| 摘要: | 本研究之目的為發展高光催化活性之光觸媒，並應用於有機污染物之分解。以貴金屬改質二氧化鈦光觸媒已被廣泛地研究，然而，如價格昂貴之鉑、鈀、金和銠等貴金屬其成本太高，而難以被一般工業所接受。本實驗主題為改用成本較低之銀金屬來改質二氧化鈦，以期增加二氧化鈦表面活性位置，進而提高光催化效率。製備銀改質二氧化鈦的方法有三，分別為溶膠凝膠法，化學沉積法與光沉積法。 在溶膠凝膠法中，所製備的二氧化鈦溶膠與銀改質二氧化鈦溶膠可以維持中性懸浮，其前驅物為四氯化鈦、氨水、過氧化氫水溶液與硝酸銀。其樣品結構鑑定方面，主要是以X光繞射儀(XRD)，穿透式電子顯微鏡(TEM)，高解析度穿透式電子顯微鏡(HR–TEM)與X光電子能譜儀(XPS)進行材料鑑定與元素分析。其奈米銀粒子大小約為 2 nm。以浸漬塗佈法所製備的二氧化鈦溶膠與銀改質二氧化鈦溶膠可塗佈於各種玻璃基材表面，其薄膜結構之鑑定是以掃描式電子顯微鏡(SEM)與原子力探針顯微鏡(AFM)進行膜厚與表面性質之分析。最後以 10 ppm 亞甲基藍水溶液為光反應標準物，利用紫外可見光光譜儀(UV–vis)分析濃度，進行光反應活性之鑑定。其結果顯示，銀改質二氧化鈦溶膠之優於二氧化鈦溶膠。本實驗所製備之溶膠具有附著性極高，不易剝落之優點，加入銀改質後，除了對亞甲基藍有更高的光催化降解活性，也具備有自潔與殺菌之效果。 在化學沉積法中，所製備之銀改質二氧化鈦其前驅物為 P–25二氧化鈦、十六烷基三甲基溴化銨、硼氫化鈉、硝酸銀，銀擔載量係利用感應偶合電漿質譜分析儀(ICP)進行測定，結果顯示，幾乎所有的銀前驅物都能夠擔載在二氧化鈦表面而不流失。其奈米銀顆粒大小約為 5–10 nm，以 10 ppm 亞甲基藍水溶液為光反應標準物，利用紫外可見光光譜儀(UV–vis)分析濃度，進行光反應活性之鑑定。其結果顯示，銀改質二氧化鈦之光催化活性優於二氧化鈦，而由於遮蔽效應，過多的銀顆粒會阻擋進入二氧化鈦表面的光子而降低光反應的量子效率，造成其光催化活性並不與銀擔載量成正比。 在光沉積法中，所製備之銀改質二氧化鈦其前驅物為 P–25二氧化鈦及硝酸銀，紫外光照射時間為 15分鐘。銀擔載量係利用感應偶合電漿質譜分析儀(ICP)進行測定，其結果顯示將會有約 70%–85% 之銀前驅物在製備過程中流失。其奈米銀顆粒大小約為 1.5–2.5 nm，以 10 ppm 亞甲基藍水溶液為光反應標準物，利用紫外可見光光譜儀(UV–vis)分析濃度，進行光反應活性之鑑定。其結果顯示，銀改質二氧化鈦之光催化活性優於二氧化鈦，且也優於化學沉積法所製備之銀改質二氧化鈦。 本研究結果顯示以光沉積法所製備之銀改質二氧化鈦之活性最佳，其原因為光沉積法所製備之銀顆粒較小且分散性佳，在不增加電子電洞再結合中心的前提下，有效地捕捉光子所激發之電子，大大地增加了二氧化鈦表面活性位置，而提高了反應活性。電子與所吸附的氧分子與水分子反應分解成氧離子與氫氧自由基，這些高活性物質會與亞甲基藍分子反應而分解成小分子如二氧化碳與水分子。從實驗結果得知，銀擔載量的多寡並不是影響活性的主要因素，而是與奈米銀顆粒的分散性及顆粒大小、附著方式有關。 The objective of this research was to develop a photocatalyst which is active in photoreaction to destruct organic compounds in waste gas and waste water. Noble metal deposited on titanium dioxide has been widely studied as a modified photocatalyst in organic pollutants destruction under UV light irradiation. However, noble metals such as Pt, Pd, Rh, and Au are too expensive to be used in industrial application. In order to find an efficient way to improve the quantum efficiency of photocatalyst, we increase the numbers of active sites by silver deposition. The materials we studied were silver modified titanium dioxide synthesis by sol–gel method, chemical deposition, and photodeposition. In sol–gel process, neutral suspension silver titanium dioxide sol was successfully prepared using titanium tetrachloride, ammonia, hydrogen peroxide, and silver nitrate. The nanoparticles in the sol were characterized by X–ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR–TEM) and X–ray photoelectron spectroscopy (XPS). Titanium dioxide has anatase–type structure in rhombus shape and the size of silver was about 2 nm. The sol of titanium dioxide and silver titanium dioxide are easy coating on the surface of glass substance by dip–coating method, and properties of the films were analyzed by scanning electron microscope (SEM), atomic force microscope (AFM), and contact angle analysis. The thickness of the films was 700 to 1200 nm depending on the coating times and the films showed super–hydrophilic property under UV light scattering. Both the sols and the films of titanium dioxide and silver titanium dioxide were completely destruct methylene blue under UV light irradiation, and the concentration of methylene blue was measured by UV–vis spectroscopy (UV–vis). The results showed that the photoefficiency of silver titanium dioxide is higher than titanium dioxide. In chemical deposition process, silver titanium dioxide was prepared using P–25 titanium dioxide, silver nitrate, cetyltrimethyl ammonium bromide, and sodium borohydride as materials. Inductively–coupled plasma–mass spectrometry (ICP–MS) were used to determined the contents of silver in the silver titanium dioxide. The particle size of silver on TiO2 was about 5–10 nm. The results of MB degradation under UV light irradiation showed that Ag/TiO2 had a higher activity than TiO2. In photodeposition process, silver titanium dioxide was prepared using P–25 titanium dioxide, and silver nitrate as materials, and UV light scattering time was 15 minutes at room temperature. Inductively–coupled plasma–mass spectrometry (ICP–MS) was used to determined the contents of silver in the silver titanium dioxide. The particle size of silver on TiO2 was about 1.5–2.5 nm. The results of MB degradation under UV light irradiation showed that Ag/TiO2 had a higher activity than TiO2. Silver titanium dioxide synthesized by photodeposition showed the best photoactivity in this study due to the smaller silver particles attached on titanium dioxide surface with high dispersion. Silver nanoparticles could successfully deposit on TiO2 surface and play important roles as electron traps. Without being recombination centers of electrons and holes, silver nanoparticles increase the actives sites and make electrons easily act with the adsorbed substances such as O2 and OH– and form O2– and OH radical. The reactive species could degrade the MB efficiently into small molecules like CO2, H2O, and etc. However, silver amounts is proposed not to be the determined factor in the synthesis, but the dispersion, particle size and attachment style of Ag. |
