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

► Ultrasonic spray pyrolysis is developed to synthesize CNx. ► CNx prepared by this method have high yield. ► Imidazole as an additive in acetonitrile to control N doping and structure in CNx. ► Imidazole decreases nanotube diameter while increases nanotube length and yield.