Microwave digestion and acidic treatment procedures for the purification of multi-walled carbon nanotubes

Abstract

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 °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.