Electronic properties of carbon nanotubes linked covalently with iron phthalocyanine to determine the formation of high-valent iron intermediates or hydroxyl radicals

Two different nanomaterial-based metallophthalocyanine catalysts were synthesized by immobilizing iron trinitrophthalocyanine with amino (FeMATNPc) covalently on multi-walled carbon nanotubes (MWCNTs) by deamination-synthesized MWCNTs-FeTNPc and on oxidized MWCNTs by amidation-synthesized MWCNTs-CONH-FeTNPc. The resulting hybrid structure was confirmed and characterized by X-ray photoelectron spectroscopy and attenuated total reflection Fourier transform infrared spectra. Catalytic activity tests showed that the introduction of MWCNTs resulted in a marked enhanced catalytic activity of FeMATNPc. A series of designed experiments proved that large amounts of hydroxyl radicals accompanied by some peroxy radicals and seldom by high-valent iron intermediates were formed in a MWCNTs-FeTNPc/H2O2 system. In a MWCNTs-CONH-FeTNPc/H2O2 system, much more high-valent iron intermediates with fewer hydroxyl radicals were formed. Conduction electron spin resonance and cyclic voltammetry was used to investigate the intrinsic difference between the two catalysts. More conducting electrons fill MWCNTs and electron transfer between MWCNTs and iron phthalocyanine is faster than that for MWCNTs-CONH-FeTNPc. This special electronic property may influence the formation of active species.