Osmotic pressure as driving force for recovering ionic liquids from aqueous solutions

An emerging challenge occurs for recovering ionic liquids (ILs) because of their exponential growth in academic and industrial applications. We report for the first time to reclaim water-soluble ILs from their aqueous solutions by osmotically driving water to spontaneously permeate through semi-permeable membranes. Theoretical simulation indicates a weak hydrability of ILs and a tendency to form micelles in water. We thus demonstrate a significant difference in osmotic pressures between the aqueous solutions of ILs and inorganic salts. Four categories of broadly representative ILs are continuously recovered from their diluent aqueous solutions (~1  wt %) with semi-permeable membranes. Eventually, a record-high concentration up to 58–78  wt % is achieved in this work. Our strategy integrates superiorities of low energy consumption, universal applicability toward ILs, diversified selection of semi-permeable membranes, almost unattenuated water flux and high rejection to ions, hopefully providing new insights into the authentic “green” industrial applications of ILs.