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We report a systematic study of the purification of nitric acid treated single-walled carbon nanotubes (SWNTs) by centrifugation at constant pH. The progress of the purification procedure was followed by estimating the purity by solution-phase near-infrared spectroscopy, and it was found that the sediment obtained by centrifugation at pH 2 had the highest purity. The stability of the aqueous dispersions of SWNTs and carbonaceous impurities (CIMP) after nitric acid treatment was investigated by measuring their zeta potential and the concentration of acidic sites. We found that, at lower pH, the CIMP has a higher zeta potential than nitric acid treated SWNTs, and it is this factor that allowed the separation of the carbonaceous impurities via centrifugation and the concomitant purification of the SWNTs.

This study demonstrates a novel approach toward development of advanced chemical sensors based on chemically functionalized single-walled carbon nanotubes (SWNTs). SWNTs with covalently attached poly(m-aminobenzene sulfonic acid), SWNT-PABS, have shown improved sensor performance for detection of NH3. Compared to purified SWNTs, devices fabricated with SWNT-PABS have shown more than 2 times higher change of resistance upon exposure to NH3. Importantly, the SWNT-PABS sensors rapidly recover their resistance when NH3 is replaced with nitrogen. Exposure to NH3 induces significant changes in the electronic structure of SWNT-PABS, which allow detection of NH3 at concentrations as low as 5 ppm. Thin film deposited between interdigitated electrodes was explored as a device configuration for development of gas sensors.

The influence of Ni−Y catalyst composition on the bulk scale synthesis of single-walled carbon nanotubes (SWNTs) is studied using solution phase near-infrared spectroscopy. We found that a wide ran...

The measurement of the bulk purity of single-walled carbon nanotubes (SWNTs) is an important outstanding problem. We report a solution-phase near-IR (NIR) spectroscopic study of a range of carbon materials with an emphasis on SWNTs, and we show that NIR spectroscopy is an extremely powerful tool in the assessment of the carbonaceous purity of SWNTs. We demonstrate the applicability of Beer's law for all of the carbon materials included in this study within a range of concentrations in dimethylformamide (DMF), and we are able to solve for the effective extinction coefficients. By analyzing the areal absorptivities of the second interband transition of semiconducting SWNTs for a number of samples of differing purities, we are able to derive an absolute molar extinction coefficient for the carbonaceous impurities in SWNT samples. We demonstrate significant progress toward the establishment of an absolute scale for the bulk carbonaceous purity of SWNTs.

The nature of single-walled carbon nanotube (SWNT)−solvent interaction that is responsible for the stabilization of ultrasonicated dispersions was investigated using various techniques. It was found that the sonochemical decomposition and polymerization of o-dichlorobenzene (ODCB) is necessary for the stabilization of SWNTs in ODCB. The rate of decomposition of ODCB was shown to be dependent on the shape of the sonication vessel. The decomposition products of sonicated ODCB interact irreversibly with SWNTs. Under similar sonication conditions, N,N-dimethylformamide (DMF) did not induce discernible modification of the near-infrared spectrum of the dispersed SWNTs.

The passage of a current through a solid requires a pathway for the movement of electrons or holes. A new class of phenalenyl-based neutral radical molecular conductors has recently been reported; a distinctive feature of these molecular solids is the absence of any obvious conducting pathway(s). These radicals do not stack in the solid state, and the requisite carbon−carbon contacts are all larger than the sum of the van der Waals distances. Magnetic susceptibility measurements show that the first compound to be isolated behaves as a free radical with one spin per molecule, apparently supporting the idea that there is little interaction between the molecules in the solid state. Nevertheless, this radical shows the highest conductivity (σRT = 0.05 S/cm), of any neutral organic solid, and the conduction mechanism is presently unresolved. In the present study, we report a structurally related radical with a resistivity 4 orders of magnitude higher than that of the previously reported radicals. We analyze th...

Full-length single-walled carbon nanotubes (SWNTs) were rendered soluble in common organic solvents by noncovalent (ionic) functionalization of the carboxylic acid groups present in the purified SWNTs. Atomic force microscopy (AFM) showed that the majority of the SWNTs ropes were exfoliated into small ropes (2−5 nm in diameter) and individual nanotubes with lengths of several micrometers during the dissolution process. The combination of multiwavelength laser excitation Raman scattering spectroscopy and solution-phase visible and near-infrared spectroscopies was used to characterize the library of SWNTs that is produced in current preparations. The average diameter of metallic nanotubes was found by Raman spectroscopy to be smaller than that of semiconducting nanotubes in the various types of full-length SWNT preparations. This observation sheds new light on the mechanism of SWNT formation.