The intercalation behavior of ionic liquids in the layered metal dichalcogenide TiS2

Abstract

The intercalation of the layered dichalcogenide TiS2 by a series of substituted imidazolium tetrafluoroborate ionic liquids was undertaken in order to determine the utility of ionic liquids as surfactants for exfoliating these layered metals. The ionic liquids were a series of straight chain substituted imidazoliums, 1,2-dimethyl-3-R-imidazolium tetrafluoroborate, where R=propyl, butyl, decyl or hexadecyl. Three different types of intercalation reactions were performed: electrochemically-induced intercalation, solution reactions in which the ionic liquid was dissolved in acetonitrile, and direct thermal reaction of the ionic liquid with the metal dichalcogenide. Results indicated ordered, first stage intercalation of the metal dichalcogenide for only the thermal reactions. Based on X-ray analysis of the interlayer distances, the planes of the propyl- and butyl-substituted imidazolium rings were arranged perpendicular to the a-b plane in a single layer, with the side chains parallel to the a-b plane. However, both the decyl- and hexadecyl-substituted imidazoliums were oriented with the plane of the imidazolium ring and the side chains perpendicular to the a–b plane. The decyl-substituted imidazoliums were oriented as a single layer within the TiS2 van der Waals gap, but the hexadecyl-substituted imidazoliums were arranged in a bi-layer between the TiS2 sheets, giving rise to a c-axis expansion of over 49Å. Results indicate that the best surfactants for exfoliating the dichalcogenide to create nanocomposites of the dichalcogenides would be either the decyl- or hexadecyl-substituted imidazoliums.