Selective synthesis of double-wall carbon nanotubes by CCVD of acetylene using zeolite supports

Double-wall carbon nanotubes (DWNTs) have been synthesized in high-yield (>80%) by catalytic chemical vapor deposition (CCVD) of acetylene over well- dispersed metal particles (typically Co/Fe binary system) embedded in heat-resistant zeolites at temperatures above 900 °C. The synthetic yield of DWNTs has been sensitively affected by reaction conditions of the CCVD such as zeolite support materials, the sintering of the metal particles, hydrocarbon sources and reaction temperatures. High-resolution transmission electron microscopy together with Raman spectroscopy shows that the outer tube diameter varies from 3 to 6 nm with inner–outer tube separations of 0.36–0.37 nm, which is much larger than the interlayer distance of graphite (0.335 nm).