title: Solid surface photochemistry of montmorillonite: mechanisms for the arsenite oxidation under UV-A irradiation.
abstract: Transformation of inorganic arsenic species has drawn great concern in recent decades because of worldwide and speciation-dependent pollution and the hazards that they pose to the environment and to human health. As(III) photooxidation in aquatic systems has received much attention, but little is known about photochemical transformation of arsenic species on top soil. As(III) photooxidation on natural montmorillonite under UV-A radiation was investigated by using a moisture- and temperature-controlled photochemical chamber with two black-light lamps. Initial As(III) concentration, pH, layer thickness, humic acid (HA) concentration, the presence of additional iron ions, and the contribution of reactive oxygen species (ROS) were examined. The results show that pH values of the clay layers greatly influenced As(III) photooxidation on montmorillonite. As(III) photooxidation followed the Langmuir-Hinshelwood model. HA and additional iron ions greatly promoted photooxidation, but excess Fe(II) competed with As(III) for oxidation by ROS. Scavenging experiments revealed that natural montmorillonite induced the conversion of As(III) to As(V) by generating ROS (mainly HO(•) and HO2(•)/O2(•-)) and that HO(•) radical was the predominant oxidant in this system. Our work demonstrates that photooxidation on the surface of natural clay minerals in top soil can be important to As(III) transformation. This allows understanding and predicting the speciation and behavior of arsenic on the soil surface.
authors.affiliation: Department of Environmental Science, Hubei Key Lab of Biomass Resource Chemistry and Environmental Biotechnology, School of Resources and Environmental Science, Wuhan University, Wuhan, 430079, People's Republic of China.
authors.forename: Yanan
authors.initials: Y
authors.lastname: Yuan
authors.affiliation: Department of Environmental Science, Hubei Key Lab of Biomass Resource Chemistry and Environmental Biotechnology, School of Resources and Environmental Science, Wuhan University, Wuhan, 430079, People's Republic of China.|School of Chemistry and Environmental Science, Guizhou Minzu University, Guiyang, 550025, People's Republic of China.
authors.forename: Yajie
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Environmental Science, Hubei Key Lab of Biomass Resource Chemistry and Environmental Biotechnology, School of Resources and Environmental Science, Wuhan University, Wuhan, 430079, People's Republic of China.
authors.forename: Wei
authors.initials: W
authors.lastname: Ding
authors.affiliation: Department of Environmental Science, Hubei Key Lab of Biomass Resource Chemistry and Environmental Biotechnology, School of Resources and Environmental Science, Wuhan University, Wuhan, 430079, People's Republic of China. ljj0410@163.com.
authors.forename: Jinjun
authors.initials: J
authors.lastname: Li
authors.affiliation: Department of Environmental Science, Hubei Key Lab of Biomass Resource Chemistry and Environmental Biotechnology, School of Resources and Environmental Science, Wuhan University, Wuhan, 430079, People's Republic of China. fengwu@whu.edu.cn.
authors.forename: Feng
authors.initials: F
authors.lastname: Wu
mesh_terms: D001151:Arsenic / Q000378:metabolism; D018053:Arsenites / Q000378:metabolism*; D001546:Bentonite / Q000737:chemistry*; D006812:Humic Substances; D007501:Iron; D008903:Minerals; D016877:Oxidants; D010084:Oxidation-Reduction / Q000528:radiation effects; D010777:Photochemistry; D014466:Ultraviolet Rays
chemical_list: D018053:Arsenites; D006812:Humic Substances; D008903:Minerals; D016877:Oxidants; D001546:Bentonite; D007501:Iron; C015001:arsenite; D001151:Arsenic
keywords: Arsenite; Hydroxyl radical; Montmorillonite; Photooxidation; Solid surface; Top soil