Anisotropy in the Adsorption of H2O on Kaolinite Surfaces

Adsorption capacities of kaolinite's edge and basal surfaces may differ. These features determine the nature of its adsorption behavior while remaining poorly studied. At the same time, the anisotropy of the edge surface stipulates the wide application of kaolinite in geochemical, environmental, and technological fields. In this work, ab initio calculations have been employed to determine the effect of kaolinite surface anisotropy on its adsorption capacity. The mechanism has been studied for binding water molecules to the most stable kaolinite surfaces, namely, (001), (00 (1) over bar), (010), and (110). It has been found that the most energetically advantageous adsorption configurations of water molecules arise on edge surface (010), with adsorption energy being similar to four times higher than that on basal surface (00 (1) over bar). The observed energy difference is due to the fact that hydroxyl groups are involved in the adsorption mechanism in addition to surface oxygen atoms. The absence of these groups on the basal surface significantly reduces the probability of hydrogen bonding. The results obtained are in agreement with the data from published studies.