Study On Preparation Of Graphene By Liquid-phase Exfoliation In NMMO Solvent

Graphene,a unique layered carbon material with sp²hybrid,has been widely used in electricity,thermology,mechanics and chemistry due to its some superior physicochemical properties,such as electronic properties,quantum effects,perfect thermal and mechanical properties.In this context,it is a key topic to develop and design an appropriate and efficient preparation strategy for improving graphene performance.Theliquid-phaseexfoliationmethod,insteadoftraditional oxidation-reduction method,became a research hotspot owing to its better preservation of the original structure of graphene,simple process and low cost.On the other hand,traditional organic solvents are sensitive to air and humidity,which pollute the environment and difficult to separate.Therefore,it has been our aim to choose a stable and green organic solvent for the exfoliation of graphite/graphene oxide raw materials.Here,NMMO was selected as the ideal solvent due to its stable structure,environmentally friendly liquid,recycling,and good reduction effect on graphite/graphene oxide.Besides,the large-scale production does not pollute the environment.In this paper,we prepared graphene by a novel technology of liquid-phase exfoliation with N-methylmorpholine-N-oxide?NMMO?as the solvent.Dispersion of graphite oxide was obtained with assistance of ultrasonic treatment.The contents of this paper are as follows:?1?Graphite oxide was performed by improved Hummers method.Graphite oxide reacted with NMMO?H₂O under mechanical stirring in vacuum.Graphene was obtained by water washing and vacuum drying.The insertion of oxygen-containing functional groups in graphite oxidation enlarged the interlayer spacing and promoted subsequent exfoliation.The thickness of the folded region of graphene sheet was 13.3nm after NMMO treatment,showing a random aggregation,thin crumpled structure.The optimal morphology and structure were achieved by the mixture of NMMO and graphite oxide after several dissolution-solidification cycles.The reduction degree of graphene increased.?2?Incompletely oxidized graphite in the above?1?was used as raw material.Dispersion of graphene oxide was obtained with assistance of ultrasonic,and then dispersed into NMMO/H₂O system.The whole reaction process lasted for 6 hours at95°C.To explore the reduction effect of NMMO molecules,NMMO and water were used as liquid-phase exfoliated solvents to exfoliate graphite oxide,respectively.The obtained sample exhibited a very thin layered structure.The thickness of the sheet changed from 143 nm to 77 nm,demonstrating that the exfoliated effect of NMMO was excellent with the assistance of ultrasonic.It was also found that the reduction degree of the sample was better,but slightly weaker than those samples which were mentioned in the above section after several dissolution-curing cycles.?3?The graphene oxide?GO?purchased in Korea was used as raw material.Dispersion of graphene oxide was obtained by ultrasonic-assisted technology and then dispersed into NMMO/H₂O system.Finally,the further exfoliated graphene sheets were obtained with well exfoliation and reduction.The test of thermal stability showed a large loss in the range of 150°C-300°C but the mass loss was only 11%after NMMO treatment.It was found that the more oxygen-containing functional groups on the surface of graphene oxide,the better reduction effect of NMMO,which indicated that NMMO could be effectively inserted into the interlayer of graphene oxide,then the good exfoliated effect was obtained.