| Abstract: | 近年來以二氧化鈦光觸媒處理空氣與水污染物已漸趨成熟，且進入商品化的階段，絕大部分產品的光觸媒均以粒狀或表面薄膜型態組成。而管狀二氧化鈦光觸媒係一新穎的光觸媒型態，由於管狀二氧化鈦光觸媒具有較大的比表面積，使其光催化降解效率應優於粉末或薄膜狀二氧化鈦。本研究之目的係以汽化的四異丙醇鈦（Titanium tetra-isopropoxide, TTIP）為前驅物，在高周波電漿輔助化學氣相沈積（Radio frequency plasma enhanced chemical vapor deposition, RF-PECVD）反應腔體中，以陽極氧化鋁薄膜為「模版」將二氧化鈦沈積於其上，以製備具規律排列二氧化鈦奈米管狀陣列。製備之實驗參數包括腔體壓力、氣體流量、基板溫度、沈積時間、以及電漿輸出功率，並藉由電子顯微鏡影像來觀察這些參數對於二氧化鈦奈米管狀陣列型態的影響。選擇最適之製備條件後，本研究並進行製備成品之晶相分析及光催化效能測試。本研究發現，在不同壓力下經由RF-PECVD所製備之二氧化鈦會隨不同壓力而呈現不同的沈積型態，在0.17 kPa形成 10 nm顆粒所組成的鍊狀產物、0.20 kPa時產生奈米管狀物、0.23 kPa形成奈米顆粒、0.27 kPa時則形成薄膜。沈積時間則以60 min或90 min為當，過長之沈積時間（120 min）則形成覆蓋於模版的薄膜狀二氧化鈦；基板溫度及電漿輸出功率則對沈積物型態無顯著影響。製備之二氧化鈦管狀陣列的管外徑約 150 - 300 nm，管長約100 nm。在光觸媒測試上，本研究以汽化異丙醇（Isopropanol）為分解目標物，在批次式反應腔體中予以照射365 nm 之近紫外線光，發現製備之二氧化鈦管狀陣列的最佳光催化降解效能可達 97％，異丙醇降解反應呈現一階反應速率，其最佳速率常數為0.0934 hr-1。
Titania (TiO2) is the most common type of photocatalysts which has been studied extensively and applied for the purification of air and water pollutants. Vast majority of the commercial products, however, are either in powder form or in thin film. Conversely, TiO2 in its tubular form, is a developing material for photocatalysts that could possess greater photocatalytic activity due to the larger specific surface area. In this study, with titanium tetra-isopropoxide (TTIP) as a single molecular precursor, TiO2 tubular arrays were synthesized using porous anode alumina oxide (AAO) membrane as a template in a radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD). This study investigated the effects of several process parameters, including chamber pressure, carrier gas flow rate, substrate temperature, plasma power intensity, and deposition time, on the formation of TiO2 tubular arrays. The as-prepared samples were examined by Scanning Electron Microscopy (SEM) to observe the formation process of the TiO2 deposits and to determine the optimum process conditions. Subsequently, this study analyzed the crystalline phase of the synthesized samples and evaluated the photocatalytic capability of the TiO2 samples. The TiO2 exhibited markedly different forms under various chamber pressures, from scattered particulate chains at 0.17 kPa, to thin tubes at 0.20 kPa, to particle aggregation at 0.23 kPa, and eventually to thin film at 0.27 kPa. A deposition time of 60 min to 90 min was optimal, as longer deposition at 120 min resulted in a thin film entirely covering the surface of the AAO template. On the contrary, the substrate temperature (100~300 ?C) and the plasma intensity (150~250 W) did not result in much difference in the synthesized TiO2 tubes. Under the appropriate conditions, the tubular TiO2 had an outer diameter of about 150 - 300 nm depending on the pore diameter of the AAO membrane, and a length of about 100 nm. When undergoing photocatalytic degradation test using isopropanol (IPA) as the target pollutant in a batch-type reactor exposed to 365-nm ultraviolet light, the TiO2 tubular arrays demonstrated an IPA degradation efficiency of as high as 97 %. The IPA degradation showed first-order reaction kinetics, with rate constants as large as 0.0934 hr-1. |
