Preparation and characterisation of ionic liquid confined hybrid porous silica derived from ultrasonic assisted non-hydrolytic sol–gel process

Abstract

A series of porous silica matrices have been synthesized using ionic liquid (IL) 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) by nonhydrolytic sol–gel method with and without ultrasonic irradiation during gelation. The properties of IL confined silica gel matrices so prepared have been studied using N2-sorption measurement (BET characterisation for determining pore parameters), pulse echo technique (for sound velocity and hence elastic modulus determination), DSC, TGA, FTIR, TEM, SEM and fluorescence techniques. From the N2-sorption measurement, it has been found that BET surface area increased (due to creation of pits on the surface caused by ultrasonic irradiation) while pore volume, average pore size and porosity for ultrasonicated samples decreased. Elastic modulus of the samples containing IL in silica matrices have been found to change with IL content. Glass transition temperature and thermal stability of the IL have been found to increase upon confinement in silica gel matrices. FTIR spectra (experimental as well as computed) show changes in vibrational bands of IL on confinement in pores of silica matrices. Particularly, for ultrasonic assisted samples, the bands related to the imidazolium ring, aliphatic chain and anion SCN of the IL are found to shift upon confinement. Optimised geometry of the IL in porous matrix shows interaction of these groups with the oxygen present on silica pore wall. Fluorescence spectra of samples containing IL shows a shift compared to the bulk IL.