Superstructures and Mineralization of Laminated Vaterite Mesocrystals via Mesoscale Transformation and Self-Assembly

It is an interesting phenomenon for natural organisms to have control over the shapes and sizes of inorganic nanocrystals and arrange them into ordered Superstructures. This phenomenon attracts many attempts to mimic the biomineralization process to synthesize novel materials. In the present work, a new superstructure of hexagonal vaterite mesocrystals consisting of nanocrystals has been synthesized via a mesoscale transformation process by controlled release of carbon dioxide through slow decomposition of dimethyl carbonate in the presence of cetyltrimethyl ammonium bromide at room temperature. The superstructures are composed of hundreds of well-stacked vaterite flakes, which build spheres with an axis and two poles. We can find that mesocrystal plates at the poles are arranged with their surfaces parallel to the axis, whereas the plates at the equator of the spheres are arranged with their surface vertical to their axes. The flakes present the unstable (001) planes and show hexagonal shapes with a thick core and thin edges. The subunits of vaterite flakes consist of oriented aggregation of nanocrystals which are transformed from the amorphous phase. New evidence of the mesoscale transformation process has been observed in detail by measuring the structures of the products at different reaction stages, revealing that the product evolves from amorphous oblate particles to doughnutlike particles, which crystallize and delaminate into superstructures. The mineralization process is discussed with the cooperative reorganization of coupled inorganic and organic components relevant for models of matrix-mediated nucleation in biomineralization. This contribution will be helpful in understanding the aggregation-driven formation of complex and higher-order structured materials as well as the biomineralization mechanisms.