In this study, the photogeneration of reactive oxygen species (ROS) from biochar suspension was investigated. The characterizations of biochar particles before and after photochemical reactions were analyzed by using FTIR, Raman, XPS and electron paramagnetic resonance (EPR) techniques. It was found that the model pollutant diethyl phthalate (DEP) was efficiently degraded and partially mineralized under UV and simulated solar lights in biochar suspension, with hydroxyl radicals ((OH)-O-center dot) and singlet oxygen (O-1(2)) as the dominant ROS. EPR coupled with chemical probe methods and free radical quenching studies were used to quantify and elucidate the formation mechanism of (OH)-O-center dot and O-1(2). The results indicated that biochar carbon matrix (BCM) accounted for 63.6%-74.6% of center dot OH and 10%-44.7% of O-1(2) formation, while dissolved organic matter (DOM) derived from biochar generated 46.7%-86.3% of O-1(2) and 3.7%-12.5% of "0H. BCM-bound persistent free radicals (BCM-PFRs) and quinone-like structure of BCM (BCM-Q) were the predominant factors affecting (OH)-O-center dot and O-1(2) formation from BCM under light. Detailed ROS generation pathways are proposed as: (i) DOM from biochar particles contributes to (OH)-O-center dot and O-1(2) formation via light-induced energy and electron transfer processes; (ii) BCM-Qforms excited triplet states ((3)[BCM-Q]*) under light irradiation and induces the formation O-1(2); (iii) UV promotes the formation of BCM-PFRs, which transfer electrons to oxygen to form superoxide anion radical (O-2(center dot-)), further yielding H2O2; and (iv) H2O2-dependent pathways including BCM-PFRs activation and photo-Fenton reaction are primarily responsible for (OH)-O-center dot production. Furthermore, BCM exhibits the excellent reusability towards DEP degradation during the three cycles under light. (C) 2017 Elsevier B.V. All rights reserved.