Browsing by Author "Peng, YW"

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High efficiency microwave digestion purification of multi-walled carbon nanotubes synthesized by thermal chemical vapor deposition
(2006-03-01)
Chen, CM
;
Chen, M
;
Peng, YW
;
Yu, HW
;
Chen, CF
Multi-walled carbon nanotubes (MWCNTs) synthesized by thermal chemical vapor deposition (Thermal CVD) have been successfully purified by high efficient microwave digestion purification method. In this paper, microwave digestion method was introduced to purify carbon nanotubes, because that acid can absorb microwave energy rapidly and dissolve metal efficiently in this method. MWCNTs were placed in 100 ml TFM (thennally resistant form of Teflon) vessels with 50 ml 5 M nitric acid. First, the temperature ramped up to 210 degrees C in 30 min and then kept for 10, 20, 30 to 120 min to digest the catalyst. The efficiency of this method was analyzed by thermogravimetric analysis (TGA) and the results showed that the catalyst content dropped from 10.39% to 1.75% only in 10-min digestion and 1.03% for 120 min treatment. Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM) were applied to analyze the property and structure of raw and purified MWCNTs. This study presents a highly efficient and non-destructive purification method for high purity MWCNTs which can be provided in many applications or intrinsic property studies. (c) 2005 Elsevier B.V All rights reserved.
Microwave digestion and acidic treatment procedures for the purification of multi-walled carbon nanotubes
(2005-03-01)
Chen, CM
;
Chen, M
;
Peng, YW
;
Lin, CH
;
Chang, LW
Multi-walled carbon nanotubes (MWCNTs) synthesized by thermal chemical vapor deposition have been successfully purified by using efficient microwave digestion method. Recently, various purification methods have been provided to eliminate metal catalysts and most were acid treatment procedures that take long time and damage the structure of nanotubes. Comparing to these methods, microwave digestion takes a tremendous advantage because the acid in this approach can absorb microwave energy rapidly and dissolve metal efficiently without damaging the wall structure and the processing time could be the shortest. The ability of microwave digestion method was studied by various experimental parameters. The efficient purification proceeded for 90 min and at 210 degrees C with 5 M nitric acid treatment in the microwave digestion system to dissolve the metal catalyst. High-resolution transition electron microscopy and Raman spectra were used to characterize the specimen. Purities were characterized by thermogravimetric analysis (TGA). Results showed that the amount of catalyst decreased with increasing acid treatment time and concentration. Purity of MWCNTs achieved as high as about 99.9%. This study presents a highly efficient purification method for carbon nanotubes with high purity and no structure destruction. In addition, carbon nanotubes synthesized by various methods were also purified and the results were comprehensively discussed. (c) 2004 Elsevier B.V. All rights reserved.