Biomimetic Synthesis And Characterization Of Calcium Carbonate Materials With Unusual Morphologies

Biological minerals are very important components of organism and high-performance composite materials. The most immediately striking aspect of biomaterials is the range of exquisite and unique morphologies observed, which are frequently disparate from their synthetic counterpart. Typical products of biomineralization are bones, teeth, shells, pearls, and so on. The general principles of biomineralization are introduced into the synthesis process of inorganic materials. Simulating the biomineralization process of the nucleation and growth of inorganic materials mediated by organic matrixes and biomimetic synthesis of inorganic materials with higher performance and more exquisite morphologies have become the study focus of material science. Calcium carbonate is one of the most abundant biomaterials and widely used in industry, the mechanical properties derive from the composite characters of CaCO₃ biomaterials, and in particular the morphology of CaCO₃. Thus, the emphasis in this paper will be placed on the morphogenesis of CaCO₃ in the light of biomimetic strategies.According to the general principles of biomineralization, we used polyacrylic acid as the organic template, which can efficiently interact with CaCO₃ crystal, to control the polymorphs and the morphologies of CaCO₃. These as-prepared CaCO₃ materials with unusual morphologies can be potentially promising candidates for advanced materials due to the importance of shape and texture in determining properties of materials. The main study contents are as following:The dendrite-shaped aragonite particles have been biomimetically synthesized through the carbonation route, in which CO2 gas at a constant gas feed rate of 0.1 L/min is bubbled through aqueous slurry of calcium hydroxide, in the presence of polyacrylic acid (PAA). The as-prepared products were characterized with scanning electron microscope, X-ray diffraction and transmission electron microscope with selected area electron diffraction. It was found that the dendrite-shaped aragonite particle present the single-crystal feature. The effects of the reaction temperature and the concentration of PAA on the nucleation and growth of aragonite crystals were investigated. The possible growth mechanism of the dendrite-shaped aragonite particles was discussed. This research not only can make us further understood the general principles of biomineralization, but also can open up a new avenue of industrial production of CaCO₃ particles with exquisite and unique morphologies due to the preparation method employed by us is simple, low-cost, mild condition.Exquisite and unusual star-shaped CaCO₃ particles were successfully biomimetically synthesized through a facile precipitation reaction of Na₂CO₃ with CaCl₂ in the presence of polyacrylic acid. Star-shaped CaCO₃ particles with 8 arms which evolved from original rhombohedral calcite crystals with their 8 points extending radially were obtained after reacting for 10min. PAA adsorbed onto the surface of the initial calcite rhombohedron and inhibited the growth of the central points of six {104} faces. The eight points of the initial calcite rhombohedron grew the fastest whereas the central points of the six {104} faces grew the slowest. Thereby, the eight points gradually extruded, resulting in eight distinct arms extending radially star-shaped CaCO₃ crystals. The most prominent advantage of our preparation method is timesaving compared with other methods reported. Star-shaped CaCO₃ particles are believed to be with a good prospect of application.Hollow CaCO₃ microspheres were successfully synthesized through the precipitation reaction in the presence of polyacrylic acid (PAA) and sodium dodecyl sulfonate (SDS). Introducing the surfactant/polymer composite into our system is in order to not only understand the effects of the surfactant/polymer composite on the crystallization and aggregation of CaCO₃, but also explore a possibly realized and simple preparation method. The"core-shell model"of PAA/SDS micellar aggregates serves as the spherical templates to generate hollow microspheres of CaCO₃ crystals in the precipitation system. Such hollow spherical CaCO₃ particles are used as paper fillers or pigments. They can improve the light scattering coefficient and thermal insulation properties of paper and bring us economic benefits owing to the industrial application.