透過您的圖書館登入
IP:3.226.254.255
  • 學位論文

探究金屬奈米材料以及包裹金屬顆粒之二氧化鈦結構及生長機制

Investigation of growth mechanisms for metal nanomaterials and metal nanoparticles -encapsulated TiO2 nanoparticles

指導教授 : 黃國柱

摘要


奈米尺寸的粗化現象是一個值得深入探討話題,在眾多用於解釋奈米粒子成長的這一個現象的理論中,奥斯瓦爾德熟化理論(Ostwald ripening theory)是最為廣泛用於解釋奈米粒子成長的理論,奥斯瓦爾德熟化理論的基本理論架構為”尺寸大的奈米顆粒其為溶解較具高化學勢能的小尺寸顆粒所生成”。 但是此理論並未探討金屬奈米材料的形狀所扮演的效應。在這此論文研究中,我們觀測到不同形狀但相同體積奈米顆粒(如奈米立方體、奈米圓球、奈米三角板以及十面體)在形狀上的演化以及它們相對的化學勢能;且我們研究發現化學勢能與表面積-體積比、結構缺陷有著顯著關聯性。同時、我們也利用硝酸鐵進行化學蝕刻不同形狀的奈米材料,討論不同晶面的對於化學勢能的影響。 為了討論奈米銀線的合併成長機制,我們設計實驗探討硝酸根在銀線成長上的所扮演的角色。依文獻上報導,銀線以十面體為晶種並沿著{111}的晶面成長成一維材料,然而、我們實驗觀測到文獻上所報導的成長機制似乎只適用於奈米棒以及短奈米線,對於極長的奈米線則無法適用。我們實驗證實長達~100微米以上的銀奈米線是從不同的銀棒以及奈米顆粒所自組裝而成。我們同時進行液態XRD的監測其生長過程中晶格的變化,在實驗中發現成長過程中會生成具有較高應力的面心四邊形的(face-centered tetragonal (fct))結構,且並在生成後的產物加入硝酸鐵以及四氯金酸進行化學蝕刻,以反應消除銀線中存有的應力。此項研究除了探討硝酸根如何影響銀線生長機制之外,我們更利用此這一些極長銀線進行導電薄膜的運用進而減低銀在導電材上的含量及成本。 金屬-半導體的奈米材料是一個具有高度研究的課題,因為金屬材料會增加半導體材料的光學性質,然而在文獻上大部分的合成核殼奈米顆粒大多以金屬奈米顆粒當作模板進行合成相異成分之殼層,然而奈米顆粒的表面晶面會隨著形狀而有所不同,我們以光將解的實驗中了解到在不同的金屬-半導體材料的電子傳遞上以(111)為主的三角奈米板較優於(100)晶面為主的奈米方塊。然而,這裡我們成功利用修飾起始物的方式調控水解速率進而成功將金屬顆粒表面包裹入二氧化鈦內。並利用反應溫度的調節生成具有高結晶結構的TiO2,而以這些具有高度結晶結構的的Ag@TiO2的殼層材料進行染料的降解實驗,進而了解其染料降解的機制討論(如高氧化力的氧生成如單重態的氧) 然而具應用價值的半導體材料”二氧化鈦”卻因其起始物容易進行水解而無法在金屬顆粒表面形成殼層。在這裡我們利用修飾起始物的方式控制水解速率進而成功將二氧化鈦包裹在金屬顆粒表面,並同時進行其不同晶面對於電子傳遞的差異探討,且同時發現在進行,其發現以金屬-二氧化鈦的核殼粒子進行染料降解時會產生具有高氧化力的單重態氧。且此物種可能對於染料降解扮演重要的角色。 除此之外我們以電紡絲技術合成二氧化矽纖維,並以氣相沉積合成出具有高度晶形的二氧化鈦管,此二氧化鈦管對於可見光區具有很好的電子訊號的反應,其反應電流遠比市售的二氧化鈦高出數倍 除此的液相形成TiO2殼層結構外,我們也同時討論以氣相的方式進行合成一維二氧化鈦材料,利用電紡絲技術進行大量合成模板,再利用氣相沉積的方式進行表面沉積二氧化鈦之殼層,並調控壓力大小以達到調控晶形狀態,並透過XPS的分析,了解透過此反應過程所合成出來的二氧化鈦會嵌合具還原態的碘,且此材料對於可見光區的光電流反應優於市售二氧化鈦(P25)與常壓合成之二氧化鈦管。

並列摘要


Coarsening process in nanoscale systems have been the subject of intensive research efforts. Among the number of processes which explains the coarsening phenomena, Ostwald ripening theory is most commonly adopted to rationalize the growth of large metal nanoparticles which are formed at the expense of small-sized nanoparticles of higher chemical potential energies. This theory did not describe whether the morphology of a metal nanoparticle plays a critical role in affecting the shape evolution of nanoparticles in the Ostwald ripening processes. In this thesis, we investigate the shape evolution among Ag nanoparticles of different morphologies in solutions, and measure chemical potential energies (or the electrochemical oxidation potentials) of Ag NPs of different morphologies, including, nanocubes, nanospheres, triangular plates, and decahedral nanoparticles with similar volume We show that the chemical potential energies of Ag NPs are strongly dependent on their morphologies, crystalline facets, surface to volume ratio (S/V ratio) and structural defects which were examined by selected area electron diffraction and X-ray diffraction. Chemical etching of Ag NPs by Fe (NO3)3 results in the preferential removal of atoms at edges/corners, and causes negative shift in the oxidation potentials. This clearly reveals the crystalline-facet dependent electrochemical behavior. To further understand the coarsening process of Ag nanowires in polyol process, we carried out the experiment, to examine the role of nitrate ion in the growth of silver nanowires. Ag nanowires (NWs) were formed via uniaxial growth of multiple twinned decahedral particles (MTPs) along the {111} facets. Herein, we show that the above MTP uniaxial growth mechanism for growth of nanorods (NRs) and short nanowires (NWs) is different from that for the growth of long Ag NWs. We provide experimental evidences to show that polycrystalline long Ag NWs (up to ∼100 μm) could be formed in high yield (∼90%) by a completely different growth mechanism via self-assembly of Ag NPs/NRs. Solution phase in-situ X-ray diffraction (XRD) measurements show that a strained face-centered tetragonal (fct) phase was gradually formed during the formation and growth of long Ag NWs, in addition to the normal face-centered cubic (fcc) phase. The strained fct phase disappears after partial etching by HAuCl4 and Fe (NO3)3. The working conditions for the MTP uniaxial growth mechanism and the nitrate-promoted self-assembly growth mechanism was compared and discussed. The as-synthesized Ag NWs were also utilized to fabricate conductive thin films (adhesive) for electrical applications. Metal-semiconductor nanocomposites belong to a particular class of popular heterostructures, for the reason that, when the metal is in contact with the semiconductor, the overall photo-abilities becomes very promising. One of the most straightforward examples of a nanoscale template that acts to guide for the growth of a plasmonic nanostructure is a metal nanoparticle. More recently, shape-controlled syntheses of metal nanostructures that can similarly be modified to act as supports for the deposition of a second element have been demonstrated, introducing the concept of shape as an additional variable that can impact the properties of the compound structure. Normally, different morphologies were bounded by different facets. To better understand the electron transfer in metal-semiconductor system with different facet via fabricated of Ag@TiO2 core-shell nanoparticles using different morphologies of Ag nanocrystals, such as, plate (which bounds by (111) facet), cube (which bounds by (100) facet, decahedron and rod by slight modification of titanium tetrabutoxide has been reported. Optical properties of these nanocrystals exhibited a slight bathochromic shift of surface plasmon resonance (SPR) of metallic nanocrystals after coating with amorphous titania (a-TiO2). As the Titania shell thickness increases, red shift in the SPR becomes dramatic. Further, temperature plays a critical role in the crystalline formation of titania shell (anatase, represented as c-TiO2). The photodegradation studies over Rhodamine B (RhB) under visible light illumination using Ag@c-TiO2 core-shell nanoparticles were compared with different morphologies of metal nanocrystal as core. The rate of photodegradation rate of RhB on Ag nanopalte@c-TiO2 is larger than that on Ag nanocube@c-TiO2. And the rate of photodegradation rate of RhB on Ag@c-TiO2 is 26 times higher than bare TiO2 (P25). Overall, we propose a photodegradation mechanism of RhB over Ag@TiO2 core-shell nanoparticles using ESR technique and near-infrared photoluminescence spectra. Besides, the metal nanoparticle in the titania ((TiO2) shell to improve electron transport, one dimensional titania nanostructures also reduce the resistance. Titania nanofiber/ hollow interior possess excellent electron mobility than nanoparticles. Electrospinning process is an easy way to fabricate ultra-long and well-aligned TiO2 nanofibers. Hence in the electrical applications, the mismatch of nanostructures would create a lot of defects in the nanomaterial. These defects would trap a lot of electrons while illumination. In the present study, we demonstrated the template-directed coating of TiO2 on SiO2 electrospun fiber with Ti metal and I2 via low temperature chemical vapor deposition. The thickness of titania shell was manipulated by the flow rate of the carrier gas. These nanostructures were characterized by XRD, EDS mapping and XPS. We also examined the photocurrent with hollow titania nanofibers under visible light illumination

參考文獻


(92) Castro, C. A.; Jurado, A.; Sissa, D.; Giraldo, S. A. Int. J. Photoenergy 2012, doi:10.1155/2012/261045
(33) Wang, Y. Z.; Li, Y. X.; Yang, S. T.; Zhang, G. L.; An, D. M.; Wang, C.; Yang, Q. B.; Chen, X. S.; Jing, X. B.; Wei, Y. Nanotechnol. 2006, 17, 3304-3307.
(46) Niu, W. X.; Zheng, S. L.; Wang, D. W.; Liu, X. Q.; Li, H. J.; Han, S. A.; Chen, J.; Tang, Z. Y.; Xu, G. B. J. Am. Chem. Soc. 2009, 131, 697-703.
(85) Wu, Z. P.; Wu, D. Z.; Zhang, T.; Jiang, L. Z.; Wang, W. C.; Jin, R. G. J. Appl. Polym. Sci. 2006, 102, 2218-2225.
(50) Yang, C.; Gu, H. W.; Lin, W.; Yuen, M. M.; Wong, C. P.; Xiong, M. Y.; Gao, B. Adv. Mater. 2011, 23, 3052-+.

延伸閱讀