改質觸媒於單壁奈米碳管之形貌調控相關研究

Abstract

單壁奈米碳管不僅具有許多獨特優異的光電及物化性質，同時也具有極高的應用價值，所以一直是科學家們所著重的研究議題之一。本實驗的目的是藉由多種改質觸媒，以化學氣相沉積法調控單壁奈米碳管之管徑以及長度。而為了提高鎳金屬奈米粒子的分散性，及避免顆粒聚集，我們以修飾後的中孔洞氧化矽材MCM-41作為載體，接著透過離子交換法將鎳離子置換入二氧化矽骨架中，最後再利用氫氣將鎳離子還原成具催化活性的鎳金屬奈米粒子。所得的觸媒材料，分別以粉末X光繞射儀、氮氣等溫吸脫附儀及感應偶合電漿質譜儀來鑑定其結構、孔洞性質和鎳金屬附載量。 化學氣相沉積法的熱處理可以分為兩部分：(1) 鎳離子的預還原(2) 奈米碳管的生成。反應後的樣品利用拉曼光譜儀鑑定碳管的特徵，並以高解析穿透電子顯微鏡觀察碳管的型態。 實驗第一部分探討載體孔徑對於鎳金屬的限制效應，以及化學氣相沉積反應時間對於單壁奈米碳管的影響。從實驗結果可知隨著孔徑的遞減，單壁奈米碳管的純度會逐漸降低，但管徑大小無明顯變化。而增加化學氣相沉積的反應時間，將會促使碳原子在高溫下進行重排，進而降低單壁奈米碳管的缺陷程度。 實驗第二部分探討觸媒的矽源 (矽酸鈉或矽晶種)以及鋁源(鋁酸鈉)的添加對於碳管生長模式及管徑的影響。若以矽酸鈉做為矽源，碳管的生長模式將會是底部成長；若是以矽晶種做為矽源，則碳管會以頂部成長模式進行。就在管徑的調控上，觸媒Ni-AlMCM-41(ss)的管徑分布最廣，而Ni-AlMCM-41(seeds)具有最好的品質以及產率。 若利用結構改質，以短孔道的中孔洞氧化矽材MCM-41作為載體，使一氧化碳通過孔道的距離大幅度的縮短。因為其能快速與金屬鎳行催化反應，則可以成功的合出管徑更細的單壁奈米碳管。管徑大約為1奈米。 實驗最後一部分利用包覆於氧化矽空心球中的鎳金屬作為觸媒，藉由三維空間的限制效應，合成長度較短的單壁奈米碳管。碳管長度約15奈米，管徑約0.8~0.85奈米。

Single-walled carbon nanotubes not only have many unique excellent optical , physical and chemical properties but also possess a very high value, so scientists have been to emphasize the study. The purpose of this study is to use a variety of modified catalysts, control the diameter and the length of single-walled carbon nanotubes by chemical vapor deposition. In order to improve the nickel metal dispersion and avoid particle aggregation, we modified the mesoporous silica material, MCM-41, as support, then through the ion exchange replacement nickel ions into the silica framework. Finally, we used hydrogen reduction nickel ions to a catalyst with the activity. The catalyst materials were characterized by using powder X-ray diffraction, nitrogen adsorption-desorption isotherms instrument and ion-coupled plasma mass spectroscopy to identify its hexagonal structures, pore physical properties and the amount of Ni loading respectively. Chemical vapor deposition heat treatment can be divided into two parts: (1) pre-reduction of nickel ions (2) the formation of carbon nanotubes. After CVD reaction, using Raman spectroscopy to identify the characteristics of carbon nanotubes, and observe its pattern by high resolution transmission electron microscopy. The first part of the experiments is to explore the pore size limit effect to the nickel, and the reaction time of chemical vapor deposition for the impact on single-walled carbon nanotubes. Experimental results show that with decreasing pore size, the purity of single walled carbon nanotubes will gradually decline, but no significant changes in diameter size. The increase in chemical vapor deposition of reaction time, will promote carbon atoms under high temperature rearrangement, thus lowering the level of single-walled carbon nanotubes defect. The second part discusses the type of silica source (sodium silicate or silicon seeds), and aluminum source (aluminum sodium) added for the single-walled carbon nanotubes growth patterns and the impact of diameter. If sodium silicate was used as the silica source, carbon nanotube growth model will be the bottom growth; if zeolite seeds were used as the silica source, the carbon nanotube growth model will the top growth. In regulating diameter, the catalyst Ni-AlMCM-41(ss) diameter with the most widely distributed, and Ni-AlMCM-41 (seeds) with the best quality and yield. In terms of structural modification of the short channels of MCM-41 silica material as support, so that the distance between carbon monoxide through the channel significantly shortened. Because it can quickly react with nickel, we can successfully control the diameter of single-walled carbon nanotubes much smaller. The diameter is about 1 nm. The last part of the experiments use of silica hollow spheres embed nickel metal as a catalyst, by three-dimensional confinement effect, can be synthesized relatively short length of single-walled carbon nanotubes. The length and diameter of carbon nanotubes are about 15nm and 0.8~0.85nm, respectively.