title: Photochemistry of Dissolved Black Carbon Released from Biochar: Reactive Oxygen Species Generation and Phototransformation.
abstract: Dissolved black carbon (BC) released from biochar can be one of the more photoactive components in the dissolved organic matter (DOM) pool. Dissolved BC was mainly composed of aliphatics and aromatics substituted by aromatic C-O and carboxyl/ester/quinone moieties as determined by solid-state nuclear magnetic resonance. It underwent 56% loss of absorbance at 254 nm, almost complete loss of fluorescence, and 30% mineralization during a 169 h simulated sunlight exposure. Photoreactions preferentially targeted aromatic and methyl moieties, generating CH2/CH/C and carboxyl/ester/quinone functional groups. During irradiation, dissolved BC generated reactive oxygen species (ROS) including singlet oxygen and superoxide. The apparent quantum yield of singlet oxygen was 4.07 ± 0.19%, 2-3 fold higher than many well-studied DOM. Carbonyl-containing structures other than aromatic ketones were involved in the singlet oxygen sensitization. The generation of superoxide apparently depended on electron transfer reactions mediated by silica minerals in dissolved BC, in which phenolic structures served as electron donors. Self-generated ROS played an important role in the phototransformation. Photobleaching of dissolved BC decreased its ability to further generate ROS due to lower light absorption. These findings have significant implications on the environmental fate of dissolved BC and that of priority pollutants.
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University , Nanjing, Jiangsu 210023, China.
authors.forename: Heyun
authors.initials: H
authors.lastname: Fu
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University , Nanjing, Jiangsu 210023, China.
authors.forename: Huiting
authors.initials: H
authors.lastname: Liu
authors.affiliation: Department of Chemistry and Biochemistry, Old Dominion University , Norfolk Virginia 23529, United States.
authors.forename: Jingdong
authors.initials: J
authors.lastname: Mao
authors.affiliation: Department of Chemistry and Biochemistry, Old Dominion University , Norfolk Virginia 23529, United States.
authors.forename: Wenying
authors.initials: W
authors.lastname: Chu
authors.affiliation: Department of Civil and Environmental Engineering, Rice University , Houston Texas 77005, United States.
authors.forename: Qilin
authors.initials: Q
authors.lastname: Li
authors.affiliation: Department of Civil and Environmental Engineering, Rice University , Houston Texas 77005, United States.
authors.forename: Pedro J J
authors.initials: PJ
authors.lastname: Alvarez
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University , Nanjing, Jiangsu 210023, China.
authors.forename: Xiaolei
authors.initials: X
authors.lastname: Qu
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University , Nanjing, Jiangsu 210023, China.
authors.forename: Dongqiang
authors.initials: D
authors.lastname: Zhu
mesh_terms: D002244:Carbon / Q000737:chemistry; D002606:Charcoal / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D038761:Photobleaching; D055668:Photochemical Processes; D017382:Reactive Oxygen Species / Q000737:chemistry*; D031787:Sasa; D026082:Singlet Oxygen / Q000737:chemistry; D053260:Soot / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry
chemical_list: D017382:Reactive Oxygen Species; D053260:Soot; D014874:Water Pollutants, Chemical; C540010:biochar; D002606:Charcoal; D026082:Singlet Oxygen; D002244:Carbon