High-yield production of large aspect ratio carbon nanotubes via catalytic pyrolysis of cheap coal tar pitch

High aspect ratio (up to 5000) multi-walled carbon nanotubes (MWCNTs) were prepared on a large scale via Co-catalyzed pyrolysis of cheap coal tar pitch at 973–1273 K in an Ar-based atmosphere. Scanning Electron Microscopy and Transmission Electron Microscopy investigations revealed that as-prepared carbon nanotubes were ca. 200 μm, 40 nm and 10 nm respectively, in length, outer diameter, and wall thickness. Density functional theory calculations suggest that the in-situ reduced Co catalyst from the original cobalt nitrate precursor facilitated the cleavage of C=C and C-H bonds in adsorbed C2H4 molecules by increasing the bond length and decreasing the bond strength via donating electrons to the C atoms. The straight MWCNTs grew from/on the Co clusters through a decomposition-diffusion-penetration mechanism. The catalytic formation of high aspect ratio MWCNTs from coal tar pitch stated above can be used to improve mechanical properties of carbon-containing refractory composites. As revealed by our work, cold crushing strength and modulus of rupture of a model Al2O3-carbon refractory containing 0.75 wt% Co catalyst were respectively 26% and 34% higher than in the case of its catalyst-free counterpart, indicating the strong reinforcement effects of in-situ formed MWCNTs.