Dopamine- and citrate-mediated, rapid synthesis of hollow calcium carbonate nanoparticles: Their formation, metastability and transformation

Exquisite design of calcium carbonate (CaCO3) is essential to meet the demands on the properties of functional materials for various applications, where additives play a crucial role in controlling over size, orientation, polymorph, and hierarchical structure. However, we are far from achieving the elaborate control over their structures and morphologies by use of the individual additive. Herein, we develop a simple and template-free approach for the rapid fabrication of hollow CaCO3-based nanocarriers via dual-additive mediated crystallization. The roles of additives and the impact of corresponding concentrations are systematically investigated to achieve a tunable and reliable design of CaCO3 particles, simultaneously yielding clues of how the additives mediated the formation of different morphology of amorphous calcium carbonate (ACC). Compared to single citrate-mediated ACC, dual-additive mediated hollow ACC renders them the prolonged stability and also facilitates their oriented crystallization into the homogeneous hierarchical architectures. Therefore, our findings indicate that the combined additives of dopamine and citrate exert synergistic effects on hollow structure formation and metastability as well as the subsequent crystallization, which contributes to deeper insight into additive-mediated crystallization pathway. These findings may offer new opportunities to design CaCO3-based materials with controllable morphology and crystal polymorphs.