Deep eutectic solvents - A new platform in membrane fabrication and membrane-assisted technologies

Deep eutectic solvents (DESs) are a new class of solvents that can offset some of the primary drawbacks of typical solvents and ionic liquids (ILs). Since DESs fall into the guidelines of "Twelve Principles of Green Chemistry", their implementation in several types of applications has exponentially increased over the last years. The usage of DESs has been directed to the designing, manufacture and purification of new materials and feedstocks. Very recently, great attention has been paid to new pioneering attempts aiming at DESs into the field of chemical engineering, including membrane science and technology. Even if just a few works have been currently reported in applying DESs in membranes, the consideration on this new type of solvents is continuously growing. This review compares and discusses the documented discoveries and breakthroughs carried out in applying DESs in membrane science. The scope of this review is emphasized in various scopes: i) new sustainable membrane preparation, ii) membrane-based technologies aided by DESs, iii) target molecules-DES interactions and iv) new membrane-DES structures providing enhanced physicochemical properties and thus separation performance. Here, besides the relevant insights in the field, we give the key hypotheses and strategies used by the scientists to reach a successful merging of both areas since the use of DESs in membranes is still challenging due to the compatibility issues of the DESs and membrane phase (either polymer and inorganic). The future directions and perspectives on using DESs in membranes are also given.