Large-scale template-free synthesis of N-doped graphene nanotubes and N-doped SiO2-coated graphene nanotubes: Growth mechanism and field-emission property

The use of dopants and other functional materials has been proven to be an effective approach in tailoring the electronic properties of the composition of graphene nanosheets. However, investigations into doping and compositing of tubular graphene are still at an early stage. Herein, the first large-scale synthesis of N-doped graphene nanotubes (GNTs) and the N-doped graphene coaxial nanotubes with amorphous SiO2 coating layer (GNTs@SiO2) have been performed in a facile free-template, one-step chemical vapor deposition method, and the growth mechanism was investigated in detail. This approach both simplifies the synthetic process and protects the nanotubes from destruction caused by template removal. Moreover, a high ratio of graphitic-N to pyridinic-N doping (∼6.5:1) was achieved, which is an important factor required to improve the various properties of graphene. The N-doped GNTs and GNTs@SiO2 displayed excellent field emission properties, with Eto of 1.2 and 0.5 V/μm and Ethr of 3.4 and 4 V/μm, respectively, and a synergistic effect mechanism has been proposed to interpret the enhanced FE properties. This present research not only offers a new route for large-scale synthesis of N-doped tubular graphene and its nanocomposite, along with excellent field emission properties and electroconductivity, but also establishes a foundation for their application in various fields.