A facile ligand-free route to calcium carbonate superstructures

Abstract

Shape control has been achievable in a wide range of mesoscale materials, while for calcium carbonate (CaCO₃) which has relatively low dispersibility, limited ligand-binding ability and therefore unmanageable growth profile, the success is currently limited. Herein, the inherent transition behavior of CaCO₃ from nanoparticles to microscale superstructures in response to changes in solvent dispersibility has been successfully captured. The transition was slow enough to enable the obtaining of superparticles with several well-defined morphologies, including rod, dumbbell, and double-semisphere shapes. The presence of a suitable amount of water in the ethanol reaction solution was vital to trigger the transition, allowing the primary nanoparticles to take a fragmentation/disolution-assembly/recrystallization route to form superparticles. No organic ligand is needed, enabling large-scale manufacturing of “pure” (ligand-free) superstructures at low cost. The transition is robust with a high tolerance to the addition of small molecules. Doxorubicin-incorporated superparticles afforded sustained drug release and significant suppression of MCF-7 tumor cells, while the drug-free particles were highly biocompatible. These results not only provide insights into the intrinsic evolution processes and basic driving forces of the spherulite growth of CaCO₃, but also lay a foundation for localized drug delivery based on mineral materials.