Liquid Exfoliation Of Two-demensional Layered Materials Via High Pressure Homogenization And Their Composites Research With Polymer

In nearly a decade,with the development of graphene and graphene-like two-dimensional material,the demand is also more and more strong.The challenges of how to prepare the 2D materials quickly and easily have become a research emphasis for scientific workers.For the preparation and application of the composite materials of them is also a hot topic in recent years.In this work,we used the basic theory of liquid phase exfoliation and high pressure homogenization methods to prepare the graphene and other 2D material.We also used the water-soluble polymer polyvinyl alcohol as dispersion system to prepare the PVA/WS2 composites.At last,chitosan acetic acid aqueous solution were used to delaminate the h-BN,MoS2 and WS2 and prepared the CS/2D composites.Firstly,we demonstrated a facile and efficient approach for the fabrication of few-layer graphene in DMF with the concentration of 0.084 mg/m L via the assistance of high pressure homogenization(HPH).The concentration of starting materials of graphite,homogeneous pressure and homogeneous time could affect the concentration of graphene.The absorption coefficient of graphene dispersion followed the Lambert–Beer law with an average absorption coefficient of α660nm=3464 m L/(mg·m).Using techniques from UV-Vis,Raman spectroscopy,transmission electron microscopy and atomic force microscopy,we revealed that the graphene dispersion had only few layers(less than 10 nm).Furthermore,we prepared the graphite nanosheets in water or ethanol directly by the method of HPH.During this homogenization,the volume of the sample was expanded by more than ten times.In addition,the higher pressure of the homogenization could achieve a greater volume of the exfoliated graphite nanosheets which is attributed to the fact that the higher pressure can cause more severe exfoliated energy.The result of SEM indicated that the layer of the exfoliated graphite nanosheets was delaminated to few layers.The crystal structure was not changed after homogenization according to the XRD research and the FT-IR spectra indicated the graphite nanosheets were not oxidized during the procedure.Secondly,we could prepare the few layer nanosheets of graphene analogues such as h-BN,MoS2 and WS2 with the same way.We had investigated the exfoliation of the above layered materials using a high pressure homogenizer under 100 MPa for 10 min to give stable dispersions of BNNS in IPA and the MoS2 and WS2 in DMF.The maximum concentration of the three nano dispersions was 0.083 mg/m L,0.068 mg/m L and 0.105 mg/m L.Using techniques from the UV-Vis,Raman spectrum,TEM,HRTEM and AFM,we revealed that the dispersions had only few layers.For the three kinds of graphene-like two-dimensional material,we made a preliminary study in the exfoliating in the pure water and the result showed that they were delaminated in a certain degree.We opened up the door of stripping two-dimensional layer under pure water system and provided a more vivid instance for liquid exfoliation.Thirdly,we demonstrated a facile,rapid and efficient approach to prepare high concentration of graphene(1.45 mg/m L),MoS2(0.0712 mg/m L)and WS2(0.120 mg/m L)nanosheets through the liquid phase exfoliation of bulk materials with the method of high pressure homogenization assisted by carboxyl methyl cellulose(CMC).What’s more,the stability of the three dispersions using CMC exfoliated two-dimensional material had a good performance and they showed a slightly settlement even after three months.Lastly,we used two kinds of water-soluble polymer: polyvinyl alcohol and chitosan solution to exfoliate the graphene-like two-dimensional materials.The concentrations of the two disulfide nanosheets were 0.092 and 0.087 mg/mL,when the exfoliated system was the 10% aqueous solution of PVA.UV-Vis and Raman demonstrated that the two dispersions were the few layer nanosheets in the solution.Then taking the exfoliated WS2 as filler,a series of PVA/WS2 composites showing the pale yellow transparent films were prepared by solution process method.Composite films showed good thermal performance.When 1 wt,% were added in the polymer matrix,the T90% improved 44℃ in the air.Furthermore,the three kinds of characteristic temperature of T10%、T50% and T90% had obvious ascension in the N2.The main reason may be the physical barrier of the 2D nanosheets and the strong interaction force between the S atom of exfoliated 2D nanosheets and polymer chain also could slow the thermal decomposition.Similarly,we used the chitosan solution exfoliated h-BN,MoS2 and WS2 with the concentration of 3.95,0.362 and 0.243 mg/m L respectively.The colors of the three composites film were milky white,gray and pale yellow.The three kinds of 2D material in chitosan solution were not completely exfoliated in composite material system which was proved by the XRD and Raman.Thermal performance of composites was improved.When 1 wt,% were added in the polymer matrix,the T50% of them wereimproved 44.2℃,35.5℃ and 40.9℃.