製備零維與一維之金奈米材料及奈米金粒子在多孔二氧化鈦上特性之研究

Synthesis of 0-D and 1-D Gold Nanomaterials and Properties of Gold Nanoparticles-deposited Mesoporous TiO2

謝倩芳(Chain-Fang Shieh)

指導教授 ： 王宏文

中原大學/理學院/化學研究所/碩士(2006年)

https://doi.org/10.6840/cycu200600216

摘要

本論文主要包含三個實驗主題(1)利用化學溶液的方式，將塊材金合成出奈米金粒子；(2)藉由模板法與電化學沉積法製備出一維的金奈米材料與(3)將奈米金粒子負載於中孔洞的二氧化鈦上，並探討其光催化特性與研究。
在第一個實驗主題中，我們利用塊材金所合成之金(III)的前驅液，藉由不同的方式來合成大小在10nm以下的金奈米粒子。在實驗結果中，以檸檬酸鈉還原法合成時，在pH=5且[穩定劑=MPA]/[Au]的比值為2時，其所合成的金奈米粒子為最小且分散狀況最好的條件；以界面活性劑(溴化三甲基十六銨鹽，CTAB)在水相製備金奈米粒子時，可以得到分散狀況最好、穩定性最佳的狀況，不過所得之金奈米粒子的形貌卻是各式形狀都有。而在以硼氫化鈉還原金奈米粒子時，可以在低溫下就得到非常穩定且小於10nm之金奈米粒子。
在第二個主題中，主要利用其電化學沉積法沉積金在模版的孔洞中，並藉由不同的沉積電壓、沉積溶液的濃度與沉積的時間來探討其成長的反應機制。而從實驗結果得知，在低電壓、低濃度的環境下，且不需任何有機物質的添加就可生成金奈米管，若是再拉長其沉積時間，即可得到奈米金條。並且利用uv-visible光譜儀探討我們所合成出之ㄧ維奈米金材料的光學特性，我們可以得知其光學特性來自於橫軸的方向的表面電漿共振吸收所造成。
在第三部份的實驗中，則是將其奈米金粒子還原在不同的二氧化鈦粒子上，希望藉由吸附的方式，使金奈米粒子負載於二氧化鈦粒子表面上，希望藉由奈米金粒子來降低電子與電洞對再結合之能力而使其光催化活性提高。在商用P25的TiO2系列中，因其P25本身材料有較好的結晶性與不同型態的組成，所以光催化效果有不錯的效果，而在金還原於TiO2上，由於金粒子還原時並無法緊密的負載於TiO2上，且反應過程中有殘餘的金(III)離子存留於其上，導致光催化效果大幅的降低；而在mesoporous TiO2系列上，金粒子是還原並且存在於其之TiO2孔洞中，雖然大大的降低其比表面積但卻使得其受光激發後的電子與電洞延長再結合的時間而增進其光催化效果。

關鍵字

奈米金管 ； 奈米金粒子 ； 光催化 ； 多孔二氧化鈦 ； 奈米金條

並列摘要

In this study, three subjects have been investigated：i.e. (1) the synthesis of gold nanoparticles from bluk gold by chemical solution process, (2) the synthesis of 1D gold nanorods/nanotubes via template growth and electrochemical deposition, and (3) the synthesis and photocatalytic properties of gold nanoparticles on the mesoporous TiO2 powders.
First, gold nanoparticles with diameter less than 10 nm were prepared by different methods using gold (III) precursor which was formed from dissolving bulk gold in aqua regia solution. The synthesized gold nanoparticles using reducing agent sodium citrate dispersed stably and the particle size was the least, about 7~8 nm at pH=5 at a stabilizer/gold ratio of 2. In the synthesis of gold nanoparticle by surfactant (CTAB) method, the most stable Au suspensions were prepared but the morphology on the surface of the particles was bumpy. The gold nanoparticles using the reducing agent sodium borohydride could be formed at low temperature (about 0°C ~5°C) and particle size was less than 10 nm.
Second, the synthesis of 1-D gold nanomaterials via template growth and electrochemical deposition using different concentrations of gold (III) precursor, deposition voltages, and deposition durations are carried out. Using a membrane with 100nm pore size, gold nanotubes are initially formed from the bottom and the wall of the pore channels. Preferred growing on the pore walls at low gold concentrations and low voltages is proposed to be responsible for the formation of nanotubes which are progressively thicker and sealed up into nanorods at longer durations. Optical property of the synthesized 1-D gold nanomaterials caused by the surface plasmon resonance of transverse (width) mode is identified using uv-visible spectrometry.
And finally, the synthesis and photocatalytic property of gold nanoparticles on the TiO2 mesoporous nanopowders by chemical reduction process was studied. The commercial P25 TiO2 exhibits well crystalline anatase and rutile phases and better photocatalystic effect than that of pristine mesoporous TiO2. However, the residence of Au (III) ions on the surface of commercial TiO2 decreased its photocatalytic activity. The gold nanoparticles formed and resided in the pore of mesoporous TiO2 powders and greatly reduced the surface area of TiO2; however, enhanced the photocatalytic effect by prolonging the lifetime of photogenerated electron-hole pairs.

並列關鍵字

mesoporous TiO2 ； gold nanoparticles ； photocatalysis ； gold nanotubes ； gold nanorods

參考文獻

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