Identifying the photoproduction sites of reactive oxygen species in dissolved black carbon: A remarkable role of oxygenated functional groups

Dissolved black carbon (DBC) can generate reactive oxygen species (ROS), playing significant roles in contaminants degradation and chemical stresses to microorganisms. However, little is known regarding the photoproduction sites to ROS generation, mainly because of its extremely complicated composition. Herein, the ROS generation and photoexcited alteration of DBC were investigated. The generation mechanisms of hydroxyl radical (center dot OH), superoxide anion (O-2(center dot-)), and singlet oxygen (O-1(2)) were inferred by employing various model chemicals. Results showed that the photo-excited aliphatic carbonyls greatly contributed to center dot OH, O-2(center dot-), and O-1(2) generation. Ether groups were identified as the main structural source of H2O2-dependent center dot OH generation. The novel non-electron transfer process involved carbonyl, ether, alcohol, and ester groups to produce O-2(center dot-) was proposed. These findings reveal the vital role of oxygenated functional groups within DBC in the photoactive generation of ROS, and thus provides new theoretical information for DBC's environmental geochemical behavior.