DFT study of urea interaction with potassium chloride surfaces

Abstract

In this work, interaction of urea on the important surfaces of potassium chloride has been investigated using density functional theory (DFT) approach. We have performed the DFT calculations using slab models for the interactions of urea with {100}, {110} and {111} surfaces of KCl. Furthermore, the influence of solvent effect was computed with the COSMO continuum model. While sodium chloride crystals are known to change their habit in presence of urea impurity, the higher homologue KCl has not been extensively studied. In one of our earlier articles, we have shown that the preferential interaction of urea with the specific surface of sodium chloride can lead to change the habit from cubes to octahedrons [A. Singh, S. Chakraborty and B. Ganguly, Computational study of urea and its homologue glycinamide: conformations, rotational barriers, and relative interactions with sodium chloride, Langmuir 23 (2007), pp. 5406–5411]. The similar surface docking approach for the interaction of urea with the KCl surfaces suggests that urea would not influence the morphology of KCl. The computed interaction energies were found to be comparable for all the important surfaces of KCl with urea. We have performed experimental studies to examine our computational analysis. The experimental results suggest that the growing KCl crystals in urea solution are cubic in nature. The combined computational and experimental studies corroborate the model of effective interaction of additives with the certain face of crystals and responsible for the change in the morphology [R. Speidel, Neues Jahrbuch fur Mineralogie, Part 4, 81m (1961); N. Cabrera, D.A. Vermilyea. Growth and Perfection of Crystals; John Wiley & Sons Inc. 393. (1958); C.W. Bunn, Adsorption oriented overgrowth and the mixed crystal formation, Proc. R. Soc. A 141 (1933), pp. 567–593].