Oxidized MWCNTs as an Oxidizing Agent and Dopant in MWCNT@Polypyrrole Composite Formation

Abstract

A new approach to the formation of composites of carbon nanotubes and polypyrrole (PPy) is proposed. Oxidized multi-walled carbon nanotubes (ox-MWCNTs) are used as oxidation agents in pyrrole polymerization. The polymeric phase is deposited both at the surface of the carbon nanotube to form a core-shell structure and in the empty spaces of the MWCNT network. Each form of the polypyrrole phase exhibits different electrochemical properties. PPy deposited directly at the carbon nanotube surface as a uniform and dense layer is oxidized at less positive potentials, compared to the polymeric material deposited in the pores of the nanotube network. MWCNTs with anions incorporated into structural defects formed during their oxidation in a piranha solution also act as dopants of the oxidized form of PPy. The polymeric film deposited directly at the ox-MWCNT surface is in its oxidized state. The redox processes involving this part of the PPy film are accompanied by the transport of cations of the supporting electrolyte. The charge transfer between ox-MWCNTs and the deposited PPy film is confirmed by the results of the theoretical calculations of the energy states at the carbon nanotube and polypyrrole interface. A neutral PPy film located in layers remote from the surface of the nanotube is oxidized at more positive potentials. The oxidation of PPy located in the pores of the ox-MWCNT network results in a broad voltammetric peak formation.