摘要：

腐植物質(humic substances)是土壤或是水體中主要的有機物質之一.目前已有許多研究指出,不同來源的腐植酸其分子特性不盡相同,另外亦有學者發現經由重複萃取同一來源之腐植酸,其分子的特性亦有所差異,由此可知腐植酸的分子特性會因來源及萃取的方式不同而改變.腐植物質與環境中有機污染物的交互作用一直是土壤及環境科學家研究及討論的焦點.然而,目前有關腐植物質構造與環境中有機污染物的相關文獻大多侷限於非極性,非解離型的污染物(例如PAHs),對於極性,解離型的化合物與腐植物質構造之間相關性的暸解甚少.因此,本研究利用重複萃取所得的腐植酸(陽明山地區和彰化快官地區),分成冷凍乾燥及溶解沈澱的腐植酸樣品,並以化學處理作為佐證,探討腐植酸的結構及其對2,4,6-三氯酚之間的吸附行為與關連性.結果顯示,由元素分析及光譜分析(FTIR和13C NMR)可知,腐植酸結構會隨著萃取次數增加而趨向於脂肪性結構.以冷凍乾燥之腐植酸樣品進行吸附實驗,結果顯示,反應24小時後,腐植酸仍以極緩慢的速率吸附2,4,6-三氯酚,而其對2,4,6-三氯酚的吸附能力,主要由腐植酸中的脂肪族碳構造所貢獻.但是,冷凍乾燥的過程可能會影響腐植酸對2,4,6-三氯酚的Koc值,因此,以冷凍乾燥的腐植酸樣品進行吸附實驗,並不能真實地呈現腐植酸對2,4,6-三氯酚的吸附能力.然而,由溶解沈澱的腐植酸樣品所進行之吸附實驗結果顯示,2,4,6-三氯酚可迅速且大量地進入腐植酸內部,並與位於內層的芳香性構造形成鍵結,能真實地反應腐植酸的吸附行為及其對2,4,6-三氯酚的吸附能力.而實驗結果發現,腐植酸中具極性碳結構亦為影響2,4,6-三氯酚吸附的因子之一.此外,化學處理腐植酸的實驗更進一步證明,芳香族碳與具極性碳構造為影響腐植酸對2,4,6-三氯酚的重要因子.由此可和,腐植酸中的芳香族碳與極性碳結構,在其對2,4,6-三氯酚吸附上,均扮演著相當重要的角色.Humic substances are one of the major components in soil or aqueous systems. They strongly affect the sorption behavior and fate of organic pollutants in the environment. Recent investigations have revealed that the chemical and structural heterogeneity of humic acids (HAs) obtained by various treatments, e.g. repetitive extraction and chemical treatments, significantly influenced their sorption capacity of organic contaminants. However, previous studies mainly focused on sorption of nonpolar organic aromatic compounds, the relationships between polar organic compounds and structures of HAs are poorly understood. In this study, the sorption of 2,4,6-trichlorophenol, a polar pollutant, in HAs treated by repetitive extraction and chemical treatments (NaClO2 oxidation and acid hydrolysis) was examined using freeze-dried and non-freeze-dried HAs. The objectives of this study are to evaluate the influences of sample preparations and chemical treatments on HA structures and subsequent 2,4,6-trichlorophenol sorption. The compositions and structures of HAs were characterized by elemental analysis, Fourier transform infrared spectroscopy, and solid-state 13C NMR. The results exhibited significantly structural differences among the repetitively extracted HAs. The later extracted HAs had relatively higher aliphaticity as compared with that of former extracted HA samples. The kinetics sorption of 2,4,6-trichlorophenol by freeze-dried HAs showed relatively slow, and a positive trend was observed between Koc and the aliphaticity. Conversely, the sorption of 2,4,6-trichlorophenol in non-freeze-dried HAs was comparatively rapid, and a positive correlation between Koc and aromaticity was observed. The results were probably from the exposure of inner aromatic domain due to the treatment of freeze-dried HAs by a base/acid cycle to loose the condensed structures of HAs. In addition, the polar carbon contents in HAs also contributed greatly to the sorption of 2,4,6-trichlorophenol. Chemical treated HAs showed a low sorption of 2,4,6-trichlorophenol due to the decrease in aromaticity and polarity of HAs through the treatments. The result is consistent with previous sorptive experiments. This study demonstrates that aromatic structures and polar carbon contents of HAs apparently play important roles in the sorption of 2,4,6-trichlorophenol only when the HA adsorbents are not freeze-dried.

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