Interactions of 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate Ionic Liquid with Alumina Nanoparticles and Organic Solvents Studied by Infrared Spectroscopy

The interface between 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EmIm][OTf]) ionic liquid (IL) supported on alumina nanoparticles and organic solvents (ethanol, tetrahydrofuran and acetonitrile) has been investigated using infrared (IR) spectroscopy. The investigations of these liquid-solid interfaces were preceded by separate studies of the IL in the different solvents and the IL supported on the alumina nanoparticles. IR analyses of the solvent-[EmIm][OTf] mixtures indicated that the triflate anion interacts differently with the three solvents. Comparison of the spectra of the IL supported on alumina with those measured for the corresponding solvent IL mixtures indicates an interaction between the SO3 group of the anion and the alumina surface. In the organic solvent-IL-alumina systems, similar interactions between the IL and the oxide surface occur. The behavior of the IL/alumina interfaces was found to be consistent with a model where the ionic liquid structure is perturbed due to charge neutralization in a thin layer at the interface. Qualitative studies of the kinetics of adsorption and desorption of the IL in the organic liquid phases indicated that the choice of the organic solvent has a significant influence on these processes. Comparative studies with a commercial Pt on alumina catalyst possessing similar surface area showed that the IL uptake strongly increases in the presence of Pt on the alumina surface. Comparison of adsorption-desorption cycles of the IL measured for the alumina support and Pt on alumina revealed a much stronger interaction of the IL with the Pt surface than with the alumina.