title: Spectroscopic characterization of the complexes between Fe/Mn and natural organic matters by electron paramagnetic resonance and synchrotron-based techniques.
abstract: The surface interaction between heavy metals and natural organic matters (NOM) substantially affects their migration and conversion in natural environments. In this study, the chemical speciation and element mapping of Fe and Mn in reduced NOM were investigated. The results show that quinone and semiquinone moieties dominated the redox properties in NOM, and the EPR signal intensity exhibited pH dependence with an increase of EPR signal intensity at a higher pH value. The EPR results indicate that the complexes displayed the characteristics of superparamagnetic oxides/oxyhydroxides after Fe/Mn complexed with NOM. μ-XRF results suggest that the scatterplots of Fe and Mn distributions at pH 11 had the most positive linearly-related plot points, indicating strong correlations for Mn-Fe binary metallic ions. μ-XANES results further interpret the presence of higher Mn oxidation state at pH 11, while Fe kept trivalent in all samples. These results reveal that the surface interactions are closely related to the redox state of NOM and are beneficial for better understanding the speciation, immobilization, transport, and toxicity of metal ions in natural waters.
authors.affiliation: CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China.
authors.forename: Hong-Wei
authors.initials: HW
authors.lastname: Luo
authors.affiliation: CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China.
authors.forename: Zhi-Qi
authors.initials: ZQ
authors.lastname: Lin
authors.affiliation: CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China. gpsheng@ustc.edu.cn.
authors.forename: Guo-Ping
authors.initials: GP
authors.lastname: Sheng
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D004784:Environmental Monitoring; D006812:Humic Substances / Q000032:analysis*; D007501:Iron / Q000032:analysis*; D008345:Manganese / Q000032:analysis*; D013052:Spectrometry, X-Ray Emission; D014874:Water Pollutants, Chemical / Q000032:analysis*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D006812:Humic Substances; D014874:Water Pollutants, Chemical; D008345:Manganese; D007501:Iron
keywords: Electron paramagnetic resonance (EPR); Heavy metals; Natural organic matters (NOM); X-ray absorption near edge structure (μ-XANES); X-ray fluorescence mapping (μ-XRF)