Controllable Preparation,Performance And Mechanism Of N-doped Tubular Graphene And Its Composites

As an important member of the carbon nanomaterial family,N-doped tubular graphene combine the excellent physicochemical properties of N-doped graphene with the characteristics of hollow tubular structures,making them has broad application prospects in field of field emission and photoluminescence,et al.At present,the research of N-doped tubular graphene and their composite materials is still in the initial stage,and the main preparation method is template method.It has become a challenging research work to develop a simple,efficient and low-cost template-free method to control the preparation of N-doped tubular graphene and their composite materials,and to explore their application performance.Based on the previous research of tubular graphene in the researchgroup,N-dopedtubulargraphene,N-dopedtubulargraphene@C nanocomposites and N-doped tubular graphene@a-SiO₂NPs nanocomposites were prepared in one step without stenciling around the modification of graphene nanotubes by template-free chemical vapor deposition.The field emission and photoluminescence properties of the prepared product,and the morphology and properties of the combined product,optimize the optimum process parameters for the preparation of different products.After analyzing the experimental results,a mechanism for product performance enhancement is proposed reasonably,which provides a theoretical basis for the industrialization of graphene nanotubes in field emission and photoluminescence.The main research contents and conclusions are as following:?1?Using template-free chemical vapor deposition method,C₃H₆N₆ as C source and N source,Si powder as auxiliary material,0.01 mol·L^-1Ni?NO₃?₂·6H₂O ethanol solution as catalyst,different morphology N-doped tubular graphene was prepared in one step without template.The effects of three process parameters,such as reaction temperature,molar ratio of raw materials and holding time,on the morphology and field emission properties of N-doped tubular graphene were systematically investigated.When the reaction temperature is 1100?,the molar ratio of the raw materials is 1.5:1,and the holding time is 0 min,the N-doped graphene nanotube sample has a very excellent field emission performance,and the turn-on electric field and the threshold electric field are 0.18 V·?m^-1and 1.08 V·?m^-1,respectively.?2?Using template-free chemical vapor deposition method,C₃H₆N₆ is used as C source and N source,Si powder is used as auxiliary material,high purity CH₄ is used as supplementary carbon source,and 0.01 mol·L^-1Ni?NO₃?₂·6H₂O ethanol solution is used as catalyst,N-doped tubular graphene@C nanocomposites with different morphologies were prepared in one step without template.The effects of secondary pass CH₄temperature and primary cooling temperature on the morphology and field emission properties of N-doped tubular graphene@C nanocomposites were investigated systematically.When the molar ratio of raw materials was 2:1,the holding time was 20min,the secondary pass CH₄ temperature was 1100?,and the secondary pass CH₄ time was 40 min,the surface of tubular graphene was successfully coated with amorphous C layer.The N-doped tubular graphene@C nanocomposites has excellent field emission performance,and its turn-on electric field and threshold electric field are 0.48 V·?m^-11 and1.16 V·?m^-1,respectively,and its electrochemical internal resistance is as low as 0.73?.When the molar ratio of raw materials was 2:1,the holding time was 20 min,a primary cooling temperature of 700?,the secondary pass CH₄ temperature was 1100?,and secondary pass CH₄ time was 40 min,the surface of tubular graphene was successfully coated with crystalline C layer.The product also has excellent field emission properties,which the turn-on electric field is 0.40 V·?m^-1and the threshold electric field is 1.0V·?m^-1.?3?Using template-free chemical vapor deposition method,C₃H₆N₆ is used as C source and N source,Si/SiO₂ mixed powder is used as auxiliary material,high purity CH₄is used as supplementary carbon source,and 0.01 mol·L^-11 Ni?NO₃?₂·6H₂O ethanol solution is used as catalyst,N-doped tubular graphene@a-SiO₂NPs nanocomposites with different morphologies were prepared in one step without template.The effects of process parameters such as reaction temperature,molar ratio of raw materials and post-heating time on the morphology,field emission and photoluminescence of the product were systematically investigated.The optimal process conditions are as follows:reaction temperature 1250?,molar ratio of raw material 1:2,post-insulation time 20 min,CH₄ventilation time 25 min,and the prepared N-doped tubular graphene@a-SiO₂NPs nanocomposites has excellent field emission performance.The turn-on electric field and threshold electric fields are 0.663 V·?m^-1and 1.575 V·?m^-1,respectively,and the photoluminescence performance is enhanced.The mechanism of synergistic effect of the unique morphology,N-doping and oxygen vacancy reasonably explains the reasons for the enhanced field emission and photoluminescence properties of N-doped tubular graphene@a-SiO₂NPs nanocomposites.