Iron-Doped Carbon Aerogels: Novel Porous Substrates for Direct Growth of Carbon Nanotubes

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• 作者：Stephen A. Steiner ; III ; Theodore F. Baumann ; Jing Kong ; Joe H. Satcher ; Jr. ; Mildred S. Dresselhaus
• 刊名：Langmuir
• 出版年：2007
• 出版时间：April 24, 2007
• 年：2007
• 卷：23
• 期：9
• 页码：5161 - 5166
• 全文大小：516K
• 年卷期：v.23,no.9(April 24, 2007)
• ISSN：1520-5827

文摘

We present the synthesis and characterization of Fe-doped carbon aerogels (CAs) and demonstrate the ability togrow carbon nanotubes directly on monoliths of these materials to afford novel carbon aerogel-carbon nanotubecomposites. Preparation of the Fe-doped CAs begins with the sol-gel polymerization of the potassium salt of 2,4-dihydroxybenzoic acid with formaldehyde, affording K⁺-doped gels that can then be converted to Fe²⁺- or Fe³⁺-dopedgels through an ion exchange process, dried with supercritical CO₂, and subsequently carbonized under an inertatmosphere. Analysis of the Fe-doped CAs by TEM, XRD, and XPS revealed that the doped iron species are reducedduring carbonization to form metallic iron and iron carbide nanoparticles. The sizes and chemical composition of thereduced Fe species were related to pyrolysis temperature as well as the type of iron salt used in the ion exchangeprocess. Raman spectroscopy and XRD analysis further reveal that, despite the presence of the Fe species, the CAframework is not significantly graphitized during pyrolysis. The Fe-doped CAs were subsequently placed in a thermalCVD reactor and exposed to a mixture of CH₄ (1000 sccm), H₂ (500 sccm), and C₂H₄ (20 sccm) at temperatures rangingfrom 600 to 800 ages/entities/deg.gif">C for 10 min, resulting in direct growth of carbon nanotubes on the aerogel monoliths. Carbonnanotubes grown by this method appear to be multiwalled (~25 nm in diameter and up to 4 ages/entities/mgr.gif">m long) and grow througha tip-growth mechanism that pushes catalytic iron particles out of the aerogel framework. The highest yield of CNTswas grown on Fe-doped CAs pyrolyzed at 800 ages/entities/deg.gif">C treated at CVD temperatures of 700 ages/entities/deg.gif">C.