| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 101 === Biomineralization is an important process which organisms use to produce biominerals in nature. One of the biominerals, for example, the nacre of the shell in the ocean is made of layered aragonite and proteins. The layered hybrid structure and the absence of cleavage planes of aragonite allow the nacre to acquire certain excellent properties such as hardness and toughness. To investigate this composite structure, we have to analyze the single-layered organic / inorganic composite calcium-carbonate thin-film first. In order to prepare this biomimetic material, serveral method including double-jet method, diffusion method, and Kitano method have been employed. In addition, Chou (2011) and Wang (2012) used the technique developed in Professor Tai’s laboratory to prepare the supersaturated CaCO3 solution stabilized in the metastable region, and a thin-film of CaCO3 was successfully prepared on the surface of a solid matrix from the supersaturated solution in the presence of a soluble polymer. This method has three advantages over the others: the ease for controlling the solution properties, the simple procedure for preparing supersaturated solution, and the time-effectiveness for growing the CaCO3 thin-film. The calcium carbonate has been found to exhibit three polymorphs formed in the biominerals. Given that the difference in crystal structures between polymorphs results in their property distinction, the control of polymorphism is of primary importance in developing biomimetic materials.
In the first part of this research work, efforts were directed toward exploring how the polymorphism of CaCO3 thin-film was affected by pH and ionic impurity (Mg2+、Fe2+) in the experimental conditions which were identical to the ones used in Wang (2012). A lower growth rate of CaCO3 thin-film formation and smaller characteristic peaks of associated XRD spectrum were observed in this work, as compared with the results reported in Wang (2012). We speculated that the difference between the results of this and Wang’s studies might be attributed to the batch-to-batch variation of the chemicals used. We found that the growth rate and the intensities of characteristic peaks of XRD spectrum could be raised by increasing the relative supersaturation of the supersaturated CaCO3 solution.
Results of our group, indicates that the polymorphism of calcium carbonate can be profoundly affected by several operating variables, including the magnetic field intensity, temperature, type of ionic impurity, pH value, and relative supersaturation. Wang (2012) have explored the effects of the first three operating variables. As a continuation, we examined the effects of three ionic impurities (Zn2+、Cu2+、Mn2+) on the polymorphism of CaCO3 thin-film in this thesis.
Our results showed that, when no ionic impurity was present (the control group), 34.82% aragonite and 65.18% vaterite were observed at the relative supersaturation of 12, 40 ℃ and [Ca2+]/[COO-]=55. At the [Mg2+]/[Ca2+] ratio of 0.2, the composition of aragonite increased from 34.82% to 60.16%. When the [Mg2+]/[Ca2+] ratios=0.4 and 0.5, the formation of vaterite was completely suppressed, and the 100% aragonite film was formed. When [Fe2+] was increased from 0 to 0.62-1.64 mg/L, the proportion of aragonite was found to increase from 34.82% (with no Fe2+) to 40.11~41.31%, whereas the proportion of calcite rose from 0% (with no Fe2+) to 0%~7.57%. However, the composition of polymorphism of CaCO3 thin-film in the presence of Zn2+ and Cu2+ due to the insignificant characteristic peaks of XRD spectrum. Similar results were obtained in the groups with the treatment of Cu2+ and Zn2+. At [Zn2+]=0.11 mg/L or [Cu2+]=0.082 mg/L, the polymorphism was composed of vaterite and aragonite, but the intensity of characteristic peaks of XRD spectrum considerably decreased. At [Zn2+]=0.21 mg/L or [Cu2+]=0.164 mg/L, the polymorphism was only composed of vaterite. At [Zn2+]=0.53 mg/L or [Cu2+]=0.414 mg/L, no characteristic peaks were observed in the XRD spctrum, whereas tiny aragonite thin-films were found at the surface of solid matrix of Cu2+ sample through POM. Moreover, while no change in the composition of calcite was detected, the proportion of aragonite was significantly decreased from 34.82% in the control group (with no Mn2+) to 1.63% when the concentration of Mn2+ was increased from 0 to 0.616~2.466 mg/L.
|
|---|
