Influence of humic acid type on the oxidation products of pentachlorophenol using hybrid catalysts prepared by introducing iron(III)-5,10,15,20-tetrakis(p-hydroxyphenyl) porphyrin into hydroquinone-derived humic acids.

An iron(III)-5,10,15,20-tetrakis(p-hydroxyphenyl) porphyrin (FeTHP) was introduced into hydroquinone-derived humic acids via formaldehyde polycondensation. The influence of humic acid (HA) type on the catalytic oxidation of pentachlorophenol (PCP) was investigated using two HAs as follows: Shinshinotsu peat (SHA) with a lower carboxylic acid content; Tohro ando soil (THA) with a higher carboxylic acid content. The levels of PCP degradation and dechlorination for the catalysts prepared using SHA (SHA-FeTHP) and THA (THA-FeTHP) were significantly higher than those for FeTHP. In terms of oxidation products, the more toxic dimer, octachlorodibenzo-p-dioxin (OCDD), was not produced in the case of the SHA-FeTHP system, while 4-7% of the PCP was converted to OCDD when the FeTHP and THA-FeTHP catalytic systems were used. These results indicate that a catalyst prepared using SHA is more active, in terms of the detoxification of PCP, than other catalysts. Comparisons of UV-Vis absorption spectra before and after the catalytic oxidation showed that the Soret band for SHA-FeTHP clearly remained after a 30-min incubation period, while the intensity of the majority of Soret bands for FeTHP and THA-FeTHP were rapidly reduced after a 5-min incubation period. These results suggest that the SHA-FeTHP is a stable catalyst, and this stability results in a more extensive oxidation of the more toxic byproducts.