Study Of Crystallization Of Calcium Carbonate Regulated By Pb²⁺/Organic Matrix

Biominerals are highly organized composites of inorganic an d organic materials precisely controlled by living organisms, such as nacre. T hey are frequently considered as inspirations for biomimetic materials because of their superior mechanical properties, complex shapes with hierarchical structures, and exceptional ability to self-assemble. In this paper, based on the principle of biomineralization, hen egg white(HEW), Chitosan Hydrochloride, lead ion/hen egg white and lead ion/Chitosan Hydrochloride were respectively served as modifiers to the preparation of different morphologies and polymorphs biomimetic calcium carbonate by direct precipitation method. The prime contents are as follows:1. The calcium carbonate particles with different morphologies were prepared in the presence of Pb2+/HEW by a direct precipitation method. The influences of Pb2+ concentrations and mineralization time on the crystallization CaCO3 are investigated. The CaCO3 particles are characterized by scanning election microscopy, X-ray diffractometer, Fourier transform infrared spectrometer and thermogravimetric analysis. The morphologies, polymorphs and comments of HEWs are obtained. The results indicate that the larger concentration of Pb2+ favor the growth of calcite, and it is the only product in the mineralized system with the volume fraction of HEW 0.5%, [Pb2+] 170 ppm, mineralization time 2 h. However, smaller larger concentrations of Pb2+ promote the formation of spheral vaterite particles. Upon prolonged crystallization time, spheral vaterite particles were first formed, which gradually transforms into stable calcite. The binding of cation ions and organic macromolecules is a key step on the control of the morphology and polymorph of calcium carbonate in the mineralized system confirmed by HEW adsorption experiments.2. The calcium carbonate particles with core-shell structure were prepared in the presence of chitosan hydrochloride by a direct precipitation method. The prepared sample was characterized using scanning election microscopy, X-ray diffractometer and Fourier transform infrared spectrometer. The influences of the adding order of reaction solutions and the standing time on the polymorph and morphology of Ca CO3 have been investigated, and the growing mechanism of core-shell structure also has been analyzed. The results indicate that the spherical particles were formed by small CaCO3 nanoparticles random aggregation with the volume fraction of chitosan hydrochloride 0.4%, standing time 1 h. SEM images of a broken Ca CO3 sphere after grinding show that vaterite particles is a typical core-shell structure. Upon prolonged crystallization time, metastable vaterite gradually transforms into stable calcite. While the standing time was fixed, calcite crystals were obtained by changed the adding order of reaction solutions. The influences of Pb2+/chitosan hydrochloride on the crystallization of Ca CO3 also have been investigated. The results indicate that the addition of Pb2+(1000 ppm) has no obvious effect on the polymorph and morphology of Ca CO3 under the same conditions.