Catalyst Design Using Nanoporous Iron for the Chemical Vapor Deposition Synthesis of Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWNTs) have been synthesized via a novel chemical vapor deposition (CVD) approach utilizing nanoporous, iron-supported catalysts. Stable aqueous dispersions of the CVD-grown nanotubes using an anionic surfactant were also obtained. The properties of the as-produced SWNTs were characterized through atomic force microscopy and Raman spectroscopy and compared with purified SWNTs produced via the high-pressure CO (HiPCO) method as a reference, and the nanotubes were observed with greater lengths than those of similarly processed HiPCO SWNTs. 1. Introduction Of vital importance to the next generation of aerospace vehicles are structurally resilient, lightweight, and space durable materials and structural health monitoring sensors that can withstand environmental rigors. Carbon nanotubes (CNTs) have shown significant potential in these and a wide variety of other applications on the basis of their remarkable mechanical and electronic properties [1, 2]. CNTs, however, can be produced by several synthesis methods, with some methods better suited for particular applications. Single-walled carbon nanotubes (SWNTs) grown between suspended pillars, for example, have been studied as potential nanoscale power lines [3]. A dominant approach for the synthesis of SWNTs is chemical vapor deposition (CVD), including the high-pressure carbon monoxide (HiPCO) technique [4]. In this paper, we present an alternative CVD method of synthesis of SWNTs for use in composites and aerospace sensor applications. Specifically, we describe the novel incorporation of iron catalysts within a mesoporous material for CNT production. Mesoporous materials (MPMs) are a class of inorganic molecular sieves [5]. Pores in the nanoscale range of 2 to 100？nm make these materials very attractive as shape selective adsorbents or catalysts. Generally, the MPM is prepared in solution by supramolecular assembly of organic molecules as templates with an inorganic precursor. In the original synthesis of MPMs is the formation of rod-like micelles using charged surfactants such as alkyltrimethylammonium surrounded by inorganic species followed by the polymerization of silicates to form the framework of MPMs. The pore size of MPMs can be tuned in the nanosize range based on the number of carbon atoms in the alkyl chain length of surfactants from about 1.6？nm for eight carbon atoms to 3.8？nm for 16 carbon atoms. The pores are separated by silicate walls whose thickness is in the range of 0.8 to 1.6？nm. As-synthesized MPMs have specific crystalline phases that can be controlled