Structure and Reactivity of the Ionic Liquid [C1C1Im][Tf2N] on Cu(111)

Abstract

We studied the adsorption and reaction behavior of the ionic liquid (IL) 1,3-dimethylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C1C1Im][Tf2N]) on Cu(111) using non-contact atomic force microscopy (nc-AFM), scanning tunneling microscopy (STM), and angle-resolved X-ray photoelectron spectroscopy (ARXPS) in ultrahigh vacuum as a function of temperature, supported by density-functional theory (DFT) calculations. Our nc-AFM results for sub-monolayer IL films show that at 200 K, the IL self-assembles into highly ordered islands, with cations and anions arranged next to each other in a checkerboard–type phase. After extended annealing at 300 K, the structure transforms first to a hexagonal phase and then to a porous honeycomb phase. Simultaneously, many small, disordered islands are formed. Complementary ARXPS reveals no IL desorption until 300 K. However, a significant fraction of the IL is converted to a new species as deduced from new, strongly shifted peaks that develop in the XP spectra at around 275 K and grow with annealing time at 300 K. We correlate the remaining unshifted peaks to the ordered phases observed in nc-AFM and the shifted peaks to decomposition products, which appear as disordered islands in nc-AFM and STM. Upon further heating to 360 K, about 50% of the anions or their decomposition products desorb from the surface, while cation-related fragments mostly remain on the surface. From DFT, we obtain additional information on the structure of the ordered phases and the interaction of the IL with the substrate.

Adsorption and thermal evolution of [C1C1Im][Tf2N] on Pt(111)

“…Notably, the orientation effects are to some extent also reflected in the bulk sensitive 0° measurements, as it was also observed for other (sub-)wetting layer IL systems. 18,21 This effect is most prominent for the F an signal at 200 K (6.7 vs. 6; see Table S1, ESI†).…”

Surface Chemistry of a [C2C1Im][OTf] (Sub)Wetting Layer on Pt(111): A Combined XPS, IRAS, and STM Study

“…In the TPXP spectra, the C cat region was fitted with a simplified single symmetric peak (without constraints in position or width) due to reduced measuring time and the resulting lower signal-to-noise ratio. In some cases, the Pt(111) surface showed a residual carbon impurity in the C cat -position; for the quantitative analysis, this signal was scaled down according to the Pt 4f attenuation and added to the IL spectra (for more information on this correction; see supplementary information to ref ). For the 10.3 ML film, all peaks were fitted with a symmetric peak shape after the subtraction of a linear background.…”

“…The different solubility of the reactants in the IL can influence the concentration of the individual reactants at the active sites. , In addition, the IL can act as a ligand blocking specific catalytically active sites on the surface. ,,,, Such strong interactions can even lead to the chemical transformation of the IL under reaction conditions. The resulting decomposition products can guide to further changes in the characteristics of the catalyst. , However, it is essential to understand these effects in detail in order to tailor the properties of IL to a specific process.…”

“…Previous studies have provided fundamental insights into film growth, wetting, thermal behavior, and orientation of ILs on the surface. ,− ,− Recently, Massicot et al investigated the IL [C 1 C 1 Im]­[NTf 2 ] on Pt(111) by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). They observed that at low temperatures until 200 K, the IL on the surface is intact and forms a checkerboard-like structure.…”

“…At temperatures above 200 K, the IL starts to decompose and part of the decomposition product desorbs while the other part passivates the surface . Also, Adhikari et al found partial decomposition of [C 1 C 1 Im]­[NTf 2 ] on Cu(111) at temperatures above 275 K using noncontact atomic force microscopy (nc-AFM), STM, and angle-resolved X-ray photoelectron spectroscopy (ARXPS) . However, most studies focused on less reactive surfaces, like Au(111) ,,,,,− or Ag(111). ,,,,, In our recent publications, we studied the IL [C 2 C 1 Im]­[OTf] on Au(111). , We found that at low temperature the IL is adsorbed in a 6-ring structure on the surface.…”