鈷、鎳摻雜與負載之二氧化鈦奈米粒子於光催化活性及水裂解之應用

Abstract

在本研究中，藉由alcohol-thermal和sol-gel hydrolysis precipitation此兩種方法，合成出不同金屬離子(鈷、鎳)含量之表面(surface)摻雜與體(bulk)摻雜二氧化鈦奈米粒子。除此之外，更進一步的研究觀察摻雜(doped)與負載(loaded)二氧化鈦奈米粒子的光催化活性的性質。本實驗所製備出的樣品皆通過粉末X光繞射儀分析(XRD)、掃描式電子顯微鏡(SEM)、X光能譜散布分析儀(EDS)分析、穿透式電子顯微鏡(TEM)分析與X-Ray光電子能譜儀(XPS)做進一步分析其特性。合成出的金屬離子(鈷、鎳)摻雜和金屬原子負載之二氧化鈦奈米粒子，通過氙燈的照射下，對於甲基橙光催化降解反應的效果來評估合成樣品的光催化活性能力。經由特性分析結果顯示出作為摻雜物的鈷與鎳，能在穩定二氧化鈦中銳鈦礦相的形象，也降低原本的帶隙能量和調節此材料的平帶電位，使得該材料更可以用於水的光電化學氧化反應上。鈷和鎳能促使比二氧化鈦還高的光催化產氫活性可能歸因於，鈷和鎳此摻雜物質的存在能增強光電靈敏度，而且鈷和鎳的協同效應能有效的分離光生電子與電洞來作為產氫反應(HER)與氧化反應(OR)的活性點。更重要的是，這些研究是第一次顯示出鎳離子能成功的增強氫化反應過程，但是鈷離子則無法。最後的結果表示，微量的金屬離子摻雜和負載都不會改變原本二氧化鈦的晶格結構，但卻能在氙燈照射下有良好的光催化產氫活性。經過氫化反應後，作為助催化劑的鎳負載在二氧化鈦上的材料，其光催化產氫活性比其它改質材料要來的高，而且也比原本未氫化的鎳負載二氧化鈦產氫量高20倍左右。

In this work, surface and bulk doped TiO2 nanoparticles with different amounts of metal ions (Co, Ni) were prepared by alcohol-thermal and sol-gel hydrolysis precipitation methods. Moreover, an additional investigation into photocatalytic activities of the doped and loaded TiO2 nanoparticles have been studied. The prepared samples were characterized by X-ray diffraction (XRD), scanning-electron microscopy (SEM), energy dispersive X-ray (EDS), transmission electron microscopy (TEM), UV-visible spectroscopy (UV-vis) and X-ray photoelectron spectroscope (XPS). Photocatalytic capabilities of metal ions (Co, Ni) doped and metal loaded TiO2 nanoparticles were evaluated by means of methylene orange (MO) degradation reaction under Xenon lamp. Characterization results suggest that as dopants, cobalt and nickel stabilizes TiO2 in the form of anatase phase, reduces its band gap energy, and adjusts its flat band potentials such that this material can be employed for photoelectrochemical (PEC) oxidation of water. The high photocatalytic H2 evolution activity over TiO2 promoted by cobalt and nickel may be ascribed to the enhanced photo-response due to the presence of cobalt and nickel impurities, and the effective separation of photogenerated electrons and holes due to the synergistic effect of cobalt and nickel, which serve as active sites for H2 evolution reaction (HER) and oxidation reaction (OR). Importantly, for the first time these studies reveal that the nickel ion can successfully enhance the hydrogenation process, but not the cobalt ion. The results reveal that the crystal structure of TiO2 is not changed by a trace amount of the doping and loading metal ions, but the photocatalytic H2 evolution from TiO2 under Xenon lamp is enhanced greatly. After hydrogenation, the photocatalytic activity of nickel as the cocatalyst loaded on TiO2 for hydrogen evolution is much higher than the other materials and about 20 times higher than Ni-loaded TiO2 without hydrogenation.