| Summary: | 碩士 === 國立臺灣大學 === 環境工程學研究所 === 93 === 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.
|
|---|
