Chemically Bonded Ceramic Oxide Coatings on Carbon Nanotubes and Inorganic Nanowires

Abstract

Carbon nanotubes (CNTs) and inorganic nanowires constitute two important classes of one-dimensional materials. [1][2][3][4][5] Several studies on the synthesis, characterization, and manipulation of these materials have been reported.[6] Thus, several workers have prepared composites of these materials and studied their properties. [1,4,7,8] CNTs have been employed as templates for the preparation of nanotubes and nanowires of inorganic materials, especially of metal oxides. [4,[9][10][11][12][13][14][15][16] For this purpose, the CNTs were covered with an oxide precursor or a gel and the nanotubes burnt off in air. [9][10][11][12][13] Han and Zettl [14] coated single-walled carbon nanotubes using a simple solution-based chemical route. While Fu et al. [15] used a high-pressure method to coat the nanotubes with layers of rare-earth oxides. Ruthenium oxide nanotubes have been obtained by Min et al. [16] by the oxidation of Ru-coated carbon nanotubes prepared by atomic layer deposition. It was our view that it would be of considerable importance if we were able to prepare composite structures of CNTs and inorganic nanowires, wherein a layer of a ceramic oxide is chemically bonded to the surface of the nanostructures. Knowing that Si-O or metal-oxygen bonds can be formed with substrates by the reaction of an appropriate chloro compound with the hydroxyl groups present on the substrate, we have explored whether ceramic oxide-coated structures can be obtained by the reaction of reactive metal chlorides with acid-treated CNTs and metal oxide nanowires. This seemed entirely feasible since the CNTs on acid treatment become functionalized with surface hydroxyl and carboxyl groups, and the metal oxide nanowires would necessarily possess hydroxyl groups on the surface. [1,2,6] The surface functional groups have been made use of for the solubilization of CNTs and other purposes. [1,6] On reaction with the vapor of a metal halide such as TiCl 4 , the surface hydroxyl groups on the nanostructures can form metal-oxygen bonds by eliminating HCl leaving extra metal-chlorine bonds. The metal-chlorine bonds can be hydrolyzed by treatment with water and the hydroxide layer again reacted with the metal chloride. On repeating the process several times followed by calcination, one should be able to obtain a CNT or a metal oxide nanowire with a chemically bonded ceramic coating of the desired thickness. We illustrate the process schematically in Scheme 1.In Figure 1a, we show a typical transmission electron microscopy (TEM) image of TiO 2 -coated multiwalled carbon nanotubes (MWNTs) obtained after ten cycles at 80°C (see Experimental for details). The color of the MWNTs changed from black to gray after the reaction. The energy-dispersive X-ray (EDX) spectrum in Figure 2a shows the presence of Ti and Cl after the reaction, the latter arising from the incomplete hydrolysis of TiCl 4 . On calcination, at 350°C for 12 h, the chlorine is eliminated as revealed by the EDX spectrum in Figure 2b. TEM images of the calcined product are shown in ...

Electrochemical properties of double wall carbon nanotube electrodes

“…DWNT and SWNT nanotubes were functionalized with carboxyl groups in concentrated nitric acid (6 M) for 24 hours at 80°C [21][22][23]. The acid/NT mixture was subsequently washed with distilled water and centrifuged several times until their aqueous solution reached neutral pH.…”

Polymer Nanocomposites: From Synthesis to Applications

“…Metal oxide coated CNTs and inorganic nanowires can be prepared as shown in scheme 5 (Gomathi et al, 2005). The ceramic oxide coating provides improved compatibility with polar matrices as well as improved thermal stability of the nanotubes and nanowires.…”

“…The ceramic oxide coating process for (a) carbon nanotubes and (b) metal oxide nanowires (from Gomathi et al, 2005).…”

Carbon Nanotubes and Carbon Nanotubes/Metal Oxide Heterostructures: Synthesis, Characterization and Electrochemical Property

“…Hence, ALD film growth is self-limiting and based on surface reactions, which enables deposition control on the atomic scale. As an example, Gomathi et al used metal chloride precursors to coat acid-treated MWCNTs with TiO 2 and Al 2 O 3 [208]. Similarly, Javey et al demonstrated coatings of ZrO 2 as thin as 8 nm covering the top of horizontally attached SWCNTs for device applications [209].…”