Monodisperse spherical CaCO3 superstructure self-assembled by vaterite lamella under control of regenerated silk fibroin via compressed CO2

In this paper, spherical calcium carbonate (CaCO3) with ordered lamella nanostructure was prepared by using regenerated silk fibroin (RSF) as a crystal modifier via compressed CO2. The crystal morphology could be tuned from lens-like to spherical by altering RSF concentration, reaction time, and temperature. Time-resolved experiments showed that the lamellas were formed by several nanoparticles' aggregation and orientation. Amorphous calcium carbonate (ACC) was seized in the early stage, which would transform to vaterite in a short period. And the dissolution-recrystallization process of CaCO3 was found in a later stage, which was consistent with Ostwald ripening, resulting in the decrease of lamella thickness and the release of RSF that was absorbed in the crystal. Finally, a possible mechanism for the formation of spherical CaCO3 crystal was proposed.