Applications of tetrabutylphosphonium-based ionic liquids: A state-of-the-art review

Phosphonium-based ionic liquids are considered superior over others imidazolium- and pyridinium-based ionic liquids (ILs) due to their stability, availability and low cost. Among phosphonium ILs, tetrabutylphosphonium (TBP)-based ILs exhibit exciting properties which make them potential candidate for academic and industrial applications. The most influential characteristics of TBP-based ILs are excellent thermal and chemical stability, affordability, faster rate, high polarity and viscosity. Their misibility with water make them even more attractive as solvents for dissolution of recalcitrant structures, enzymatic hydrolysis and extraction of biomolecules. In electrochemistry, high conductivities and wide electrochemical window make them credible electrolyte material in supercapacitor batteries. Additionally, they are slowly gaining the ground of conventional organic solvents and catalysts as greener alternatives. The most significant application of TBP-based ILs is CO 2 absorption, the proton-donating capacity of TBP cation allows the stable ylide formation and facilitates the CO 2 sorption. All in all, the outstanding physiochemical properties and applications of TBP-based ILs provide fundamental understanding of these ILs with future rational design to explore them further in many different industrial, chemical and biological fields.