Study of intercalation compounds using ionic liquids into montmorillonite and their thermal stability

• Intercalation of three ionic liquids into clay using eco-friendly method was studied.
• Solid–liquid state nano-structure compound was successfully characterized by TEM.
• Atomic arrangement of three intercalated compounds was proposed.
• Improving the thermal stability of intercalated compounds was measured by TG-DTA.
• Ionic liquid is useful for fabricating electrically conductive transparent thin film.

In the present study, we investigated the direct intercalation of three kinds of ionic liquids (ILs) of different salts (imidazolium and ammonium) and cation sizes into montmorillonite (M) clay, and successfully fabricated the IL intercalated montmorillonite (MIL) compounds. The peak shifts of the MIL intercalated compounds in comparison with dried montmorillonite powder as observed by XRD results showed that crystal swelling was significantly influenced by the cation sizes of the ILs. The intercalation behaviors of the MIL compounds were also compared by TEM and the results are in good agreement with the XRD. The TEM–EDS results further confirmed the intercalation of three types of ILs into the montmorillonite. Based on the cation exchange capacity as measured by ICP and mathematical calculations, the extent of the intercalation and arrangement of cations in the interlayers of the montmorillonite are proposed. The TG-DTA results showed an improved thermal stability of all three kinds of MIL intercalated compounds, and the XRD indicated that the remaining IL initiates a carbonization process with the montmorillonite at 1000 °C. Furthermore, the AC impedance results of the MIL compounds showed an ionic conductivity. These results suggest the possible application of the MIL intercalated compounds in electrical conductive films, solar cells, fuel cells, etc.