Key Parameters for Size- and Shape-Controlled Synthesis of Vaterite Particles

Calcium carbonate (CaCO3) has attracted scientific attention due to its essential role in both inorganic and bioorganic chemistry. Vaterite is the least thermodynamically stable CaCO3 polymorph and has elicited great interest as an advanced biomaterial for tissue engineering, drug delivery, and a broad range of personal care products. Numerous methods of vaterite particle synthesis with different sizes and morphologies have highlighted the submicron porous particles of spherical or ellipsoidal shape as the most useful ones. In this regard, the current study is aimed at development of a reliable method for synthesis of such structures. Herein, submicron vaterite particles are synthesized by dropwise precipitation from saturated sodium carbonate and calcium chloride solutions in the presence of ethylene glycol while manipulating the concentration ratios of reagents. We demonstrate that our novel technique named "dropwise precipitation" leads to changing calcium concentrations in the reaction solution at each moment affecting the crystallization process. The proposed technique allows routine obtainment of vaterite particles of a required shape, either spherical or ellipsoidal, and a controlled size in the range from 0.4 to 2.7 μm and (0.4 × 0.7) to (0.7 × 1.1) μm, respectively. The key parameters influencing the size, shape, and percent of vaterite fraction for synthesized CaCO3 particles are discussed.