Nanocomposites of ionic liquids confined in mesoporous silica gels: preparation, characterization and performance

Abstract

A series of nanocomposites of ionic liquids (ILs) were prepared via a modified sol-gel method. The ILs were physically confined in mesoporous silica gels with 5-40% content. ILs from imidazolium, thiophenium and ammonium with different anions were prepared and used. Characterization using the Brunauer-Emmett-Teller (BET) method, Fourier transform infrared (FT-IR) spectroscopy, temperature-programmed desorption (TPD), differential scanning calorimetry (DSC), inverse gas chromatography (IGC), temperature-controlled Raman and fluorescence emission spectroscopies was conducted to explore any confinement effects. BET results showed that, depending on the ILs and their contents, the average pore diameter of the pure silica gel was 3-12 nm after the confined ILs were removed completely. It was suggested that ILs aggregated on the nanoscale in the mesoporous silica gel. In comparison with bulk ILs and ILs coated onto silica gels (IL/sg), IL nanocomposites (IL-sg) displayed remarkably low specific heat capacities (C(p) was in the range 0.3-1.2 J g(-1) K(-1)), disordered vibrational conformations (without phase transitions in the range -100-200 degrees C), greater interactions with hydrocarbon solutes (adsorption capacities of 0.3-0.4 g per 100 g for confined ILs with CO(2) gas), and greatly enhanced fluorescence emission (up to 200 times stronger than bulk ILs). Furthermore, Based on the specific solubility of different compounds, the nanocomposites could also be applied to the separation of CO(2) from CO(2)/N(2) mixtures and thiophene from thiophene/octane mixtures.