A treatment method to give separated multi-walled carbon nanotubes with high purity,high crystallization and a large aspect ratio

摘要

CNT agglomerates,prepared by catalytic chemical vapor deposition in a nano-agglomerate fluidized-bed reactor are separated and dispersed.The effects of shearing,ball milling,and ultrasonic and chemical treatments on the dispersing of the carbon nanotubes were studied using SEM,TEM/HRTEM and a Malvern particle size analyser.The resulting micro-structures of the agglomerates and the efficiency of the different dispersion methods are discussed.Representative results of annealed CNTs are highlighted.The as-prepared CNT product exists as loose multi-agglomerates,which can be separated by physical methods.Although a concentrated H_2SO_4/HNO_3 (v/v=3:1) treatment is efficient in severing entangled nanotubes to enable their dispersion as individuals,damage to the tube-wall layers is serious and unavoidable.A high temperature annealing (2000 deg C,5 h) before the acid treatment (140 deg C,0.5 h) is recommended and can give well separated nanotubes with a high aspect ratio and 99.9% purity.These highly dispersed CNTs contain few impurities and minimal defects in their tube-bodies and will be of use in further research and applications.