利用自組合反應法合成中孔洞二氧化鈦之研究

The Study of Synthesis of Mesoporous TiO2 by Evaporation-induced Self Assembly Process

王毅(Yi Wang)

指導教授 ： 洪逸明

元智大學/工程學院/化學工程與材料科學學系/碩士(2008年)

https://doi.org/10.6838/YZU.2008.00041

摘要

所謂中孔洞 (mesoporous)是指孔洞尺寸介於2 ~50 nm之間。中孔TiO2具有高表面積、高孔隙率、體密度低、熱穩定性高及孔洞排列規則等優點，可運用於催化、染料敏化太陽能電池、太陽能製氫及光觸媒等用途。本研究以自組合反應 (evaporation-induced self assembly, EISA)合成方法，利用三嵌段共聚塊界面活性劑產生之微胞為模板，四丁基鈦酸塩 (tetrabutyl orthotitanate) 為無機前驅物，在適當溫度及濕度熟化後，經350 ℃煆燒製備出的中孔洞TiO2，以恆溫氮氣吸/脫附、小角度X光繞射 (small-angle X-ray diffraction, SXRD)及穿透式電子顯微鏡 (transmission electron microscopy, TEM)等分析其特性。
實驗結果顯示：以乙醇為溶劑所合成之中孔洞TiO2，其最適微胞堆積之比例為PEO/Ti = 0.7，遲滯迴圈為標準中孔H2型式，BET比表面積值為224.8 m2/g。此試樣經SXRD分析，於2θ = 0.8o處有明顯繞射峰。由TEM影像圖觀察出孔洞呈蟲狀排列 (worm-like)，孔徑約為6~7 nm，孔壁由TiO2微晶結構構成。不同TBOT含量，因降低無機前驅物之交聯作用(cross-linking)，經煆燒後顯示其並非能有效改善孔洞排列規則。
利用正丁醇 (butanol)及丙二醇單甲醚(1-Methoxy-2-porpanol, propylene glycol monomethyl ether, NMP)取代乙醇為溶劑，推斷其沸點較高可增加微胞組織排列時間。實驗結果顯示：以正丁醇為溶劑，以PEO/Ti = 0.8比例所製備之試樣，其遲滯迴圈屬H1型式，BET比表面積值為186.3 m2/g。經TEM觀測，孔洞呈高規則六角堆積排列，孔徑大小約 5~5.5 nm之間，孔壁由TiO2微晶所構成。而以NMP為溶劑，PEO/Ti = 0.8比例所製備之試樣分析結果得知，遲滯迴圈屬H2型式，BET比表面積值為239.2 m2/g，TEM影像圖可觀察出其正向及直條孔洞亦呈高六角堆積排列，孔徑大小約6 nm，孔壁由TiO2微晶結構構成。由TEM影像圖顯示降低溶劑之揮發速率可增長微胞規則排列時間，經高溫350 ℃煆燒後之試樣孔洞排列規則度明顯改善。

關鍵字

中孔洞 ； 二氧化鈦 ； 自組合反應法

並列摘要

The pores with diameters in the size range of 2~50 nm are considered mesoporous materials. Mesoporous titania has unique properties such as high specific surface area, high porosity, low bulk density, high thermal stability, and order pores arrangement. They can be applied in catalysis, dye sensitized solar cell, hydrogen production, and photocatalysis fields. In this study, we prepared mesoporous titania based on the evaporation-induced self assembly (EISA) process using triblock copolymer as template agent and tetrabutyl orthotitanate as inorganic precursor via aging treatment under appropriate temperature and relative humidity, then the gels were calcined at 350℃. The characterization of mesoporous titania materials were investigated by N2 adsorption-desorption isothermal, small-angle X-ray diffraction (SXRD), and transmission electron microscopy (TEM).
We determined the optimal molar ratio of PEO/Ti to be 0.7 for synthesis mesoporous titania using ethanol as main solvent. The results of N2 adsorption-desorption isothermal shows that the hysteresis loop belong to H2 type and the BET specific surface area is 224.8 m2/g. In the SXRD results, the pattern shows a main peak at 2θ = 0.8o. The TEM images show the pore arrangement is worm-like structure, the pore size is 6~7 nm, and the pore wall was composted of nanocrystallites TiO2 Both for high and low TBOT concentration, the ordered arrangement of micelle can not be improved apparently.
In addition, the mesoporous titania were synthesized by using both butanol and propylene glycol monomethyl ether (NMP) as solvent which were inferred to extend the organization time of organization micelle due to the higher boiling point than that of ethanol. The results of samples synthesis using butanol as main solvent at the PEO/Ti ratio of 0.8 show that the hysteresis loop belong to H1 type and the BET specific surface area is 186.3 m2/g. The TEM images show that the samples have a uniform , well-order hexagonal mesostructure with the pore size of 5~5.5 nm, and the pore walls were composed of nanocrystallites TiO2. The results of samples synthesis using NMP as main solvent at the PEO/Ti ratio of 0.8 show that the hysteresis loop belong to H2 type and the BET specific surface area is 239.2 m2/g. The TEM images show that the pore arrangement was highly order hexagonal mesostructure with the pore size of 6 nm, and the pore walls were composed of nanocrystallites TiO2. From the results of N2 adsorption-desorption isothermal, SXRD and TEM, it was demonstrated that the mesoporous titania synthesis using high boiling point point solvents, such as butanol and NMP, can improve the pore order arrangement due to extend the organization time of micelle.

並列關鍵字

mesoporous ； TiO2 ； Evaporation induced Self Assembly Process

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