零價金屬錫與鈀錫雙金屬對水中四氯化碳還原脫氯反應之研究

Degradation of Carbon Tetrachloride in Aqueous Solution by Nanoscale Sn0 and Pd/Sn0 Particles

吳軒(Hsuan Wu)

指導教授 ： 駱尚廉

國立臺灣大學/工學院/環境工程學研究所/碩士(2005年)

https://doi.org/10.6342/NTU.2005.00346

摘要

運用零價金屬滲透性反應牆處理土壤及地下水中含氯有機化合物是近年來熱門且廣泛的研究。而判別各種零價金屬的適用性，是根據目標汙染物的降解速率以及還原脫氯過程中所產生的副產物來決定。本研究主要利用化學還原法，製造出比表面積大於微米級商業錫粉100倍以上的奈米級零價錫以及鈀/錫雙金屬，探討其對四氯化碳還原脫氯反應的效果與機制。
批次試驗結果顯示，粉末狀微米級與懸浮態奈米級零價金屬降解四氯化碳的反應均可套用擬一階反應動力模式，得到奈米化後Pd/Sn雙金屬的降解速率比奈米錫快5倍，比粉末狀金屬快將近100倍的效果。
由產物的分佈可推斷：本研究利用錫金屬還原脫氯四氯化碳的系統同時包含三種反應機制。第一種是產生三氯甲烷以及二氯甲烷的氫解反應，在粉末狀金屬系統中三氯甲烷產率是20-60%，無二氯甲烷；懸浮態零價金屬系統中三氯甲烷則佔70-80%，二氯甲烷10%。至於第二種及第三種反應路徑均產生二氯碳烯基(:CCl2)，反應機制分別為碳烯基水解與碳烯基還原，最終產物是甲烷。粉末狀金屬系統中甲烷佔10-30%，懸浮態零價金屬系統中甲烷則僅有10%的產率。
值得注意的是，本研究發現奈米化之後，單一金屬錫系統中，甲烷的產率較Pd/Sn雙金屬高，且三氯甲烷有緩慢降解趨勢。然而由於尺寸縮小，反應活性亦加大，奈米錫在水中對氫離子的競爭性提升，因此加強了氫解反應的發生機率，造成奈米化金屬系統三氯甲烷的產率較粉末狀金屬系統高出許多。

關鍵字

零價金屬 ； 奈米粒子 ； 還原脫氯 ； 四氯化碳

並列摘要

Zero-valent metal as a permeable barrier material for degradation of chlorinated organic compounds has been extensively studied recently. The practicality of this treatment method depends on the reduction rates of the target compounds and their byproducts. In this study, nano-scale Sn and Pd/Sn particles are synthesized by chemical reduction method so that they could be used to rapidly degrade carbon tetrachloride (CT). Their BET surface areas are two orders higher than those of commercial micro-scale Sn and Pd/Sn particles.
Batch reduction experiments of CT show that both micro-and nano-scale particles follow pseudo-first-order kinetics. The specific reaction rate constants with the nano-scale Pd/Sn particles are 5 times higher than nano- scale Sn particles and are 100 times higher than those of the micro-scale particles.
Product formation studies indicate that CT transformation occurs via three parallel pathways. The first pathway (hydrogenolysis) results in the formation of chloroform (CF, 20-60% in micro-scale particles system, 70~80% in nano-scale particles system) and dichloromethane (DCM, 10% by nano-scale particles). The second and third pathways involve a dichlorocarbene intermediate (:CCl2) via either carbene hydrolysis or carbene reduction to yield methane (10-30% in micro-scale particles system, 10% in nano-scale particles system).
Significantly more methane are generated with the use of the nano-scale Sn particles than with the nano-scale Pd/Sn particles. Nevertheless, due to the increase of the surface area and activity, the possibility of hydrogenolysis also increases so that more chloroform are generated with the use of nano-scale particles than with the micro-scale particles.

並列關鍵字

zero-valent metal ； nanoscale ； dechlorination ； carbon tetrachloride

參考文獻

胡景堯，「電膠羽浮除法去除廢水中氟離子之研究」，國立台灣大學環境工程研究所博士論文，2005。

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