以反溶劑法與氯化膽鹼型離子液體製備奈米結構氧化鋅

我們發展證實出一種嶄新的方法「反溶劑法」來製備奈米結構氧化鋅，而本方法使用一種深共熔離子液體為溶劑，這是一種新型的離子液體，具有低蒸汽壓、高極性與良好的生物相容性，近來被廣泛使用，又被稱為一種綠色溶劑，我們使用尿素與氯化膽鹼（縮寫：UCC）所混合而成的深共熔離子液體為溶劑，UCC具有可以溶解許多金屬氧化物的能力，因而可以作為氧化鋅的溶劑，反溶劑的選擇則必須要與溶劑UCC互溶之外，還要是溶質的非溶劑，本研究中，我們使用水與乙醇作為反溶劑，經由控制成核與經體成長，達到控制氧化鋅型態與尺寸的目的。在低氧化鋅濃度下使用反溶劑法，可以經由進料流速與反溶劑組成來控制氧化鋅型態為雙圓錐或奈米棒狀物，反溶劑中的乙醇可以降低氧化鋅的成長速率也同時可以降低產物的尺寸，進料流速降低可使鋅原子進料成為氧化鋅成長的控制步驟，進而達到降低晶體成長速率，可使氧化鋅偏向偏好的一維方向成長，如此一來，就可以使雙圓錐氧化鋅改變型態成為奈米棒狀物。多孔結晶氧化鋅是一種由奈米晶體經由有規則性的組合而成，因此具有高比表面積與類似單晶的特殊晶體結構，我們使用一種名為Tris的生化緩衝劑來幫助氧化鋅奈米顆粒進行規則自組裝，氧化鋅奈米粒子先由反溶劑法產出，Tris則在水中使水解離出氫氧根，這些氫氧根接著附著在氧化鋅奈米粒子的氧空洞缺陷上，結果造成氧化鋅粒子的極性增加，進而使這些粒子做規則性的自組裝，形成多孔結晶型氧化鋅，而Tris扮演幫助氧化鋅粒子組裝的角色，因此高Tris濃度下，可以得到較大尺寸、較佳結晶性、較小比表面積的多孔結晶氧化鋅，然而在光觸媒應用方面，結晶性比比表面積更為重要，因此，在較高Tris濃度下所合成的多孔結晶氧化鋅具有更佳的光催化特性。在高氧化鋅濃度與低進料流速下，同樣使用反溶劑法，我們可以得到由氧化鋅與碳酸氫氧化鋅所構成的奈米板狀物，經過300~400 oC的鍛燒，碳酸氫氧化鋅將被分解成為氧化鋅，進而得到一種單晶多孔的氧化鋅奈米平板，這些多孔奈米板厚度很薄僅有10 nm左右，而上面的恐洞大小約只有5-60 nm，此氧化鋅多孔奈米板不只具有單晶的良好結晶性，還擁有高比表面積（約90 m2/g），而其暴露面為(11-20)，此材料具有用於水溶液中分解亞甲基藍具有良好的分解效能，其光催化效果與常見商用TiO2 P25相當。

關鍵字

氧化鋅；型態控制；反溶劑法；深共熔溶劑；離子液體；氯化膽鹼

並列摘要

In this article, we demonstrate a new, facile and green antisolvent process to prepare nanostructure ZnO. The deep eutectic solvent (DES) is a new class green solvent that is negligible vapor pressure, high polar and biocompatible. UCC is one of DES that shows high solubility of many metal oxides that can be used as solvent in this approach. The antisolvent should be miscible with the DES UCC and non-solvent for the solute. By controlling the nucleation and growth, various morphologies of ZnO can be made by this method. At low ZnO concentration in UCC, ZnO twin-cone and rods can be prepared with morphology and size controls by injection rate and the ethanol content in antisolvent. The ethanol in the antisolvent can reduce the growth rate of ZnO and also lower the product dimensions. If the injection rate of ZnO-containing DES was reduced, the supply of Zn source became limited and the crystal growth became 1D dominated and grows on the preferred direction. It turns the product structure from twin-cones to nanorods. Mesocrystal ZnO is a mesoporous material fabricated from nanocrystals (NCs) with ordered orientation superstructure. Thus the material possesses high surface area and good crystallinity as single crystal. We use a biological buffer Tris as an oriented agent in antisolvent. ZnO NCs were made in antisolvent then Tris can increase the concentration of hydroxyl group in antisolvent. The hydroxyl group can attach on the oxygen vacancies on the polar O-terminated surface then increased the polarity of the ZnO NCs and then be attached together with the same orientation to form a mesocrystal ZnO. The increasing amount of Tris can make a larger size, better crystallinity and smaller surface area mesocrystal ZnO. The crystallinity is the more important factor rather than surface area. Thus a mesocrystal ZnO prepared in high Tris concentration shows better photocatalytic reactivity. At high ZnO dissolved concentration and low injection rate, the ZnO-ZCH nanosheet can be made by this antisolvent approach. After the annealing, single crystal mesoporous ZnO nanosheet can be parpared. The sheet is thin with a thickness of 10 nm and many pores with size of 5-60 nm can be found on the nanosheets. The ZnO nanosheet is single crystal and high surface area (~90 m2/g) with the exposed plane of (11-20). It can be used as photocatalyst for degradation of methylene blue (MB) in aqueous solution. The single crystal mesocrystal ZnO nanosheet shows performance as good as TiO2 P25.

並列關鍵字

ZnO ； morphology control ； antisolvent ； deep eutectic solvent ； ionic liquid ； choline chloride

參考文獻

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以反溶劑法與氯化膽鹼型離子液體製備奈米結構氧化鋅

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