Study of the Features of the Formation of Water Films on the Surfaces of Montmorillonite and Kaolinite by Infrared Spectroscopy

Ab Initio Simulation of the IR Spectrum of Hydrated Kaolinite

“…Investigations aimed at studying the adsorption of water molecules were carried out by the methods of DFT [10,12], and MD [12,13]. A comparison of the results obtained was made in [14] where it was noted that in the models used, H 2 O molecules are predominantly adsorbed on the hydroxyl surface of kaolinite. The adsorption energies calculated in [10][11][12] differ insignificantly.…”

“…The difference may be due to the details of the simulations and the accuracy of the potentials used in the calculations. A review of the results made in [14] makes it possible to note that, in the absence of additional ions, the average adsorption energies on hydroxyl and siloxane basal surfaces in kaolinite differ by a factor of about 5 and amount to 0.5 and 0.1 eV, respectively.…”

“…When calculating theoretical profiles of the bands, the width of the lines associated with free vibrations of surface ions was estimated from the experiment and taken equal to 5 cm −1 . The line widths associated with the vibrations of water ions and collective vibrations are taken from [14]; they are 400-500 cm −1 , depending on the moisture content. These line widths were used to generate Lorentzian curves representing individual calculated vibrations which were summed up.…”

“…The reasons leading to the need for a shift in the theoretical spectra can be related to the limited size of the clusters, and the basis sets used to describe one-electron orbitals, as well as with the need to use a multiconfigurational approach when calculating the potentials of oscillators. Figures 9 and 10 also show the experimental O−H vibration lines of the hydroxyl surface and water from [14]. The profiles of theoretical IR spectra are compared with the experiment in Figure 11.…”

“…In this work, the features of hydration of kaolinite are studied by theoretical methods, which made it possible to understand experimentally recorded changes in the position and intensity of a broad band at 3400 cm −1 in the IR spectrum [14]. It is known that dangling chemical bonds on the lateral surfaces of kaolinite particles take part in the chemical adsorption of both ions and water molecules.…”