Development of thermomorphic ionic liquids derived from organophosphorus acids for homogeneous extraction processes

The objective of this study is to develop ionic liquids (ILs) derived from organophosphorus acids, featuring thermomorphic phase behavior tailored for homogeneous liquid–liquid extraction applications, addressing the challenges posed by the high viscosity of ILs. The novelty of our work includes a logP-based guideline for designing thermomorphic water/organophosphorus IL solvent systems and a proof-of-concept study on homogeneous liquid–liquid extraction applications. Specifically, we reported a series of novel ILs exhibiting lower critical solution temperature behavior in aqueous solutions by exploring various combinations of tetraalkylammonium cations with organophosphorus acid-based anions. Practical applications utilizing this type of thermomorphic solvent system for extracting metal ions and acids were demonstrated. The benefits of homogeneous extraction, as well as the limitations stemming from the salting-out effect, were presented and discussed.