The electrochemical properties of ferricyanide redox couple at aligned and randomly dispersed SWNTs modified electrodes was studied by Gooding et al. For an acid treated aligned SWNTs modified electrode, Flavopiridol Alvocidib a peak separation of 59 mV with a half wave potential of 0.231 V for the ferricyanide redox couple was observed. On the other hand, the peak separation was observed to be 99 mV when the acid treated but randomly dispersed SWNTs modified electrode was used. The aligned SWNTs modified electrode shows the better electrochemical properties. It means that the electrochemistry of CNTs is dominated by the ends of the tubes. The length of the aligned CNTs also has a significant effect on the electron transfer rate. The electron transfer rate constant varied inversely with the mean length of the CNTs.
Gooding et al. investigated the effect of the length of CNTs on the apparent electron transfer rate constant of the surface attached ferrocenemethylamine Nutlin-3 on to the vertically aligned CNTs with cutting times of 2, 4, and 6 hrs during acid treatment. The apparent rate constants were determined to be 98 25, 187 98, and 459 132 s 1 for the mean lengths of 1175, 507, and 257 nm, respectively. When the nanotube dispersed randomly, the rate constant was found to be 12 8 s 1 for a mean tube length of 257 nm, which was 40 times slower than that obtained at vertically aligned nanotubes modified electrode. The electron transfer rate at the CNTs modified electrode could be further increased by dialyzing the CNTs after purification and shortening treatment.
During purification and shortening of the SWNTs in concentrated nitric and sulfuric acids mixture, some residual acid moieties adsorbed on single walled carbon nanotubes. Using TEM and HR TEM techniques, Pumera et al. confirmed that CNTs contain residual metal impurities after acid wash with concentrated nitric acid at temperature of 80. These acid moieties can be reduced by dialyzing the purified and dialyzed CNTs against a solution of Triton? X 100. The electrochemical measurements using self assembled ferrocenefunctionalized nanotube monolayers on a gold electrode showed that the dialyzed nanotubes exhibited a faster rate of electron transfer compared to the nondialyzed nanotubes. The adsorbed acid moieties during purification and acid treatment processes can also decrease the electrocatalytic activity of CNTs in electroanalysis.
Pumera and his colleague suggested the use of dc magnetic susceptibility and electron paramagnetic resonance for screening and quality control of CNTs before use them in electroanalysis. Recently, Dai and co workers reported that vertically aligned nitrogen doped CNTs can act as a metal free electrode with a much better electrocatalytic activity. The electrocatalytic activity and the electroanalytical performance at CNTs modified electrodes are strongly depended on the mode of production of the CNTs, either by chemical vapor deposition or the ARC discharge process. CNTs produced by CVD appear to be more electrochemically reactive in their voltammetric study than those produced using the ARC methodology. The differences in the electrochemical reactivity are attributed to the smaller fraction of exposed edge planes at ARC CNTs and higher density of edge plane defects at CVD CNTs. The