• amino acids;
  • carbon dioxide capture;
  • ionic liquids;
  • phosphorus;
  • physicochemical properties


Thumbnail image of graphical abstract

CO2is locked up: Dual amino-functionalised phosphonium ionic liquids (ILs; see figure) have been prepared. The ILs have excellent thermal properties, such as low glass transition temperatures and high thermal decomposition temperatures. The supported CO2 absorption of four of the ILs on porous SiO2 was found to approach one mol CO2 per mol IL, a factor of two greater than that reported before.

A series of 20 dual amino-functionalised phosphonium ionic liquids, (3-aminopropyl)tributylphosphonium amino acid salts ([aP4443][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 [aP4443][AA] ionic liquids (ILs) have low glass transition temperatures ranging from −69.7 to −29.6 °C and high decomposition temperatures (all above 200 °C). The effects of the variation of the structure of [AA] on the above physicochemical properties are discussed. Furthermore, the CO2 absorption of [aP4443][Gly], [aP4443][Ala], [aP4443][Val] and [aP4443][Leu], taken as examples, was investigated. It was found that the supported absorption of CO2 by the [aP4443][AA] ILs almost reaches equilibrium within 80 min, the chemical absorption of CO2 by the [aP4443][AA] ILs approaches 1 mol CO2 per mol ionic liquid (twice that reported before) and the [aP4443][AA] ILs can be repeatedly recycled for CO2 uptake.