Tuning the physicochemical properties of diverse phenolic ionic liquids for equimolar CO ₂ capture by the substituent on the anion

Phenolic ionic liquids for the efficient and reversible capture of CO ₂ were designed and prepared from phosphonium hydroxide and substituted phenols. The electron-withdrawing or electron-donating ability, position, and number of the substituents on the anion of these ionic liquids were correlated with the physicochemical properties of the ionic liquids. The results show that the stability, viscosity, and CO ₂-capturing ability of these ionic liquids were significantly affected by the substituents. Furthermore, the relationship between the decomposition temperature, the CO ₂-absorption capacity, and the basicity of these ionic liquids was quantitatively correlated and further rationalized by theoretical calculation. Indeed, these ionic liquids showed good stability, high absorption capacity, and low absorption enthalpy for CO ₂ capture. This method, which tunes the physicochemical properties by making use of substituent effects in the anion of the ionic liquid, is important for the design of highly efficient and reversible methods for CO ₂-capture. This CO ₂ capture process using diverse phenolic ionic liquids is a promising potential method for CO ₂ absorption with both high absorption capacity and good reversibility.