Preparation And Properties Of Carbon-Based Nanomaterials By MPCVD

Carbon-based nanomaterials whose sources and storages are extremely abundant on the earth,generally demonstrate good conductivity,high carrier mobility,flexibility and light weight.They are widely used in chemical and biological sensors,flexible substrate integrated circuits,high performance lithium-sulfur batteries,catalysis and environmental protection.Chemical Vapor Deposition?CVD?is the most commonly used method to prepare carbon nanomaterials.Compared with traditional CVD,microwave plasma chemical vapor Deposition?MPCVD?uses microwave to excite high density plasma,its non-electrode desigh avoids the contamination of electrodes.Hence,it can efficiently heat the substrate homogeneously,reduce the deposition temperature and realize industrialized production of carbon nanomaterials.It provides a new idea and method for the preparation and regulation of carbon-based nanomaterials.Based on this,multi-walled carbon nanotubes?MWCNT?and carbon nanospheres were prepared by MPCVD.The effects of atmosphere,chamber pressure,temperature,bias,reaction time and substrate on the growth of carbon nanomaterials were further studied.On this basis,the sensing and electrochemical properties of carbon-based nanostructured materials were studied.The main research results of this paper are as follows:1.Preparation of Carbon-based Nanomaterials by MPCVD?1?MWCNTs with different nitrogen contents and tube wall numbers were prepared by adjusting process parameters.The samples demonstrate ca.10-70 layers of tublar carbon sheets with different N and C ratio of 0.11-0.23;?2?Carbon microspheres were successfully grown using isotropic graphite as substrate.With the increase of reaction temperature or time,the morphology of carbon nanospheres change from irregular self-assembled sphere sturcture?consist of carbon nanoparticles?to soccer-like polyhedral microspheres,and the diameter of carbon nanospheres increase during preparation.2.Mechanism of Preparation of Carbon-based Nanomaterials by MPCVD?1?The growth mechanism of CNT under atmospheric regulation was studied by experimental and theoretical methods.N₂ atmosphere can significantly reduce the dissociation energy of the reactant CH₄.It is found that the dissociation barrier decreases from 18.31 eV to less than 2.87 eV.The results show that the yield of CNT can be greatly increased under appropriate N₂ flow.In addition,the content of N in CNT is positively correlated with the concentration of N₂ in the reaction.?2?The growth mechanism of carbon nanospheres was studied by adjusting the reaction temperature and time.The growth mechanism of carbon nanospheres was explained in three stages from nucleation/growth and crystal plane expansion.In the first stage,carbon atoms are aggregated in the structure of carbon nanospheres to form a carbon microsphere structure;in the second stage,active crystal planes expand until they are blocked and stop growing;in the third stage,the active crystal planes continue to expand until they come into contact with other active surfaces and stop growing.3.Properties of Carbon-based Nanomaterials Prepared by MPCVD Method?1?Polyaniline/multi-walled carbon nanotubes?PANI/CNT?composites were prepared by low temperature polymerization using SiO₂?300nm?/Si as the substrate.The gas sensing properties of PANI/CNT composites were studied.It was found that PANI/CNT was specifically sensitive to NH₃ at room temperature.?2?The electrochemical properties of carbon nanospheres were studied by cyclic voltammetry and galvanostatic charge-discharge test.It was found that the carbon nanospheres have good specific capacitance and can be controlled by reaction.