The role of multiwalled carbon nanotubes in enhancing the catalytic activity of cobalt tetraaminophthalocyanine for oxidation of conjugated dyes

Muldwalled carbon nanotubes (MWCNTs) used to support a metallophthalocyanine catalyst (CoTAPc-MWCNTs) were prepared using covalent immobilization of cobalt tetraaminophthalocyanine (CoTAPc) on them, and characterized by X-ray photoelectron spectroscopy, attenuated total reflection Fourier transform infrared spectra and thermogravimetric analysis. The oxidative decoloration of rhodamine 6G (Rh6G) in the presence of CoTAPc-MWCNTs and H2O2 was investigated by examination of UV-Vis absorption spectra. The results showed that Rh6G was oxidized efficiently in the CoTAPc-MWCNTs/H2O2 system. The introduction of MWCNTs resulted in a marked enhanced catalytic activity that CoTAPc does not have. Electron paramagnetic resonance spin-trap experiments indicated that CoTAPc-MWCNTs have a novel non-radical pathway, which is different from common CoTAPc catalytic systems. Furthermore, the result of online electrochemical measurement in the CoTAPc-MWCNTs/H2O2 system suggested that MWCNTs might participate directly in the electron transfer process in the catalytic oxidation of this conjugated dye. in this catalytic system, MWCNTs provide strong adsorption to conjugated Rh6G due to their special Sp2-hybridized surface, and are able to rapidly oxidize the conjugated dye by a special electron transfer pathway. (C) 2009 Elsevier Ltd. All rights reserved.