Photo-oxidation of Single-walled Carbon Nanotubes
- PDF / 1,000,973 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 83 Downloads / 205 Views
0887-Q01-07.1
Photo-oxidation of Single-walled Carbon Nanotubes. B. Parekh, T. Debies1, C. M. Evans2, B. J. Landi2, R. P. Raffaelle2 and G. A. Takacs* Department of Chemistry, Center for Materials Science and Engineering, Rochester Institute of Technology, Rochester, NY, 14623, U.S.A. 1 Xerox Corporation, Webster, NY 14580, U.S.A. 2 NanoPower Research Laboratories, RIT, Rochester, NY, 14623, U.S.A. ABSTRACT UV- and vacuum UV-assisted photo-oxidation of single-walled carbon nanotube (SWNT) paper occurred with: (1) atmospheric oxygen pressure using low-pressure Hg lamps (λ = 253.7 and 184.9 nm), (2) low oxygen pressure employing emission downstream from an Ar microwave plasma (λ = 106.7 and 104.8 nm), and (3) high pressures of He in a rotating d.c. arc that was designed to produce a spectral continuum from He excimers (λ = 58 - 110 nm). The photo-oxidized materials were characterized by x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Raman spectroscopy. UV photo-oxidation was demonstrated to be a controlled dry procedure for introducing oxygenated functional groups (C-O-C, C=O, O-C=O and O=C-O-C=O) on SWNTs. INTRODUCTION Previously, a number of methods have been used to oxidize carbon nanotubes (CNTs). Gas-phase oxidation in air at around 750 ºC leads to over oxidation often removing or severely damaging the CNTs in addition to reacting with amorphous carbon [1]. Liquid-phase oxidation, involving nitric and/or sulfuric acids, is mild and slow and produces high yields of oxidized CNTs [2] having a mixture of –C-O-, -C=O and -COOfunctional groups as observed by x-ray photoelectron spectroscopy (XPS) [3]. Ozonolysis, both in the liquid [4] and gas phase [5 - 7], introduces oxygenated functionalities directly onto the sidewalls and not simply at the end caps or isolated defects [8]. Use of UV/O3 in air with single-walled carbon nanotubes (SWNTs), shows by TGA and Raman analysis that ca. 5% of the carbons were functionalized and rapid initial oxidation occurs within 1 h of treatment which stops after 3 h probably due to exhaustion of active surface sites [9]. The UV/O3 method is a dry technique that produces ozone in situ and, therefore, does not involve transport of reactive ozone to the reaction chamber from an electric ozonizer or liquid waste from solvent or a hydrolysis step. XPS analysis of the top 2 – 5 nm of the surface of multi-walled carbon nanotubes (MWNTs) shows that gas-phase UV and vacuum UV (VUV) photo-oxidation achieves oxygen concentrations up to 7.5 and 9.5 at% after treatment times of 4 and 2 h, respectively [10]. Curve fitting of the XPS C1s spectra reveals mainly the C-O-C functional group with the presence of C=O, O-C=O and O=C-O-C=O moieties [10]. In the present work, purified laser generated SWNT papers are photo-oxidized with UV and VUV radiation and studied with XPS, Raman and SEM microscopy.
0887-Q01-07.2
EXPERIMENTAL DETAILS Synthesis of SWNTs was performed using an Alexandrite laser vaporization process, previously described in detail [11]. In summary, a graph
Data Loading...
