Recent progress of hygroscopy of ionic liquids

Abstract

Most ionic liquids can absorb some water when exposed to air. Water has a certain degree of influence on the microstructure and physio-chemical properties of ionic liquids,and further affecting the application of ionic liquids,thus it is necessary to carry out compenhensive study on the hygroscopy of ionic liquids. We reviewed the recent progress on this topic. Based on the hydrogency of more than 50 kinds of ionic liquids we reviewed the effects of structure factor of ionic liquids and external factors such as temperature and humidity. Also mechanism of sorption as well as three kinds of parameters derived for characterization the absorption process were reviewed. The hygroscopy of ionic liquids was proposed to classify into four levels. For a deeper understanding of the sorption of ionic liquids,we further reviewed the intermolecular interactions of ionic liquids and water,and the method for predicting the sorption ability of ionic liquids according to the solvochromatic parameters of ionic liquids. Then,we used two-dimensional correlation spectroscopy to study the dynamical process of water sorption of ionic liquids and discoved theat the sorption process can be divided into several stages by the intermolecular forces. Finally,according to phase law,we proposed to adjust the relative humidity with two phases systems of hydrophobic ionic liquid with water. Since acetate ion liquid has strong water sorption ability,it can be used as the absorbent under certain conditions.