溶解性有機質對全氟辛酸於氧化矽、氧化鋁及氧化鐵吸附行為之影響

Effects of Dissolved Organic Matter on Sorption of Perfluorooctanoic Acid onto Silica, Alumina and Iron Oxides

阮祈潔(Ci-Jie Ruan)

指導教授 ： 林正芳

國立臺灣大學/工學院/環境工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.03026

摘要

近年來，全氟碳化合物(perfluorochemicals, PFCs)因其持久性有機物的性質受到全球的關注，了解水體中全氟辛酸(perfluoroocanic acid, PFOA)的宿命及其傳輸現象尤其重要。自然水體中之固相物質包含有二氧化矽、氧化鋁以及氧化鐵，因此本研究分別以此三種物質作為吸附劑，觀察PFOA在溶解性有機物(dissolved organic matter, DOM)存在下的吸附行為，PFOA對二氧化矽及氧化鋁的吸附平衡時間分別為3天及10天，PFOA對二氧化矽之吸附行為並受溶液pH值之影響甚微，這表示溶液中主導吸附行為之作用力為非靜電作用力，吸附密度範圍介於0.3~5.7 μg/g；然而PFOA對於氧化鋁的吸附行為則明顯受到溶液pH值影響，PFOA的吸附密度隨溶液pH值降低而增加，在pH=6時，PFOA在氧化鋁的吸附密度範圍介於3.6~10.4 μg/g，而在pH=8時並沒有觀察到吸附作用，這可能歸因於帶負電荷的PFOA分子與帶正電荷的吸附劑表面之靜電吸引力。
DOM加入反應的時間點對於PFOA吸附行為會有不同的影響，當PFOA先與吸附劑平衡之後，額外加入的DOM對於PFOA在氧化鋁的吸附行為沒有明顯差異，但在PFOA對於二氧化矽的吸附密度上會增加，這可能與PFOA對於吸附劑不同的吸附模式差異有關；在PFOA與DOM同時加入反應的實驗，在氧化鋁的吸附密度會增加，這可能與溶液中的主要作用力有關；另一個情況則是DOM先與吸附劑表面平衡之後再加入PFOA，在此情形中，PFOA的吸附密度之於吸附劑皆大幅降低，甚至幾乎沒有觀察到吸附行為，因此在自然界真實水體的情況，當PFOA排放進入水體後可能會因為水中本身就存在有DOM而使得PFOA無法吸附在底泥中，增加PFOA的傳輸性，DOM對於PFOA的吸附行為是一項重要的影響參數。

關鍵字

全氟辛酸 ； 溶解性有機質 ； 吸附 ； 二氧化矽 ； 氧化鋁

並列摘要

Perfluorochemicals(PFCs) have attracted global concern in recent years with their persistent nature. The abundance of perfluoroocanic acid (PFOA) in the aquatic environment makes it important to understand its fate and transport. As most solid phases in nature water contain silica and alumina, the interactions between PFOA and these two mineral surfaces with a focus on dissolved organic matter (DOM) were systematically investigated. The results of adsorption kinetics showed the sorption equilibrium takes 3 days for silica, and 10 days for alumina. The sorption density of PFOA on silica was not affected by solution pH, and ranged from 0.3~5.7 μg/g likely due to hydrophobic interaction. In contrast, PFOA uptake by alumina increased significantly at lower pH, which was likely attributed to electrostatic force between negatively charged PFOA molecules and positively charged mineral surfaces. The sorption density ranged from3.6~10.4 μg/g on alumina at pH=6. With the presence of DOM in the aqueous phase, the sorption behavior was distinct from different DOM adding timing. After PFOA got equilibrium with mineral surfaces, the addition of DOM made PFOA uptake was increased on silica, where no difference on alumina. The reason might be the difference adsorption model. When PFOA and DOM were added in to the reaction at the same time, the sorption density also increased but on alumina. It seems the interaction forces in system dominated the sorption. Another situation that DOM was first equilibrium with mineral surfaces and then PFOA added was also investigated. The sorption density of PFOA on all two mineral surfaces was greatly reduced even to zero. That is, in the nature environment PFOA might not be adsorbed onto nature minerals due to the existing DOM, so that PFOA remains to be in the water phase and transports easily in the aquatic environment. This study revealed DOM as an important solution-specific parameter in PFOA sorption.

並列關鍵字

perfluoroocanic acid (PFOA) ； dissolved organic matter (DOM) ； sorption ； silica ； alumina

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