光催化應於於染料降解與產氫效應為本研究之目的。近年來，由於可見光佔太陽光譜中極大比例，因此學者致力於找尋可應用於可見光區之半導體性質之光催化劑。此外，結合兩種具備合適能隙之半導體材料可有效降低電子、電洞對再結合機率，進而提升光催化之效率。
作用於可見光區之氮化鉭及氧化鎢為本研究之半導體材料，並製備為粉末、薄膜、微孔結構等不同形式之異質材料，以探討表面積對光催化效率的影響。
本研究利用溶膠凝膠法及原子層沉積法製備氮化鉭-氧化鎢異質薄膜於矽基板及多孔結構之聚碸模板上。五(二甲氨基)鉭與氨氣為製備氮化鉭薄膜之前驅物，其通入、沉浸、抽出之原子層沉積時間分別為2 - 10 - 2秒和2.5 - 10 - 2秒。形成之異質薄膜經由各類退火處理，並使用X光繞射儀進行晶相分析。結果顯示當製備於矽基板上之樣品經由快速高溫退火後，得到氮化鉭及非化學劑量比之氧化鎢結晶相；而當製備於多孔結構聚碸模板上之樣品經高溫退火後，得到氮化鉭及氧化鎢之結晶相。此外，亦利用掃描式電子顯微鏡、電子能譜儀、氮氣等溫吸附脫附法等分析探討材料表面形貌、化學元素組成及不同結構之比表面積。
光催化染料降解與產氫效應之結果顯示結合氮化鉭-氧化鎢異質薄膜有效提升其光催化效率，而承載適量之鉑元素作為助催化劑更能進一步提升效率。使用具備Z-scheme機制之氮化鉭-氧化鎢於亞甲基藍降解試驗經太陽模擬器(AM 1.5)照射反應一小時後，其染料吸收度趨近於0，表示亞甲基藍經由氮化鉭-氧化鎢光催化作用已充分降解；而在水解產氫試驗中，更證明製備具有直接Z-scheme機制之氮化鉭-氧化鎢異質薄膜能有效提升產氫效率，其產氫值達3072 μmol g-1。因此，本研究證明結合氮化鉭-氧化鎢異質薄膜為具前瞻性之光催化材料。

Many visible light-driven photocatalysts have been developed recently because they possess the advantage to utilize the visible light of solar spectrum more efficiently. In addition, combination of two photocatalysts is further studied based on the mechanism of Z-scheme system. In this system, two semiconductor-based photocatalysts with relatively suitable band positions are chosen to address the drawback of self-recombination of electrons and holes in a single photocatalyst. In this research, visible light-driven Ta3N5 is the main material to be investigated, and WO3 is further combined with Ta3N5 in order to achieve higher efficiency in photocatalysis. The synthesized powders of two semiconductors were examined to study the performance of H2 evolution. Furthermore, considering that the existence of a shuttle redox mediator might compete with the photoexcited electrons in the H2-evolution photocatalyst, different forms of catalyst, i.e., powder, film, and microporous structure, were prepared and the performances in photocatalytic reaction were examined and discussed.
Ta3N5 - WO3 heterojunctions on silicon (Si) wafer and polysulfone (PSF) hollow fiber were fabricated by sol-gel and atomic layer deposition (ALD). The excellent conformal film of Ta3N5 was obtained by ALD using the precursors of PDMAT and NH3, with the lengths of pulse - purge - pump time of each half-reaction being 2 - 10 - 2 s and 2.5 - 10 - 2 s, respectively. The as-deposited heterojunctions were subjected to various annealing conditions. The crystalline phases were examined by X-ray diffraction (XRD). For Ta3N5 - WO3 on Si, the major phases were
Ta3N5 and substoichiometric WO2.72 after rapid thermal annealing (RTA). While for Ta3N5 - WO3 on PSF, the major phase was Ta3N5 together with a minor WO3 phase after annealing in a tube furnace. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) analyses were conducted to determine the morphology, elemental composition, and specific surface area, respectively.
The results of the performances of various photocatalysts demonstrate that applying the Ta3N5 - WO3 heterojunction exhibited enhanced efficiency compared with utilizing only one single photocatalyst. Furthermore, loading with a proper amount of Pt as co-catalyst also enhanced the performance. In the test of photocatalytic dye degradation, the absorbance of methylene blue (MB) solution was almost decomposed to 0 after 1 h of irradiation by AM 1.5 using the Ta3N5 - WO3 powders as catalyst. The test in photocatalytic water splitting also indicated that the direct Z-scheme system of Ta3N5@WO3@Si with 50 cycles of Pt deposition by ALD performed extremely good efficiency. The H2 production reached the value of 3072 μmol g-1 without applying the filter. Therefore, combination of Ta3N5 with WO3 based on the Z-scheme system was proved to be a promising photocatalyst.

摘要 ……………………………………………I
Abstract ……………………………………………………II
誌謝 ………………………………………………………………III
Chapter I Introduction
1-1 Energy crisis …………………………………………………………1
1-2 Photocatalyst …………………………………………………2
1-3 Heterojunction photocatalysts ……………………………5
1-4 Co-catalyst ……………………………………………………8
1-5 Microporous structured materials ………………………10
1-6 Deposition techniques for thin films …………………12
Chapter II Literature Review
2-1 The development of Photocatalyst ……………………………16
2-2 Photocatalyst for dye degradation ……………………………18
2-3 Photocatalyst for water splitting ………………………23
2-4 Basic properties of tantalum (oxy)nitride ….……..…..………………...25
2-5 The superiority of Z-scheme system ……….....…..…..………………...34
2-6 The technique of atomic layer deposition ………………39
Chapter III Experimental Designs
3-1 Synthesis of Ta3N5 and WO3 powders by sol-gel method.……47
3-1.1 Synthetic process
3-1.2 Heat treatment
3-2 Fabrication of tantalum (oxy)nitride thin film by ALD …47
3-2.1 Experimental procedures
3-2.2 Heat treatment
3-3 Fabrication of Ta3N5 - WO3 heterojunctions on silicon wafer and polysulfone fiber …………………………………………51
3-3.1 Ta3N5 - WO3 on silicon wafer
3-3.2 Ta3N5 - WO3 on polysulfone fiber
3-3.3 Heat treatment
3-4 Deposition of Pt nanoparticles on Ta3N5 - WO3 as co-catalyst …53
3-5 Characterization…………………………………………53
3-5.1 X-ray diffraction (XRD)
3-5.2 Scanning electron microscopy (SEM)
3-5.3 Energy dispersive spectroscopy (EDS)
3-5.4 X-ray photoelectron spectroscopy (XPS)
3-5.5 Brunauer-Emmett-Teller (BET) analysis
3-5.6 High resolution transmission electron microscopy (HRTEM)
3-5.7 UV-visible spectrometry
3-6 Photocatalytic dye degradation ………………………56
3-7 Photocatalytic water splitting …………………………57
Chapter IV Results and Discussion
4-1 Ta3N5 and WO3 powders …………………61
4-2 Tantalum (oxy)nitride thin film ………………………66
4-3 Ta3N5 - WO3 heterojunctions on silicon wafer ………70
4-4 Ta3N5 - WO3 heterojunctions on polysulfone fiber …79
4-5 Pt-loaded Ta3N5 - WO3 ……………………………………88
4-6 Photocatalytic dye degradation ……………93
4-6.1 Efficiencies of Ta3N5, WO3, and Ta3N5 - WO3 powders
4-6.2 Efficiency of Ta3N5@WO3@PSF
4-7 Hydrogen generation efficiency for photocatalytic water splitting……99
4-7.1 Ta3N5 and Ta3N5 - WO3 powders
4-7.2 Ta3N5@WO3@Si
4-7.3 Ta3N5@WO3@PSF
4-7.4 Effect of co-catalyst
Chapter V Conclusions ……………………………………109
Chapter VI Suggested Future Work ……………………112
References …………………………………………………113

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