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

铁（III）-卟啉催化剂（Fe-Por）的催化活性的降低可归因于Fe-Por的自降解。为了防止自降解，我们首先研究了羟丙基-β-环糊精（HP-β-CD）的加入，它被认为是腐殖物质（HS）中疏水部分的模型。Fe-Por与HP-β-CD形成超分子复合物，抑制了Fe-Por的自降解，从而促进了五氯酚（PCP）的氧化降解。其次，从机理上研究了HSs对Fe-Por氧化PCP的促进作用。HSs的加入也有效地抑制了Fe-Por的自降解，并导致PCP的氧化增强。对Fe-Por、HSs及其混合物的D_2O溶液的~ 1H NMR研究表明，HSs中的芳香基团有助于Fe-Por中磺酸基苯基的结合。第三，使用尺寸排阻色谱根据分子大小分离HS。用固相CPMS ~ 1C NMR测定了三个馏分的芳碳数<13>。随着分馏HS中芳香碳含量的增加，Fe-Por的自降解速率降低。此外，Fe-Por与分级HS之间的超分子复合物的形成常数随着HS样品的芳香度的增加而增加。这支持了超分子复合物的形成是由于Fe-Por中的磺酸基苯基与HS中的芳香族基团之间的相互作用。这些结果表明，HS对Fe-Por氧化PCP的促进作用是通过形成超分子复合物来稳定催化剂的。

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.