CO₂-Switchable Phase Separation of Nonaqueous Surfactant-Free Ionic Liquid-Based Microemulsions

Abstract

Surfactant-free microemulsions (SFMEs) have shown great potential in many aspects such as chemical reactions and material preparation. Ionic liquid (IL)-based SFME is a promising member in this family. However, switchable phase separation of nonaqueous IL SFMEs has not been reported up to now although it is of great importance for the separation of products and recycling of the systems. Herein, a new kind of CO2-responsive SFMEs composed of quaternary ammonium IL, dimethyl sulfoxide, and ethyl acetate has been developed. It is worth noting that the microemulsion can be reversibly switched between emulsification and complete phase separation upon alternative CO2 and N2 bubbling at atmospheric pressure. The microstructures and phase behavior of the systems before and after CO2 bubbling have been systematically studied by phase diagrams, electrical conductivity, dynamic light scattering, optical microscopy, and atomic force microscopy, respectively. Mechanism studies verify that the reversible switching is attributed to the generation and restoration of more hydrophilic carbamate salts from the reaction of CO2 with IL anions, which results in poor solubility of ILs in the nonaqueous microemulsions and thus reversible breaking and rebuilding of the microemulsions. Based on this unique phase behavior, the CO2-switchable SFMEs are used as a microreactor for room temperature synthesis of Zn-based metal–organic frameworks, and effective reaction and microemulsion recycling have been achieved. This study may provide a new strategy for the integration of reaction, separation, and recycling procedures to obtain sustainable chemical processes.

CO2-Switchable Emulsification and Demulsification of Pickering Emulsion Stabilized by Zirconium-Based Metal–Organic Frameworks

“…According to their high-resolution XPS spectra, the binding energies at approximately 179.2 and 181.5 eV were ascribed to Zr 3d 5/2 and Zr 3d 3/2 (Figure S1a), respectively, which indicated the presence of Zr 4+ for the zirconium-oxo cluster. 53 Three main peaks of C 1s at 284.8, 286.5, and 288.9 eV belonged to C−C/C�C, C−N, and C� O 54 (Figure S1b), respectively. The structure spectrum of N 1s showed two peaks at 398.4 and 400.1 eV (Figure 2b), indicating the existence of C−N and N−H bonds, respectively.…”

CO2-Driven reversible transfer of amine-functionalized ZIF-90 between organic and aqueous phases

“…4a, two new signals at 160.4 and 164.5 ppm appeared and belonged to bicarbonate and carbamate, respectively, which indicated the generation of hydrophilic ammonium salts. 28,29 Moreover, the two signals disappeared after removal of CO 2 , proving that the reaction process is perfectly reversible.…”

“…CO 2 is abundant, nonhazardous, inexpensive and nonaccumulating in the system and can be utilized as a trigger for many switching processes. 28,29 Here, for the first time, we prepared a new kind of CO 2 -switchable functionalized ZIF-90 by the covalent post-modification of ZIF-90 with diamines and investigated its phase transfer behavior between organic and aqueous solutions. It was observed that the aminefunctionalized ZIF-90 was initially well dispersed in the organic phase.…”

Solid polymer electrolytes of ionic liquids via a bicontinuous ion transport channel for lithium metal batteries

“…[31][32][33] Recently, nonaqueous ionic liquid based microemulsions have been investigated as ion-conductive electrolytes. [34][35][36][37] However, they have not been applied for LMBs primarily due to their weak mechanical strength.…”