Morphology and Polymorph Selectivity Control in Calcium Carbonate Mineralization
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Morphology and Polymorph Selectivity Control in Calcium Carbonate Mineralization
Swaminathan Sindhu,1 Parayil K. Ajikumar,2 Subbiah Jegadesan,3 and Suresh Valiyaveettil*123 1 NUS- Nanoscience and Nanotechnology Initiative, National University of Singapore, Singapore-117543 2 Singapore -MIT Alliance, National University of Singapore, Sinapore-117576 3 Department of Chemistry, 3 Science Drive 3, National University of Singapore, Singapore – 117543, *Email: [email protected] ABSTRACT The present paper describes the mineralization of calcium carbonate at a low temperature (4 °C) and in presence of additives. Aspartic acid immobilized polyacrylic acid (PA-Asp) induced the nucleation of spherical vaterite polymorph at 4 °C. But at room temperature, a thin film of calcite was deposited. Moreover, stable amorphous calcium carbonate was precipitated in presence of magnesium at low temperature. The observed results show that low temperature and presence of additives influence the nucleation, polymorph selectivity and morphology of the precipitated calcium carbonate.
INTRODUCTION Biomimetic synthesis of inorganic materials is an emerging and promising approach for the controlled fabrication of crystalline materials with complex forms and novel properties.[1] Being an abundant biomineral in Nature, the crystallization of CaCO3 has been extensively studied and used as model system for the biomimetic/bio-inspired material synthesis.[2] Generally, templating by structured organic surfaces such as self-assembled monolayers (SAMs), Langmuir monolayers, biomacromolecules, functionalized polymers [3-10] and solution precipitation in presence of growth modifiers [11-18] such as ions, proteins, and synthetic polymers are used for the nucleation of calcium carbonate with interesting polymorph selectivity. We are interested in elucidating the mechanism of biosynthesis of mineralized materials as well as developing new strategies for biomimetic synthesis of calcium rich materials.[19-23] Herein we summarize some of our results about the synthesis of calcium carbonate with interesting morphology and polymorph selectivity using a functionalized synthetic polymer or magnesium ions as additives at 25 °C and 4 °C.
EXPERIMENTAL DETAILS Poly (acrylic acid) (PA, Mw = 5.0 x 103) was obtained from Aldrich, N-α-t-Boc-L-aspartic acid α-t-butyl ester (H-Asp-(OtBu)-OtBu), 1-Hydroxybenzotriazole (HOBt) and 1-ethyl-3-(3dimethylaminopropyl)-carbodiimide (EDC) were obtained from Novabiochem. Analytical grade CaCl2 and MgCl2 were purchased from Merck and used without any purification. Deionized ultra pure water was used throughout the experiment. For the synthesis of aspartic acid incorporated
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poly(acrylic acid), a mixture of H-Asp-(OtBu)-OtBu, N,N-diisopropylethylamine(DIEA), PA and HOBt in N,N-dimethylformamide (DMF) was added to EDC at 0 °C, and the resulting mixture was stirred at room temperature for 36 hours. The reaction mixture was filtered as the organic layer was washed with 1N HCl, 1N K2CO3 and saturated NaCl. The organic l
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