Dual amino-functionalised phosphonium ionic liquids for CO2 capture.

A series of 20 dual amino-functionalised phosphonium ionic liquids, (3-aminopropyl)tributylphosphonium amino acid salts ([aP(4443)][AA], in which [AA](-) = [Ala](-), [Arg](-), [Asn](-), [Asp](-), [Cys](-), [Gln](-), [Glu](-), [Gly](-), [His](-), [Ile](-), [Leu](-), [Lys](-), [Met](-), [Phe](-), [Pro](-), [Ser](-), [Thr](-), [Trp](-), [Tyr](-) and [Val](-)), has been prepared. Their physicochemical properties, such as density, viscosity, glass transition and thermal decomposition temperatures and conductivity, have been determined. In particular, the [aP(4443)][AA] ionic liquids (ILs) have low glass transition temperatures ranging from -69.7 to -29.6 degrees C and high decomposition temperatures (all above 200 degrees C). The effects of the variation of the structure of [AA](-) on the above physicochemical properties are discussed. Furthermore, the CO(2) absorption of [aP(4443)][Gly], [aP(4443)][Ala], [aP(4443)][Val] and [aP(4443)][Leu], taken as examples, was investigated. It was found that the supported absorption of CO(2) by the [aP(4443)][AA] ILs almost reaches equilibrium within 80 min, the chemical absorption of CO(2) by the [aP(4443)][AA] ILs approaches 1 mol CO(2) per mol ionic liquid (twice that reported before) and the [aP(4443)][AA] ILs can be repeatedly recycled for CO(2) uptake.