Electrochemical functionalization of vertically aligned carbon nanotube arrays with molybdenum oxides for the development of a surface-charge-controlled sensor

Abstract

The modification of inorganic polymeric oxides at the surface of carbon nanotubes is of paramount importance for developing new sensors. In this study, molybdenum oxide (MoOx) film was electrodeposited on the surface of multi-walled carbon nanotubes (MWNTs) by cycling the potential between +0.20 and ?0.80?V (versus 3?M KCl?Ag|AgCl) in Na2MoO4 solution. The MoOx-modified nanotube (MoOx/MWNT) electrode displays well-defined redox transitions in 5?mM H2SO4 or in phosphate buffer solution (PBS), which can be attributed to the reductive formation and the re-oxidation of hydrogen molybdenum oxides. X-ray photoelectron spectra (XPS) showed that the deposited MoOx films are mainly Mo6+ complexes. Both MWNT and MoOx/MWNT electrodes have ideal reversibility in 5?mM K3[Fe(CN)6] in 1?M KCl as supporting electrolytes at all sweep rates (0.02?1.00?V?s?1) by cyclic voltammetry. The negatively charged surface of MoOx/MWNTs can further attract molecular cations such as Ru(NH3)63+. The MoOx/MWNT electrode exhibited electrocatalytic ability towards the reduction of bromate due to high surface area and the fast electron transfer rate of nanotubes. Thus, electrochemical modification of inorganic polymeric oxides on the carbon nanotube provides a simple method for the preparation of novel sensors.