The Effect of Hydrogen, Helium and Their Mixtures on the Synthesis of Carbon Nanotubes in a DC Arc‐Discharger

Abstract

Multiwalled carbon nanotubes (MWCNTs) have been produced with a DC arc-discharger in the presence of hydrogen, helium or hydrogen-helium mixtures using high gas pressures (60 kPa-140 kPa) and varying gas pressure ratios (10%-100% hydrogen in helium at 100 kPa). Variation of He pressure hardly affected the cathode deposit formation while increased H 2 pressure resulted in an increase in chamber soot and cathode material formation but a relative decrease in the % MWCNT production. Varying H 2 /He gas ratios at a constant total pressure of 100 kPa revealed that increasing H 2 content gave increased cathode deposit formation because of a faster anode consumption rate as well as more total gaseous product formation. Further, a maximum MWCNT deposit was obtained from a 50/50 gas mixture. GC-MS analysis of the gaseous products trapped from these reactions showed evidence for the presence of linear alkynes (ethyne, butyne, pentyne, hexyne etc.), benzene, naphthalene, anthracene, and their methylated analogues. The relative in-situ temperature of the reaction with the pure gases was monitored and revealed that the highest temperature was recorded for the reaction with 60 kPa H 2 , which also produced the maximum amount of MWCNTs (80%). Impure samples from the cathode deposit were analysed by TEM and showed that in the majority of cases rectangular closed-tipped nanotubes were synthesised, together with varying amounts of onion-like sheets and folded graphene sheets.

A Theoretical Study of Dibenzothiophene Absorbed on Open-Ended Carbon Nanotubes

“…As carbon nanotubes show a cylindrical shape, research efforts have concentrated on the possibility of controlling alignment, diameters, and lengths , so that many theoretical and experimental studies on these topics have been reported. , Classical and path integral molecular simulations were used to study the physisorption of hydrogen, helium, neon, nitrogen, argon, and methane in cylindrical pores, SWCNTs, and bundles of SWCNT for a range of pressures, temperatures, tube radii, and bundle structures . There is currently a considerable interest in the functionalization of carbon nanotubes, one motivation being to increase their very low solubility in both aqueous and organic solvents .…”