Experimental Study On Preparation Of Graphene By Laser Irradiation In Alkaline Liquid Medium

Graphene is the thinnest two-dimensional material with extremely excellent electrical,mechanical and optical properties,and it has a broad application prospect in new energy vehicles,sensors,biomedicine and other fields.Compared with conventional methods of preparing graphene,laser irradiation is widely used in the preparation of carbon nanomaterials due to its advantages of green environment protection,high controllability and simple operation.In this dissertation,flake graphite is used to conduct experimental study on the preparation of graphene by laser irradiation in alkaline liquid medium.The formation process of graphene and experimental influencing factors are discussed.The main research work and conclusions are as follows:(1)The process of laser action on graphite particles in liquid medium was theoretically analyzed.Combined with the formation model of laser-induced plasma and the law of cavitation pulsation in liquid medium,and the development process of plasma from emergence,collapse,cooling to carbon droplet and finally graphitization was summarized.On this basis,the transformation path from graphite to graphene was studied.The results show that the transformation process of graphite to graphene undergoes two sub processes:high temperature and pressure and rapid cooling.The high temperature and pressure caused by laser create conditions for the formation of free carbon atoms,and the rapid cooling process after laser removal creates conditions for carbon atoms to recombine into fine graphene fragments.(2)Using sodium hydroxide solution as the dispersion of graphite raw materials,the graphene suspension was successfully prepared by irradiation.The centrifugated and purified samples were characterized by a variety of characterization methods.The results show that under the same experimental conditions,the viscosity increase with the increase of the concentration of sodium hydroxide solution,resulting in the nanoparticles produced during laser irradiation of the suspension cannot be diffused in time.The possibility of adsorbing nanoparticles on the surface of graphene increased,and the quality of graphene formation is ultimately affected.Based on the results of experimental characterization and physical theory,the other factors that influence the preparation of graphene by liquid-phase laser irradiation are studied.The positive mechanism is explained,and it is of great significance to optimize the preparation process and improve the preparation efficiency.(3)Based on the formation mechanism of graphene,the effect of sodium hydroxide solution with different concentration on the conversion of carbon atom to graphene was analyzed from the perspective of solution viscosity and bubble pulsation.The results show that solution viscosity has a direct effect on the bubble pulsation.The greater the viscosity of the solution,the longer the pulsation period of the cavitation.The prolonging of the cavitation pulsation period reduces the preparation efficiency of graphene.The probability of graphene fragments superimposed on each other increased because of the higher liquid viscosity,resulting in a relatively large number of graphene layers.(4)Using sodium hydroxide solution as a stable dispersion of graphene oxide,it was successfully reduced to graphene by laser irradiation.The samples before and after laser irradiation were characterized by a variety of characterization methods.It is found that with the increase of reduction degree,the oxygen-containing functional groups in graphene oxide are removed.The surface wrinkles and the number of new SP~2 hybrid structures increase as the degree of reduction increases.