Probing the local environment of hybrid materials designed from ionic liquids and synthetic clay by Raman spectroscopy

Abstract

Hybrid organic-inorganic material containing Laponite clay and ionic liquids forming cations have been prepared and characterized by FT-Raman spectroscopy, X-ray diffraction, and thermal analysis. The effect of varying the length of the alkyl side chain and conformations of cations has been investigated by using different ionic liquids based on piperidinium and imidazolium cations. The structure of the N,N-butyl-methyl-piperidinium cation and the assignment of its vibrational spectrum have been further elucidated by quantum chemistry calculations. The X-ray data indicate that the organic cations are intercalated parallel to the layers of the clay. Comparison of Raman spectra of pure ionic liquids with different anions and the resulting solid hybrid materials in which the organic cations have been intercalated into the clay characterizes the local environment experienced by the cations in the hybrid materials. The Raman spectra of hybrid materials suggest that the local environment of all confined cations, in spite of this diversity in properties, resembles the liquid state of ionic liquids with a relatively disordered structure.

Keywords: Clay; Hybrid material; Ionic liquid; Raman spectroscopy.