添加物對碳酸鈣形態及晶相控制之探討

Morphology and Polymorph Control of Calcium Carbonate by Additives

黃雨潔(Yu-Chieh Huang)

指導教授 ： 陳振中

國立臺灣大學/理學院/化學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.02218

摘要

生物礦化是指生物體內形成礦物質的過程，舉凡在貝殼、骨骼、牙齒等礦物中都可發現這種現象。碳酸鈣是自然界中含量最豐富的生物礦化物，廣泛存在於軟體動物外殼、珊瑚以及海膽中。有趣的是，科學家發現這些生物可以選擇性地生成特定的碳酸鈣晶相。因此，探討生物體中晶相選擇的現象成為一個重要議題。在本研究中，我們運用兩種不同的實驗方法製備出碳酸鈣晶體並藉由添加鎂離子或簡單有機分子調控無機物的晶相與形態。其一，利用常溫常壓下氣體擴散法，可得到熱力學上最穩定的方解石，若在合成過程中加入鎂離子，則觀察到方解石轉變成文石的相轉變過程。其二，利用高溫高壓水熱法，可以得到文石的碳酸鈣晶相，而方解石及球霞石晶相可利用不同的有機添加物合成出來。這些生成的碳酸鈣晶體先運用IR、SEM、ICP-MS和 XRD等儀器做初步鑑定。接著利用固態核磁共振技術去探討碳酸鈣及其添加物分子層級的結構。我們成功地調控不同晶相的碳酸鈣生成並提出可能的相轉變機制。實驗結果對了解生物礦化中方解石和文石相轉變的過程以及生物體內晶相選擇的現象具有重要意義。

關鍵字

生物礦化 ； 碳酸鈣 ； 晶體晶相 ； 固態核磁共振 ； 鈣-43核磁共振

並列摘要

Biomineralization refers to a process of forming inorganic minerals such as shell, skeleton, tooth and etc., in biological systems of various organisms. Calcium carbonate, one of the most plentiful biominerals, is the major inorganic composition in mollusk shells, coral, and sea urchin. Organisms such as calcitic coccolithophoridae, the aragonitic pteropoda and ascidians with vaterite spicules are highly selective in the biomineralization of one polymorph or another. How Nature achieves such a precise polymorph selection in organisms is a key issue in the field of biomineralization. To shed light on this process, calcium carbonate is precipitated in the presence of different simple molecules to study how these additives affect the polymorph and morphology of calcium carbonate.
In this study, aragonite polymorph is obtained without any additives under high temperature and pressure using hydrothermal method. However, other polymorphs of calcium carbonate such as calcite and vaterite can be induced by adding various additives in the same system. In the gas diffusion system at ambient temperature and pressure, we obtain the calcite phase without additives while phase transformation from calcite to aragonite is observed in the presence of magnesium ions. The as-synthesized calcium carbonates are characterized by various methods including IR, SEM, ICP-MS, XRD and NMR. Various techniques of solid-state NMR techniques are used to investigate the structure of calcium carbonate as well as the additives at the molecular level. Particularly, 43Ca and 13C nuclei are utilized for the characterization of calcium carbonate environments. Our study reveals that pure polymorphs can be selectively acquired under sophisticated physical/chemical conditions. In addition, a possible mechanism of calcite-to-aragonite transformation is proposed with the emphasis on the role of magnesium ions.

並列關鍵字

Biomineralization ； calcium carbonate ； polymorphism ； solid-state NMR spectroscopy ； Ca-43 NMR

參考文獻

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