Growth Model And Influence Factors Study Of Carbon Nanohorn Aggregates Synthesized By Nanosecond Laser

Single-wall carbon nanohorn aggregates(SWCNHs)is a kind of novel carbon nano-materials.It is widely used in field of gas adsorption,solid phase extraction and biological medicine for its unique structure and excellent performance.Many researchers have been searching for the method to prepare it controllably,stably,and efficiently.The traditional method has higher requirements on the preparation environment.Laser is a kind of clean energy,the high temperature and high pressure conditions can be realized easily under normal temperature and pressure for phase transition of graphite.This paper made research on the raw material of graphite.Graphite particles suspended in a liquid medium was irradiated by nanosecond pulse laser with high energy.The product was observed by HRTEM,Raman spectra,XPS,etc.And the formation mechanism was discussed after thermodynamics and dynamics analysis.The main research contents and conclusions of this paper are as follows:(1)Single-wall carbon nanohorn aggregates(SWCNHs)was successfully prepared by laser irradiation of graphite particles in the liquid medium.The type of product is seed,bud,dahlia and petal-dahlia type.The product was clear and uniform in size with a high purity.The particle size of four different types of product was distributed within 10 nm to 80 nm.The mean particle size was 29 nm,33 nm,36 nm and 38 nm,respectively.(2)The influence of different factors on the final product was explored.When the graphite raw materials with smaller diameter was selected,the final product was composed of carbon clusters and amorphous carbon.When the laser power density is too high,the phenomenon of completely evaporation of the graphite particles will occur,which is not conducive to the accumulation of carbon nanohorn particles.The liquid medium provides a large degree of supercooling,which is good for the graphite phase transition.When the concentration of graphite suspension was controlled in the range of 0.02 ~ 0.03 g/ml,the experimental results were ideal.(3)The dispersity of product before and after oxidation treatment in different solution was investigated.It is found that the product dispersed poorly in strong acid and strong base.After oxidation treatment,the amount of polar oxygen-containing functional groups increased,which improved the dispersity significantly.(4)The mechanism of graphite phase transition under the conditions of this experiment was discussed.Based on the thermodynamics and dynamics analysis,the growth model was proposed.The graphite particles absorbed energy from laser irradiation,and the surface temperature increased rapidly.Then,an area of gaseous carbon plume was formed.Carbon plasma was induced by further ionization of the gaseous carbon plume.The high-speed movement and collision of carbon plasma formed the horn structure.When the pulse was over,the temperature and pressure in the system begin to decrease.During the cooling process,the horn structure gradually grew,and eventually grew into a carbon nanohorn aggregates structure.