Carbon nanostructures formed on mesoporous silica by catalytic chemical vapor deposition of ethene
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Three different strategies, wet impregnation, in situ reduction, and grafting with silane coupling agents, have been used to introduce CoNi nanoparticles with different existing forms into mesoporous silica. These composites were used as catalysts to grow nanostructured carbons by catalytic chemical vapor deposition using ethene. Carbon nanotubes (CNTs) with different inner diameters can grow out of mesoporous silica particles incorporated with CoNi nanoclusters. Many fewer CNTs could be found in the pore channels of the sample prepared by using silane coupling agents than in those of the sample synthesized via wet impregnation. No CNTs formed in the pore channels of the sample prepared by in situ reduction. After the removal of silica, different carbon nanostructures have been obtained in the pore channels. Ordered graphite carbon mesostructure was obtained from the sample prepared by in situ reduction. Highly dispersed metal catalysts inside mesopore channels are favorable for the formation of graphite carbons with ordered mesostructures.
I. INTRODUCTION
Mesoporous materials, which have uniform and ordered pore structures, have proved to be excellent templates to confine the growth of guest nanoclusters and nanowires.1 Their pore size can be tuned, so the controlled synthesis of nanomaterials with different sizes could be realized. Recently, mesoporous silica-based composites loaded with, for example, Fe, Co, and Ni nanoclusters, have been reported as catalysts to produce carbon nanotubes (CNTs) by catalytic chemical vapor deposition (CCVD).2–10 However, few reports can be found on the diameter control of CNTs in mesoporous silica.4 In fact, the sizes of catalyst nanoparticles can be strictly confined by the pore wall. The diameter of CNTs is usually dominated by the catalyst particle size; thus, the diameter of a CNT can be tuned. Systematic experiments are necessary to prove this assumption. On the other hand, the incidental deposition of a carbon source inside the mesopore channels, besides CNT deposition in pore channels, should be a common phenomenon by CCVD. However, this has never been reported in the literatures. Alternatively, mesostructured carbon replicas of mesoporous silica have been prepared by the carbonization
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0047 J. Mater. Res., Vol. 23, No. 2, Feb 2008
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of organic precursors, which are introduced by nanocasting, wet impregnation, and chemical vapor infiltration.11–23 These carbon materials are attracting much attention for their potential applications as new adsorbents, catalysts, and electrode materials.18,21,23 Among the carbon materials, mesoporous carbons with a graphitized structure are still an interesting research topic because of their better electric/catalytic properties and higher potential in many electrochemical applications (e.g., fuel cells and lithium ion batteries) than conventional amorphous carbons.18 To obtain the graphit
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