title: Modification of a Ca-montmorillonite with ionic liquids and its application for chromate removal.
abstract: Ionic liquids (ILs), due to their low vapor pressure, have been explored as green solvents for organic synthesis. In this study, the uptake of ILs on a high charge Ca-montmorillonite (MMT) and the use of the IL-modified MMT for the removal of anionic contaminants from water were systematically studied. Uptake of ILs by MMT was exclusively resulted from a cation exchange mechanism when the initial IL concentrations were less than the critical micelle concentration (CMC) and the sorbed ILs formed a monolayer conformation on the surface of MMT. When the initial IL concentrations were greater than the CMC, both cation exchange and hydrophobic interactions were responsible for the IL uptake. The IL molecules formed admicelles and the surface charge was reversed to positive balanced by counterion Cl(-) when the IL loading was higher than the cation exchange capacity of the mineral. The modified MMT could remove chromate from water instantaneously, with an adsorption capacity of 190 mmol/kg and a 99.5% removal efficiency at an initial chromate concentration of 2.6 mmol/L. These features could further expand the application of ILs and enable IL-modified MMT to be used as inexpensive sorbents for the removal of chromate and other oxyanions from water.
authors.affiliation: School of Materials Science and Technology, China University of Geosciences, Beijing 100083, China; Department of Earth Sciences, National Cheng Kung University, Tainan 70101, Taiwan; Geosciences Department, University of Wisconsin-Parkside, Kenosha, WI 53144, USA. Electronic address: li@uwp.edu.
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Li
authors.affiliation: Department of Earth Sciences, National Cheng Kung University, Tainan 70101, Taiwan.
authors.forename: Wei-Teh
authors.initials: WT
authors.lastname: Jiang
authors.affiliation: Department of Earth Sciences, National Cheng Kung University, Tainan 70101, Taiwan.
authors.forename: Po-Hsiang
authors.initials: PH
authors.lastname: Chang
authors.affiliation: School of Materials Science and Technology, China University of Geosciences, Beijing 100083, China.
authors.forename: Guocheng
authors.initials: G
authors.lastname: Lv
authors.affiliation: Department of Geosciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53201, USA.
authors.forename: Shangping
authors.initials: S
authors.lastname: Xu
mesh_terms: D000327:Adsorption; D001546:Bentonite / Q000737:chemistry*; D002840:Chromates / Q000737:chemistry*; D007474:Ion Exchange; D052578:Ionic Liquids / Q000737:chemistry*; D017680:Potassium Compounds / Q000737:chemistry*; D013499:Surface Properties; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods
chemical_list: D002840:Chromates; D052578:Ionic Liquids; D017680:Potassium Compounds; D014874:Water Pollutants, Chemical; D001546:Bentonite; C027373:potassium chromate(VI)
keywords: Adsorption; Anion exchange; Contaminants; Ionic liquid; Water treatment