Oxidative degradation of 2,6-dibromophenol using anion-exchange resin supported supramolecular catalysts of iron(III)-5,10,15,20-tetrakis (p-hydroxyphenyl)porphyrin bound to humic acid prepared via formaldehyde and urea-formaldehyde polycondensation

Abstract

An iron(III)-porphyrin catalyst, iron(III)-tetrakis(p-hydroxyphenyl)porphyrin (FeTHP), was introduced into a humic acid via a formaldehyde or urea-formaldehyde polycondensation reaction to stabilize the catalyst. The prepared supramolecular catalysts were then attached to Dowex-22, an anion-exchange resin. The oxidation of 2,6-dibromophenol (2,6-DBP) was then used, to evaluate the catalytic activities of the supported catalysts. The supported catalyst prepared via the urea-formaldehyde polycondensation reaction showed the highest catalytic activity of all catalysts tested. However, no debromination was observed under any conditions. To examine the reusability of the supported catalysts, they were evaluated on the basis of the decrease in the percent degradation of 2,6-DBP for the number times that they could be used. To determine why the catalytic activities decreased with increasing use, the surface of the supported catalysts were observed by scanning electron microscopy and energy dispersive X-ray spectrometry (SME-EDS) after each use. The poor reusability of the supported catalysts can be attributed to the fact that 2,6-DBP and/or brominated byproducts are tightly absorbed to the catalyst in the vicinity of the active site, which leads to inactivation of the supported catalysts.

Keywords:

• 2,6-Dibromophenol
• catalytic oxidation
• iron(III)-porphyrin
• humic acid
• urea-formaldehyde polycondensation
• anion-exchange resin
• supported catalyst
• SEM-EDX

Acknowledgments

This work was supported by Grants-in-Aid for Scientific Research of the Japan Society for the Promotion of Science (21310048).