分散性奈米鐵和鈀/鐵雙金屬粒子降解四氯乙烯之研究

Degradation of Perchloroethylene with Dispersed Nano-Fe and Nano-Pd/Fe Bimetallic Particles

林建宇(Lin Chienyu)

指導教授 ： 黃益助

國立屏東科技大學/工學院/環境工程與科學系所/碩士(2011年)

https://doi.org/10.6346/NPUST.2011.00161

摘要

含氯有機化合物被廣泛運用在化學、農業和醫藥等行業上。然而，若儲存、使用、處理與處置不當，則可能洩漏至土壤，進而污染地下水層，這些含氯化合物因其急性毒性與高生物累積性，造成對環境的污染與對人體的危害。
本研究應用奈米零價鐵(nano zero valent iron, NZVI)改質技術提升其對PCE之降解效果，實驗設計包括：第一階段為選用NZVI作為還原降解PCE的反應性材料；第二階段將金屬鈀(palldium, Pd)覆鍍於NZVI表面當作活化劑，合成奈米鈀/鐵雙金屬粒子(nano-Pd/Fe bimetallic particles, nano-Pd/Fe)；第三階段利用NZVI分散化技術，選用分散劑-羧甲基纖維素(carboxymethyl cellulose, CMC)，增強NZVI的分散效果；第四階段為添加CMC於nano-Pd/Fe溶液增加其分散性。
使用奈米粒徑分析儀鑑定實驗室合成的NZVI、分散性NZVI、nano-Pd/Fe 1:100、1:250、1:500與分散性nano-Pd/Fe之尺寸大小，各粒子之粒徑介於101.5~111.1 nm，差異不大。經由比表面積儀測定，以NZVI之比表面積最小(38.04 m2 g-1)，nano-Pd/Fe 1:100的比表面積最大(56.05 m2 g-1)，nano-Pd/Fe比表面積隨其Pd含量增加而增大。
PCE揮發試驗中，在各背景條件情況下，PCE濃度並無太大差異。添加CMC與配製pH緩衝溶液的相關藥品亦不會對PCE濃度變化及揮發情形造成影響而干擾後續批次試驗之進行。
NZVI(5 g)與不同比例nano-Pd/Fe(5 g)降解PCE試驗中，NZVI未能完全降解PCE，不同比例之nano-Pd/Fe (1:100、1:250、1:500)皆可完全降解PCE，由此可知nano-Pd/Fe對PCE還原降解效果明顯高於NZVI。NZVI與nano-Pd/Fe (1:100、1:250、1:500)之假一階反應速率常數kobs分別為0.14、2.55、1.51、1.59 hr-1，顯示Pd覆鍍量的增加對於nano-Pd/Fe能產生更多的活化效果而增強其對PCE降解之能力。
分散性NZVI與分散性nano-Pd/Fe降解PCE試驗中，2.5 g和5 g分散性NZVI與5 g分散性nano-Pd/Fe皆可完全降解PCE，不同克數分散性NZVI(5 g、2.5 g、1 g)與分散性nano-Pd/Fe(5 g)之kobs分別為2.88、1.68、0.62、10.45 hr-1，顯示分散劑可提升奈米粒子之分散效果並加速其對PCE降解的能力。
不同pH值緩衝溶液降解PCE批次試驗中，nano-Pd/Fe (5 g)在pH=4、pH=7、pH=8(a)、pH=8(b)環境下於反應時間3 min第一次採樣時就已完全降解PCE。在pH=9時，NZVI和nano-Pd/Fe對PCE的降解能力非常小。在pH=8時，將nano-Pd/Fe添加量減少為1 g亦能在80 min時，完全降解PCE，其kobs為3.08 hr-1，高於nano-Pd/Fe (5 g)在未控制pH值還原降解PCE的kobs值(2.55 hr-1)。在pH=8，NZVI之kobs值(0.31 hr-1)亦高於未控制pH值的批次kobs值0.14 hr-1。
Cl-釋出量皆接近降解PCE所產生Cl-之理論釋出量，兩者之間成正相關性。在本實驗所有還原降解PCE的試驗中，皆未檢測出副產物。經由SEM-EDS進行奈米粒子元素分析，在有無添加分散劑或是於不同初始pH值還原PCE後，其各元素佔有率與反應前類似且無規律性。表面型態觀察中，奈米粒子於反應前後之表面型態主要並無太大差別，皆呈現串聯鏈狀分佈。經由FTIR鑑定後，各奈米粒子皆可於波數約620與1110 cm-1位置發現反應前後之差異性。
解決NZVI團聚現象可大幅提升NZVI降解還原污染物之效能。將nano-Pd/Fe結合CMC所形成的分散性nano-Pd/Fe更具有高度之降解能力，可得知結合兩種改善與增強NZVI還原降解能力之方法是可行且有效的，可提供現地整治技術之另一選擇參考。
關鍵字：四氯乙烯、奈米零價鐵、鈀/鐵雙金屬、羧甲基纖維素

關鍵字

四氯乙烯 ； 奈米零價鐵 ； 鈀/鐵雙金屬 ； 羧甲基纖維素

並列摘要

Chlorinated organic compounds are widely used in chemical, agricultural, and pharmaceutical industries. However, if the storage, use, and disposal of those compounds are not properly handled, they may leak into soil, and further pollute the aquifer. Chlorinated solvents due to their high acute toxicity and bioaccumulation cause environmental pollution and are harmful to human body.
In this study, some modification techniques of nano zero valent iron (NZVI) were utilized to enhance the degradation of perchloroethylene (PCE). The experimental design included four stages. The first one was to select NZVI as the reactive materials for degradation of PCE. The second one was to coat palldium (Pd) onto NZVI as surface active agents to synthesize the nano-Pd/Fe bimetallic particles (nano-Pd/Fe). The third one was to employ the dispersed technology to raise the dispersion of NZVI using carboxymethyl cellulose (CMC) as dispersant. And the last one was to add CMC in solution to enhance the dispersion of nano-Pd/Fe.
The average size, measured by particle size analyzer, of lab-synthesized NZVI, dispersed NZVI, nano-Pd/Fe (weight ratios of Pd to Fe of 1:100, 1:250, 1:500) and dispersed nano-Pd/Fe were between 101.5 to 111.1 nm. NZVI had the lowest specific surface area of 38.04 m2 g-1 and nano-Pd/Fe 1:100 had the largest one of 56.05 m2 g-1. The specific surface area of nano-Pd/Fe increased with higher Pd contents.
In the PCE blank tests, PCE concentration did not obviously varied under various test conditions. Addition of CMC and buffer solution had little effects on PCE concentration and therefore would not interfere with the subsequent batch tests.
For the tests of PCE degradation with NZVI and various proportions of nano-Pd/Fe, NZVI did not fully degrade PCE while various proportions of nano-Pd/Fe (1:100, 1:250, 1:500) did completely degrade PCE. It showed that the reduction capacity of nano-Pd/Fe on PCE degradation was obviously higher than that of NZVI. The pseudo first order reaction rate constant (kobs) of NZVI and nano-Pd/Fe (1:100, 1:250, 1:500) were 0.14, 2.55, 1.51, 1.59 hr-1, respectively. The more the amount of Pd contents on Pd/Fe particles, the higher their degradation capacity on PCE.
For the tests of dispersed NZVI and nano-Pd/Fe on PCE degradation, both of 2.5 g and 5 g dispersed NZVI and 5 g dispersed nano-Pd/Fe was able to entirely degrade PCE. The kobs of various amounts of dispersed NZVI (5 g, 2.5 g, 1 g) and dispersed nano-Pd/Fe (5 g) were 2.88, 1.68, 0.62, and 10.45 hr-1, respectively. It showed that nano particles with dispersant could enhance their degradation capacity on PCE.
For the tests of various pH buffer on PCE degradation, PCE was completely degraded with 5 g of Pd/Fe at reaction time of 3 min of the first sampling at pH buffer of 4, 7, and 8. At pH buffer equal to 9, PCE degradation with NZVI and nano-Pd/Fe was minimal. PCE As the amount of nano-Pd/Fe reduced to 1 g, PCE was also fully degraded at reaction time of 80 min at pH buffer of 8 with kobs equal to 3.08 hr-1 which was higher than that (2.55 hr-1) of 5 g nano-Pd/Fe without pH buffer. The kobs value of 0.31 hr-1 for 5 g NZVI at pH buffer of 8 was also higher than that (0.14 hr-1) without pH buffer.
The concentration of Cl- released from PCE degradation was close to the theoretical release amount of Cl-. The higher the PCE degradation, the greater the Cl- concentration releases. In this study, dechlorinated by-products were not detected. The contents on the surface of nano particles measured by SEM-EDS showed no obvious differences under various test conditions. The surface morphology of nano particles observed by SEM also showed chain-like distribution and no significant variations between pre-reacted and post-reacted with PCE. With FTIR identification, some differences at wave number of 620 and 1110 cm-1 were observed on the surface of nano particles pre- and post-reacted with PCE.
To solve the aggregation phenomenon of NZVI with dispersant will greatly enhance its reduction capacity on pollutants. NZVI modification with Pd plating and CMC dispersant to form dispersed nano-Pd/Fe is feasible and can significantly enhance the degradation of PCE that can provide an alternative for in-situ remediation of chlorinated solvents.
Keywords: perchloroethylene (PCE), nano zero valent iron (NZVI), palladium/iron bimetal, carboxymethyl cellulose

並列關鍵字

perchloroethylene (PCE) ； nano zero valent iron (NZVI) ； palladium/iron bimetal ； carboxymethyl cellulose

參考文獻

行政院環境保護署，2011，土壤及地下水污染整治網

陳禹鈞，2005，以Fe、V改質光觸媒處理1,2-二氯乙烷之研究，碩士論文，國立成功大學，環境工程學系，台南。

林財富，2008，土壤與地下水污染整治-原理與應用，中華民國環境工程學會編印，台北。

Lien, H. L., Elliott, D. W., Sun, Y. P., and Zhang, W. X., 2006, “Recent Progress in Zero-Valent Iron Nanoparticles for Groundwater Remediation,” Journal of Environmental Engineering, Vol. 16, No. 6, pp. 371-380.

Liu, Y. H., Quan, X., Chen, J. W., Yang, F. L., Chen, G. H., 2000,Quantitative