Catalytic activity of Fe-porphyrins grafted on multiwalled carbon nanotubes in the heterogeneous oxidation of sulfides and degradation of phenols in water

A biomimetic heterogeneous catalyst was prepared by immobilization of meso-tetrakis(4-carboxyphenyl)porphyrinatoiron(III) chloride (Fe(TCPP)Cl) on multiwalled carbon nanotubes (MWCNTs). The anchored catalyst was characterized by transmission electron microscopy, powder X-ray diffraction, ultraviolet-visible, and Fourier transform infrared spectroscopy. The amount of Fe-porphyrin loaded on the nanotubes was estimated by atomic absorption spectroscopy The thermogravimetric analysis demonstrated that the catalyst was thermally stable up to almost 350 °C, exhibiting high thermal stability. Oxidation of sulfides and phenols with urea hydrogen peroxide (UHP) in water was efficiently enhanced with excellent selectivity under the influence of [Fe(TCPP)Cl@MWCNT]. The title heterogeneous catalytic system facilitates a greener reaction because the reaction solvent is water and UHP is used as a safe oxidant.

A poor catalytic activity was observed for hydrophilic porphyrins in the homogeneous system, which may be due to the aggregation of porphyrins, but these metalloporphyrins can be supported into solid substrates and used as an efficient heterogeneous catalyst because of the prevention of the aggregation of metalloporphyrins.256