核殼結構奈米貴金屬/二氧化鈦之合成及其在光催化反應之應用

M@TiO2 (M= Pd, Au, Ag) catalysts with core/shell structure and application on photocatalytic destruction of dye.

江佳蓉(Chia-Jung Chiang)

指導教授 ： 陳郁文

國立中央大學/工學院/化學工程與材料工程學系/碩士(2012年)

摘要

本研究之目的在於發展高效率催化活性之核殼結構光觸媒，並將其應用於有機汙染物之分解。利用摻雜貴金屬改質二氧化鈦表面以提高光催化效率，由於金屬在表面形成電子活性點以促進界面電荷轉移。此種觸媒結構雖然活性好，但容易造成暴露在外的金屬與其他表面介質產生作用，使金屬容易溶解或腐蝕，導致觸媒活性衰退。核殼結構可以克服此缺點，將貴金屬置於內核，而二氧化鈦當作殼層。本研究係利用膠體凝膠法合成貴金屬/二氧化鈦核殼結構光觸媒，並利用不同製備條件(貴金屬前驅物濃度與水熱時間)來達到控制貴金屬擔載量以及二氧化鈦的結晶性。觸媒鑑定方面，主要是以X光繞射儀、穿透式電子顯微鏡、紫外可見光漫反射光譜儀與X光電子能譜儀進行鑑定與分析。並以兩支8w波長為254 nm的紫外燈管與250 w的鹵素燈為光源進行亞甲基藍的光催化反應測試，光降解樣品取樣利用紫外可見光光譜儀分析濃度，進行光反應活性之鑑定。第一部分為合成不同的貴金屬（鈀、銀、金）作為內核，二氧化鈦為外殼，並探討結構，表面組成與活性之間的關係。由TEM圖中顯示其金屬核的顆粒大小約為3-12nm，殼層之二氧化鈦厚度約為6-20nm。在X光繞射分析顯示金屬核為鈀的觸媒其二氧化鈦具有較高的結晶性。光反應活性之鑑定以10 ppm亞甲基藍水溶液為光反應標準物，以兩支8 w 波長為254 nm 的紫外光燈管與250w的鹵素燈當作光源。結果顯示鈀/二氧化鈦在上述兩種光源中都具有較高的活性。其主要的因素為二氧化鈦的結晶性，晶型結構明顯的二氧化鈦，可以增加光子進入內核的量子效率。而在可見光的活性測定中，其主要的因素為較低的能隙與在可見光中具有較高的吸收。第二部分以貴金屬擔載量與水熱時間作為變因並探討與活性之間的關係， 光反應活性之鑑定以10 ppm亞甲基藍水溶液為光反應標準物以兩支8 w 波長為254 nm 的紫外光燈管當作光源。在Pd@TiO2 ，Ag@TiO2與Au@TiO2中最適化的金屬擔載量分別為0.5wt.%，0.5wt.% 及 1.0wt%。水熱時間以18小時最佳。此外光催化活性也與二氧化鈦結晶性成正相關。總結結果，在metal@TiO2核殼型光觸媒中，貴金屬核的大小並不是影響活性的主要因素，而是與二氧化鈦殼層的結晶性、貴金屬的種類、擔載量與氫氧基含量有關。

關鍵詞：二氧化鈦、核殼結構、光觸媒、奈米鈀、奈米銀、奈米金、膠體溶膠法、水熱法、亞甲基藍降解

關鍵字

水熱法 ； 奈米銀 ； 奈米金 ； 核殼結構 ； 奈米鈀 ； 光觸媒 ； 二氧化鈦

並列摘要

The purpose of this study was to develop a catalyst with high efficiency photocatalytic activity and had core/shell structure. It could be applied to the degradation of organic pollutants under UV light illumination. The literature shows that doping noble metal on the surface of titanium dioxide can enhance the photocatalytic activity because noble metal can form active sites to promote the electronic charge transfer in the interface of metal and titanium dioxide. Although the activity of this kind of structure is high, the exposed metal is easy to dissolve or corrosive, leading to catalyst decay. Core/shell structure can be used to overcome this shortcoming, noble metals located in the core, while titanium dioxide is in the shell. In this study, M@TiO2 (M = Pd, Ag, Au) catalysts with core/shell structure were synthesized by sol-gel method with hydrothermal treatment with different preparation parameters. These catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectra (UV-vis DRS), and X-ray photoelectron spectroscopy (XPS). The photoreaction was carried out in a 10 ppm methylene blue solution with two 8w 254 nm UV light and 250W halogen lamp as the light source. The concentration of MB in the degradation samples were measured by UV-vis spectrometer (UV-vis). This thesis is divided into two parts, the first part is on the preparation of M@TiO2 (M = Pd, Ag, Au) with core/shell structure and its photocatalystic activity. The TEM micrographs results show that the particle size of metal cores was about 3-12nm, and the shell thickness of titanium dioxide was about 6-20nm. The XRD pattern results show that Pd@TiO2 has highest crystallinity. The photoreaction was carried out in a 10 ppm methylene blue solution with two 8w 254 nm UV light and 250W halogen lamp as the light source. Pd@TiO2 had the highest activity under UV light and halogen lamp illumination. Because Pd@TiO2 had higher crysallinity, lower band gap energy, and higher absorption at visible region. The second part is on discussion different preparation parameters: metals loading amount, and hytrothermal time, and found the relationship with the photocatalystic activity by methylene blue degradation under the UV light illumination. The optimal amounts of Pd, Ag, and Au loading were 0.5 wt. %, 0.5 wt. %, 1.0 wt. %.The optimal hytrothermal time was 18 hours. Furthermore, the sample for 18 hour had the highest activity due to the highest crystallinity. From these results, the photocatalytic activity of M@TiO2 (M = Pd, Ag, Au) catalyst mainly depended on the crystallinity of TiO2, the kind of metals, the amount of noble metal loading and the OH group contents.

Keywords: titanium dioxide, core/shell structure, photocatalyst, palladium, silver, gold, sol-gel method, hydrothermal method, methylene degradation.

並列關鍵字

hydrothermal method ； gold ； silver ； palladium ； titanium dioxide ； photocatalyst ； core/shell structure

參考文獻

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