Micellization of long-chain ionic liquids in deep eutectic solvents

Abstract

The aggregation behavior of the ionic liquid (IL) 1-alkyl-3-methylimidazolium chloride with different alkyl chain lengths in a deep eutectic solvent (DES, composed of choline chloride and glycerol in a 1 : 2 mole ratio) was studied for the first time. The critical micellar concentration, micellar size and intermolecular interactions in IL/DES solutions were investigated by different techniques including the fluorescence probe technique, small angle X-ray scattering and Fourier transform infrared spectroscopy. The solvophobic effect dominates the micellization of C_nmimCl in DES and the intermolecular hydrogen-bond interaction plays a positive role to promote micelle formation. The micellar solutions were utilized for the synthesis of the water-unstable metal–organic framework Cu₃(BTC)₂ (BTC = 1,3,5-benzenetricarboxylate) at room temperature. X-Ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption–desorption isotherms confirm the formation of crystalline Cu₃(BTC)₂ nanocrystals with mesoporous structures. The morphologies and porosity properties of Cu₃(BTC)₂ nanocrystals can be modulated by varying the concentration of C_nmimCl.