Research Of Liquid-exfoliation Of Graphite To High Concentration Graphene

Graphene has attracted the attention of many researchers recent years due to its excellent properties.The preparation of graphene has become the key to the breakthrough of carbon materials.Presently,several preparation methods of graphene have been reported,including chemical oxidation reduction,chemical vapor deposition?CVD?,mechanical exfoliation,etc.The method-liquid phase exfoliation has become the research focus because of its simple preparation method,no structural defect and easily realization of industrialized production.However,the graphene prepared by this method still has some problems such as low exfoliation efficiency,small graphene sheets and non-environmental of some agents.In this paper,the selection of exfoliation agents,material pretreatment and exfoliation method are explored.The optimal binary exfoliation system?N-methylpyrrolidone and n-butanol?was selected by Hansen solubility parameters.Ultrasonic cleaner was used as the exfoliation force to explore the effect of binary system exfoliation preparation of graphene.The best exfoliation ratio was obtained.In comparison,the concentration and stability of the graphene dispersion were improved,and the exfoliation mechanism was explained by the combined action of the mixed enthalpy theory and hydrogen bonding.The appearance was characterized by transmission electron microscopy and structure of the graphene was characterized by Raman spectroscopy.The thickness of graphene was determined by atomic force microscopy.The absorbance coefficients of the graphene dispersions were obtained by regression analysis.After high-speed centrifugation,the obtained graphene dispersion is 15%monolayer,80%or more is few-layer graphene,the structure is complete,the sheet size can reach 3?m⁴?m,and the concentration of graphene solution is up to 7.2mg/mL.The influence of the process conditions of liquid phase exfoliation graphene was studied by orthogonal experiment.After determining the binary solvent exfoliation system,the effects of different process conditions on liquid-phase exfoliation of graphene were explored in detail.The initial graphite concentration,exfoliation time,centrifugal speed,addition of auxiliaries,different treatment methods for raw materials,and influence of different exfoliation ways on exfoliation were investigated in detail.It was found that the concentration of graphene dispersion firstly increased and then decreased with the initial graphite concentration increasing;the longer of exfoliating time,the concentration of the obtained graphene dispersion first increases and then almost unchanged,and long-time exfoliation will make the graphene dispersion unstable and small layer;through choosing different centrifuge speed,we can get the different distribution of the graphene sheet size,and with the centrifugal rotation speed be increased to a certain extent,graphene dispersion concentration almost no longer changes,more stable graphene can be obtained by high rotation speed;high temperature treatment of graphite in N₂ can improve the exfoliation efficiency;The addition of alkali can not improve the exfoliation efficiency in the N-methylpyrrolidone/n-butanol binary solvent system,but the addition of salt can greatly improve the stability of the graphene dispersion.By contrasting the ultrasonic bath and tip-ultrasound as a power source to exfoliate the graphite and it was found that using the ultrasonic cleaner to exfoliate graphite had a better effect.