Controlled synthesis of calcium carbonate nanocrystals with multi-morphologies in different bicontinuous microemulsions

The nucleation and growth of calcium carbonate nanocrystals were studied in two types of bicontinuous microemulsions, consisted of P-octyl polyethylene glycol phenylether (OP)/n-amyl alcohol/cyclohexane/water, and the above microemulsion containing dl-aspartic acid (dl-Asp). The produced CaCO3 nanocrystals were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FT-IR) and X-ray diffraction (XRD). The results indicated that OP and dl-Asp used as soft template could control synthesis of CaCO3 nanocrystals well. The various shapes of CaCO3 nanocrystals, such as solid sphere, network, whisker, rod, and hollow sphere were successfully prepared by altering the concentration of the reactants, adding dl-Asp, and adjusting the pH values of dl-Asp/CaCl2 aqueous solution. Sole calcite phase was obtained in OP bicontinuous microemulsion. The presence of dl-Asp was helpful for the formation of thermodynamically unstable vaterite phase. In OP/dl-Asp bicontinuous microemulsion, the higher pH value of dl-Asp/CaCl2 aqueous solution is, the more vaterite will be formed. A nucleation-limited growth and limited aggregation (NGA) model was used to explain growth mechanism of the network-like calcium carbonate in this study.