Adsorption Motifs and Molecular Orientation at the Ionic Liquid/Noble Metal Interface: [C₂C₁Im][NTf₂] on Pt(111)

Abstract

In solid catalysts with ionic liquid layers (SCILLs), ionic liquid (IL) thin films are used to modify the activity and selectivity of catalytic materials. In this work, we investigated the adsorption behavior of the IL 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide [C 2 C 1 Im][NTf 2 ] on Pt(111) by combining experimental and theoretical studies. Under ultrahigh vacuum (UHV) conditions, the IL was deposited onto a Pt(111) single crystal surface by physical vapor deposition (PVD) at different surface temperatures (200, 300, and 400 K). The adsorption process was monitored by in situ infrared reflection absorption spectroscopy (IRAS). Complementary to the IRAS studies, we performed density functional theory (DFT) calculations and analyzed the adsorption motifs and orientation of the IL ions. In total, we calculated four different systems: (a) [C 2 C 1 Im] + and [NTf 2 ] − ions in the gas phase; [NTf 2 ] − anions in (b) small (4 × 4) and (c) large (6 × 6) Pt(111) supercells; and (d) a complete ion pair of [C 2 C 1 Im][NTf 2 ] in a (6 × 6) Pt( 111) supercell. Based on DFT, we simulated IR spectra and compared them to the experimental data. Our results suggest that the binding motif and orientation of the IL is strongly dependent on the actual IL coverage. In the monolayer (ML), [NTf 2 ] − interacts strongly with the metal surface and adopts a specific orientation in which it interacts with the Pt surface via the SO 2 groups. Also the [C 2 C 1 Im] + cations adopt a preferential orientation up to coverages of 1 ML. Upon transition to the multilayer region, the specific orientation of the ions is gradually lost.

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

“…Moreover, evaporated IL films of the very similar IL [C 2 C 1 Im][Tf 2 N] on Pt(111) had already been studied by means of infrared spectroscopy. 26,27 We will compare our results to this study, and provide additional insights also for this system. For our model catalytic approach, we used in situ physical vapor deposition (PVD) to prepare ultra-thin films of [C 1 C 1 Im][Tf 2 N] on Pt(111).…”

Rheological Characteristics of Ionic Liquids under Nanoconfinement

“…It has been widely reported that IL ions organize in layers near a charged surface. 11−13 Extensive efforts have been made to investigate structural and dynamic properties of ILs near a solid interface as well as the influence of nanoconfinement using spectroscopy, 14,15 X-ray reflectivity, 16 neutron scattering, 17 NMR, 18,19 and electrochemical techniques. 20,21 Nanomechanical methods have provided unique perspectives about the transition of IL behavior upon nanoconfinement toward elastic or solid behavior, which is often referred to as solid-like behavior.…”

“…It has been widely reported that IL ions organize in layers near a charged surface. − Extensive efforts have been made to investigate structural and dynamic properties of ILs near a solid interface as well as the influence of nanoconfinement using spectroscopy, , X-ray reflectivity, neutron scattering, NMR, , and electrochemical techniques. , Nanomechanical methods have provided unique perspectives about the transition of IL behavior upon nanoconfinement toward elastic or solid behavior, which is often referred to as solid-like behavior. For example, the mechanical impedance of 1-butyl-3-methylimidazolium tetrafluoroborate (abbreviated as [BMIM]­[BF4]) measured under the excitation of a tuning-fork-based atomic force microscope suggested that the interfacial film exhibits a change of properties toward a solid-like phase below a threshold thickness, pointing to capillary freezing or crystallization in confinement.…”

Electrochemically Triggered Energy Release from an Azothiophene‐Based Molecular Solar Thermal System

“…Note that positive (pointing upwards) and negative (pointing downwards) bands indicate consumed and formed species, respectively. Other bands at 1574 cm −1 ( ν (C=N) ring , ν (C=C) ring ), 1350 cm −1 ( ν as (SO 2 )), 1200 cm −1 ( ν ([NTf 2 ] − )), and 1135 cm −1 ( ν s (SO 2 ), ν as (CF 3 )) we attribute to the supporting electrolyte [C 2 C 1 Im][NTf 2 ] [34] (for details of the ATR‐IR spectrum see Supporting Information) and bands at 2309 cm −1 and 1260 cm −1 to the solvent DCM [32] . Time‐resolved spectra (see Supporting Information Figure S2) show that under our experimental conditions we obtain a quantitative photo‐conversion of the photoswitch in the thin‐layer within a few tenths of a second.…”