近年來，頻繁發生的極端氣候以及氣候變遷導致的天災，引起大家開始關心氣候變遷及全球暖化的議題。因此，許多先進國家已經開始發展再生能源。氫能是其中一種備受期待的綠能，而光催化產氫為一種具有發展潛力的氫氣生產方式。此外，Z-scheme能帶結構可以降低光催化材料的電子、電洞再結合機率，進而提升光催化效率。
　　石墨相氮化碳是近幾年來的新星材料，因為其擁有合適的能帶位置、能隙及較低的生產成本。本研究中，以石墨相氮化碳及氧化鎢兩種材料形成Z-scheme複合材料，並探討鉑與金作為助催化劑對光催化產氫之效果。助催化劑有降低電子、電洞再結合之效果，亦能作為催化反應的有效位置。此外，金奈米顆粒有表面電漿共振效應，可以吸收部份的可見光波段，並強化奈米顆粒附近的電場而增加光催化效率。
　　本研究以尿素作為石墨相氮化碳之前驅物，並利用溶膠凝膠法及多孔結構之聚碸模板製備氧化鎢奈米顆粒，再藉由溼式研磨及後續的熱處理製備複合材料。而助催化劑是以硼氫化鈉化學還原法的方式附著在材料上。材料的晶體結構、表面形貌、氧化鎢含量、吸收光譜、元素分布分別使用X光繞射儀、掃描式電子顯微鏡、熱重分析儀、紫外光/可見光光譜儀、能量散射X光光譜儀進行分析。
　　經由在太陽能模擬光照射下的產氫結果比較，加入5 wt.%的氧化鎢的石墨相氮化碳能提升約兩倍的產氫效率。此外，鉑奈米顆粒最佳的沉積量為1 wt.%；而金奈米顆粒的最佳沉積量則是3 wt.%。光催化產氫結果顯示，加入助催化劑的氧化鎢/石墨相氮化碳，其效率大幅提升。以鉑當作助催化劑之複合材料，其效率高達2290.6 μmol/g∙h；以金當作助催化劑之複合材料，其效率為1104.2 μmol/g∙h。另外，在可見光下的光催化產氫結果顯示，鉑作為助催化劑之效率比金之效率更佳。因此，本研究證明氧化鎢/石墨相氮化碳為具有發展潛力的材料，而鉑奈米顆粒適合當此材料系統之助催化劑。

　　Recently, extreme climate change has been noticed by many countries because it has been speeded up and caused many horrible disasters. Most of advanced countries have been developing renewable energies. Hydrogen energy is considered as an alternative. Photocatalytic hydrogen evolution is a potential approach to produce hydrogen. In addition, Z-scheme band structure is an effective way to reduce the recombination rate of electrons and holes so that the photocatalytic efficiency can be improved.
　　g-C3N4 is a popular material for photocatalytic water splitting in recent years due to its suitable band positions, bandgap, and low cost. In this research, g-C3N4 was combined with another photocatalyst, WO3, in order to enhance the photocatalytic efficiency. The Z-scheme composite was fabricated by simple wet grinding urea-derived g-C3N4 and WO3 powders, followed by heat treatment at 300 ℃ for 2 h. Furthermore, Pt and Au nanoparticles were deposited as co-catalysts by wet reduction. The co-catalyst significantly improves the photocatalytic performance by serving as the electron sinks and active sites. For Au, it has extra surface plasmonic resonance absorption of visible light. The enhanced electric field around the nanoparticles has benefit on photocatalytic efficiency. The crystal structures, morphologies, contents of WO3, bandgap energies, and elemental distributions of g-C3N4, WO3, and the composite samples were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), UV-vis spectroscopy, and energy-dispersive X-ray (EDX) mapping, respectively.
　　The optimal weight ratio of WO3 in WO3/g-C3N4 composite was 5 wt.%, which led to 2.2 times of H2 production compared to bare g-C3N4 under solar irradiation. Moreover, the optimal loadings for Pt and Au were 1 wt.% and 3 wt.%, respectively. The efficiencies for 1 wt.% Pt-loaded and 3 wt.% Au-loaded WO3/g-C3N4 composites were 2290.6 and 1104.2 μmol/g∙h under solar irradiation, respectively. For the photocatalytic efficiency under visible light (> 420 nm), the Pt-loaded g-C3N4 performed better than Au-loaded g-C3N4. Hence, WO3/g-C3N4 is a promising photocatalyst, and Pt was proved to be a more suitable co-catalyst than Au under either solar light or visible light irradiation.

摘要---I
Abstract---III
誌謝---V
Chapter I Introduction---1
1-1. Energy crisis---1
1-2. Photocatalyst for water splitting---4
1-3. Z-scheme structure---8
1-4. Co-catalyst---10
1-5. Motivation---12
Chapter II Literature Review---15
2-1. Graphitic carbon nitride (g-C3N4)---15
2-2. Tungsten oxide (WO3)---18
2-3. Surface plasmonic resonance effect---23
2-4. Au-deposited photocatalyst---26
2-5. Direct Z-scheme WO3/g-C3N4 photocatalyst---31
Chapter III Experimental Procedures---42
3-1. Synthesis of g-C3N4 powder---42
3-2. Synthesis of WO3 powder---42
3-3. Fabrication of WO3/g-C3N4 composite---42
3-4. Co-catalyst loading---44
3-5. Characterization---44
3-5-1. X-ray diffraction (XRD)---44
3-5-2. Scanning electron microscopy (SEM)---44
3-5-3. Thermogravimetric analysis (TGA)---45
3-5-4. UV-visible absorption spectroscopy---45
3-5-5. Measurement of Pt loading---46
3-6. Photocatalytic H2 evolution test---46
Chapter IV Results and Discussion---50
4-1. Characterization of g-C3N4 and WO3 powders---50
4-2. Characterization of WO3/g-C3N4 composite---57
4-3. Characterization of the noble-metal-loaded g-C3N4 and WO3/g-C3N4 composite---63
4-4. Photocatalytic H2 evolution---70
4-5. Proposed mechanism---80
Chapter V Conclusions---85
Chapter VI Suggested Future Work---87
References---88

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