Abstract:
It was not until 2005 that the rather obvious compatibility of ionic liquids with ultra-high vacuum (UHV)-based spectroscopies was fully realised. Since that time, an ever-increasing portfolio of UHV based techniques including XPS, UPS, SIMS, TPD, SEM, TEM, and related synchrotron based experiments have been applied to the study of both pure ionic liquids and solutions thereof. UHV techniques give tremendous insight into many aspects of ionic liquid properties and the role that they play in chemical reactions and processes.
Since 2005 we have developed a series of robust spectroscopic protocols that allow the direct comparison of spectroscopic data, and more critically allows the investigation of subtle changes in binding energy that result from chemistry within the sample itself.
The chemistry of ionic liquid mixtures is an emerging area of research that offers tremendous potential in applied fields, particularly those that are based upon the electrolytic properties of the liquid itself. The direct combination of different ions could provide a fine tuned balance between electrochemical stability, viscosity, conductivity and melting points. We explore the nature and local electronic environments within simple ionic liquid mixtures by direct XPS measurement. Common cation mixtures based upon both dialkyl imidazolium and dialkyl pyrollidinium8 based liquids are investigated and XPS data will be used to illustrate speciation and bulk structure in mixed anion-based systems as a function of molar fraction. The experiments illustrate opportunities to tune the electronic environment within ionic liquid mixtures and highlight a strategy that may be used to develop a palette of ionic liquids that may be blended to produce mixtures with tuneable chemical properties that could potentially impact upon catalytic performance.
This lecture will review progress using laboratory based XPS instrumentation employing both monochromatised Al KI± and Ag LI± X-rays.
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