The coupling of metallophthalocyanine with carbon nanotubes to produce a nanomaterial-based catalyst for reaction-controlled interfacial catalysis

A nanomaterial-based metallophthalocyanine catalyst (CoTAPc-MWCNTs) was prepared by covalently immobilizing cobalt tetraaminophthalocyanine (CoTAPc) on multiwalled carbon nanotubes (MWCNTs). The decomposition reaction of H₂O₂ was chosen to investigate the coupled catalytic performance. The results of electron paramagnetic resonance and online electrochemical experiments indicated that the catalytic mechanism of CoTAPc-MWCNTs is different from that of cobalt phthalocyanine molecular catalysts. The catalytic pathway of CoTAPc-MWCNTs involves the following steps: first, electron transfer from CoTAPc to H₂O₂ occurs through the coordination between the central cobalt ion and H₂O₂, reducing H₂O₂ to H₂O; second, electrons are transferred from MWCNTs to the oxidized CoTAPc, forming hole-doped MWCNTs; finally, hole-doped MWCNTs accept electrons from H₂O₂, oxidizing H₂O₂ to O₂. When using N,N-diethyl-1,4-phenylenediamine as a chromogenic substance, one obtained a quantitative estimate of holes injected in MWCNTs, corresponding to 1 hole for about 55 carbon atoms. Furthermore, CoTAPc-MWCNTs exhibit very unusual characteristics of controlled catalysis due to the special hydrophobic surface of the MWCNTs, and can be used as an interfacial catalyst for the determination of H₂O₂ concentration.