Biomimetic nucleation and growth of hydrophobic vaterite nanoparticles with oleic acid in a methanol solution

Hydrophobic vaterite nanoparticles were prepared via crystallization of CaCO₃ with oleic acid in methanol by mimicking the process of biomineralization. The molar ratio of oleic acid to calcium ion was varied from 0.1 to 0.5. By changing the concentration of the oleic acid, CaCO₃ particles with different shapes and polymorphism were obtained. High concentration of the oleic acid gave stable vaterite crystals, the polymorph of which did not change when the composite was kept in water for more than one week. Fourier transform infrared spectroscopy (FT-IR) and TGA analysis of the obtained product indicated that the oleic acid was bound to the crystalline CaCO₃. The contact angle of the modified vaterite reached 122°. We have succeeded in crystallization of hydrophobic CaCO₃ nanoparticles in situ.