| 초록 |
Multi-walled carbon nanotubes (MWCNTs) have been massively produced by chemical vapor deposition using metal catalysts such as Fe, Ni, and Co on alumina support. As-synthesized MWCNTs inevitably contain carbonaceous and metallic impurities due to the use of metallic catalysts for CNT synthesis. Highly pure CNTs are very important for their high-end applications, in particular, to Li-ion batteries, super capacitors, high-voltage cables, etc. In this study, a facile, effective purification method has been developed to completely remove metal catalysts using gas and liquid phase processes. Chloroform (CHCl3) was used to remove metallic particles such as Fe, Co, and Al, where chlorine produced by decomposition of chloroform at high temperature reacted with metal catalysts, producing volatile matters. In detail, as-prepared (AP) MWCNTs were placed in a quartz tube located in a vertical-type furnace and slowly heated up to 800℃. Thereafter, chloroform vapor carried by nitrogen gas was injected at a flow rate of 100 ml/min for purification. After chloroform treatment, the sample was cooled down to room temperature. To further remove the remaining metal catalysts, mostly Al, the chloroform-treated MWCNTs were refluxed in the concentrated hydrochloric acid for 6 h. According to analysis of inductively coupled plasma atomic emission spectroscopy (ICP-AES) for the purified MWCNTs, most of metallic impurities completely disappeared by combining the chloroform and hydrochloric acid treatments. MWCNTs were characterized by x-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectroscopy, etc., at each step in the purification processes. |
