Photogeneration of Reactive Species from Biochar-Derived Dissolved Black Carbon for the Degradation of Amine and Phenolic Pollutants

Due to agricultural waste combustion and large-scale biochar application, biochar-derived dissolved black carbon (DBC) is largely released into surface waters. The photogeneration of reactive species (RS) from DBC plays an important role in organic pollutant degradation. However, the mechanistic interactions between RS and pollutants are poorly understood. Here, we investigated the formation of DBC triplet states (³DBC*), singlet oxygen (¹O₂), and hydroxyl radical (^•OH) in straw biochar-derived DBC solutions and photodegradation of typical pharmaceuticals and personal care products (PPCPs). Laser flash photolysis and electron spin resonance spectrometry showed that DBC exhibited higher RS quantum yields than some well-studied dissolved organic matter. The RS caused rapid degradation of atenolol, diphenhydramine, and propylparaben, selected as target PPCPs in this study. The ³DBC* contributed primarily to the oxidation of selected PPCPs via one-electron-transfer interaction, with average reaction rate constants of 1.15 × 10⁹, 1.41 × 10⁹, and 0.51 × 10⁹ M^-1 s^-1, respectively. ^•OH also participated in the degradation and accounted for approximately 2.7, 2.5, and 18.0% of the total removal of atenolol, diphenhydramine, and propylparaben, respectively. Moreover, the photodegradation products were identified using high-resolution mass spectrometry, which further confirmed the electron transfer and ^•OH oxidation mechanisms. These findings suggest that DBC from the combustion process of agricultural biomass can efficiently induce the photodegradation of organic pollutants under sunlight in aquatic environments.