Study of Synthesis and Photodegradation Properties of Metal Oxide Nanostructures

[[abstract]]本論文研究以金屬氧化物奈米結構的合成及其光降解特性做深入的探討，本研究成功的利用簡單與可靠之微胞媒介水熱法(Micelle-mediated hydrothermal method)及二價鎘離子(Cd(II)-ions)摻雜製程合成出多孔鎘摻雜二氧化鈦光觸媒，藉由鎘摻雜的製程使二氧化鈦奈米顆粒上具有很高的比表面積(Specific surface area)之奈米結構並且透過金屬離子摻雜進而降低整體能隙，更有效的使電子–電洞對分離時減少再複合的機率，結合高表面積的特性與降低整體能隙之特性用以提升光降解反應時產生氫氧自由基與超氧離子，達到更有效的光降解特性，本研究發現5%-鎘摻雜之二氧化鈦具有極大的比表面積(389.05 m2/g)與寬頻吸收等特性可將光吸收波長由紫外光區延伸至可見光區域，充分利用紫外光與可見光波長形成具有寬頻特性之光觸媒，此外於光降解試驗中本研究以兩種非生物可降解之偶氮染劑，羅馬素黑色5號(Remazol Black 5, RB-5)與羅馬素亮橘色3R (Remazol Brilliant Orange 3R, RBO-3R)作為汙水樣本進行試驗，有系統地針對不同濃度的二價鎘離子濃度，光觸媒含量，不同pH值環境下進行不同光波長下的吸收值及光降解效率分析，進而研究其動力學模型應證此光降解反應遵守二階動力學模型(Second-order kinetic model)之特性，此外5%-鎘摻雜之二氧化鈦奈米顆粒降解RB-5與3R偶氮染劑於紫外光波段光降解能力更達到80%以上，相較於未經摻雜之二氧化鈦奈米顆粒更於可見光波段提升其降解能力達55%。 本論文研究另一主軸係以使用晶種輔助水熱法(Crystal seed-assisted hydrothermal method) 製備氧化鋅(Zinc Oxide, ZnO)奈米柱陣列(Nanorod arrays)再由硫化製程(Sulfidation process) 製備出氧化鋅/硫化鋅核殼結構，並以二價銅離子(Cu(II)-ions)摻雜製程建構出銅摻雜之核殼奈米結構，氧化鋅/硫化鋅核殼結構利用簡易的水熱法進行硫化製程並達到表面鈍化的效果，也使原先容易吸附環境中的水氣或氫氧基而親水的氧化鋅改變為疏水表面，於此改善了氧化鋅的氧缺陷並透過核殼結構間的異質介面而使光吸收範圍延伸至可見光波長下，並能夠有效的分離電子–電洞對，使光觸媒特性更為顯著，然而摻入銅離子目的為降低電阻提高電流值同時減少氧化鋅內部的氧空缺，製備出三階核殼型態，藉以降低整體奈米結構之能隙並使得電子–電洞對更容易分離、降低複合發生率，於光觸媒之研究中，減少其複合機率亦就提升光降解反應時產生之自由基反應，能更有效的提升光降解效率，本研究所成功製備之銅摻雜氧化鋅/硫化鋅核殼結構於近紫外光、可見光波段有效降解80%以上之亞甲基藍(Methylene blue, MB)染劑，更可展現出寬頻及優越之降解能力。[[abstract]]This study investigated the synthesis of a metal-oxide nanostructures and explored their photodegradation characteristics. The simple and reliable micelle-mediated hydrothermal method was employed to create the porous cadmium-doped titanium dioxide photocatalysts. Subsequently, through cadmium doping, the titanium dioxide nanoparticles possessed a high specific surface area and the band-gap energy of the overall nanostructures was reduced. Therefore, the possibility of recombination was reduced duo to efficient electron–hole pair separation. Additionally, we took advantage of the characteristics of high specific-surface area and reduced band-gap energy to initiate the generation of hydroxyl radicals and superoxide via light excitations, thereby resulting in the superior photodegradation characteristics. We found that the doping of titanium dioxide with 5% of cadmium possessed superior characteristics— large specific surface area (389.05 m2/g) and wideband light-absorption capability, which extended the light absorption range from ultraviolet regions to visible regions. Moreover, this study used two nonbiological degradable azo dyes, including Remazol Black 5 (RB-5) and Remazol Brilliant Orange 3R (RBO-3R), as organic targets in the photocatalytic experiments. This study further investigated the dynamic model and proved that the involcing photodegradation reaction was in accordance with the characteristics of second-order kinetic model. Furthermore, the photo-degradation capability of titanium dioxide nanoparticles doping with 5% cadmium could result in 80% degradation of both RB5 and 3R dyes. Compared with the undoped titanium dioxide nanoparticles, with the improved photodegradation activity of 55% higher than that of undoped titanium dioxide nanoparticles under the irradiation of the visible light. In addition, a crystal seed-assisted hydrothermal method was used to prepare zinc oxide nanorod arrays. Subsequently, a vulcanization process was adopted to prepare a zinc oxide/zinc sulfide core-shell structure, which was then doped with the divalent copper ions to create a copper-doped core-shell nanostructures. A simple hydrothermal method was used to induce a vulcanization process to facilitate surface passivation in the zinc oxide/zinc sulfide core-shell structure and altered the surface of zinc-oxide nanorods from being hydrophilic (due to adsorbing the environmental moisture or hydroxyl groups) to hydrophobic. In addition, by introducing the heterogeneous interfaces in the core-shell structures, light-absorption range was extended to visible wavelengths and electron–hole pairs were effectively separated, enhancing their photocatalytic properties. It was found that the introduction of copper ion doping could reduce the resistance of nanostructures and decreased the oxygen defects in zinc-oxide nanorods, and further facilitated the separation of electron–hole pairs and lower their possibility of carrier recombination. In photocatalytic tests, the efficiency of photodegradation for degrading the methylene blue dyes was found to be effectively increased based on the Cu-doped ZnO/ZnS core-shell structures under the illuminations of ultraviolet lights and visible lights, which demonstrated the broadband and superior photodegradation capabilities.[[note]]碩