Fabrication of a Composite Structure of Three-dimensional Macroporous Silica and Carbon Nanofilaments
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H. Li and B. Sheldon Materials Engineering, Division of Engineering, Brown University, Providence, Rhode Island 02912
H. Du Department of Chemical, Biomedical, and Materials Engineering, Stevens Institute of Technology, Hoboken, New Jersey 07030 (Received 4 March 2005; accepted 25 May 2005)
We explored the possibility of incorporating carbon nanotubes in a patterned and macroporous silica structure replicated from a thin polystyrene template. A V-shaped thin, vertical channel was constructed and successfully used to assemble 10.06-m polystyrene spheres into a dense three-dimensionally ordered template of uniform thickness. Infiltration of a single Co/silica precursor sol into the template followed by thermal treatments in vacuum and H2 produced three-dimensionally ordered silica pores with embedded Co nanoparticles. Wormlike carbon nanofilaments of 50–120 nm in diameter were grown on the inner surface of silica pores with plasma-enhanced chemical vapor deposition.
I. INTRODUCTION
Porous materials with three-dimensional (3D) periodicity and carbon nanotubes are currently two of the most intensively studied subjects in nano-science and technology. The 3D porous materials are highlighted by their large specific surface area and 3D ordered array of pores, which encompass a wide scope of potential applications to photonic crystals,1 chemical sensors,2,3 catalysts,4,5 membranes,6 and biomaterials.7 On the other hand, carbon nanotubes, with exceptional mechanical and electrical properties,8,9 hold great promise as membrane materials for batteries and fuel cells, anodes for Li-ion battery, capacitors, and chemical filters.10,11 Thus, the grafting of these two materials with unique intrinsic properties is challenging yet rewarding because it can yield potentially robust systems in which an abundance of nanotube array would be necessary for system efficiency, sensitivity, and miniaturization. In addition, the novel structure of huge packing density of nanotubes will afford further studies for applications such as entrapment of DNA and proteins, catalytic support, desalination of seawater, and
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Address all correspondence to this author. Present address: Department of Chemical and Environmental Engineering, Illinois Institute of Technology, Chicago, IL 60616. e-mail: [email protected], [email protected] DOI: 10.1557/JMR.2005.0303 2498
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 9, Sep 2005 Downloaded: 02 Apr 2015
hydrogen storage for fuel cells. A big advantage of this structure is that the functionality of the 3D porous framework can be tailored by controlling the size and the degree of interconnectivity of pores. The fabrication of 3D porous structures employs colloidal crystals as template, which simply serves as a 3D scaffold whose interstices are filled with materials to be synthesized. For the present study, 10.06-m polystyrene (PS) spheres were chosen as templates to provide a sufficient volume of silica pore for carbon nanotubes to grow at a later stage. However, such large PS spheres are not sui
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