Control of Crystalline Forms and Morphologies for CaCO_3 Crystals on 3-Mercaptopropionic Acid Self-assembled Monolayers
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In the present study,the crystals of CaCO3 were obtained by the slow diffusion of NH3 and CO2 into the CaCl2 solutions.Experimental results showed that both 3-mercaptopropionic acid self-assembled monolayers(SAMs) and solution temperature have significant influence on the crystalline forms and morphologies of calcium carbonates crystals.The precipitations of calcium carbonate were easily obtained from solutions at 25 ℃ but with polymorphism including calcite,vaterite and aragonite,while on the self-assembled monolayers there exist calcite crystals only.The morphologies of calcite crystals can be mediated by temperature.For example,the calcite precipitated at 25 ℃ has smooth surface while that precipitated at 60 ℃ has porous structure even though they were obtained on the same SAMs.XRD analysis showed that the growth of calcite on SAMs were along(104) and(006) planes.Keywords:
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The influence of structured organic surfaces on the oriented overgrowth of inorganic crystals is a fundamental aspect of biomineralization. This paper describes the dramatic changes in the crystallization of calcium carbonate within thermally evaporated stearic acid films by varying the pH of the electrolyte solution. Reaction of CO2 with electrostatically entrapped Ca2+ ions within the lipid films leads to the in situ growth of CaCO3 crystals. Whereas crystallization at pH = 6 gave rise to calcite of rhombohedral morphology, crystals nucleated at pH = 3 of the electrolyte solution were discrete crystals of the metastable polymorph, vaterite, along with calcite exhibiting unusual morphology. The process of Ca2+ ion incorporation in the stearic acid matrix was followed by quartz crystal microgravimetry and Fourier transform infrared spectroscopy, while scanning electron microscopy and X-ray diffraction measurements were employed to study the morphology and orientation of the crystallites within the lipid bilayer stacks.
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Controlled growth of calcium carbonate crystals with complex forms was achieved using dextran as a crystal growth modifier beneath a dipalmitoylphosphatidylcholine (DPPC) monolayer, and calcite-core-calcium bilirubinate (CaBR)-side multiple crystals were also observed owing to the epitaxial growth of CaBR crystals on calcite. During the process, interactions between the DPPC monolayer and calcium ions were studied based on the analysis of the surface pressure−molecular area isotherms. Control over the crystallization of calcite with novel morphologies, such as octahedral crystals and round calcite disks, has been observed. Remarkable morphological changes and continuous structural evolution of calcite from rhombohedral crystal to octahedral crystal to uniform round disks and polyhedrons as concentrations of dextran increased have been observed. Moreover, semirigid multiplex templates consisting of calcium carbonate crystals and DPPC monolayers were established under physiological pH conditions, and epitaxial growth of sheet calcium bilirubinate crystals on calcite had been observed to form calcite-core-CaBR-side multiple crystals. The dynamic process of formation of multiple crystals was analyzed by monitoring the morphologies and components of crystals in different crystal stages. The possible formation mechanism of polymorphous calcite and calcite-core-CaBR-side crystal has been proposed, which provides an important insight into the epitaxial relationships between the surfaces of inorganic and bioorganic complex crystals and affords a detailed nanoscale understanding of how inorganic seeds may have a significant effect on crystal nucleation and growth processes.
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One of the most common crystal habits of the thermodynamically stable polymorph of calcium carbonate, calcite, is the rhombohedral one, which exposes {10.4} faces. When calcite is precipitated in the presence of Li+ ions, dominantly {00.1} faces appear together with the {10.4}, thus generating truncated rhombohedrons. This well-known phenomenon is explored in this work, with the aim of obtaining calcite crystals with smooth {00.1} faces. In order to achieve this objective, the formation of calcite was examined in precipitation systems with different c(Ca2+)/c(Li+) ratios and by performing an initial high-power sonication. At the optimal conditions, a precipitate consisting of thin, tabular {001} calcite crystals and very low content of incorporated Li+ has been obtained. The adsorption properties of the tabular crystals, in which the energetically unstable {00.1} faces represent almost all of the exposed surface, were tested with model dye molecules, calcein and crystal violet, and compared to predominantly rhombohedral crystals. It was found that the {00.1} crystals showed a lower adsorption capability when compared to the {10.4} crystals for calcein, while the adsorption of crystal violet was similar for both crystal morphologies. The obtained results open new routes for the usage of calcite as adsorbing substrates and are relevant for the understanding of biomineralization processes in which the {00.1} faces often interact with organic macromolecules.
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Supersaturation
Tartaric acid
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In this paper,2-hydroxybenzoic acid is used as additive to control the crystallization of CaCO3.The polymorph and morphology of crystals are characterized by X-ray diffraction(XRD)、scanning electron microscopy(SEM) and thermogravimetric analysis(TGA).As the results have shown,both spherical vaterite and calcite are produced after 6h and 12h when the amount of 0.04mmoL of 2-hydroxybenzoic acid is added and the pH reached 7.0.When the mineralization time is 24h,however,only calcite crystals are formed while spherical vaterite crystals almost disappeared.
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The authors studied the synthesis of calcium carbonate (CaCO3) in hexamethylenetetramine (HMT) aqueous solution using diethyl carbonate as CO2 supplier. Scanning electron microscopy and X-ray powder diffractometry were used to characterize the products. The results showed that calcite crystals with rough surface were formed in solution, while calcite polyhedrons and “flowers” were formed at the air/solution interface. The FTIR results indicated a strong interaction between HMT molecules and Ca2+ ions. The possible formation mechanism of the CaCO3 crystals obtained in the solution and at the interface was discussed, which could be explained by mesocrystal assembly.
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