Isotopic exchange of kaolinite hydroxyl protons: a diffuse reflectance infrared Fourier transform spectroscopy study†

Abstract

Specific surface reactions on kaolinite were investigated by deuterium exchange of the hydroxyl protons of kaolinite. The kaolinite samples were reacted with deuterium oxide for 48 h and 2.5 and 5 weeks, at various pH values (3, natural and 8) and at different temperatures (ambient, and 30, 60 and 100 °C). Analyses were performed using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The spectral results show that it is very difficult at room temperature to exchange the hydroxyl protons isotopically with deuterons at the surface of kaolinite. The temperature and the reaction time must be increased for successful exchange. It was found that the most suitable temperature for isotopic exchange was 60 °C. The pH did not significantly influence the deuteration. Only at high pH were changes of the OD bands in the DRIFT spectra observed. This study shows that it is possible to deuterate kaolinite without using intercalation. All three types of hydroxyl protons from the inner, inner surface and edge were exchanged.