Potassium monopersulfate oxidation of 2,4,6-tribromophenol catalyzed by a SiO₂-supported iron(III)-5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin

Abstract

Iron(III)-porphyrin complexes are generally regarded as green catalysts, since they mimic the catalytic center of cytochrome-P450 and widely used as green catalysts for degrading halogenated phenols in wastewater, such as landfill leachates. However, iron(III)-porphyrins are deactivated by self-oxidation in the presence of an oxygen donor, such as KHSO₅. In the present study, to enhance the reusability of an iron(III)-porphyrin catalyst, iron(III)-5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin (FeTCPP) was immobilized on a functionalized silica gel. The oxidative degradation of 2,4,6-tribromophenol (TrBP), a widely used brominated flame retardant that is found in landfill leachates, was examined using the prepared catalyst. In addition, the influence of humic substances (HSs), major components of leachates, on the TrBP oxidation was investigated. Concerning the effect of pH, more than 90% of the TrBP was degraded in the pH range of 3–8 in the absence of HS, while the optimal pH for the reaction was in the range of pH 5-7 in the presence of HS. Although the oxidation of TrBP was inhibited in the presence of HSs, more than 90% of the TrBP was degraded in the presence of 50 mg L⁻¹ of HS. Thus, the prepared catalyst, SiO₂-FeTCPP, showed a high catalytic activity and could be reused up to 10 times even in the presence of HS.

Keywords:

• Humic substances
• 2, 4, 6-Tribromophenol
• Iron(III)-porphyrin catalyst
• surface charges
• catalytic oxidation

Acknowledgments

This work was supported by Grants-in-Aid for Scientific Research of the Japan Society for the Promotion of Science (25241017).