微波液相合成奈米碳球暨將碳材表面快速改質及其在甲醇燃料電池上應用

Preparation of carbon nanoparticles in solution using domestic microwave oven and surface functionalization of carbon materials as promising catalyst supports for direct methanol fuel cell

辛玉麟(Yu Lin Hsin)

指導教授 ： 黃國柱

國立清華大學/理學院/化學系/博士(2007年)

https://doi.org/10.6843/NTHU.2007.00009

摘要

我們研發出一種新穎、簡單又經濟的液相製備奈米碳球和奈米碳球包覆金屬的方法。在甲苯裡加入一些銅絲在微波照射下便能產出奈米碳球,再加入一些金屬前驅物後便能產出碳包覆鐵之奈米粒子。這些產物的微觀結構可以利用高解析度電子顯微鏡來觀察研究。這些樣本的晶體結構可以利用選區電子繞射、粉末X光繞射和拉曼散射加以探索。碳包覆鐵奈米粒子的磁性可以利用超導量子干涉儀來量測。另外我們發現在被包覆在碳奈米膠囊內部的鐵在聚焦微波照射下與碳產生反應。我們研究這個反應並且提出一個合理機制來說明鐵和碳在非常微小尺寸侷限下的反應。這樣機制可以提供鐵催化劑如何催化生長奈米碳管的機制一些相關有用訊息。
本研究也發展出一種快速將奈米碳管表面官能基化的方法。經由超音波震盪和微波照射下促進自由基化聚合反應而快速將奈米碳管的表面官能基化。親油性(如聚乙烯苯和聚甲基丙烯酸甲酯)和親水性(如聚丙烯醯胺、聚丙烯酸和聚乙烯醇)的聚合物都可以利用此法在十分鐘內化學鍵結在奈米碳管表面。鍵結在奈米碳管的聚合物可以利用傅立葉紅外線光譜、熱分析儀、電子顯微鏡和電子能量損失光譜來加以分析。這些表面改質後的奈米碳管溶解度可以達到每升溶解1200~ 2800毫克程度。中空填充鐵的奈米碳管也可以利用此法官能基化。在填充金屬鐵的奈米碳管表面修飾聚丙烯酸在室溫下具有飽和磁力矩約每克40高斯和幾乎等於零高斯的磁滯力。
而我們發展奈米碳管官能基化的方法也可以應用在不同碳材上當作直接甲醇燃料電池( Direct Methanol Fuel cell, DMFC)的陰極支撐物。在本論文不同碳材表面均勻地被修飾成聚乙烯引朵(Poly vinyl pyrrolione, PVP)當作甲醇燃料電池催化劑的支撐物。修飾在碳材上的聚合物利用紅外線光譜、熱分析儀和拉曼散射加以證實。高解析電子顯微鏡、粉末繞射和X光光電子能譜顯示這些微小尺寸和很窄尺寸分佈(1-2 nm)的鉑催化劑均勻分佈在修飾聚乙烯引朵(PVP)的碳材表面上。在本論文我們也研究在不同碳材上修飾聚乙烯引朵(PVP)和強酸氧化方式在甲醇燃料電池上效能的影響。我們發現鉑沉積在修飾聚乙烯引朵(PVP)的脊狀奈米碳纖維在甲醇燃料電池上展現最好的效能,幾乎是強酸氧化的脊狀奈米碳纖維的四倍以及活性碳的三倍。我們預計這個方法將可以廣泛應用在不同碳材當作催化劑支撐物應用在甲醇燃料電池上。
另外在本論文裡不同種類的以表面官能基化奈米碳管為基材的複合材料(例如: 金/奈米碳管, 鉛/奈米碳管, 硫化鋅/奈米碳管和硫化鎘/奈米碳管等複合材料)都可以經由簡單室溫化學反應成功被製備。這個方法預期是一般性製備各種以奈米碳管為基材的複合材料方式。

關鍵字

奈米碳管 ； 奈米碳球 ； 表面官能基化 ； 微波 ； 甲醇燃料電池

並列摘要

We have developed a novel, simple, efficient and economical synthetic route for preparation of carbon nanoparticles and graphite-encapsulated metal nanoparticles in solution. The carbon nanoparticles were prepared in toluene that contains copper wires under microwave irradiation. Graphite-encapsulated metal nanoparticles were prepared similarly after a metal precursor was added. The morphologies of the products were examined using TEM and HRTEM. The crystalline structures of the samples were characterized using SAED, XRD and Raman spectroscopy. The magnetic characteristics of the metallic carbon products were explored using SQUID. Reactions that proceeded in the interior metal core of carbon nanocapsules occurred under focused microwave irradiation are examined. A possible mechanism of the reactions of carbon shells with iron cores was proposed. Results of this study provide further insight into the mechanism of the iron-catalyzed growth of carbon nanotubes.
This thesis also presents a technique for rapidly surface functionalization the of carbon nanotubes (CNTs). CNTs were surface-functionalized with various functionalities via a rapid, single-step process that involved ultrasonication-assisted and microwave-induced radical polymerization. Both hydrophobic (such as polystyrenes and poly methyl methacrylate) and hydrophilic (such as poly acrylamide, poly acrylic acids and poly allyl alcohols polymer chains) can be chemically grafted onto the surface of MWCNTs by the same process within ~10 min. The surface grafted polymers were identified by FTIR, TGA, TEM, EELS and Raman spectroscopy. The solubilities of the surface derivatized MWCNTs were in the range 1200~ 2800 mg/L. Iron-filled multi-walled carbon nanotubes (Fe@MWCNTs) can also be functionalized by this strategy. The poly (acrylic acid) modified iron filled MWCNTs have a saturated magnetic dipole moment of ~40 emu/g at room temperature with a coerceive field of nearly zero Gauss.
The surface modifying strategy was applied to various graphite materials (such as graphite nanofiber and carbon nanotubes) as catalyst supports for the oxidation of methanol at the anode. The surfaces of various graphite materials were homogenously modified with poly vinyl pyrrolidone(PVP) and used as supports for the oxidation of methanol at the anode. The PVP-carbon supports were characterized by FTIR, TGA and Raman spectroscopy. The HRTEM, XRD and XPS results demonstrated the small (1-2 nm) and narrow size distribution of the Pt nanoparticles catalyst could be deposited on these PVP-carbon supports. Various graphite materials functionalized with PVP radicals and carboxylic acid via acid oxidation were used as supports for the Pt catalyst in a methanol oxidation reaction. The Pt-PVP-herringbone graphite nanofiber (PVP-GNF) nanocomposite gives the best electro-catalytic performance in direct methanol fuel cell among all carbon nanosupports, being nearly four times oxidation current of that from the Pt/acid oxidizing GNF(AO-GNF) nanocomposite, and nearly three times that of the Pt-XC-72 carbon black. The developed methodology is expected to be very useful in future DMFC studies when applied to other metals or metal alloy catalysts.
In additional, the various nanocomposited (such as Au/CNT, Pb/CNT, ZnS/CNT and CdS/CNT) with the surface functionalized CNTs can successful be prepared by simple room temperature chemical reaction in this thesis. This method could expect be the generality assembly of nanocrystal-carbon nanotube composite approach.

並列關鍵字

carbon nanotube ； carbon nanoparticles ； surface functionalization ； microwave ； direct methanol fuel cell

參考文獻

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