數十年來，光觸媒被廣泛地研究，並逐漸應用在環保、能源、殺菌、自我潔淨等方面。自1972年，Fujishma和Honda首次在Nature發表TiO2經照光後會分解水成H2及O2後，越來越多人投入TiO2光催化性質相關的研究，並致力於各種可能的改質方法，以提高TiO2光觸媒的效果。而其中添加金屬改質，即為常見的一種改質方法。本研究主要的目的，是為了去除水中的污染物。由於工業製程中會產生高濃度的廢水，不易處理，且不同產業亦會產生各種不同的廢水組成；因此，我們藉二氧化鈦具光催化的性質，利用其特殊的反應機制，來分解水中的污染物。為了進一步提高二氧化鈦光催化的效果，添加適當金屬加以改質，而本實驗的重點就在於研究加銀 (Ag)的效果，並且以甲烯藍 (Methylene Blue)為標準測試的對象物質，探討不同合成及添加方法對去除效率的影響。實驗大致分為兩大類，其一為不同合成方法製備二氧化鈦，另一為不同添加方法合成含銀二氧化鈦，然後藉由UV照光反應器進行液相光催化反應，搭配分光光度計於特定波長下，每隔固定時間取樣量測吸收值，然後利用所得之數據，來交叉比較分析。基本上主要採用含浸法添加銀，取一定量之AgNO3(s)溶於適量溶劑中，再與定量之TiO2(s)混合攪拌約1小時，將其先於120℃烘乾磨粉，再於250℃煅燒2小時，製得2wt%Ag/TiO2粉末。實驗結果發現，添加銀可提升光催化的效率，且使用不同溶劑，光催化效果亦不同。其中混有乙醇的溶劑效果最顯著，優於混有異丙醇或純水的溶劑。此外，在合成粉體進行反應前，若先充分照射UV光，可進一步提升光催化效率。有趣的是，照光後粉體顏色會改變，其中以純水做溶劑的樣品會從淺灰色變成棕色，而混有乙醇或異丙醇做溶劑的粉體會從淺灰色變成深灰色。若跳過120℃烘乾磨粉步驟，直接由液相升溫到250℃煅燒2小時，則所合成之Ag/TiO2即接近深灰色，其催化效果介於未照光與照光之間。另外，由XRD圖譜可知，不論添加方法為何，微量的銀不會改變既有二氧化鈦之晶相，其Anatase與Rutile比例不會改變。若未經煅燒，只於100℃烘乾製得之粉末，不但不能增進催化效果，甚至會降低光催化性質。由此可知，溫度是一重要因素，可能此時硝酸根尚未去除。通常高溫煅燒會使粒子顆粒變大，若以一般觸媒理論，顆粒變大，接觸表面積減少，反應效率會明顯變差。但實驗觀察得知，雖然煅燒後的Ag/TiO2比TiO2來的粗糙 (離心時明顯不同，於250℃煅燒之粉末較容易分離；而pure P-25 TiO2懸浮性明顯較好，較難分離)，但添加極微量的Ag卻可提高光催化效率，由此可知，表面積大小並非影響光催化效率的唯一因素，亦即光觸媒之作用機制與一般觸媒不盡相同。 Many researches on photocatalysis by TiO2 have been investigated for decades after the first report by Fujishma and Honda in 1972. Metal modification has been extensively used to improve the activity of titania. The purpose of this research focused on the decomposition of contaminants in wastewater produced from industrial process. The usage of TiO2 with specific photocatalytic property is a potential way to decompose the pollutants in wastewater. This research emphasized the effect of silver modification and the photocatalytic activity has been tested by decomposition of methylene blue (MB). During pre-test stage, silver modification has shown remarkable performance in deNOx reaction. Ag/TiO2 powders prepared with impregnation method under proper condition could enhance the photocatalytic activity on MB degradation when compared with the bare TiO2. The usage of ethanol as solvent showed the higher activity than those with isopropanol or pure water during preparation. Catalysts prepared with calcinations and without drying showed higher photocatalytic activity than those prepared with calcinations and drying. Pretreatment by UV illumination (at 254 nm) could enhance the photocatalytic activity of Ag/TiO2 catalysts and the color of the catalysts changed. Ag-TiO2 suspension prepared with adding hydrogen peroxide (H2O2) was very active during MB test for both UV and visible light while TiO2 suspension was only active under UV illumination. According to the XRD analysis, silver modification did not change the crystalline phase of the original bare TiO2. In addition, the deposited silver changed from Ag+ or Ag2+ to metallic form (Ag0) after UV illumination. The role of deposited silver metal on titania surface could be explained as either an electrons trapper or enhancement of electrons transfer from catalysts to dissolved molecular oxygen. Negative charging of deposited silver metal results in faster holes transfer from catalysts to adsorbed MB or to water.
