A Computer Modeling Study of the Inhibiting Effect of Organic Adsorbates on Calcite Crystal Growth

Computer modeling techniques were employed to investigate the adsorption of a selection of organic molecules to a series of monatomic growth steps of the major calcium carbonate polymorph calcite. Incorporation of the organic material by replacement of preadsorbed water at calcite {101̄4} surface features is calculated to be considerably exothermic for organic molecules containing carbonyl and hydroxy functional groups with adsorption energies at the growth steps ranging from about −30 to −140 kJ mol -1 . The calculated energies suggest that carboxylic acids, hydroxy aldehydes, or amides will be effective growth inhibitors through their strong adsorption to the growth steps, usually binding across the step to the terrace below, thereby blocking these sites to further attachment by calcium carbonate. Organic molecules containing only the amine functional group do not adsorb very strongly to the growth steps and thus will not be particularly effective in inhibiting crystal growth. On the stoichiometric steps, which are found in abundance on the experimental surface, hydroxy ethanal preferentially blocks the faster growing obtuse steps, which will slow calcite growth significantly. On the steps terminated by either calcium or carbonate groups, the adsorbates are found to attach preferentially to either the acute or the obtuse steps, which may lead to asymmetric growth and surface morphology. The results from this study suggest that computer simulations may provide a route to the identification or even design of particular organic additives for specific tailored crystal growth.