title: Mechanism study of humic acid functional groups for Cr(VI) retention: Two-dimensional FTIR and13C CP/MAS NMR correlation spectroscopic analysis.
abstract: Undissolved humic acid (HA) is known to substantially effect the migration and transformation of hexavalent chromium [Cr(VI)] in soils. The mechanisms of Cr(VI) retention in soils by undissolved HA have been reported; however, past studies are inconclusive about the types of HA functional groups that are involved in Cr(VI) retention and the retention mechanisms. Utilizing a two-dimensional correlation spectroscopy (2DCOS) analysis for FTIR and13C CP/MAS NMR, this study investigated the variations of HA function groups and molecular structures after reactions with aqueous Cr(VI) under different pH conditions. Based on the changing sequence of functional groups interpreted from the 2DCOS results, a four-step mechanism for Cr(VI) retention was determined as follows: (1) electrostatic adsorption of Cr(VI) to HA surface, (2) complexation of adsorbed Cr(VI) by carboxyl and ester, (3) reduction of complexed Cr(VI) to Cr(III) by phenol and polysaccharide, and (4) complexation of reduced Cr(III) by carboxylic groups. These functional groups that are involved in Cr(VI) retention were determined to occur in aromatic domains.
authors.affiliation: Beijing Key Laboratory of Water Resources & Environmental Engineering, China University of Geosciences, Beijing 100083, China.
authors.forename: Jia
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Beijing Key Laboratory of Water Resources & Environmental Engineering, China University of Geosciences, Beijing 100083, China.
authors.forename: Linpeng
authors.initials: L
authors.lastname: Chen
authors.affiliation: Beijing Key Laboratory of Water Resources & Environmental Engineering, China University of Geosciences, Beijing 100083, China.
authors.forename: Huilin
authors.initials: H
authors.lastname: Yin
authors.affiliation: Department of Civil and Architectural Engineering, University of Wyoming, 1000 East University Avenue, Laramie, WY 82071, USA.
authors.forename: Song
authors.initials: S
authors.lastname: Jin
authors.affiliation: Beijing Key Laboratory of Water Resources & Environmental Engineering, China University of Geosciences, Beijing 100083, China. Electronic address: feiliu@cugb.edu.cn.
authors.forename: Fei
authors.initials: F
authors.lastname: Liu
authors.affiliation: Beijing Key Laboratory of Water Resources & Environmental Engineering, China University of Geosciences, Beijing 100083, China.
authors.forename: Honghan
authors.initials: H
authors.lastname: Chen
mesh_terms: D000327:Adsorption; D002857:Chromium / Q000032:analysis / Q000737:chemistry*; D006812:Humic Substances / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D012987:Soil; D017550:Spectroscopy, Fourier Transform Infrared; D014867:Water; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*; D018508:Water Purification / Q000379:methods
chemical_list: D006812:Humic Substances; D012987:Soil; D014874:Water Pollutants, Chemical; D014867:Water; D002857:Chromium; C074702:chromium hexavalent ion
keywords: 2DCOS; Adsorption; Complexation; Hexavalent chromium; Humus