Tuning the Properties of Confined Water in Standard and Hybrid Nanotubes: an Infrared Spectroscopic Study

Imogolite is a natural nanotubular aluminum silicate clay mineral, originally found in volcanic soils. Its well-defined, yet tunable structure makes it a good candidate for the study of water confined in a one-dimensional structure. Water confined in imogolite self-sustaining thin films was studied by means of infrared spectroscopy [1]. Two types of synthetic imogolites were investigated: a pristine imogolite (IMO-OH) with a hydrophilic inner surface fully covered with Si-OH groups and a hybrid imogolite (IMO-CH3) with a hydrophobic inner surface fully covered with Si-CH3 groups. Both imogolites have the same outer surface, covered with Al-OH groups. The infrared spectra were recorded in the 20-4000 cm-1 spectral range as a function of the relative humidity. In particular, a detailed analysis of the O-H stretching band provides information on the H-bonding of confined water molecules inside and outside the IMO-OH tubes. The analysis of the various infrared signatures reveals the scenario for water filling as a function of relative humidity for the two systems. The adsorption in the IMO-OH tubes starts at the lowest relative humidity (