Behaviour of ionic liquid adsorbed on the surface of nano silica particles and in confined system of silica matrices

Abstract

This paper presents studies on behaviour of a solid ionic liquid (IL); 1-butyl-2,3-dimethylimidazolium hexafluorophosphate [BMMIM][PF6] based ionogels obtained by two different techniques, first by physical confinement of IL into nano porous silica matrix and second by adsorption of IL on the outer surface of nano silica particles. The properties of samples have been investigated using various experimental techniques like N2-sorption measurements, TEM, DSC, TGA, and FTIR. It has been observed that the properties of IL have been affected more in confined geometry of silica pores as compared to the adsorption on the surface of nano silica particles. Loading of IL initially increases size and volume of pores while decrease the surface area by ~ 23 %. However, further increase in loading of IL does not produce significant change. This might be explained on basis of π-π stacking of imidazolium ring and an additional π-π stacking association between imidazolium cations. The Fourier transform infrared (FTIR) results show that stronger interaction of IL with the silica pore wall surface in confined matrix while weaker interaction due to the interfacial interaction of nano silica particles with the ions of the IL in surface adsorbed IL. The interactions and method of confinement of IL have been found to be the key parameters that determine the properties of confined and adsorbed IL.