Effect of chemical treatment on electrical conductivity, infrared absorption, and Raman spectra of single-walled carbon nanotubes.
ABSTRACT We investigate the magnitude and temperature dependence of electrical conductivity, the optical and infrared absorption, and the Raman spectra of single-walled carbon nanotube (SWNT) bucky-paper after chemical treatment and determine the correlations between the changes in these properties. Ionic-acceptor doping of the SWNT bucky-paper (with SOCl(2), iodine, H(2)SO(3), etc.) causes an increase of electrical conductivity that correlates with an increase of the absorbance in the far-IR region and an increase in the frequency of Raman spectral lines. Conversely, treatment with other molecules (e.g., aniline, PyPhF(5), PhCH(2)Br, etc.) leads to a decrease in both conductivity and far-IR absorption. The temperature dependence of the conductivity gives a good indication of the presence of metallic charge carriers and is in agreement with the model of interrupted metallic conduction.
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ABSTRACT: Spectroscopic and molecular modeling studies were performed to investigate the underlying dispersion mechanism of single-walled carbon nanotubes (SWCNTs) in imidazolium-based ionic liquids. Both the experimental and the simulation evidence indicate that the ionic liquids interact with SWCNTs through weak van der Waals interaction other than the previous assumed "cation-pi" interaction. Therefore the electronic structure of SWCNTs in the dispersions can be kept intrinsically. The SWCNTs do not significantly influence the local structure of the imidazolium cations, though the local environment of anions adjacent to SWCNTs is somewhat perturbed because of the interfacial effect. The ionic liquids basically keep their overall bulk phase organization. A pi-pi interaction-shielding model is proposed to account for the dispersion of SWCNTs in the ionic liquids. The ionic liquids, which possess very high dielectric constants, can effectively shield the strong pi-pi stacking interaction among SWCNTs and thus evidently disperse the SWCNTs. The retaining of SWCNTs' intrinsic property and the higher SWCNT content make the ionic liquids ideal media for the study and application of SWCNTs.ACS Nano 01/2009; 2(12):2540-6. · 10.77 Impact Factor
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ABSTRACT: Graphene sheets offer extraordinary electronic, thermal and mechanical properties and are expected to find a variety of applications. A prerequisite for exploiting most proposed applications for graphene is the availability of processable graphene sheets in large quantities. The direct dispersion of hydrophobic graphite or graphene sheets in water without the assistance of dispersing agents has generally been considered to be an insurmountable challenge. Here we report that chemically converted graphene sheets obtained from graphite can readily form stable aqueous colloids through electrostatic stabilization. This discovery has enabled us to develop a facile approach to large-scale production of aqueous graphene dispersions without the need for polymeric or surfactant stabilizers. Our findings make it possible to process graphene materials using low-cost solution processing techniques, opening up enormous opportunities to use this unique carbon nanostructure for many technological applications.Nature Nanotechnology 02/2008; 3(2):101-5. · 27.27 Impact Factor