Increase in the yield of (and selective synthesis of large-diameter) single-walled carbon nanotubes through water-assisted ethanol pyrolysis

Single-walled carbon nanotubes (SWCNT) were synthesized using Co-MCM-41 catalysts through water-assisted ethanol pyrolysis. The effect of varying the water to ethanol ratio in the reactant mixture was studied. The data from X-ray absorption spectroscopy indicate that with the addition of water, the cobalt metal particles were oxidized. X-ray diffraction analysis of CoCx suggests that the formation of amorphous carbon on the surface of the Co particles was suppressed. Cobalt magnetization measurements were performed to study the size and anisotropy of cobalt particles. Thermogravimetric analysis data demonstrate that with a water concentration of 7%, the yield increases by about 100% relative to pure ethanol synthesis. Raman and photoluminescence excitation spectroscopic data demonstrate that the SWCNT diameter increases (within the diameter range detected) with the water/ethanol ratio. From the statistical SWCNT diameter distribution obtained from transmission electron microscopy, 65% of the SWCNT synthesized with 20% water in ethanol have diameters larger than 1.5 nm, but there is a severe decrease in yield and a modest decrease in selectivity of SWCNT. The mechanism of how the water influences the yield and diameter of SWCNT is discussed.