Abstract

Spurred by lessons learnt from the ability of nature to “design” biominerals with a high degree of control over their shape, size, mineral phase and hierarchical assembly over multiple length scales, a multitude of bottom-up research strategies have been geared towards developing self-assembled inorganic materials. The self-assembly route could lead to materials with novel functionality and complexity for applications in fields such as photonics, electronics and photovoltaics. Of particular interest in our labs are biomimetic 3D nanocrystalline composite materials, characterized by long-range orientational order and highly curved surfaces. These composite materials can be synthesized from the coupled reaction of the carbonates of barium, strontium and aragonite-type calcium carbonate with silica in alkaline (pH ca. 10–12) environments under the influence of atmospheric CO2. It has been shown that the complexity of these microstructures can be enhanced under dynamic reaction-diffusion conditions. To replicate this approach, we aim to characterize the effect of changes in solution conditions (i.e. pH, CO2 concentration and temperature) on the growth, structural morphology and the hierarchical organization of silica-carbonate biomorphs. The interaction between the organic and inorganic components of biological systems leads to some of the most beautiful (and often chiral) patterns seen in nature, as demonstrated by snail shells and the chiral narwhal tusk. Attempts to control the handedness of the helices during their formation involved the use of enantiomerically pure amino acids at the molecular level and chiral vaterite crystal templates at the mesoscale, to break the symmetry towards helices of a single handedness. Finally, we aim to show how the size and predominant morphologies of silica-carbonate microstructures was tuned as a function of concentration of Chicago Sky Blue (CSB; a sulphonated azo dye) in addition to its method of incorporation in the crystallization solution. This research also provides indirect evidence for accelerated growth rates of the microstructures from solutions containing dye as demonstrated by an increase in size relative to control experiments without dye during a growth period of 1.5–2 hours. Light and scanning electron microscopies were the principal tools used for the characterization of the as-formed biomorphs.