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

Abstract

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.