Oxidative degradation of 2,4,6-trichlorophenol and pentachlorophenol in contaminated soil suspensions using a supramolecular catalyst of 5,10,15,20-tetrakis (p-hydroxyphenyl)porphine-iron(III) bound to humic acid via formaldehyde polycondensation

Abstract

A supramolecular catalyst consisting of 5,10,15,20-tetrakis(p-hydroxyphenyl)porphine-iron(III) (FeTPP(OH)₄) bound to humic acid (HA) was synthesized via formaldehyde polycondensation. The catalytic system, which included the synthesized catalyst (resol) and an oxygen donor (KHSO₅), was applied to the oxidative degradation of 2,4,6-trichlorophenol (TrCP) and pentachlorophenol (PCP) in contaminated soil suspensions. The optimal conditions (catalyst, KHSO₅ and substrate concentrations) were investigated. In both FeTPP(OH)₄ and resol catalytic systems, more than 95% of TrCP (100 μ M) and PCP (25 μ M) degraded at pH 4, [catalyst] 20 μ M and [KHSO₅] 1 mM. When initial concentrations of TrCP and PCP were increased to [TrCP]₀ 200 μ M and [PCP]₀ 50 μ M, the percent degradation of the CPs and the levels of dechlorination in the resol catalytic system were significantly greater than the values obtained using the FeTPP(OH)₄ system. These results show that the synthesized resol catalyst effectively enhances oxidative degradation of TrCP and PCP in contaminated soil suspensions. The resol catalysts adsorbed to contaminated soils were at levels that were significantly greater than those of FeTPP(OH)₄. Therefore, the enhanced degradation of CPs by resol catalysts can be attributed to the interactions between adsorbed CPs on the soil surface and the catalytic center of the resol catalysts.

Keywords:

• 2,4,6-Trichlorophenol
• pentachlorophenol
• contaminated soil
• catalytic oxidation
• iron(III)-porphyrin
• supramolecular
• formaldehyde polycondensation

Acknowledgments

This work was supported by Grants-in-Aid for Scientific Research of the Japan Society for the Promotion of Science (18201013).

Notes

∗ The pH of the soil slurry was determined for a mixture of soil and water at a ratio of 1:2.5 (soil/water = w/w).

∗∗∗BET-N₂ specific surface area.

∗∗∗∗Organic carbon.