Biomimetic synthesis of aragonite superstructures using hexamethylenetetramine

In this paper, biomimetic synthesis of aragonite superstructures using a low molecular weight organic-hexamethylenetetramine (HMT) as an additive in the presence of CO2 supplied by an ammonium carbonate ((NH4)2CO3) diffusion method at room temperature was studied. The products were characterized by scanning or transmission electron microscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray powder diffractometry, and selected area electron diffraction. The results showed the aragonite superstructures especially dumbbell-flower-like ones were obtained. The formation process of calcium carbonate (CaCO3) in HMT aqueous solution was investigated, suggesting that the products transformed from calcite to vaterite primarily, and then changed into a mixture of aragonite and calcite with an increase of reaction time. The formation mechanism of CaCO3 in HMT solution was also discussed, revealing that aragonite might be controlled by HMT molecules and NH4+ ions together.

Graphical abstractThe well-defined aragonite hierarchical superstructures are formed using hexamethylenetetramine in aqueous solution.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights▶ Aragonite superstructures are formed with hexamethylenetetramine at about 25 °C. ▶ Dumbbell-flower-like aragonite produces when hexamethylenetetramine/Ca2+=10:1. ▶ CaCO3 formation in hexamethylenetetramine solution violates the Ostwald ripening. ▶ Hexamethylenetetramine and NH4+ might control the growth of aragonite together.