Non-classical Controllable Fabrication And Mineraliztion Of Calcium Carbonate

Inorganic minerals in organisms have attracted extensive attention because of their diverse components,complex structures,outstanding functions,and unique formation mechanisms.In fact,in the formation of natural biominerals,a process that does not accord with the classical "nucleation-growth" crystallization mechanism has been identified,which is termed as "nonclassical mineralization" process.Such process involves the formation of a variety of intermediates,different crystal growth pathways,and complex regulatory factors.As a common biological mineral,calcium carbonate is regarded as a standard model in the field of biomineralization.Based on calcium carbonate,a lot of detailed studies have been carried out on the nonclassical mineralization process.However,there are still many mysteries in the mechanism of nonclassical mineralization.Specifically,despite intensive investigations,the mineralization process of calcium carbonate is yet to be thoroughly understood.Therefore,in this dissertation,detailed analyses of the calcium carbonate mineralization process are carried out,whereby the following results are achieved:1.Amorphous calcium carbonate nanoparticles were synthesized by gas diffusion reaction in ethanol-water system.By means of freeze transmission electron microscopy,it was observed that amorphous calcium carbonate nanospheres had a secondary structure-2 nm cluster structure.This structure suggests that the formation mechanism of amorphous calcium carbonate nanospheres is not via a classical "nucleation growth"process but should be formed by cluster assembly growth.Through the analysis of the formation principle of clusters in the ethanol-water system,it is found that the formation of this cluster structure is related to the content of water in the reaction system,that is,the reaction products can show secondary cluster structure only in less water environment.The structural transformation of the cluster assembly is studied by heating-induced crystallization.It is revealed that water is an important factor to maintain the cluster structure.By introducing hard templates with different shapes into the reaction system,calcium carbonate clusters can grow evenly on the surface of the templates.It is found that the mechanical properties of the bulk material prepared by graphene oxide nano sheets coated with amorphous calcium carbonate are significantly improved than those of pure graphene.The results shows that this calcium carbonate cluster assembly has good shapeability and can be used to grow ultra-thin and uniform calcium carbonate coatings on a variety of substrate surfaces.2.By controlling the concentrations of the reactants,the H+ concentration,the reaction solvent and the small molecular additives,the synthesis of amorphous calcium carbonate nanoparticles prepared in gas-phase diffusion reaction can be regulated,and the effects of reactants and reaction environment on the formation and assembly of calcium carbonate clusters are studied.Adjusting the concentration of reactants and H+concentration of the reaction system mainly affects the formation of cluster assembly,and then affect the size of amorphous calcium carbonate nanoparticles.The results reveal that the change of the reaction solvent can significantly affect the growth of cluster assemblies and produce larger or more heterogeneous particles.Also,the addition of additives with great solubility differences in ethanol and water also have a significant impact on the morphology of amorphous calcium carbonate nanoparticles.Therefore,we conclude that several factors including the concentration of reactants,the H+concentration of the reaction environment,the polarity of reaction solvent and the role of small molecular additives can affect the clustering process in this reaction system.The loading properties of the amorphous calcium carbonate nanoparticles are tested by using several dye molecules.It is proved that amorphous calcium carbonate nanoparticles with cluster structure have loading capacity for small molecules These results will lay a foundation for more delicate control of the synthesis of amorphous calcium carbonate nanoparticles.3.The mechanism of magnesium-controlled calcium carbonate mineralization has been studied by investigating the phenomenon of magnesium isotope fractionation in the process of magnesium-controlled calcium carbonate mineralization in water.By adjusting the concentration of magnesium in the reaction system,the phase transformation pathway of the amorphous calcium carbonate can be tuned,and the crystallization product changes from calcite to aragonite.Two different crystallization pathways of calcium carbonate have been distinguished by observing the phenomenon of magnesium isotope fractionation.The transformation of amorphous calcium carbonate to calcite is mainly through "dissolution recrystallization".After adding a large amount of magnesium,the dissolution is inhibited,and the amorphous calcium carbonate tends to in-situ phase transformation and finally crystallizes into aragonite.The roles of magnesium in various stages of calcium carbonate mineralization have also been demonstrated,including stabilizing amorphous calcium carbonate,inhibiting calcite nucleation,and promoting the material exchange between calcium carbonate and reaction solution.This study clearly reveals the mechanism of different mineralization processes of calcium carbonate and explains the regulatory role of magnesium in it in detail.