Nitrogen-doped carbon nanotubes with tunable structure and high yield produced by ultrasonic spray pyrolysis

Nitrogen-doped carbon nanotubes (CN_x) were prepared by ultrasonic spray pyrolysis from mixtures of imidazole and acetonitrile. Imidazole, as an additive, was used to control the structure and nitrogen doping in CN_x by adjusting its concentration in the mixtures. Scanning electron microscopy observation showed that the addition of imidazole increased the nanotube growth rate and yield, while decreased the nanotube diameter. Transmission electron microscopy study indicated that the addition of imidazole promoted the formation of a dense bamboo-like structure in CN_x. X-ray photoelectron spectroscopy analysis demonstrated that the nitrogen content varied from 3.2 to 5.2 at.% in CN_x obtained with different imidazole concentrations. Raman spectra study showed that the intensity ratio of D to G bands gradually increased, while that of 2D to G bands decreased, due to increasing imidazole concentration. The yield of CN_x made from mixtures of imidazole and acetonitrile can reach 192 mg in 24 min, which is 15 times that of CN_x prepared from only acetonitrile. The aligned CN_x, with controlled nitrogen doping, tunable structure and high yield, may find applications in developing non-noble catalysts and novel catalyst supports for fuel cells.