Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Ministry of Education, College of Environment, Hohai University, Nanjing 210093, China; Key Laboratory of Environmental Engineering of Jiangsu Province, Jiangsu Provincial Academy of Environmental Science, Nanjing 210036, China; State Key Laboratory of Pollution Control and Resource Reuse, Nanjing University, Nanjing 210023, China; Central Environmental Laboratory, Natural Resources and Environment Research Institute, Ministry of Natural Resources and Environment, Vientiane 999012, Laos
guoyong@hhu.edu.cn, guoyinghhu@163.com
Abstract: We investigated the influence mechanism of N-doping for dissolved black carbon (DBC) photodegradation of organic pollutants. The degradation performance of N-doped dissolved black carbon (NDBC) for tetracycline (TC) (71%) is better than that for methylene blue (MB) (28%) under irradiation. These levels are both better than DBC degradation performances for TC (68%) and MB (18%) under irradiation. Reactive species quenching experiments suggest that h+ and ⋅O2- are the main reactive species for NDBC photodegraded TC, while ·OH and h+ are the main reactive species for NDBC photodegraded MB. ·OH is not observed during DBC photodegradation of MB. This is likely because N-doping increases valence-band (VB) energy from 1.55 eV in DBC to 2.04 eV in NDBC; the latter is strong enough to oxidize water to form ·OH. Additionally, N-doping increases the DBC band gap of 2.29 to 2.62 eV in NDBC, resulting in a higher separation efficiency of photo-generated electrons-holes in NDBC than in DBC. All these factors give NDBC stronger photodegradation performance for TC and MB than DBC. High-performance liquid chromatography-mass spectrometry (HPLC-MS) characterization and toxicity evaluation with the quantitative structure-activity relationship (QSAR) method suggest that TC photodegradation intermediates produced by NDBC have less aromatic structure and are less toxic than those produced by DBC. We adopted a theoretical approach to clarify the relationship between the surface groups of NDBC and the photoactive species produced. Our results add to the understanding of the photochemical behavior of NDBC.
Key words: Dissolved black carbon (DBC); N-doping; Organic pollutants; Band gap; Photodegradation
Chinese Summary <14> 掺杂氮元素使溶解性黑碳对有机污染物具有更高的光降解性能:实验和理论研究