Boundary films at metal oxide-ionic liquid interfaces studied by solid-state NMR spectroscopy
2013 (English)Conference paper, Poster (Refereed)
Solid-state NMR spectroscopy is a useful method for elucidating mechanisms of formation of boundary films at solid-liquid interfaces of different metal oxides in contact with different ionic liquids having halogenated anions, such as NTF2- and PF6- [1,2]. However, these halogen-based ionic liquids are susceptible to hydrolysis and generate HF that erode the surface and pollute the environment. In this study, we employed a similar NMR approach to understand the mechanism of film formation by halogen-free orthoborate ionic liquids (hf-BILs) on the metal oxide surfaces.Samples were prepared by grinding the inorganic oxide and 10 wt% of hf-BIL using mortar and pestle. The boundary films on inorganic metal oxides (Al2O3, MgO and SiO2) surfaces in contact with hf-BILs have been characterized using solid-state MAS (11B, 31P and 29Si) NMR spectroscopy. The single pulse 11B NMR data indicate that bis(mandelato)borate anion, [BMB]-, in [P6,6,6,14][BMB] BIL strongly interacts with these metal oxides, in particular, at elevated temperatures (100 °C). In contrast, no products of decomposition were detected for surface of these oxides exposed to [trihexyltetradecylphosphonium][bis(salicylato)borate] ILs at different temperatures. Therefore, it was suggested that the [BScB]- anion is weakly interacting with these oxides. 31P NMR data on the same IL/metal oxide systems revealed strong interactions of the [P6,6,6,14]+ with these oxides. We suggest that [P6,6,6,14]+ cations are also present in immobile surface layers of ILs on particles of these oxides, because 31P resonance lines of ILs were detected using 1H-31P cross polarization MAS NMR giving rise to NMR signals of solid phases with a low molecular mobility only. The existence of strongly adhered surface layers of ILs on particles of metal oxides was further confirmed by 1H-29Si CP/MAS NMR. This study suggests that the boundary film formation between hf-BILs and metal oxide surfaces is a complex process involving various chemical reactions at the interfaces. These findings can be important for understanding of mechanisms of formation and structure of tribofilms in the process of lubrication of nonferrous metal surfaces by hf-BILs.
Place, publisher, year, edition, pages
Research subject Chemistry of Interfaces
IdentifiersURN: urn:nbn:se:ltu:diva-29584Local ID: 3195cb45-0ffa-4aed-9702-e820bcade422OAI: oai:DiVA.org:ltu-29584DiVA: diva2:1002808
Congress on Ionic Liquids : 21/04/2013 - 25/04/2013
Godkänd; 2013; 20130418 (faisha)2016-09-302016-09-30Bibliographically approved