Synthesis of carbon nanotubes on carbon fibers by modified chemical vapor deposition

Carbon nanotubes (CNTs) were synthesized on carbon fibers by a modified thermal chemical vapor deposition (CVD) method. The fibers were first treated at a temperature of 973 K and then treated by a mixture of sulfur acid and nitric acid with a volume ratio of 1∶3 to improve the dispersion of catalyst precursor Fe(NO3)3 · 9H2O on the surface before impregnation with a catalyst solution. The carbon fibers then underwent simultaneous catalyst reduction and CNT growth to decrease the contact time between the transition metal and the carbon fiber surface, and a uniform and thick CNT forest could be obtained with no significant decrease of the mechanical strength of the carbon fibers compared with those produced by traditional thermal CVD. An in-depth analysis shows that the process parameters have a great influence on the CNT growth rate, such as the type of solvent, concentration of Fe(NO3)3 · 9H2O, the ratio of H2 to C2H2, and the growth time. It was revealed that a better CNT forest could be obtained when the catalyst solvent is ethanol, the Fe concentration is 100 mmol/L, the ratio of H2/C2H2 is 4/1, the temperature is 1 023 K and the growth time is 30 min.