Water Adsorption in Single- and Double-Walled Inorganic Nanotubes

Imogolite forms a class of inorganic nanotubes whose inner and outer surfaces can be tuned on a molecular level. The combination of this property with their monodisperse diameters makes imogolites ideal to study water confinement in a one-dimensional environment. Here, we have investigated, by means of infrared (IR) spectroscopy, water confined in two types of germanium-based imogolites: (i) the hydroxylated imogolite (Ge-IMO-OH), a double-walled structure with an interstitial space of about 2 A and the interior of the tube covered by Ge–OH groups; and (ii) the hybrid, methylated, imogolite (Ge-IMO-CH3), a single-walled structure with Ge–CH3 groups covering the interior of the tube. In both cases, the external surface is covered by Al2-(μOH) groups. Small-angle X-ray scattering has also been exploited to determine the nanotube geometry of the two confining systems. Using thermogravimetric analysis, we show here that the interstitial space of Ge-IMO-OH fills with water in a significant proportion. Indeed, ...