以零價銅金屬及維生素 B12催化二氯甲烷還原降解之研究

Abstract

二氯甲烷是地下水中一種頑強的含氯有機汙染物，難以藉由零價鐵金屬還原降解。本研究發現在還原條件下，藉由零價銅金屬奈米顆粒與維生素 B12作為催化劑能有效催化二氯甲烷還原降解。批次實驗指出當存在銅金屬於硼氫化納還原條件時，二氯甲烷會被迅速降解。而當單獨使用銅金屬但無外加還原劑、或者單獨硼氫化鈉還原條件而無添加銅金屬催化劑時則無法降解二氯甲烷。而銅金屬對於維生素 B12（一種電子媒介體，可催化含氯有機物的還原降解）在檸檬酸鈦還原條件下去除二氯甲烷也有明顯的加強效果，當添加零價銅進入維生素 B12系統後，二氯甲烷的降解速率會比添加銅金屬之前增加五倍，效果十分顯著。二氯甲烷的降解速率會隨著銅金屬劑量或維生素 B12劑量的增加而增加。產物分析證明二氯甲烷的消失是經由還原降解。系統中產生的銅離子濃度低於飲用水標準，這顯示銅金屬奈米顆粒的使用不會造成二次汙染、是很有潛力的汙染物去除材料。可預期此結合零價銅金屬奈米顆粒與維生素 B12（或其他電子媒介體）之系統很有潛力作為地下水汙染整治之用，特別是對於零價鐵無法整治的頑強含氯有機汙染物。

Dichloromethane (DCM) is a recalcitrant groundwater contaminant that shows nearly no reactivity with zero-valent iron (ZVI) nanoparticles. In this study, an effective dechlorination of DCM has been demonstrated using zero-valent copper (Cu0) nanoparticles and vitamin B12 as catalysts under reduction conditions. Batch experiments revealed that DCM was rapidly degraded in the presence of Cu0 nanoparticles under reduction conditions of sodium borohydride. No degradation of DCM was observed in the presence of Cu0 nanoparticles alone, nor under sodium borohydride reduction conditions alone. A synergistic effect of Cu0 nanoparticles on the reductive degradation of DCM by vitamin B12 (an electron mediator) under reduction conditions of titanium citrate was found. The reaction rate of DCM degradation by the Cu0–B12 system was five times greater than that of using vitamin B12 alone. The DCM degradation rate is a function of the Cu0 nanoparticle and vitamin B12 dose. Increasing the dose increased the observed reaction rate. Product analysis indicated that the degradation of DCM involved hydrodechlorination. Soluble copper ions generated by the dissolution of Cu0 nanoparticles were lower than the World Health Organization drinking water standard, which suggests that the use of Cu0 nanoparticles under reduction conditions may be potentially useful. It is expected that the combination of Cu0 nanoparticles and vitamin B12 (or other electron mediator) system may have the potential for treating recalcitrant chlorinated contaminants that cannot be degraded by ZVI technology.