| 摘要: | 不同的光觸媒材料研究，近年來受到一些學者的討論。本研究之水分解反應主要可分為紫外光及可見光兩部分。我們探討InVO4、InTaO4、InNbO4、In6WO12、K4Nb6O17一系列光觸媒作為可見光之水分解製氫反應的研究，而紫外光部分是探討NaTaO3觸媒。這一系列的光觸媒主要是以固態反應法製備而成。我們改變了不同的製備條件（共觸媒金屬氧化物、氧化鎳含量、植入的金屬及經過氧化還原處理的效應），探討對水分解產生氫氣及氧氣活性的影響。觸媒的物化特性，以下列方法鑑定：X-光繞射分析 (X-ray diffraction)，掃瞄式電子顯微鏡 (scanning electron microscopy)， X-射線光電子譜 (X-ray photoelectron spectroscopy) 和UV-Vis吸收光譜 (Ultravillet-Visible spectroscopy)。 不同的觸媒製備方法明顯地影響觸媒的晶相與水分解活性。X-光繞射分析顯示所製備的InVO4、InTaO4、InNbO4、In6WO12、K4Nb6O17與NaTaO3觸媒，均具有良好的晶相。觀察SEM圖，In6WO12系列的觸媒，粒徑最小，約1~2 μm。而添加氧化鎳、氧化鈷或氧化釕於InVO4上時，可看到InVO4上有小洞產生。由UV-Vis吸收光譜得知，InVO4 能帶間隙為1.8 eV、InTaO4為2.7 eV、InNbO4為2.6 eV、In6WO12為2.6 eV、 K4Nb6O17為3.0 eV、NaTaO3為3.3 eV，所以這些觸媒是有足夠能力使水分解產生氫氣及氧氣的。 在InVO4觸媒，發現NiO具較佳的水分解活性，而0.3 wt.% NiO具有最高的活性，其產生氫氣和氧氣分別為750 μmolh-1gcat.-1和375 μmolh-1gcat.-1。在前處理的活化下對於觸媒的活性是有很大的幫助的。NiO/InVO4 於500oC下還原2小時，然後在室溫下氧化48小時，產生氫氣為896 μmolh-1gcat.-1。由上述結果得知，NiO/InVO4 觸媒的前處理過程扮演著獲得高水分解活性的重要角色。 對於InTaO4，我們也改變了不同的金屬氧化物作為載體，發現NiO有較佳的活性。其產生氫氣和氧氣分別為842 μmolh-1gcat.-1和420 μmolh-1gcat.-1。對於InNbO4也是發現NiO有較佳的活性。而經前處理的活化下，對於NiO/InTaO4 NiO/InNbO4觸媒的活性是沒有幫助的，反而使活性下降了。 對於In6WO12，我們改變了不同的金屬氧化物 (NiO, CoOx and RuOx) 於In6WO12上，發現RuO2有較佳的活性。其產生氫氣和氧氣分別為774 μmolh-1gcat.-1和365 μmolh-1gcat.-1。而觸媒在經氧化還原的前處理下，對活性有些微的增加。K4Nb6O17是我們新研究的觸媒。在沒有任何共觸媒的存在下，發現其較先前研究的觸媒佳。其產生氫氣和氧氣分別為839 μmolh-1gcat.-1和415 μmolh-1gcat.-1。 NaTaO3光觸媒在紫外光照射下，水分解產生氫氣和氧氣分別為1476 μmolh-1gcat.-1和738 μmolh-1gcat.-1。 Develop a photocatalyst system for solar energy conversion to electric energy or chemical energy is a topic of great interest for fundamental and practical importance. In this study, photocatalytic activities of InVO4, InTaO4, InNbO4, In6WO12, K4Nb6O17 catalysts for water splitting under visible light irradiation were investigated. Photocatalytic activities of NaTaO3 catalysts for water splitting were studied under UV light irradiation. The effect of different preparation parameters, such as type of cocatalyst and amount of NiO loading, doping metal and pretreatment process on the photocatalysis reaction was investigated. The photocatalysts was synthesized by solid-state reaction method using metal oxide as the starting materials. The catalysts were characterized by powder X-ray diffraction (XRD), scanning electron spectroscopy (SEM), ultraviolet-visible spectroscopy (UV-Vis) and X-ray photoelectron spectroscopy (XPS). The photocatalytic reaction was carried out in a Pyrex reactor with a 500 W halogen light as visible light source and 400 W high pressure mercury lamp as UV light source. All of the catalysts were fully crystallized. SEM results In6WO12 catalysts had the smallest particle size were ca. 1~2 μm. In addition, many pin-holes appeared on InVO4 particles, after loading NiO, CoOx and RuOx. The band gap of InVO4, InTaO4, InNbO4, In6WO12, K4NB6O17 and NaTaO3 were 1.8 eV, 2.7 eV, 2.6 eV, 2.6 eV, 3.0 eV and 3.3 eV, respectively, showing that these catalysts had ability to split water into H2 and O2. For InVO4 catalyst, NiO was the best cocatalyst for water splitting, which gave the highest activity (750 μmolh-1gcat.-1 for H2 evolution and 375 μmolh-1gcat.-1 for O2) when the loading was 0.3 wt%. The pretreatment method had a great effect on the activity of the catalyst. The NiO/InVO4 catalyst which was reduced at 500oC for 2 h and oxidized at ambient condition for 48 h gave the highest activity with a rate of 896μmolh-1gcat.-1. It demonstrated that the pretreatment process plays a key role in creating high catalytic performance for the NiO/InVO4 catalyst. For InTaO4 catalysts, we also have tested various metal oxides as the additive and NiO gave the highest activity. The yields of H2 and O2 on NiO-InTaO4 were 842 μmolh-1gcat.-1 and 420 μmolh-1gcat.-1, respectively. Similarly, NiO was found to be best catalyst on InNbO4 catalyst. However, the negative of reduction-oxidation treatment was observed on NiO/InTaO4 and NiO/InNbO4. For In6WO12 catalyst, RuO2 additive gave the highest activity. The pretreatment method had a little effect on the activity of the catalyst. The yields of H2 and O2 were 774 μmolh-1gcat.-1 and 365 μmolh-1gcat.-1, respectively. K4Nb6O17 is a very active catalyst. The yields of H2 and O2 were 839 μmolh-1g cat.-1 and 415 μmolh-1g cat.-1, respectively. Photocatalytic activities of La-NaTaO3 catalysts for water splitting were studied under UV light irradiation. The yields of H2 and O2 were 1476 μmolh-1gcat.-1 and 738 μmolh-1gcat.-1, respectively. |
