Function of humic substances for enhancing catalytic oxidation of chlorinated organic compounds

铁(III)-卟啉催化剂(Fe-Por)催化活性的下降可归因于Fe-Por的自降解。为了防止腐殖质的自降解，我们首先考察了羟丙基-β-环糊精(HP-β-CD)的添加，它被认为是腐殖质中疏水部分的模型。Fe-Por与HP-β-CD形成超分子络合物，抑制了Fe-Por的自身降解，促进了五氯苯酚的氧化降解。其次，从机理上研究了HSS对Fe-Por强化过硫酸盐氧化PCP的作用。HSS的加入也有效地抑制了Fe-Por的自降解，促进了PCP的氧化。对Fe-POR、HSS及其混合物D_2O溶液的1H核磁共振研究表明，HSS中的芳香族基团对Fe-POR中磺基苯基的结合起到了促进作用。第三，根据分子大小，用大小排除色谱分离HS。得到了三个馏分，并用固体CPMS和~(13)GT；C核磁共振确定了它们的芳香碳。随着馏分HS中芳香碳含量的增加，Fe-POR的自降解率降低。此外，随着HS样品芳香度的增加，Fe-POR与分级HS形成超分子络合物的常数增大。这支持了超分子络合物的形成是由于Fe-POR上的磺基苯基与HS上的芳香族部分相互作用所致。这些结果表明，HS对Fe-Por催化过氧硫酸盐氧化PCP的促进作用可归因于通过形成超分子络合物来稳定催化剂。

The decrease of catalytic activity of an iron(III)-porphyrin catalyst (Fe-Por) can be attributed to self-degradation of Fe-Por. To prevent the self-degradation, we first examined the addition of hydroxypropyl-β-cyclodextrin (HP-β-CD) that is regarded as a model of hydrophobic parts in humic substances (HSs). The self-degradation of Fe-Por was suppressed by forming supramolecular complex between Fe-Por and HP-β-CD, and this resulted in enhancing oxidative degradation of pentachlorophenol (PCP). Second, the effects of HSs on the enhancement of peroxosulfate oxidation of PCP by Fe-Por were studied mechanistically. The addition of HSs was also effective in suppressing the self-degradation of Fe-Por and resulted in an enhanced PCP oxidation. ^1H NMR studies of D_2O solutions of Fe-Por, HSs and mixtures there of showed that the aromatic moieties in HSs contributed to the binding of the sulfonatophenyl groups in Fe-Por. Third, an HS was separated according to molecular size using size exclusion chromatography. Three fractions were obtained and their aromatic carbons were determined by solid-state CPMS ^<13>C NMR. The rate of self-degradation of Fe-Por decreased with increasing the content of aromatic carbon in the fractionated HS. In addition, formation constant of supramolecular complex between Fe-Por and fractionated HS increased with increasing the aromaticity of HS sample. This supports that formation of supramolecular complex is due to interactions between sulfonatophenyl groups in Fe-Por and aromatic moieties in the HS. These results led to a conclusion that function of HS for enhancing peroxosulfate oxidation of PCP by Fe-Por can be attributed to stabilization of the catalyst by forming supramolecular complex.