Tuning the phase behavior of ionic liquids in organically functionalized silica ionogels

Abstract

We have synthesized mesoporous silica monoliths functionalized with 2-(4-pyridylethyl)triethoxysilane 1 and N,N-dimethyl-pyridine-4-yl-(3-triethoxysilyl-propyl)-ammonium iodide 2. The organically modified silica monoliths were characterized via IR spectroscopy, nitrogen sorption, small angle X-ray scattering (SAXS), thermogravimetric analysis-differential thermal analysis (TGA-DTA), and acid-base titration. The degree of functionalization can be changed by the ratio of the functional silane to the silica precursor tetramethyl orthosilicate (TMOS). The functionalized silica monoliths were filled with 1-ethyl-3-methyl imidazolium [Emim]-X (X = dicyanamide [N(CN)2] or triflate [TfO]) ionic liquids (ILs) using an established methanol-IL exchange technique. The phase behavior of the resulting ionogels was investigated via differential scanning calorimetry (DSC). DSC curves show that the modification of the silica pore walls with organic groups strongly affects the phase behavior of the confined ILs. Modification with silane 1 completely suppresses the glassy state of [Emim][TfO] previously observed in unmodified silica monoliths (Göbel et al., Phys. Chem. Chem. Phys. 2009, 11, 3653). In contrast, modification with silane 2 leads to the appearance and disappearance, respectively, of a presumed additional phase in [Emim][TfO] and [Emim][N(CN)2] with varying degree of monolith functionalization. The data thus show that organic modification of silica matrix materials could be a viable approach for the tuning of ionogel properties.

Synergistic enhancement of CO2 uptake in highly ordered mesoporous silica-supported zinc-functionalized ionic liquid sorbents

“…In general, the confinement of IL by a non-conducting support, such as SiO 2 , results in a decrease in thermal stability [18]. However, for ILs that show strong interaction with the support, an increase in thermal stability is observed [17,19]. In our systems, the stronger interaction of EZT3 with the support in S15-10 and -25 (compared with S15-50 and -80) as manifested in the frequency shifts (vide supra) and the monotonic spreading of the IL on the pore walls (Fig.…”

Properties of Ionic Liquid Confined in Porous Silica Matrix

“…[41][42][43] Recently, Gçbel et al [44] have studied the DSC, NMR and IR spectra obtained from inserting 4 ] etc) in silica of different pore sizes, which was achieved by varying base catalysts like pyridine, 3-fluoropyridine and 2-picoline. More recently Gçbel et al [45] obtained IL-silica monoliths of different pore sizes by functionalizing the silica pore walls by adding N,N-dimethyl-pyridine-4-yl-(3-triethoxysilylpropyl)-ammonium iodide and 3-fluoropyridine and 2-(4-pyridylethyl)triethoxysilane in TMOS in different ratios. Functionalization [45] of silica matrix was also found to affect the phase behavior of confined IL.…”

“…More recently Gçbel et al [45] obtained IL-silica monoliths of different pore sizes by functionalizing the silica pore walls by adding N,N-dimethyl-pyridine-4-yl-(3-triethoxysilylpropyl)-ammonium iodide and 3-fluoropyridine and 2-(4-pyridylethyl)triethoxysilane in TMOS in different ratios. Functionalization [45] of silica matrix was also found to affect the phase behavior of confined IL. Gçbel et al [44] showed from DSC studies that in restrictive geometry, the melting point of [EMIM] based ILs decreases by~8 to 148C.…”

High capacity CO2sorbents based on zinc-functionalized ionic liquid confined in morphologically diverse porous matrices

“…Moreover, the shape of the PSD and the position of the mean were preserved, with the decrease in peak intensity indicating the presence of the adsorbed IL layer only. 55,56 Singh et al 47 and Gobel et al 57 both observed the reduction in thermal stability upon confinement of IL into porous substrates. If we assume an ideal case where all the EZT3 penetrates the pores, the pore volume lost due to impregnation (V p,lost ) would be equal to the volume of the EZT3 (V EZT3 ) loaded.…”