engleski

Solubilisation, opening/closing, and water-filling of single-wall carbon nanotubes: a spectroscopic study'

The many potential applications of single-wall carbon nanotubes (SWNTs) have long been hampered by the fact that they are virtually insoluble in any solvent, which was a problem for their purification, separation of different types of SWNTs, and further processing in devices. However, we have found that the bile salts are unusually effective surfactants for the solubilisation of SWNTs in water. (1). Bile salts (e.g. sodium deoxycholate or sodium taurodeoxycholate) are antural steroid detergents, and are inexpensive and available in high purity. With the bile salts, much higher concentrations of individually isolated SWNTs are obtained than with traditional synthetic surfactants, without the need for any chemical or ultrasonic treatments, which are known to damage SWNTs. In addition, the bile salts, with their semi-rigid cholesterol groups, form very regular micellar layers around the SWNTs, thus acting as a homogeneous, non-perturbing environment for the SWNTs, a sshown by the unusually high resolution in Raman and optical absorption spectra, and by the intense band-gap emission (1). The high resolution in 2D Raman maps obtained for these bile salt solubilised SWNts has also allowed us to resolve, for the first time, the resonance from empty (end-capped) and water-filled (opened) SWNTs.(2) This allowed us to determine the effect (shift and damping) of the water-filling on both the vibrational and electronic resonances of the nanotubes. It also provides a simple and quantitative ratiometric technique to monitor, and thus optimize, the degree of tube opening under various chemical and mechanical treatments (air oxidation/acid treatment, ultrasonication, stirring) (2). In particular, we found that even prolonged, but very gentle stirring can open (cut) a significant fraction of the SWNTs. Solutions with a composition ranging from 90% closed tubes to more than 97% opened tubes (chemical treatment) were obtained. Tubes can be reclosed by vacuum annealing. 1. W. Wenseleers et al. Adv Funct Mater, 2004, 14, 1105 2. W. Wenseleers et al. Adv Mater, 2007, 19, 2274

Dispersion and purification of CNTs; Transport in CNTs

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