Characterization of Supported Ionic Liquid Phase (SILP) materials prepared from different supports

Abstract

Supported ionic liquid phase (SILP) materials are a recent concept where a film of ionic liquid (IL) is immobilized on a solid phase, combining the advantages of ILs (non volatility, high solvent capacity, etc.) with those of heterogeneous support materials. In this work, new SILP materials were prepared using a series of supports with different porosity and chemical nature. An imidazolium-based IL, 1-methyl-3-octylimidazolium hexafluorophosphate (OmimPF6), was confined at variable contents (5–60% w/w) in three different activated carbons (ACs), silica (SiO2), alumina (Al2O3) and titania (TiO2). For the first time, a systematic characterization of different SILP systems has been carried out applying a variety of analytical and spectroscopic techniques to provide information of interest on these materials. Elemental analysis (EA), adsorption–desorption isotherms of N2 at 77 K, mercury porosimetry, termogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electronic microscopy (SEM) and energy dispersive X-ray (EDX) were conducted to explore confinement effects. The results demonstrate that EA is a useful tool for quantifying the amount of imidazolium-based IL incorporated on support, independently of the nature of the solid. An excellent correlation has been obtained between the percentage of elemental nitrogen and the IL loaded on the support. The combination of nitrogen adsorption–desorption isotherms at 77 K and mercury porosimetry measurements was used to characterize the pore structure of both supports and SILP materials. It was found that depending on the available pores in the solid support, the IL tends to fill micropores firstly, then mesopores and lately in macropores. Thermal properties of SILP materials were studied herein by using both TGA and DSC methods, evidencing that the stability of SILP materials and the decomposition mechanism are strongly dependent on the surface chemistry of the solid support. SEM and EDX provided evidences of external surface coverage by ILs and filling of macropores at high IL load.