In Situ Probing of Oxygen-Containing Groups on Acid-treated Carbon Nanofibers using Aromatic Molecules

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Development of chemical nanotechnology to control the structure of materials on a nanosize scale is necessary in order to obtain certain physical and chemical properties of the nanomaterials. Carbon nanofibers (CNFs) (Oberlin et al., 1976; Endo, 1988; Endo et al., 2001) are very large multi-walled carbon nanotubes and are technologically easier and economically more favorable to produce than individual single- or double-walled carbon nanotubes (Iijima, 1991; Iijima & Ichihashi, 1993). The CNFs are valuable materials for electronic, mechanical, and optical devices because of their unique structural and quantum characteristics that are similar to small-sized carbon nanotubes (Oberlin et al., 1976; Endo, 1988; Endo et al., 2001; Endo et al., 2002; Yang et al., 2003; Wang et al., 2005; Tan et al., 2006). For practical use, such carbon nanomaterials need to be well dispersed throughout other raw materials. An example of this is the incorporation of carbon nanomaterials into plastics or ceramics, which provide practical materials with well-defined shape and increased strength. Composites of matrices with dispersed carbon nanotubes have been prepared by the polymerization of a polyimide under sonification (Park et al., 2002) and by the sol−gel reaction of a system containing a relatively large amount of N,N’-dimethylformamide as the starting material (Hongbinget al., 2004). However, carbon nanomaterials have a high specific surface area and easily aggregate. Surface functionalization of the carbon nanomaterials is an effective method to disperse them throughout various media for producing new functional materials, which utilize their unique characteristics (Zhu et al., 2003; Gao et al., 2005; Singh et al., 2005). In order to functionalize these carbon nanomaterials one must treat their surface with acids or other chemicals. Treatment of the carbon nanomaterials with nitric acid and sulfuric acid leads to the oxidation of their surface that forms oxidized groups such as −COOH and −C=O within the graphene sheet (Liu et al., 1998; Hamon et al., 2001; Hamon et al., 2002). Generally, the surface functional groups of the modified CNFs are characterized by IR or Raman spectroscopy. It is, however, difficult to obtain quantitative information of the chemical species existing in a monolayer or only a few layers of the oxidized surface of the CNFs using these analyses. We have previously shown that observing the fluorescence spectra of 1-naphthol (1-NP) is a useful probe on a molecular level for studying the physicochemical properties of the