A High-Pressure Study of the Effects of TiO₂ Nanoparticles on the Structural Organization of Ionic Liquids

Abstract

The local structures between nano-TiO2 and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI+TFS–) and 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMI+TFS–) were investigated using high-pressure infrared spectroscopy. No significant changes in C–H spectral features of EMI+TFS– were observed in the presence of nano-TiO2 under ambient pressure. As the EMI+TFS–/nano-TiO2 mixture was compressed to 0.3 GPa, the imidazolium C–H absorptions became two sharp bands at 3108 and 3168 cm–1, respectively, and the alkyl C–H stretching absorption exhibits a new band at 3010 cm–1 associated with a weaker band at 3028 cm–1. It appears that pressure stabilizes the isolated conformations due to pressure-enhanced imidazolium C–H---nano-TiO2 interactions. Our results also reveal that alkyl C–H groups play non-negligible roles at the conditions of high pressures. The results of BMI+TFS–/nano-TiO2 are remarkably different from what is revealed for EMI+TFS–/nano-TiO2. The spectral features and band frequencies of BMI+TFS–/nano-TiO2 are almost identical to those of pure BMI+TFS– under various pressures. This study demonstrates that changes to the alkyl chain length of the cation could be made to control the order and strength of ionic liquid/nano-TiO2 interactions.

Probing Structures of Interfacial 1-Butyl-3-Methylimidazolium Trifluoromethanesulfonate Ionic Liquid on Nano-Aluminum Oxide Surfaces Using High-Pressure Infrared Spectroscopy

“…The sharper structures of imidazolium C-H bands revealed in Figure 3b-g are in part due to the anisotropic environment in a solid structure. We note that spectral features of the [BMIM][TFS]/Al 2 O 3 mixture in Figure 3 are almost identical to those of pure [BMIM][TFS], as revealed in our previous studies [21]. The results of Figure 3 indicate that the presence of nano-Al 2 O 3 does not perturb ion/ion interactions from the perspective of the C-H stretching motions of the cations.…”

“…Pressure calibration was performed following Wong's method [19,20]. Figure 1a shows two imidazolium C-H bands at 3116 and 3155 cm −1 , a shoulder to the 3155 cm −1 band at 3098 cm −1 , and three alkyl C-H bands at 2877, 2940, and 2967 cm −1 , respectively [21]. As shown in Figure 1, no appreciable changes in spectral features and band frequencies of C-H vibrations occurred as [BMIM][TFS] was mixed with nano-Al2O3, except for a noticeable absorption caused by O-H groups from the surfaces of nano-Al2O3 that appears in Figure 1d.…”

Local structures of ionic liquids in the presence of gold under high pressures

“…The nearly degenerated peaks, i.e., 3100 and 3118 cm −1 , suggest that the imidazolium C-H may exist at least in two different types due to the perturbation of neighboring ions in the liquid state. 33 The elevation of pressure to 0.4 GPa leads to a phase transition and the major imidazolium C-H bands were blue shifted to 3133 and 3175 cm −1 in Fig. 2(b).…”

“…[1][2][3][4][5] It is known that the imidazolium C-H stretching absorptions may be described by four bands (two doublets), one doublet at the lower frequency is assigned to the C 2 -H stretching mode and another doublet at the higher frequency is attributed to the coupled 4 -H and C 5 -H stretching modes. 33 The nearly degenerated imidazolium C-H features at ca.3100 and 3118 cm −1 are related to hydrogen bonding structures and microheterogenity. 33 The hydrogen bonding structures may be larger ion clusters (or ion pair) and the dissociation into smaller ion clusters.…”

“…33 The nearly degenerated imidazolium C-H features at ca.3100 and 3118 cm −1 are related to hydrogen bonding structures and microheterogenity. 33 The hydrogen bonding structures may be larger ion clusters (or ion pair) and the dissociation into smaller ion clusters. The red shifts in frequency revealed in Fig.…”