Reversible Hydrophobic-Hydrophilic Transition of Ionic Liquids Driven by Carbon Dioxide

Ionic liquids (ILs) with a reversible hydrophobic–hydrophilic transition were developed, and they exhibited unique phase behavior with H2O: monophase in the presence of CO2, but biphase upon removal of CO2 at room temperature and atmospheric pressure. Thus, coupling of reaction, separation, and recovery steps in sustainable chemical processes could be realized by a reversible liquid–liquid phase transition of such IL‐H2O mixtures. Spectroscopic investigations and DFT calculations showed that the mechanism behind hydrophobic–hydrophilic transition involved reversible reaction of CO2 with anion of the ILs and formation of hydrophilic ammonium salts. These unique IL‐H2O systems were successfully utilized for facile one‐step synthesis of Au porous films by bubbling CO2 under ambient conditions. The Au porous films and the ILs were then separated simultaneously from aqueous solutions by bubbling N2, and recovered ILs could be directly reused in the next process. Drei auf einen Streich: Hoch hydrophobe ILs wurden entwickelt. Deren reversibler Hydrophob‐hydrophil‐Übergang, der durch das Einblasen und Entfernen von CO2 bei Umgebungsbedingungen ausgelöst wird, ist durch die reversible Reaktion zwischen CO2 und dem Anion zu hydrophilen Ammoniumsalzen verursacht. Homogene Synthese und heterogene Abtrennung poröser Au‐Filme und das Rückgewinnen der ILs wurden für nachhaltige chemische Prozesse genutzt.