Synthesis And Nitrogen-doping Of Carbon Nanotubes And Graphene

Carbon nanotubes (CNTs) and graphene exhibit novel structure-related physical and chemical properties due to their unique one-dimensional tubular and two-dimensional flat structure, and show significant potential applications for electronic devices, composite materials and catalysts. Doping CNTs and graphene with nitrogen is a practical way to tailor their properties and facilitate their applications. Developing new methods for large-scale synthesis and nitrogen-doping of CNTs and graphene with low cost is of considerable significance in practice.In this work, detonation-assisted chemical vapor deposition was developed to synthesize CNTs and nitrogen-doped carbon (CNx) nanotubes with iron-group metals or CNTs as catalysts, according to its unique characteristics:quickness, self-heating and easy fabrication of carbon clusters. The dynamic growth mechanisms of CNTs and CNx were studied systematically. Based on the synthesis of graphene by detonation, graphene and nitrogen-doped graphene were achieved with the assistance of microwave irradiation. Besides, a preliminary exploration on the graphene-based composites was carried out. The main contributions are summarized as follows.1) Bamboo-like CNTs were synthesized by detonation-assisted chemical vapor deposition, with iron-group metals (Co, Ni, Fe) as catalysts and paraffin as carbon sources. A certain sulfur addition can promote the growth of hollow CNTs. The structure transformation of CNTs from bamboo to hollow channel was independent on the catalyst crystalline structure.2) The synthesis of bamboo-like CNTs with Ni as catalysts followed the spatiotemporal dynamic growth model. The dynamic reshaping of catalyst particles was essential for the continuous growth of CNTs. The graphene sheets (bamboo knots) within the nanotube preferentially nucleated on the multi-step Ni-graphite edges. Sulfur promoter preferentially bound to Ni step edges and suppressed the bamboo knot growth.3) Hollow CNTs and bamboo-like CNx were synthesized by detonation-assisted chemical vapor deposition with CNTs, paraffin and melamine as catalysts, carbon sources and nitrogen sources, respectively. The synthesized CNx contained high concentration of nitrogen (ca.17.3 at%), with the presence of pyridine-like N and graphitic N incorporated into the graphitic network. The catalytic activity of CNTs was ascribed to the nanocurvature and opening edges of CNT tips, which adsorbed Cn/CN species and assembled them into CNTs or CNx.4) Rapid thermal exfoliation and reduction of graphite oxide to graphene was achieved with the assistance of microwave irradiation. The as-prepared graphene was transparent and wrinkled. Using NH4+ intercalated graphite oxide instead of graphite oxide as precursor, the reduction and nitrogen-doping of graphene was simultaneously achieved. The nitrogen content in the synthesized nitrogen-doped graphene was ca.1.6 at%, corresponding to pyridinc N, pyrrolic N and graphitic N incorporated into the graphitic network.5) Microwave irradiation of graphite oxide in N-methyl-2-pyrrolidinone resulted in exfoliation and reduction to yield a stable colloidal dispersion. The as-prepared graphene was transparent, and consisted of 2-5 graphitic layers with high crystalline structure.