We investigated the adsorption, surface enrichment, ion exchange, and on-surface metathesis of ultrathin mixed IL films on Ag(111). We stepwise deposited 0.5 ML of the protic IL diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]) and 1.0 ML of the aprotic IL 1-methyl-3-octylimidazolium hexafluorophosphate ([C8 C1 Im][PF6 ]) at around 90 K. Thereafter, the resulting layered frozen film was heated to 550 K, and the thermally induced phenomena were monitored in situ by angle-resolved X-ray photoelectron spectroscopy. Between 135 and 200 K, [TfO]- anions at the Ag(111) surface are exchanged by [PF6 ]- anions and enriched together with [C8 C1 Im]+ cations at the IL/vacuum interface. Upon further heating, [dema][PF6 ] and [OMIm][PF6 ] desorb selectively at ∼235 and ∼380 K, respectively. Hereby, a wetting layer of pure [C8 C1 Im][TfO] is formed by on-surface metathesis at the IL/metal interface, which completely desorbs at ∼480 K. For comparison, ion enrichment at the vacuum/IL interface was also studied in macroscopic IL mixtures, where no influence of the solid support is expected.
Keywords: X-ray photoelectron spectroscopy; catalysis; ionic liquids; on-surface metathesis; ultra-thin films.
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