High‐Magnesium Calcite Mesocrystals: Formation in Aqueous Solution under Ambient Conditions

• Published in: Angewandte Chemie International Edition 2017-12, Vol.56 (51), p.16202-16206
• Main Authors: Yu, Pao‐Tao, Tsao, Chieh, Wang, Chun‐Chieh, Chang, Chun‐Yu, Wang, Chia‐Hsin, Chan, Jerry Chun Chung
• Format: Article
• Language: English
• Subjects: amorphous calcium carbonate; Aqueous solutions; biomineralization; Calcite; Calcium; Calcium carbonate; Diffraction patterns; Electron diffraction; Image transmission; Magnesium; Microspheres; Moisture content; Phase transitions; phospholipids; secondary nucleation; Solid state; tomography; Water content
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201708507

Mesocrystals of high‐magnesian calcites are commonly found in biogenic calcites. Under ambient conditions, it remains challenging to prepare mesocrystals of high‐magnesian calcite in aqueous solution. We report that mesocrystals of calcite with magnesium content of about 20 mol % can be obtained from the phase transformation of magnesian amorphous calcium carbonate (Mg‐ACC) in lipid solution. The limited water content on the Mg‐ACC surface would reduce the extent of the dissolution–reprecipitation process and bias the phase transformation pathway toward solid‐state reaction. We infer from the selected area electron diffraction patterns and the dark‐field transmission electron microscopic images that the formation of Mg‐calcite mesocrystals occurs through solid‐state secondary nucleation, for which the phase transformation is initiated near the mineral surface and the crystalline phase propagates gradually toward the interior part of the microspheres of Mg‐ACC. Mesocrystals of high‐Mg calcites are prepared in aqueous solution using phospholipids as additives. The dark‐field images originating from the (104) diffraction spot indicate that a large collection of the nanocrystallites of Mg‐calcites have the same orientation.