- 學位論文
以原子層沉積法成長TiO2薄膜/奈米碳管之殼-核結構及其光催化性質研究
Preparation of TiO2/CNT Core-Shell Structure by Atomic Layer Deposition and Characterization of the Photocatalytic properties
摘要
本論文係研究以摻雜氮原子之二氧化鈦薄膜形成之觸媒對光催化分解 (photodecomposition) 有機污染物之能力。二氧化鈦薄膜是由原子層沉積法 (atomic layer deposition, ALD) 直接將二氧化鈦鍍覆在奈米碳管上形成核－殼結構 (core-shell structure) ；於氮氣氛圍在不同的退火溫度下造成混晶效應 (mixed phase)，降低光生電子電洞對再結合之速率；再使用熱擴散處理 (thermal diffusion) 在純氨氣氛下進行氮原子摻雜，增加二氧化鈦可見光波長吸收範圍以提升光催化分解之能力。 選擇多壁奈米碳管作為光觸媒擔體，未施予任何表面處理之。奈米碳管其表面結構較為完整，二氧化鈦不易沉積於表面。因此，藉由硝酸和奈米碳管反應，以便在奈米碳管表面產生缺陷或官能基，使二氧化鈦較易沉積分布於奈米碳管表面。經表面修飾之奈米碳管其物、化性質再藉由比表面積測試儀 (BET)、X光光電子光譜議 (XPS)來測試。欲分解的環境有機污染物則選擇以酚 (phenol) 作為測試對象。所有光觸媒特性由X光繞射儀 (XRD)、穿透式電子顯微鏡 (TEM)、掃描式電子顯微鏡 (SEM)、差示掃描量熱計 (DSC)、能量散佈光譜儀 (EDS) 和紫外-可見光吸收光譜儀 (UV-vis) 來分析。 結果顯示，經酸處理過的奈米碳管可成功的沉積二氧化鈦，TiO2鍍覆深度可達約4 μm。經由ALD本身自我侷限機制，控制不同ALD循環數，可於碳管表面得到不同膜厚之二氧化鈦。二氧化鈦的成長速率為0.55 Å/cycle。所得之TiO2/CNT複合結構在氮氣氛圍中退火，於300 ℃時已有銳鈦鑛相 (anatase) 的二氧化鈦產生；當溫度達800 ℃以上時，可觀察到金紅石相 (rutile) 的二氧化鈦產生。在熱擴散處理中，隨著溫度從500 ℃到600 ℃，摻雜之氮原子含量從0.9 at %明顯上升至12 at %。
並列摘要
A series of TiO2 films coated on carbon nanotubes with different thicknesses and phase ratios were doped with nitrogen and used as catalyst for photodecomposition of organic pollutants. The TiO2 thin film was directly deposited on multiwall carbon nanotubes (MWCNTs) by atomic layer deposition (ALD) method using TiCl4 and H2O as precursors. The different phase ratios were controlled by thermal treatment in vacuum to enhance the catalytic efficiency. The purpose to get mixed phases of TiO2 is to lower the electron/hole recombination rate to enhance the photo-induced decomposition ability. In addition, nitrogen was doped to TiO2 by ammonia gas to increase visible light absorption for better efficiency of photocatalyst. The support for TiO2 deposition was commercial MWCNTs that were inert and not easy to deposite with TiO2 by ALD method without treatment. By reaction with HNO3, defects and functional groups could be produced on the surface of MWCNTs so that TiO2 could be deposited on the surface as photocatalyst. The physical and chemical properties of modified carbon nanotubes were analyzed by BET and XPS. The pollutants chosen for photo-induced decomposition test was phenol. The compositions and properties of the photocatalysts were analyzed by XRD, TEM-EDS, DSC, SEM-EDS, XPS, and UV-vis spectrometry. The result showed that the saturation growth rate of TiO2 was about 0.55 Å/cycle for pristine and acid treated MWCNTs with sufficient TiCl4 and H2O pulse time. The penetration depth of TiO2 deposition was about 4 μm for CNTs dispersed on silicon wafer. The anatase phase of TiO2 was obtained by heating at above 300 oC, and the rutile phase was found when annealed at above 800 oC. The doping of TiO2/CNT composite with nitrogen could be achieved in NH3 atmosphere at 500 to 600 oC. The content of nitrogen increased from 0.9 at % to 12 at % as temperature increased.