Self-supporting thin films of imogolite and imogolite-like nanotubes for infrared spectroscopy

Abstract : Due to their narrow and well-defined structure, single wall nanotube, aluminosilicate nanotubes (imogolites) are excellent candidates to study how water is modified by either confinement or by the interface nature. A protocol is provided here to produce imogolite films that are ideally suited for infrared studies. Two types of imogolites were selected: a hydrophilic imogolite (IMO-OH) with inner surface fully covered with Si–OH hydrophilic groups and a hybrid imogolite (IMO-CH 3) with inner surface fully covered with hydrophobic Si–CH 3 groups. Films with different thicknesses were characterized by Small Angle X-ray Scattering (SAXS). The initial water content and the porosity of the films were estimated from ThermoGravimetric Analysis (TGA). Infrared spectroscopy was used to deduce the molar absorption coefficient of the bending mode that is significantly modified in confined water as compared to bulk water. Moreover, the interest of these films which allow avoiding extra-absorption features from the salt matrix or the supporting wafer is illustrated by an infrared study of the processes occurring in the IMO-OH film when it is heated from room temperature up to 350 °C. The evolution of the IR bands while heating shows the dehydration/dehydroxylation processes.