以硼摻雜氧化鈦奈米管陣列光催化甲基橙之研究

Abstract

本研究利用陽極氧化法製備氧化鈦奈米管陣列，藉由改變電解液組成與操作參數合成不同縱橫比之氧化鈦奈米管陣列，並以化學氣相沉積法與電沉積法摻雜硼原子進行改質，降低二氧化鈦之能帶間隙，提升其對可見光的吸收能力。透過場發射掃描式電子顯微鏡、X光粉末繞射儀、拉曼光譜儀、紫外可見光光譜儀以及傅立葉氏轉換紅外線光譜儀分析，將對改質前後之光觸媒進行分析，並選定目標污染物甲基橙進行光催化實驗，探討各光觸媒之光催化活性。 由XRD 的分析結果可知，經500℃高溫鍛燒後，氧化鈦奈米管陣列之anatase晶型強度隨著提高縱橫比而增加。而經過硼原子的改質後，其anatase晶型的強度減弱。由UV-Vis吸收光譜圖可知，改質後的氧化鈦奈米管陣列的在紫外光及可見光區有較好的吸收效果，並且吸光範圍有些許的紅位移。 實驗結果顯示，氧化鈦奈米管陣列的結構特性影響其光催化活性，其中，高縱橫比之氧化鈦奈米管陣列對光催化甲基橙具有最佳的降解速率。利用化學氣相沉積法及電沉積法製備硼摻雜氧化鈦奈米管陣列，皆可發現改質後之觸媒光催化活性較佳。而利用電沉積法所得到的最佳摻雜量較低，就可達顯著的修飾效果；相較之下，利用化學氣相沉積法時，硼摻雜的濃度較高，才可提升其光催化效率。而當摻雜濃度相同時，低縱橫比的管長較短，可受到的修飾比例較多，故修飾效果較明顯；而隨著縱橫比的增加，硼原子只分佈於氧化鈦奈米管表面，無法深入氧化鈦奈米管底部，使其改質效果較不明顯。此外，由FT-IR的結果可知，MO的鍵結訊號在照光30分鐘後，即從硼摻雜之觸媒上逐漸消失，而未改質前的觸媒，直至照光2小時後MO的鍵結訊號才明顯削弱。

The objective of this study was to modify TiO2 nanotube arrays with boron via two doping methods including chemical vapor deposition and electrodeposition. With various characterizations including Field-Emission Scanning Electron Microscope (FE-SEM), Raman Spectrophotometer, X-Ray Diffractometer (XRD), UV-Visible Spectrophotometer (UV-Vis) and Fourier Transform Infrared Spectrophotometer (FT-IR), the effects of aspect ratios of TiO2 nanotube arrays on the doping performance were investigated. The photoactivity of B-doped TiO2 nanotube arrays was also examined in terms of the oxidation efficiency of methyl orange (MO). The XRD patterns of TiO2 nanotube arrays calcined at 500 ℃ showed that the intensity of anatase peak increased with increasing the aspect ratio. After boron doping, the intensity of anatase peaks decrease. The UV-Vis DRS spectra indicated that the absorption intensity of the B-doped TiO2 nanotube arrays was enhanced both in the UV and visible regions. In addition, all the B-doped TiO2 nanotube arrays exhibit red shifts. The results indicated that the photoactivity of TiO2 nanotube arrays is significantly dependent on the aspect ratio. An increase in the aspect ratio of TiO2 nanotube arrays leads to an improved efficiency of MO oxidation. Furthermore, the photoactivity of TiO2 nanotube arrays was enhanced after B doping via either chemical vapor deposition or electrodeposition. The optimum boron doping concentration prepared by electrodeposition was lower than that by chemical vapor deposition. Meanwhile, the enhancement of photocatalytic performance of B-modified TiO2 nanotube arrays is apparent when the aspect ratio is lower. This result is probably owing to the fact that the larger the aspect ratio, the less TiO2 nanotube arrays can be modified. Based on the FT-IR spectra, the intensity of MO absorption bands over B-modified TiO2 nanotube arrays vanished after 0.5 h UV illumination whereas the MO signal over unamended TiO2 nanotube arrays remained obvious after 2 h UV illumination.