光催化應用於產氫效應為本研究之目標。近年來，由於永續能源議題相當熱絡以及政府政策導向所致，太陽能源產業尤為發展目標，因此造就許多研究上的題材，學者們致力於找尋可應用於太陽光之光催化劑。此外，結合兩種具備Z-scheme之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。 氮化鉭,(Ta3N5)具有合適的能階位置與能隙大小用以水解產氫，並擁有優良的太陽能轉換氫能效率，為本研究之主要材料。氧化鋅, (ZnO)為環境友善之材料，並應用於多方領域中。本研究將Ta3N5與ZnO製備成粉末、薄膜結構等不同形式之異質材料，以探討表面積與異質結構對光催化效率的影響。在粉末結構中，當Ta3N5與ZnO混合之比例為1:3時，所產生之光催化效率為所有比例中之最高值。 本研究所組構之直接Z-scheme，係利用氮化熱處理製備Ta3N5粉末，再以原子層沉積法鍍覆ZnO薄膜於已置入Ta3N5粉末之矽基板上。乙二基鋅與水為製備ZnO薄膜之前驅物。其充氣-驅氣-抽氣(pulse-purge-pump)之時間分別為0.2-10-1秒與0.5-10-1秒。該異質薄膜使用X光繞射儀進行晶相分析，結果顯示製備於矽基板上之樣品包含Ta3N5及ZnO結晶相，而Ta3N5為主要結晶相；此外亦利用掃描式 IV 電子顯微鏡、能量散射X-射線光譜、紫外線/可見光光譜儀等分析探討材料表面形貌、元素分布、材料吸收光譜及不同結構之比表面積。 光催化產氫效應結果顯示Ta3N5-ZnO之異質結構能有效提升其光催化效率，使用具備 Z-scheme機制之Ta3N5-ZnO經300瓦之氙燈 (Xe lamp) 照射三小時後，結果顯示鍍覆300次循環之ZnO於Ta3N5時，其水解產氫效率為不同循環數之中最高者，達500 μmol/g-h。由於其造成Ta3N5-ZnO之介面最多接觸面積，使得Z-scheme 機制得以發揮最佳效益，但當循環數更高時，其顆粒與薄膜厚度的提升反而造成該機制無法完全發揮效用。 並非所有的助催化劑皆能提升效率，其分布之數量與位置均造成影響。以適量之銀作為助催化劑置於Ta3N5-ZnO異質結構之頂部時，因為大量的銀覆蓋於材料表面反而造成ZnO與Ta3N5無法吸收光而激發，產氫量比起原異質結構更差；當銀置於兩者之間時，因銀可以作為直接Z-scheme機制中電子電洞的傳輸媒介，延長載子生命週期，而進一步提升產氫量達600 μmol/g-h。

Due to the global warming, climate change has threatened our living environment. The development of renewable energy and to implement government’s green energy policies are highly expected. In addition, based on the Z-scheme mechanism, the combination of two semiconductors with a suitable bandgap can reduce the recombination rate of electrons and holes in a single material to enhance water splitting efficiency. Ta3N5, a promising material with suitable band gap positions for water splitting and powerful solar-to-hydrogen efficiency, is the promising material to be investigated in this research. In order to raise hydrogen production rate, ZnO is further combined with Ta3N5 to form a Z-scheme. The Ta3N5 powder was physically mixed with ZnO powder at different ratios and NaI solution was added as a mediator to form an indirect Z-scheme system. The ratio of ZnO to Ta3N5 at 3 to 1 yielded the best photocatalytic efficiency, which also outperformed each individual material. The existence of a shuttle redox mediator in the indirect Z-scheme, however, would affect the H2 production by competing with the materials to combine with the photoexcited electrons. To avoid the effect of mediator, physical contact at the interface between two photocatalysts, so-called direct Z-scheme system was then applied in Ta3N5-ZnO. For fabricating direct Z-scheme system, ZnO thin film was deposited by ALD on Ta3N5 powder to form a heterojunction on Si wafer. The precursors of diethyl zinc (DEZ) and H2O were applied with the half reactions of DEZ pulse-N2 purge-pumping at 0.2-10-1 (s) and H2O pulse-N2 purge-pumping at 0.5-10-1 (s), respectively. The crystal structure was examined by grazing incidence X-ray diffraction (GIXRD). ZnO deposited on Ta3N5 by various ALD cycles shown both phases of ZnO and Ta3N5 present simultaneously. The major phase was Ta3N5. The surface morphologies, elemental distributions, and band gap edges of the Ta3N5-ZnO heterojunction were examined by scanning electron microscopy (SEM), energy dispersive spectrometric mapping, and UV-visible spectroscopy, respectively. In the direct Z-scheme, ZnO was deposited on Ta3N5 by various ALD cycles. Among them, based on the distribution and particle size, 300 cycles show the highest efficiency, with the hydrogen evolution rate being about 500 μmol/g-h. Deposition of ZnO by more than 300 cycles would form larger particles and raise the thickness of ZnO, thus reducing the light intensity to activate Ta3N5. In addition, sliver was loaded as a cocatalyst by a photodeposition method either on the top of ZnO-Ta3N5 heterostructure or in between ZnO and Ta3N5. Not all the existence of cocatalyst would enhance the photocatalytic performance. It was seen that Ag@ZnO@Ta3N5 showed lower efficiency, and on the other hand, ZnO@Ag@Ta3N5 reached the value of 600 μmol/g-h. The presence of Ag between ZnO and Ta3N5 could act as metallic mediators for carriers transfer, avoid back reactions, and prolong the lifetime of carriers.

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