Mesoporous binder-free monoliths of few-walled carbon nanotubes by spark plasma sintering

Abstract

Carbon nanotubes with few walls (FWCNTs) are prepared by catalytic chemical vapor deposition. Transmission electron microscopy investigations for each sample show the average number of walls (3, 4 and 8) as well as the internal and external diameter distributions. Binder-free FWCNT monoliths are prepared by spark plasma sintering (SPS) at temperatures in the range 1000–1600 °C. A combination of techniques including Raman spectroscopy, scanning- and transmission electron microscopy, electron microdiffraction is used to characterize the samples. Compared to the FWCNT powders, the high temperatures used for SPS favor the elimination of surface defects in CNT walls but also some limited amorphization, without dramatic damage to the CNTs. Increasing the SPS temperatures produces an increase in densification. N2 adsorption–desorption cycles revealed that the powders and monoliths show microporosity and, mostly, mesoporosity. Some monoliths show a specific surface area equal to about 500 m2/g. The 4WCNTs when consolidated into monoliths by SPS at 1000 or 1100 °C are able to retain a high amount of mesoporosity that contributes to a high porous volume of the order of 0.8 cm3/g.