|关键词||多环芳烃 粘土矿物 非生物转化 土壤有机质 有机酸|
Polycyclic aromatic hydrocarbons (PAHs), a group of typical persistent toxic substances, have attracted more and more attention due to their high degree of eareinogenieity，teratogenieity and mutagenicity. PAHs are harmful to human health and environment. Soil is considered as a major environmental reservoir for PAHs due to its high storage capacity. PAHs in soil undergo abiotic and biotic transformation. Biotic transformation mainly is conducted by the degrading strains, while abiotic transformation mainly includes chemical oxidiation and photocatalysis. Clay minerals, soil organic matter (SOM) and organic acid are all reactive soil compontens and play important role in the fate and transformation of PAHs in the soil environment. In the present study, we focus our attention on the chemical oxidiation without light ,photocatalysis under visible light and the effects of SOM fractions and organic acid on photocatalysis. The main conclusions of the thesis will be shown as following: Firstly, chemical oxidiation reaction is conducted without light under relatilvely humidity(RH). The reaction is affected mainly by the physichemical properities of clay minerals and environmental factors. The rate of anthracene transformation follows the order: Fe-smectite >> Cu-smectite > Al-smectite ≈ Ca-smectite ≈ Mg-smectite ≈ Na-smectite. Among Fe(III)-saturated clays, Fe(III)-smectite exhibits the highest catalytic activity followed by Fe(III)-illite, Fe(III)-pyrophyllite and Fe(III)-kaolinite, which is in agreement with the interlayer Fe(III) content. Moreover, effects by two common environmental factors, pH and relative humidity (RH), were evaluated. With increase in pH or RH, the rate of anthracene transformation decreases rapidly at first, and then is leveled off. Secondly, the reactivity of PAHs molecule is related to the IP. The final product of anthracene transformation is anthraquinon, a more bioavailable molecule compared to anthracene. The transformation process mainly involves cation-π bonding, electron transfer leading to cation radical, and further oxidation by chemisorbed O2. Thirdly, under visible light, for five types of cation-modified smectite clays, the photodegradation rates of phenanthrene follow the order: Fe3+ > Cu2+ >> Ca2+ > K+ > Na+, which is explained in terms of photo-Fenton-like catalysis. To further inspect the effect of clay type, additional two types of clays were paralleled. Among three types of Fe(III)-modified clays, Fe(III)-smectite shows the highest photodegradation rate followed by Fe(III)-vermiculite and Fe(III)-kaolinite. Fouthly, SOM fractions including dissolved organic matter (DOM), humic acid (HA), and fulvic acid (FA), showed different effect on the degradation of phenanthrene. A critic content is observed with FA (0.70 mg/g) and HA (0.65 mg/g). Before reaching the critic content, the removal of phenanthrene is accelerated; while after that, the photodegradation rate is suppressed. However, DOM showed negligible influence on the degradation process. Fifthly, anthracene degradation was promoted by the addition of malic acid and oxalic acid, while it was inhibited with EDTA and NTA. For Fe(III)-smectite–malic, citric, EDTA, NTA complex systems, pKa1 and redox potential have positive effect on the degradation rate. However, Fe(III)-smectite–oxalic acid complex system, though with low pKa1 and redox potential, showed high catalytic effect. This may attribute to the fact that Fe(C2O4)2- and Fe(C2O4)33- are much more efficiently photolyzed and the formation of Fe(II) and active reaction intermediates is faster in the presence of oxalaic acid.
|李莉. 粘土矿物促使土壤中多环芳烃非生物转化过程及机理研究[D]. 北京. 中国科学院大学,2014.|
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