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

铁(III)-卟啉催化剂（Fe-Por）的催化活性下降可归因于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）的添加，羟丙基-β-环糊精被认为是腐殖质（hs）中疏水部分的模型。Fe-Por与HP-β-CD之间形成的超分子络合物抑制了Fe-Por的自降解，从而增强了五氯苯酚（PCP）的氧化降解。其次，研究了HSs对Fe-Por过硫酸盐氧化PCP的强化作用机理。HSs的加入也能有效抑制Fe-Por的自降解，并导致PCP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中磺基的结合。第三，采用排相色谱法对HS进行分子大小分离。用固态CPMS ^<13>C NMR测定了三个馏分的芳香族碳。随着分馏HS中芳香族碳含量的增加，Fe-Por的自降解速率降低。此外，Fe-Por与分馏HS之间的超分子络合物的形成常数随着HS样品芳香性的增加而增加。这支持了超分子络合物的形成是由于Fe-Por中的磺胺苯基与HS中的芳香族之间的相互作用。这些结果表明，HS对fe - PCP过硫酸盐氧化的促进作用可能是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.