| Graphene is a kind of 2D material with only one-carbon-atom-thick and has gained the reputation for its thin,tough and flexible flims.Graphene sheets possesse unique carrier transport properties,ultra-high specific surface area,remarkable electrical conductivity,ultra high transparency,exellent thermal conductivity and strong mechanical strength.These specific characteristics make it a new superstar in material science and condensed matter physics.The outstanding property of graphene has aroused tremendous research enthusiasm in most science fields in the past few years,no matter for theoretic advances or practical applications.Unfortunately,achieving the mass production of low cost,defect-free and pure graphene still remains a tremendous challenge.Therefore,developing a low-cost yet scalable and high financial benefit route to realize its mass production is of great significance for both fundamental research and application.In this thesis,three different preparation methods were adopted to exfoliate graphite into pristine graphene and finally realized the low cost and mass production via optimizing experiment methods and processes.We also systematically studied the structures,properties as well as potential applications of the as-prepared graphene.The main contents and results of this thesis were listed as follow:1.The chemically modified water-soluble polymer containing sulphonate groups was used as a degradable alternative intercalator for the exfoliation of graphite,which generated noncovalent?–?stacking interactions with graphite under ultrasonic conditions,and consequently exfoliated graphite into few-layered graphene sheets.Moreover,this intercalator could be fully removed through chemical degradation with HOAc or alkali,which will not destroy the electric strcture of the graphene sheets.The micro morphology of the graphene sheets was characterized by transmission electron microscopy?TEM?,atomic force microscopy?AFM?and scanning electron microscopy?SEM?.The results confirmed that our as-prepared graphene sheets are few-layerd and transparent and have wrinkled and folded structures,more typically,these graphene sheets were extremely thinwith the thickness of approximately 1nm.XRD and Raman spectrum were also carried out to further convince that the graphene sheets processed few-layered structures and less defect density.Besides that,our method is simple and the solvent system is eco-friendly,the resulting graphene ethanol dispersion waskept stable over 2 months.The production rate of graphene could be as high as 6 wt.%,while the concentration of the resulting graphene could reach 1.5g/h,which is singnificantly higher than other liquld-phase exfoliation.The as–prepared graphene/polyvinyllidene fluoride?PVDF?composites also showed a high electrical conductivity and a low percolation threshold value of 0.1 vol.%.2.A surfactant-free binary solvent system?DMF/NBA?was used to exfoliate graphite into graphene under sonication and gentle mechanical stirring.We further comfirmed that these graphene sheets are single-layerd though micro morphology characteristic.Moreover,by studying the mechanism of exfoliate graphite into graphene,we concluded that the formation of hydrogen bond system can greatly affect the exfoliation efficiency.The experiment results demonstrate that the hydrogen bond system formed when DMF/NBA are at the mole ratio of 1:3,and pristine few-layer graphene dispersion with the concentration of 6.5 mg/mL is obtained.when the DMF/Glycerol mole ratio is 1:2,there are also hydrogen bonds between DMF and Glycerol molecules and the concentration of graphene dispersion is 7.5 mg/mL,which prove that exfoliation efficiency can be improved by hydrogen bond and the NMP/NBA hydrogen bond system can also improve production rate under the shear force(104 s-1).The DMF/NBA graphene dispersion is highly stable without the observation of precipitation for at least 9 months.We also summarized the optimum technological parameter:stirring rate:120 rpm;ultrasonic power 5W/mL and centrifuging for 30 minutes at 4000 rpm,under which the production rate can be as high as 9.5g/h.More significantly,we also demonstrated that the desposited part can be recycled,thus prividing a potential approach to meet the demands of industry-level production Finally,we demonstrated that the binary solvent systems of NMP/NBA can also be suitable for the exfoliation of BN and MoS2,which contributing an effective approach to the exfoliation and application of two-dimensional materials.3.We prepared conductive graphene thin films via vacuum filtration,which exhibited an average electrical conductivity of 19,000 S/m,and the highest value reached 27,000 S/m.Such high conductivity behaviour was attribute to the entire structure and less defect of the as-preared graphene.The composites of as-prepared graphene with polyvinyllidene fluoride?PVDF?obtained by hot-press also show a high electrical conductivity and a low percolation threshold value of 0.04 vol.%,Such a low percolation threshold for a graphene/PVDF composites is evidently due to the extremely high specific surface area of the graphene sheets and their excellent homogeneous dispersion in the composites,which is much lower than previously reported.Such pristine few-layer graphene was further used as the electrode of supercapacitor,and showed high capacitance of 600 F/g at the current density of 0.4A/g.TEM images illustrate that the graphene present a large specific surface area ca.900 m2/g,which contribute to the high capacitance as mentioned above.4.We demonstrate that glycerol can function as dispersing agent of graphene and assist stripping agent A to exploiate graphite in binary solvent system.The stripping agent A/glycerol system was usedto exploiate graphite.The excellent exfoliated disperation and eco-friendly system consist of stripping agent A/glycerol?A/G?can function as an efficient approach to high-quality,less defect few-layer graphene at yields of 12.5 wt%or even higher.Moreover,the graphene dispersion remains highly stable in stripping agent A/glycerol dispersion for over 10 months.As clearly shown in HR-TEM and AFM images,few-layered graphene were well exfoliated while the ratio of single-layered graphene was 55%,indicating the effective exfoliation.According to X-ray photoelectron spectroscopy?XPS?and EDS,the as-prepared graphene mainly consist of sp2 bond carbon atoms,which was consistent with UV-vis spectroscopy.Raman characterisation further showed that the exfoliated graphene sheets exhibited good integrity,and no new defects were introduced under proposed stirring speed,which consquently confirmed that unoxidized,less defect and integrated pristine graphene was obtained by this useful method.5.The mechanical property of as-prepared graphene/polyethylene terephthalate composites has been tested after melt mixing and plastics shaping.We found the strength and toughness has reached the best when adding 0.06 wt%graphene to polyethylene terephthalate?PET?.The graphene/PVDF composites show a low percolation threshold value of 0.05 vol.%.Their thermal conductivity increase from 0.1420 W/mK to 1.051 W/mK when the volume ratio of graphene increase from 0 vol.%to 4.5 vol.%.The thermal ressistance increasement is much less compared with thermal conductivity,owing to the high thermal conductivity,low internal thermal resistance and huge specific surface area of graphene.When calculated by the Brunauer–Emmett–Teller model,the specic surface area of as-prepared graphene is as high as 900 m2 g-1.We further use the as-prepared graphene as the electrode of supercapacitor and Li-ions battery.The results showed a high capacitance of 400 F/g at the high density of 2 A/g,and 208 F/g at a high discharge rate of 40 A/g.For Li-ions battery,the discharge specific capacity is 475mAh g-1 after 100 cycles at 0.1 C and has a low internal resistance.That is because the graphene possess a high specific surface area and excellent conductivity which can provide a sufficient electrode–electrolyte interface for accumulation of charges or ions. |
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