Membrane-based strategy for purification of ionic liquids from aqueous solutions enabled by polarity-controlled selective superwettability

Efficient technologies to purify ionic liquids (ILs) from aqueous mixtures are urgently needed for the increasing demand for environmentally-friendly solvents. However, current IL separation methods are often characterized by low-flux, energy-intensive processes or complex separation procedures. Here we develop a novel polarity-controlled superwetting membrane-based separation strategy by introducing a water-structuring salt and modifying the membrane surface with medium-polar molecule. As the Hofmeister effect of water-structuring salt, higher-polarity water/salt structure forms, which can concurrently weaken the interactions between water with the medium-polar porous membrane and medium-polar ILs. Thus, ILs can selectively interact with the porous membrane and be transported while water/salt mixture being effectively blocked. This newly-developed membrane-based separation method demonstrates exceptional separation efficiency and flux, recyclability, and self-cleaning for various water-soluble IL/water systems. Moreover, it can be applied without any additional energy input, thus presenting a novel concept in functional liquid separation and holding the potential for the development of eco-friendly industrial processes.