Characterisation of halloysite by spectroscopy.

This chapter provides an overview of results obtained by a variety of spectroscopic techniques. The most common techniques employed are infrared (IR)and Raman spectroscopy, which enable detailed observation of the behaviour of water and OH-groups and the type of H-bonds formed. The inner-surface OH-groups that normally form H-bonds with adjacent layers in the kaolins and form H-bonds with water in the interlayer in halloysite. Infrared emission spectroscopy showed that the four inner and inner-surface OH-groups were removed at different temperatures, at different rates, or both. A slight increase in the Al 2p binding energy observed in the spectra of X-ray photoelectron spectroscopy from kaolinite to halloysite reflects a change in the stacking order due to the interlayer water. The overall shape of the O 1s is indicative of two peaks associated with the oxygen atoms and with the OH-groups. A third, very weak peak was observed to be associated with interlayer water that is still present despite the ultrahigh vacuum.