Two competitive nucleation mechanisms of calcium carbonate biomineralization in response to surface functionality in low calcium ion concentration solution

摘要

Four self-assembled monolayer surfaces terminated with –COOH, –OH, –NH₂ and –CH₃ functional groups are used to direct the biomineralization processes of calcium carbonate (CaCO₃) in low Ca2+ concentration, and the mechanism of nucleation and initial crystallization within 12?h was further explored. On ?COOH surface, nucleation occurs mainly via ion aggregation mechanism while prenucleation ions clusters may be also involved. On ?OH and ?NH₂ surfaces, however, nucleation forms via calcium carbonate clusters, which aggregate in solution and then are adsorbed onto surfaces following with nucleation of amorphous calcium carbonate (ACC). Furthermore, strongly negative-charged ?COOH surface facilitates the direct formation of calcites, and the ?OH and ?NH₂ surfaces determine the formation of vaterites with preferred crystalline orientations. Neither ACC nor crystalline CaCO₃ is observed on ?CH₃ surface. Our findings present a valuable model to understand the CaCO₃ biomineralization pathway in natural system where functional groups composition plays a determining role during calcium carbonate crystallization.