Effects Of Alkaline Earth Metals On Mineralization Of Carbonate-based Biominerals

CaCO₃-based biominerals are important components of biominerals.They have a wide distribution and excellent composition-structure-property correspondences,so they are key research objects in the field of biomimetic mineralization and materials.During the formation of biological minerals,the organic matrix and inorganic ions play an important inducing and regulating role.Among them,the many types of organic matrix and the biomineralization mechanism itself have both been studied extensively and in depth.In contrast,but the effects of inorganic ions on biomineralization have received less attention.In terms of breadth,the types of ions studied are very limited.In depth,the research on inorganic ions is mainly limited to the control the crystal type and morphology of the CaCO₃ biomineralization.Aiming at the above two problems,this paper takes calcium carbonate as the biomimetic mineralization object.On the one hand,the effects of alkaline earth metal ions(Mg²⁺,Sr²⁺,Ba²⁺)on the biomimetic mineralization process of calcium carbonate are systematically studied to solve the defects of breadth.On the other hand,through the simplified model of BaCO₃ to simulate CaCO₃,the fine-tuning effect of metal ions was studied to supplement the lack of research depth.The main research contents and results of this article are as follows:?1?Using egg white protein as the organic matrix and Mg²⁺,Sr²⁺,and Ba²⁺as the inorganic ions,the effects of the three ions on the calcium carbonate mineralization process were studied by direct precipitation and gas diffusion methods,and the products were XRD,FT-IR The crystalline form and morphology of the product were analyzed by SEM and SEM characterization.The results show that Mg²⁺can obtain pure aragonite crystals by direct precipitation method and gas diffusion method,and its morphology is submicron beam.Sr²⁺obtains calcite and vaterite by the direct precipitation method,and the mixed crystals of calcite,vaterite and aragonite can be realized by the gas diffusion method.Ba²⁺is obtained by direct precipitation method of calcite and vaterite.When the reaction solution is added dropwise in reverse,pure vaterite crystals are obtained at a barium ion concentration of 3.6×10^-4 mol/L.The gas diffusion method can be used to prepare mixed crystals of calcite,vaterite and aragonite.The mechanism analysis shows that under certain conditions,the alkaline earth metal ions Mg²⁺,Sr²⁺,and Ba²⁺can all induce the formation of aragonite,but their inductive ability decreases in order:Mg²⁺>Sr²⁺>Ba²⁺,which is related to the difference between their ionic radius and calcium ion radius The smaller the gap,the easier it is to induce the production of aragonite calcium carbonate.?2?Taking the mineralization process of the cone layer in the eggshell as the research object,in order to create a simplified model of this process,BaCO₃ and Ca²⁺replace CaCO₃and Mg²⁺,respectively,and egg white simulates uterine fluid,resulting in non-isodiametric growth of BaCO₃ nanocrystals.By comparing the samples prepared under different conditions,it was found that Ca²⁺and egg white have relatively independent regulatory effects on the mineralization of BaCO₃.Egg white protein primarily limits the growth of the nanocrystals,resulting in a reduction in the particle size of the product.while Ca²⁺is the key to achieve their non-isodiametric growth.Elemental analysis tests show that Ca²⁺in BaCO₃ non-equidistant nanocrystals has a gradient distribution along the axis center to both ends,and the Ca²⁺content is proportional to the diameter of the nanocrystals.Simulation of the molecular dynamics involved indicates that Ca²⁺affects the diameter of the nanocrystals mainly by replacing Ba²⁺and changing the surface energy of crystal face?111?,thereby altering the crystals'growth habit.The research results in this article will expand people's understanding of the modulation of inorganic ions,enrich the mineralization mechanism of carbonate-based biological minerals,and provide theoretical guidance for biomimetic preparation of fine structure.