We report results of theoretical evaluation of the mechanisms of possible radical reactions on the edge-site of biochar with CO2 center dot-, O(H) over dot, and (H) over dot in irradiated aqueous solution. The computational studies were performed for model poly aromatic systems. Obtained mechanisms reflect one of the routes of the oxygen loss accompanied by increase of hydrogen content, as observed in photochemical experiment. The reaction of CO2 center dot- with the edge site of biochar mainly leads to reduced rather than oxidized products. The mechanism of CO2 capturing is mapped by different routes of one-electron reduction and radical addition to the aromatic ring. (C) 2017 Elsevier B.V. All rights reserved.