Experiment And Growth Mechanism Study On Preparation Of Few-Layer Graphene By Liquid-Phase Pulsed Laser Ablation

Graphene has perfect large?conjugate system,which makes it has unique physical and chemical properties,such as mechanical,optoelectronic,thermal and magnetic properties.Graphene has broad development space and applications in the fields of energy storage,memory devices,composite material,energy conversion and environmental monitoring.Compared with the traditional methods of preparing graphene,liquid-phase pulsed laser ablation(LPLA)is more flexible and environmentally friendly,and it plays an increasingly important role in the preparation of carbon nanomaterials.In this paper,the traditional carbon of graphite was taken as the research object.Different experimental methods were used to study the graphite suspension which was irradiated by high-energy nanosecond pulsed laser.The growth processes and formation mechanisms of graphene were discussed under different experimental conditions.The main conclusions of this paper are as follows:(1)The mechanism of laser on graphite in liquid phase was theoretically analyzed,and the conditions for the generation of graphite surface plasma were obtained through analysis and calculation.The transformation process of graphite to graphene under pulsed laser irradiation was studied from the perspective of thermodynamics and kinetics.The results show that the formation of graphene in the liquid phase follows the liquefaction nucleation mechanism,and the preparation mechanism of graphene is considered to be a solid-vapor-plasma-liquid-solid process.(2)Graphene suspension was prepared via laser ablation of flake graphite particles(1250 mesh).The structure and morphology of the obtained products were analyzed.Bilayer graphene were obtained after centrifugation and purification.The results show that the preparation of graphene suspension is accompanied by the production of hydroxyl radicals.These hydroxyl radicals will react with the sp~2 hybrid carbon atom,resulting in an increase in oxygen-containing functional groups of the product.Laser treatment induces a thermal reduction of GO to graphene-like sheets by removing the oxygen-containing functional groups according to the specific dehydration reaction.Through the comparative analysis of the two phenomena,it is considered that the process of preparing graphene by laser liquid phased ablation involves redox reactions.(3)The formation of few-layer graphene films on pretreated Cu foil using liquid-phase pulsed laser ablation of small flake graphite particles was demonstrated.With the increase in laser energy(from 0.1 to 0.3 J),the layer number of graphene increases from3 to 11 and the morphology(size and disorder degree)of obtained graphene structure changes accordingly.(4)The unrestricted growth mechanism of graphene on the surface of copper substrate was analyzed:High temperature and high-pressure plasma will eventually collapse and form a cavitation bubble after laser process.At this time,the pulsed laser plays an important role in decomposing carbon source to free carbon atom.With the intervention of the solid-liquid interface,the bubble has a pressure difference between the two sides.The high-pressure region of the vacuole wall is deformed and depressed,finally forming a micro-jet towards the solid surface.In this case,the metal substrate is used to adsorb carbon atoms and catalyze the graphitization of carbon atoms on the surface,which is conducive to the formation of large-sized graphene.Liquid-phase pulsed laser directly catalyzes the decomposition of the carbon source into carbon atoms and ions.The deposition of few-layer graphene prepared by this method on Cu foil is not a self-limiting process.