Regulation of Calcite Morphology by Low-Molecular-Weight Organic Acids: Alcohol Hydroxyl and Carboxyl Matters

Replicating the key structural feature of calcium carbonate (CaCO3) by biomolecules provides unique inspiration for synthesis of CaCO3 suitable for industry application. The biomolecule-based morphological strategies generally contain the strong interaction between crystal and functional groups, such as carboxyl group and alcohol hydroxyl group. Here, a comparative study of low-molecular-weight organic acids (OAs) with structural similarity on calcite crystallization is presented. The morphological evolution of calcite from rhombohedron to ellipsoid is observed, needle-like or dumbbell-like in the presence of monohydroxy OAs of lactic acid, malic acid, or citric acid, suggesting carboxyl group shows more remarkable effect on the morphologies of calcite than that of Li+. The strong adsorption behavior of carboxyl group on calcite can decrease the crystallinity with increased number of carboxyl groups. In contrast, the dicarboxylic OA of tartaric acid showed stronger effects on the phase transition process from vaterite to calcite than that of succinic acid and monohydroxy OAs. These findings will aid in synthesizing CaCO3 with specific morphology and polymorph by biochemical methods and are of great significance to the industrial application of CaCO3. By analyzing the morphological evolution, crystal phase of CaCO3, and adsorption behavior of organic acids at CaCO3 surface, it is found that the carboxyl group has a more remarkable effect on the morphologies and crystallinity of calcite than that of Li+ and hydroxyl groups; the alcoholic hydroxyl can retard the phase transition process from vaterite to calcite.image