Adsorption Of Hydrophilic Imidazolium-based Ionic Liquids On Clay Minerals

A growing concern for the environmental and biological effects of ionic liquids (ILs) has accompanied their increasing use. Assessing the environmental risks posed by ILs necessitates better understanding of their sorption behavior on natural matrices.We compared the sorption behavior of a model imidazolium-based IL, l-butyl-3-methylimidazolium chloride (Bmim Cl), on three popular clay minerals:Na-montmorillonite (Na-MMT), Na-illite, and Na-kaolinite. The impact factors in the sorption and desorption progresses include contacting time, ionic strength, pH of the system and initial concentrations of IL. The distribution coefficient of Bmim on Na-MMT is about a magnitude higher than those on Na-illite and Na-kaolinite under the same conditions, indicating that MMT significantly contributes to the retention of imidazolium-based ILs in the environment. X-ray diffraction (XRD) and thermogravimetric analysis indicate that cation exchange reaction occurs in the interlayer space of Na-MMT, thereby forming a monolayer of non-hydrated Bmim cations that are thermally stabilized by MMT. The XRD study of sorption kinetics suggests that a process complementary to cation exchange reaction occurs most likely on edge sites; the driving forces for such process are Van der Waals forces, electrostatic attraction, hemimicelle formation, and hydrogen bonding. Blue shifts of the C-H stretching vibration of sorbed Bmim suggest the weakening of cohesion between Bmim and Cl-during sorption. The sorption kinetics studied by Fourier transform infrared spectroscopy suggests that the chemical environments of Bmim during cation exchange and complementary sorption on edge sites are similar.Furthermore, we also studied the sorption behavior of1-hexyl-3-methylimidazolium chloride (HmimCl) and1-Octyl-3-methylimidazolium chloride (OmimCl) on MMT using the same method and compared the three ILs. The results shows that there are more hemimicelle with the longer side chains which could affect the sorption kinetics and the shape of isotherms.A growing concern for the environmental and biological effects of ionic liquids (ILs) has accompanied their increasing use. Assessing the environmental risks posed by ILs necessitates better understanding of their sorption behavior on natural matrices.