| AVS 64th International Symposium & Exhibition | |
| Novel Trends in Synchrotron and FEL-Based Analysis Focus Topic | Tuesday Sessions |
| Session SA+AS+HC+SS-TuA |
| Session: | Frontiers of Photoelectron Spectroscopy: Surface & Interface Processes with Variable Depth Probe, High Spatial or Temporal Resolution |
| Presenter: | Hans-Peter Steinrück, University Erlangen-Nuernberg, Germany |
| Correspondent: | Click to Email |
Ionic liquids (ILs) are molten salts with a melting point below 100∘C. They represent a new class of liquid materials with unique property profiles originating from a complex interplay of Coulombic, hydrogen bonding, and van der Waals interactions of their ions. The enormous variety of cation-anion combinations enables tuning of the physico-chemical properties over a wide range. Functional groups can be implemented in their chemical structure to adapt them for specific tasks - such functionalized ILs are known as ’task-specific ionic liquids’. Applications range from catalysis and organic synthesis to tribology, protective coatings and gate dielectrics. In catalysis, two important concepts are Supported Ionic Liquid Phase (SILP) and Solid Catalyst with Ionic Liquid Layer (SCILL). In both, a high surface area solid substrate is covered with a thin IL film, which contains either a homogeneously dissolved transition metal complex for SILP, or which modifies catalytically active surface sites at the support for SCILL. The interface of the IL with the gas phase/vacuum or with the solid support plays an important role. Therefore, knowledge about surface and interface properties and their relation to the chemical structure is of pivotal importance for choosing the right IL for a specific application. In contrast to most other liquids, ionic liquids have a very low vapor pressure, and thus can be studied with the methods of ultrahigh vacuum-based surface science. One particularly powerful method is angle-resolved X-ray photoelectron spectroscopy. Thereby, detailed information on their surface composition, on segregation and enrichment effects, on the dissolution and reactivity of catalytically active metal complexes, on the growth of ultrathin IL-layers, and even on reactions in the liquid phase, can be obtained. Several examples will be discussed illustrating the power of surface science to study this new materials class. Many of the derived conclusions are considered representative for liquid surfaces in general.
F. Maier, I. Niedermaier, and H.-P. Steinrück, "Perspective: Chemical Reactions in Ionic Liquids Monitored through the Gas (Vacuum)/Liquid Interface", J.Chem. Phys. 2017 (in press)
H.-P. Steinrück and P. Wasserscheid, "Ionic Liquids in Catalysis", Catal. Lett. 2015, 145, 380.
H.-P. Steinrück, "Recent developments in the study of ionic liquid interfaces using X-ray photoelectron spectroscopy and potential future directions", Phys. Chem. Chem. Phys. 2012, 14, 2510.
H.-P. Steinrück, "Surface Science goes liquid !", Surf. Sci. 2010, 604, 481.