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.