achieved by a one-pot method. It showed good adsorption on O 3 and atrazine (ATZ), which promoted the in-situ formation of surface ROS, as well as resists the interferences of multiple coexisting anions (NO 3 - , Cl - , PO 4 3- , SO 4 2- and HCO 3 - ) on ATZ removal. In-situ Raman spectra revealed the interface catalytic mechanism of O 3 decomposition into adsorbed peroxide species (*O 2 ) and adsorbed atomic oxygen (*O). Additionally, • OH was the dominant ROS and surface-O 3 further strengthened direct ozonation via intramolecular electron transfer. In this process, sp 2 -hybridized system with delocalized π 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.