title: Enhanced Photoreduction of Nitro-aromatic Compounds by Hydrated Electrons Derived from Indole on Natural Montmorillonite.
abstract: A new photoreduction pathway for nitro-aromatic compounds (NACs) and the underlying degradation mechanism are described. 1,3-Dinitrobenzene was reduced to 3-nitroaniline by the widely distributed aromatic molecule indole; the reaction is facilitated by montmorillonite clay mineral under both simulated and natural sunlight irradiation. The novel chemical reaction is strongly affected by the type of exchangeable cation present on montmorillonite. The photoreduction reaction is initiated by the adsorption of 1,3-dinitrobenzene and indole in clay interlayers. Under light irradiation, the excited indole molecule generates a hydrated electron and the indole radical cation. The structural negative charge of montmorillonite plausibly stabilizes the radical cation hence preventing charge recombination. This promotes the release of reactive hydrated electrons for further reductive reactions. Similar results were observed for the photoreduction of nitrobenzene. In situ irradiation time-resolved electron paramagnetic resonance and Fourier transform infrared spectroscopies provided direct evidence for the generation of hydrated electrons and the indole radical cations, which supported the proposed degradation mechanism. In the photoreduction process, the role of clay mineral is to both enhance the generation of hydrated electrons and to provide a constrained reaction environment in the galley regions, which increases the probability of contact between NACs and hydrated electrons.
authors.affiliation: †State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, P.R. China.
authors.forename: Haoting
authors.initials: H
authors.lastname: Tian
authors.affiliation: †State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, P.R. China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Guo
authors.affiliation: ‡Faculty of Environmental Science and Engineering, Kunming University of Science and Technology, Kunming 650500, P.R. China.
authors.forename: Bo
authors.initials: B
authors.lastname: Pan
authors.affiliation: †State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, P.R. China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Gu
authors.affiliation: §Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, Michigan 48824, United States.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.affiliation: §Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, Michigan 48824, United States.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Boyd
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates; D000814:Aniline Compounds / Q000737:chemistry; D001546:Bentonite / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D000077215:Clay; D004136:Dinitrobenzenes / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D004583:Electrons; D007211:Indoles / Q000737:chemistry; D008027:Light; D009574:Nitro Compounds / Q000737:chemistry*; D009578:Nitrobenzenes / Q000737:chemistry; D055668:Photochemical Processes; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D000538:Aluminum Silicates; D000814:Aniline Compounds; D002412:Cations; D004136:Dinitrobenzenes; D007211:Indoles; D009574:Nitro Compounds; D009578:Nitrobenzenes; D001546:Bentonite; C030374:indole; C403062:3-nitroaniline; C017906:3-dinitrobenzene; C036077:nitrobenzene; D000077215:Clay