The Study Of Fabrication Of Calcium Carbonate Micro-nano Materials Based On Biomineralization Process

Calcium carbonates?CaCO₃?are abundant crystalline biogenic minerals found in nature.Moreover,CaCO₃ have been widely studied owing to their significance in biomineralization processes producing unique organic/inorganic material,which inspired scientists to produce CaCO₃ crystals with different morphologies and properties,and propose the formation mechanisms in vitro by mimicking the biomineralization processesIn this study,chitosan gel was used as substitute membrane,and sodium caseinate?NaCas?was added into the process to affect the crystallization of calcium carbonate.The results showed that in the presence of casein,the reaction induced the change in crystal shapes from the typical rhombohedral morphology with a flat surface to peanut-like shaped calcite crystals and stimulated a rough surface,no matter with or without the chitosan membrane.On this basis,by the measurement of SEM,XRD,FTIR,TGA and so on,we focused on the mechanism of the morphology change of calcium carbonate caused by sodium caseinate,and we found that sodium caseinate attributed significant effects on the morphology of calcium carbonate.With the increase of concentration of sodium caseinate,the shape changed from rhombohedral to Peanut-like,to hamburg-like and finally to a uncompleted ellipsoid-like shape.X-ray diffraction measurements showed that calcium carbonates obtained under our experimental conditions,were always calcite,while the height of the characteristic peak decreased.The Thermal gravimetry analysis?TGA?and Fourier transform infrared?FTIR?spectrometer confirmed that the sodium caseinate was contained in the crystal by the mass loss corresponding to the protein decomposition of sodium caseinate and by analyzing the characteristic peaks of protein secondary structure between 1600 cm^-1 and 1700 cm^-1.Next,we explored the co-effects of sodium caseinate and magnesium ions(Mg²⁺)on calcium carbonate crystals.With the addition of magnesium ions,the morphology of the calcium carbonate crystals could be shuttle-shaped.When sodium caseinate and Mg²⁺were added at the same time,the morphology of the calcium carbonate crystals could also appear peanuts-like,burgers-ike and incompletely spherical shape trend,at a lower concentration of sodium caseinate.In this research,magnesium ions possibly affected the the aggregation and self-assembly of casein,resulting in a bigger size of casein micelles.Although casein micelles or pure CaCO₃ particles exhibited negative surface charges,the surface charge of casein micelles was lower than that of CaCO₃ particles.This may explain the incorporation of casein in CaCO₃ mineralization decreased the surface charge of CaCO₃ crystals.When Mg²⁺ions were included in the mineralization system,the surface charge of deposited CaCO₃ crystals was increased.However,the involvement of casein in mineralization still decreased the surface charge of CaCO₃ minerals.In conclusion,the research presented the direct involvement of casein and magnesium ions in CaCO₃ mineralization.The morphology of CaCO₃ crystals is significantly affected by the concentration of casein.The secondary structure of casein proteins and the size of casein micelles play important roles in the CaCO₃ morphology constructing process.Mg²⁺can affect the mineralization of CaCO₃ via direct interaction with CaCO₃ crystals.Mg²⁺may also affect the casein assisted mineralization of CaCO₃ in an indirect way by affecting the size of casein micelles that have roles in controlling the CaCO₃ mineralization.This process is similar to that of in vivo biomineralization under the control of various mineral proteins and ions.