Abstract
The interfacial interactions between ionic liquids (1,3-dimethylimidazolium methyl sulfate and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate) and solid surfaces (mesoporous aluminum oxide and mica) have been studied by infrared spectroscopy at high pressures (up to 2.5 GPa). Under ambient pressure, the spectroscopic features of pure ionic liquids and mixtures of ionic liquids/solid particles (Al2O3 and mica) are similar. As the pressure is increased, the cooperative effect in the local structure of pure 1,3-dimethylimidazolium methyl sulfate becomes significantly enhanced as the imidazolium C–H absorptions of the ionic liquid are red-shifted. However, this pressure-enhanced effect is reduced by adding the solid particles (Al2O3 and mica) to 1,3-dimethylimidazolium methyl sulfate. Although high-pressure IR can detect the interactions between 1,3-dimethylimidazolium methyl sulfate and particle surfaces, the difference in the interfacial interactions in the mixtures of Al2O3 and mica is not clear. By changing the type of ionic liquid to 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, the interfacial interactions become more sensitive to the type of solid surfaces. The mica particles in the mixture perturb the local structure of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate under high pressures, forcing 1-ethyl-3-methylimidazolium trifluoromethanesulfonate to form into an isolated structure. For Al2O3, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate tends to form an associated structure under high pressures.
Highlights
Aluminum oxide, known as alumina, is utilized in various applications
Even though porous alumina has many applications, the interactions and physical arrangement of ionic liquids at porous alumina surfaces are still poorly understood, some studies have shown that certain ionic liquid and porous alumina mixtures have complicated interfacial interactions [15]
Samples were prepared by using 1,3-dimethylimidazolium methyl sulfate (>97%, Fluka, Morris Plains, NJ, USA), 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (99%, UniRegion Bio-Tech, Taoyuan, Taiwan), mica, and mesoporous aluminum oxide
Summary
Known as alumina, is utilized in various applications. It can be used as the major component in ceramics, catalysis, paints, lubricants, and medical products [1,2,3,4,5,6,7,8]. Nanoporous anodic alumina can be obtained from electrochemical anodization of aluminum foil. This material has highly ordered and monodisperse pores, a large surface area, and many more useful properties [9]. Porous alumina can be used as filters with high selectivity for sensing ions or biomolecules [10,11,12,13,14]. Even though porous alumina has many applications, the interactions and physical arrangement of ionic liquids at porous alumina surfaces are still poorly understood, some studies have shown that certain ionic liquid and porous alumina mixtures have complicated interfacial interactions [15]
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