Effects of pH on electrocatalytic activity of functionalized carbon nanotubes

In this study, we modified carbon nanotubes (CNTs) by grafting with poly(ethylene glycol) (PEG) using the grafting to method. The PEG-grafted CNT (CNT-g-PEG) was cast on indium tin oxide (ITO) electrode to investigate the electrocatalytic activity of CNT to the redox reactions of the Fe(CN) (6) (3-/4-) as a probe using cyclic voltammetry and electrochemical impedance spectroscopy. The electrocatalytic activity of CNT was correlated with CNT dispersion in the cast film on ITO as a function of pH of aqueous solution from which the film was cast. The CNT dispersions in aqueous solutions of different pH and in the cast films were examined by visual observation and zeta potential, scanning electron microscopy and transmission electron microscopy, respectively. At a pH in the range of 3-11 at which ITO electrode was modified, two functionalized CNT (fCNT and CNT-g-PEG) were both found to electrocatalyze the redox reactions of the Fe(CN) (6) (3-/4-) probe and the PEG grafts in CNT-g-PEG could help CNT adhere to the electrode to obtain durable modified electrode. The more uniform CNT dispersions in aqueous solutions and in the cast films appeared to have greater electrocatalytic acitivity.