Adsorption Studies of Molecules on the Halloysite Surfaces: A Computational and Experimental Investigation

We report the results of joint computational and experimental investigations on the adsorption capability of halloysite toward a set of common molecules (water, alcohols, halides, and carboxylic acids). The halloysite system has been modelized by means of a cluster approach choosing a portion of a spiral nanotube; it has a slight curvature, with a convex aluminic layer. The adsorption geometries are described in terms of hydrogen bond network structures; calculated interaction energies invariably indicate that the inner aluminic surface is the place for preferential adsorption of polar molecules. The presence of substitutional defects on the outer or inner surface of the halloysite model causes sometimes slight variations in the adsorption properties. The calculated adsorption energy values confirm that the carboxylic group interacts with the substrate much more strongly than the alcoholic group, which in turn interacts stronger than the halides, a trend that is in agreement with the results obtained by means of thermogravimetric analysis on vapor phase adsorption.