Preparation Of Three-dimensional Nitrogen-doped Nanocarbon Composites By Chemical Vapor Deposition

Owing to the excellent mechanical strength,thermal and electrical properties,carbon nanomaterials such as graphene,carbon nanotubes and carbon nanofibers have attracted a large number of attentions.Recently,the relevant researches have illustrated that the three-dimensional(3D)nanocarbon composites can not only effectively overcome the defects of pure low-dimensional nanocarbon materials,but also alleviate irreversible agglomeration which results from the existence of van der Waals force between molecules at a large extent,leading to the unique physical and chemical properties.Therefore,scientists are dedicated to utilizing appropriate approaches to synergistically integrate different low-dimensional carbon nanomaterials and obtain novel three-dimensional nanocarbon composites.Simultaneously,nitrogen is the "neighbor" of carbon.Compared with other atoms,nitrogen is relatively easy to incorporate into the lattice of carbon materials because of the similar atomic radius and it is used to adjust the chemical properties of sp2 hybridized carbon materials.In addition,nitrogen doping will also form disordered carbon structure and produce certain defects,resulting in enhanced electronic conductivity of materials and so on.In contrast to other synthesis methods,chemical vapor deposition(CVD)is a wide and effective method to fabricate 3D nitrogen-doped nanocarbon composites.In this way,a large number of three-dimensional composite materials are synthesized by employing various carbon and nitrogen precursors at different temperatures.These nanocarbon composites are expected to be a promising choice in future applications.In this paper,one-step chemical vapor deposition(CVD)technique is employed to simultaneously synthesize the nitrogen-doped one-dimensional and two-dimensional carbon nanomaterials by using diverse precursors on the substrate surfaces.The specific synthesis and relevant experimental results are as follows:Firstly,three-dimensional nitrogen-doped carbon nanotubes/graphene(N-CNTs/N-graphene)composites were synthesized by using melamine(carbon and nitrogen source)and nickel foam(growth substrate)in a one-step chemical vapor deposition technique.According to the experimental condition,the optimal growth temperature of this kind of nanocarbon composite were determined,and the influence of solid precursor on the three-dimensional morphology was investigated and the probable growth mechanism was proposed.Secondly,large-area Ni nanoparticle-loaded nitrogen-doped carbon nanofibers(Ni/N-CNFs)were synthesized in a CVD furnace by chemical vapor deposition by using imidazole as single source and nickel foam as the growth substrate.The relevant result showed that optimal reaction temperature was determined to be 800?.Then,when annealing at enough growth time,the nickel nanoparticles generated by nickel foam were uniformly dispersed on the surface of N-CNFs,which provided the possibility for the growth of carbon nanotubes.Finally,three-dimensional nitrogen-doped carbon nanotubes/carbon nanofibers(N-CNTs/N-CNFs)composites were fabricated by utilizing imidazole as carbon and nitrogen source and nickel foam as growth substrate in a one-step chemical vapor deposition technique.Simultaneously,the experimental results exhibit that the transformation from nitrogen-doped carbon nanofibers(N-CNF s)to N-CNTs/N-CNFs can be achieved by simply controlling the flow rate of argon.Moreover,the influence of carrier gas:flow rate on the growth of nitrogen-doped carbon nanotubes and the morphology of carbon nanofibers was investigated,and the growth mechanism of the N-CNTs/N-CNFs composite was proposed.