本論文係研究以無模板方式合成微孔洞結構含鉭半導體。鉭酸鋅(zinc tantalate)為起始材料，以溶膠凝膠法(sol-gel)合成。將鉭酸鋅於800 oC以上之氨氣氛下退火，以移除材料裡的鋅，形成微孔洞結構。而留下來的鉭會完全反應成氮化鉭(tantalum nitride)，或是在少量氧氣氛下，形成氮氧化鉭(tantalum oxynitride)。此微孔結構係由掃描式電子顯微鏡(SEM)、穿透式電子顯微鏡(TEM)，及比表面基測試儀(BET)檢驗，最高表面積可達每克25平方公尺。
此微孔氮化鉭及氮氧化鉭遂應用於亞甲基藍降解及水分解以測試其光催化效果。實驗結果顯示在800oC下退火之微孔氮化鉭比起從商業氧化鉭反應而成之氮化鉭具有較好的光催化活性。這可能是因為微孔氮化鉭比起商業氮化鉭擁有較高的表面積及較小的粒徑。而由於氮氧化鉭為氧化鉭及氮化鉭間的中間產物，其光催化效果可能與氧及氮之間的比例有關。
為提升光催化效率，作為助催化劑之白金及氫氧化鎳分別以兩種不同的方式鍍覆於微孔氮(氧)化鉭上。其中，白金遂以自行組裝之原子層沉積(ALD)儀鍍覆。隨著循環數的增加，鍍覆在光催化劑上的白金也跟著增加。但是，氮(氧)化鉭的光催化效率並沒有因為白金的鍍覆而增加，反而隨著白金鍍覆量的增加，呈現下降的趨勢。
另一方面，氫氧化鎳則是以化學沉積法鍍覆於光催化劑上。此助催化劑之相及穩定性由X光光電子能譜儀(XPS)進行確認。實驗結果發現對於氮(氧)化鉭的材料，氫氧化鎳比起白金是為更佳的助催化劑。在加上氫氧化鎳的情形下，氮化鉭可以在第六小時產出約20 μmol/g的氫氣，而氮氧化鉭則能生成約10 μmol/g的氫氣。

Mesoporous tantalum-based semiconductors were fabricated without the utilization of a sacrificial template. Zinc tantalate (ZnTa2O6), acting as a starting material, was synthesized by a sol-gel method. The subsequent removal of zinc under ammonia gas at temperatures higher than 800 oC resulted in the formation of mesopores, and the remaining Ta was nitridized to form tantalum nitride (Ta3N5), or with partial oxygen pressure to form tantalum oxynitride (TaON). The mesoporous structure was examined by SEM, TEM, and BET analyses. The highest surface area was about 25 and 20 m2/g for Ta3N5 and TaON, respectively.
The mesoporous Ta3N5 and TaON were employed to conduct methylene blue (MB) degradation and water splitting. The mesoporous Ta3N5 annealed at 800 oC showed better photocatalytic activitiy than the Ta3N5 from commercial tantalum oxide (Ta2O5). This result might be ascribed to smaller particle size and larger surface area. The photocatalytic activity of TaON, on the other hand, largely depended on the ratio of O to N, which made it visible light or UV-prone.
Platinum and nickel hydroxide (Ni(OH)2) were loaded as co-catalysts on Ta3N5 and TaON by two different approaches. Pt was deposited by a homemade ALD. The amount of Pt loaded increased with the increase of ALD cycle numbers. However, the photocatalytic efficiency does not increase with the addition of Pt. With the increase of ALD cycle numbers, the amount of H2 production decreases.
Ni(OH)2, on the other hand, was loaded by a precipitation method. The phase and the stability of Ni(OH)2 were confirmed by XPS. The photocatalytic efficiency of Ni(OH)2 was better than that of Pt on tantalum (oxy)nitrides. The amount of H2 reached about 20 μmol/g after 6 h of irradiation for the Ta3N5 system, and about 10 μmol/g after 6 h for the TaON system.

摘要 III
Abstract V
誌謝 VII
Chapter I Introduction 1
1-1. The development of photocatalyst 1
1-2. Mechanism for photocatalytic water splitting 3
1-3. Reaction sites for water splitting 6
1-4. Tantalum-based photocatalysts 8
1-5. Motivation of the research 8
Chapter II Literature Review 14
2-1. Template-free mesoporous TiN 14
2-2. Fabrication of ZnTa2O6 17
2-3. Ta3N5 as photocatalyst 21
2-4. TaON as photocatalyst 26
Chapter III Experimental Design 40
3-1. Synthesis of zinc tantalate (ZnTa2O6) 40
3-2. Fabrication of mesoporous tantalum-based photocatalysts 40
3-2-1. Tantalum nitride (Ta3N5) 40
3-2-2. Tantalum oxynitride (TaON) 41
3-3. Loading of co-catalysts 41
3-4. Photocatalytic efficiency test 42
3-4-1. Dye degradation 42
3-4-2. Water splitting 42
3-5. Characterization 45
Chapter IV Results and Discussion 49
4-1. Characterizations of ZnTa2O6, Ta3N5, and TaON 49
4-1-1. XRD analysis 49
4-1-2. SEM analysis 53
4-1-3. TEM analysis 62
4-1-4. BET analysis 62
4-2. Photocatalytic activity of tantalum (oxy)nitride 66
4-2-1. Ta3N5 66
4-2-2. TaON 69
4-3. Co-catalysts deposition 73
4-3-1. The effect of Pt loading 75
4-3-2. The effect of Ni-based compound loading 80
4-4. Overall comparison 83
Chapter V Conclusions 92
Chapter VI Suggested Future Work 94
References 95

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