| 研究生: |
謝欣媛 Hsieh, Hsin-Yuan |
|---|---|
| 論文名稱: |
溶液燃燒合成法製備可見光光觸媒TiO2之製程開發 Process Development for Liquid Combustion Synthesis of visible-photocatalytic titanium dioxide |
| 指導教授: |
鍾賢龍
Chung, Shyan-Lung |
| 學位類別: |
碩士 Master |
| 系所名稱: |
工學院 - 化學工程學系 Department of Chemical Engineering |
| 論文出版年: | 2005 |
| 畢業學年度: | 93 |
| 語文別: | 中文 |
| 論文頁數: | 144 |
| 中文關鍵詞: | 可見光 、光觸媒 、燃燒合成法 |
| 外文關鍵詞: | visible-light, photocatalyst, combustion synthesis method |
| 相關次數: | 點閱:69 下載:2 |
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光觸媒可稱謂新世紀的環保尖兵,無論是在有機污染物的分解、抗菌、除臭及自我清潔等領域皆有極佳的表現。由於TiO2 具無毒、化學性質穩定及較佳的能隙結構,故為應用最為廣泛的光觸媒;TiO2 的應用光源主要為紫外光,這是因為TiO2 的能隙約為3.2eV,予一小於388nm 的紫外光波長即可激發光觸媒產生光催化作用。不過,由於太陽光中紫外光僅佔5% 的能量,而可見光 (波長400~700nm) 約佔45%的能量,因此,為了有效利用現有的太陽光能量,並期望在室內等紫外光較微弱的地方也能夠使用光觸媒,可見光光觸媒的開發逐漸成為光觸媒的研究主流;本研究利用溶液燃燒合成的方式(SCS method)將TiO2 改質,藉由燃燒反應產生的C 取代TiO2 中的O 原子,得到能隙較小的TiO2 ,以提升TiO2 在可見光下的應用性,並經由XRD、TGA、FT-IR、C/S Analyzer、UV-vis spectrum 等儀器分析,驗證粉體特性。
研究內容主要探討兩種還原劑glycine、urea 在使用上的特性以及選擇;並且改變燃燒熱、計量比等參數分析粉體特性。結果發現使用glycine做為還原劑,x≧2.5 會有Rutile 結晶相出現;使用urea 做為還原劑,x≧2即有Rutile 結晶相出現。因此,可以得知經由引燃進行氧化還原作用所放出的熱量大小將決定粉體的結晶強弱以及型態。
經由掃描式電子顯微鏡觀察,得知本研究合成粉體的表面形貌皆為多孔洞結構,這是因為SCS 製程在引燃進行氧化還原作用時所產生的大量氣體衝擊粉體所致。因此,得知氣體含量的多寡將控制粉體碳的含量、孔洞數量以及比表面積大小。
實驗結果顯示使用urea 做為還原劑,Ti(OH)4、氧化劑與還原劑的比例為1:1.5:1,所得到的這組粉體u(1:1.5:1)在太陽光的MB分解實驗表現出極佳的光觸媒活性,30 分鐘內即可達到97%的分解效率,分解速率優於商業化ST-01 的70.2%。並且經由碳硫分析儀(C/S Analyzer)以及元素分析儀(EDS)的分析得知,利用溶液燃燒合成法製備的TiO2皆有碳元素的存在,含量介於(0.03%~1.49%)。粉體能隙(Eg)將隨著碳含量的增加而減小,因此,推論碳的摻雜可以改變TiO2 材料結構,提升粉體在λ>400nm 的吸收能力。
Since photoinduced decomposition of water on TiO2 electrodes was discovered, semiconductor-based photocatalysis has attracted extensive
interest. One particular focus has been on applications in which organic molecules are photodegraded, such as water and air purifications. Most of the investigations have focused on TiO2 , which shows relatively high reactivity and chemical stability under ultraviolet light( λ<388nm ), whose energy
exceeds the band gap of 3.2eV in the anatase crystalline phase.
The development of photocatalysts that can yield high reactivity under visible light( λ>388nm ), should allow the main part of the solar spectrum, and even poor illumination of interior lighting, to be used. One approach has been to dope transition metals into TiO2 . However,doped materials suffer from a thermal instability, an increase of carrier-recombination centers, or the
requirement of an expensive ion-implantation facility. From Asahi’s report, using anionic species for the doping is better than cationic metals, which often give quite localized d stated deep in the band gap of TiO2 and result in
recombination centers of carriers. Like C、S、N、P and F.
In order to dope anionic species(Carbon)into powder to change structure,we use solution-combustion-synthesis method (SCS method). Combustion process gives short reacting time, and large amounts of gases to get modified
TiO2 . was characterized by X-ray diffraction(XRD),thermgravimetric Analyzer(TGA), Diffuse Reflectance Infrared Spectroscopy(FT-IR), C/S Analyzer and UV-Vis Spectrum.
From the thesis, we use glycine and urea as reducing agents to analyze synthesized powder’s characteristics. We can get the best data-u(1:1.5:1), which has great specific surface area(86.37 g m2 ), and quick degradation for
methylene blue experiment. It can extend so high decomposed efficiency-97% during 30 min, better than commercial ST-01-70.2%. From C/S analyzer, there are carbon atoms (0.05%) into the u(1:1.5:1), and has great optical absorption at 400 to 440 nm. It can be proved that C doped into
substitutional sites of TiO2 is indispensable for band-gap narrowing and photocatalytic activity.
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