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Abstract: Vertically aligned nitrogen-doped carbon nanotubes (CNTs) with modulated nitrogen content have been synthesized in a large scale by using spray pyrolysis chemical vapor deposition technique. The effects of nitrogen doping on the growth, structure and electrical performance of carbon nanotubes have been systematically examined. Field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman techniques have been employed to characterize the morphology, composition, and vibrational properties of nanotubes. The results indicate that the nitrogen incorporation significantly influences the growth rate, morphology, size and structure of nanotubes. Electrical measurement investigation of the nanotubes indicates that the change in electrical resistance increases with temperature and pressure as the nitrogen concentration increases inside the tubes. This work presents a versatile, safe, and easy way to scale up route of growing carbon nanotubes with controlled nitrogen content and modulated structure, and may provide an insight in developing various nitrogen-doped carbon-based nanodevices. [Copyright &y& Elsevier]

Abstract: Spray pyrolysis chemical vapor deposition (CVD) in the absence of hydrogen at low carrier gas flow rates has been used for the growth of carbon nanotubes (CNTs). A parametric study of the carbon nanotube growth has been conducted by optimizing various parameters such as temperature, injection speed, precursor volume, and catalyst concentration. Experimental observations and characterizations reveal that the growth rate, size and quality of the carbon nanotubes are significantly dependent on the reaction parameters. Scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy techniques were employed to characterize the morphology, structure and crystallinity of the carbon nanotubes. The synthesis process can be applied to both semiconducting silicon wafer and conducting substrates such as carbon microfibers and stainless steel plates. This approach promises great potential in building various nanodevices with different electron conducting requirements. In addition, the absence of hydrogen as a carrier gas and the relatively low synthesis temperature (typically 750°C) qualify the spray pyrolysis CVD method as a safe and easy way to scale up the CNT growth, which is applicable in industrial production. [Copyright &y& Elsevier]

• Spray pyrolysis chemical vapor deposition used for carbon nanotubes synthesis. • Pristine and nitrogen-doped nanotubes deposited with high loads on metallic foam. • Li-air battery cathodes fabricated using nanotubes without binders or additives. • Doped nanotubes show better electrochemical properties than pristine nanotubes. • The coulombic efficiency of electrodes decreases after 10 cycles. Spray pyrolysis chemical vapor deposition was used to synthetize carbon nanotubes and nitrogen-doped carbon nanotubes directly on metallic foam substrates. Cathodes containing pristine and nitrogen-doped nanotubes with mass loads of 4.2 mg cm−2 were investigated for lithium-air batteries. Pristine nanotubes presented a maximum specific discharge capacity of 3320 mAh g −1 in air, while nitrogen-doped nanotubes exhibited a maximum specific discharge capacity of 3934 mAh g −1. These results demonstrate that is possible to deposit high amounts of carbon nanomaterials on metallic substrates and use them directly as electrode materials with high electrocatalytic activity for the cathode reaction for developing advanced energy storage devices. [ABSTRACT FROM AUTHOR]

Abstract: 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 5.2at.% 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 192mg in 24min, 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. [Copyright &y& Elsevier]