Terahertz time domain detection of imidazolium ionic liquid reactivity in nanohybrid materials based on Kaolinite and Halloysite

Abstract

A new nanohybrid material based on kaolinite intercalate with imidazolium ionic liquid (IL) was compared in its physical-chemical behavior with an analogue specimen prepared from halloysite. The intercalation of well-ordered kaolinite and poorly ordered halloysite, was successfully observed by terahertz time-domain spectroscopy (THz-TDS) in the far infra-red region. The prepared specimen showed unique spectral response: e.g. four broadened bands were observed for kaolinite-IL intercalate, whereas only one broadened band was observed for halloysite-IL intercalate. These spectra make it possible to observe intercalation and guest reactivity in this type of materials using THz (far infra-red) spectroscopy. The intercalation reactions were confirmed by independent techniques such as X-ray powder diffraction, Fourier transform infrared spectroscopy, simultaneous thermal analysis with mass spectrometry, and high-resolution solid-state NMR spectroscopy. TEM showed that kaolinite nanolayers upon repeated intercalation with IL preserved their platy morphology. This was in contrast to X-ray powder diffraction data showing transformation of kaolinite to halloysite-like material. Such delaminated kaolinite preserving its platy morphology has a good potential for application in nanocomposite materials with barrier properties.