Introduction of functional groups into humic substances is a novel trend in humic technology. In the present study, a biomimetic catalyst, 5-(p-hydroxyphenyl)-5,10,15,20-tetrasulfonatophenyl porphine iron(III) (FeTPPSOH), was introduced into humic acid via formaldehyde polycondensation. In the presence of KHSO5, the self-degradation of the prepared catalysts, which were called "resol," was retarded. In addition, the catalytic activity, which was evaluated by the percent pentachlorophenol (PCP) disappearance and levels of dechlorination, was significantly greater for the resol catalysts. The results of the present study show that resol catalysts effectively enhance oxidative degradation of PCP. The byproducts of oxidation were investigated by GC/MS analysis of n-hexane extracts of the reaction mixtures. This analysis demonstrated that another advantage of resol catalysts is that they prevent the formation of more harmful dimers, such as octachlorodibenzo-p-dioxin. (C) 2008 Elsevier B.V. All rights reserved.