製備高度水分散性TiO2奈米粒子以提升有機染料的可見光光催化降解研究

光觸媒技術是指利用光的能量照射在固體材料上，此材料可將光能轉換成化學能，促使有機物污染物的分解或合成，進而達到除污、除臭、工業合成等目的。在眾多的光觸媒材料中，TiO2有相當優良的光觸媒活性，而且有物理與化學性質穩定，耐酸鹼、價格便宜、容易製備、無毒等優點，所以成為最具發展潛力的光觸媒材料。雖然TiO2已廣泛地應用於染料敏化太陽能電池及水體污染物降解等能源及環境領域，但TiO2觸媒存在易聚集、難以回收、能隙大等缺點而限制了該材料的應用性。本論文以製備高度水分散性TiO2奈米粒子為主軸，研究內容主要分成三大部分，第一部分探討鹼性過氧化氫(alkaline hydrogen peroxide, AHP)處理市售TiO2粉末(AHP-TiO2)之製備流程條件。利用熱重分析儀(TGA)、電子能譜儀(XPS)、傅立葉轉換紅外線光譜儀(FT-IR)等儀器分析AHP-TiO2表面變異，結果顯示AHP-TiO2表面的氫氧官能基總量比未修飾TiO2增加了2.6倍。從穿透式電子顯微鏡(TEM)、動態光散射儀(DLS)及原子力顯微鏡(AFM)觀察到AHP-TiO2的形狀與粒徑均一，能有效地分散於極性溶液中減少聚集。第二部分則是將AHP-TiO2應用於染料光敏化系統，並探討過渡金屬離子的影響。因AHP-TiO2的分散性高，能有效地利用可見光能量，使得染料污染物的降解速率明顯提升。在此系統中加入不同的金屬離子(Fe3+、Cu2+、Zn2+以及Al3+)測試，結果發現Fe3+離子能與表面的氫氧官能基錯合，當染料經可見光激發出的電子會轉移到此錯合物而釋放出額外的活性氧化物種(reactive oxygen species, ROS)以提升染料降解速率，此反應速率與市售二氧化鈦(Degussa P25)相比高出一個數量級。活性氧化物種包含超氧離子(superoxide anion)、單一態氧(singlet oxygen)、氫氧自由基(hydroxyl radical)，為了探討此系統的活性氧化物種，第三部分研究主題為甲醇氧化(methanol oxidation)及香豆素衍生法(coumarin derivation)偵測系統中產生的氫氧自由基。結果顯示AHP-TiO2-Fe3+光敏化系統裡，主要是產生氫氧自由基，經由此兩種方法捕捉氫氧自由基能力的不同，推測出此系統所產生的氫氧自由基主要來自於AHP-TiO2-Fe3+表面。關鍵字: 二氧化鈦(TiO2)、分散性、染料敏化、鐵離子、活性氧化物種

關鍵字

二氧化鈦；分散性；染料敏化；鐵離子；活性氧化物種

並列摘要

Alkaline hydrogen peroxide treatment was proposed as a simple and green way to improve the performance of commercial TiO2 powder for water-dispersibility and visible-light photocatalytic activity on the degradation of organic dyes. The performance of treated TiO2 (AHP-TiO2) was evaluated as a function of NaOH concentration, H2O2 concentration, and treatment time. The optimal conditions were determined to be 24 h in 100 mM H2O2 and 8 M NaOH. The treated samples were characterized by Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and ultraviolet-visible spectrophotometry. The analysis revealed that the crystal structure, morphology, and absorption band gap were retained, but the surface of AHP-TiO2 was dramatically changed. AHP-TiO2 could be highly dispersible with a uniform hydrodynamic size of 41 ± 12 nm and stable over months in acidic water without any stabilizing ligand. It could also significantly enhance the visible-light photodegradation of dye pollutants. The superior performance was attributed to the formation of abundant surface hydroxyl groups, estimated to 12.0 OH/nm2. Effect of Fe3+ ion on the photocatalytic activity of the treated TiO2 was studied. The results show that Fe3+ accelerated the photodegradation of dyes in aqueous AHP-TiO2 dispersions with one order of magnitude larger than that of commercial P-25. This may be ascribed to the complexation of the surface hydroxyl groups of AHP-TiO2 with Fe3+ to form Fe(OH)2+. A plausible reaction mechanism for this system was proposed. The apparent quantum efficiency of hydroxyl radical formation was calculated for different TiO2 suspensions by methanol oxidation and coumarin derivatization. The experimental observations suggest that Fe3+ ion could accelerate the generation rate of hydroxyl radical species in AHP-TiO2 and the system oxidation should be caused by adsorbed hydroxyl radical species, rather than free hydroxyl radical species under visible light irradiation. Keywords: TiO2, Dispersion, Dye photosensitization, ferric ions, Reactive oxygen species

並列關鍵字

TiO2 ； Dispersion ； Dye photosensitization ； ferric ions ； Reactive oxygen species

參考文獻

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製備高度水分散性TiO2奈米粒子以提升有機染料的可見光光催化降解研究

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