Bottom-up Synthesis Of Few-layer Graphene Powders And Their Applications

Graphene,as a typical two-dimensional material,has excellent physicochemical properties and shows very broad application prospects,among which powders are an important type of graphene that can be compounded into other materials as special additives to improve the material’s own properties and give more functions in a comprehensive way.In composite materials,the properties of graphene powders are heavily dependent on the structure and synthesis method of graphene powders.At present,various methods for the production of graphene powders such as liquid phase exfoliation（LPE）,chemical redox methods,electrochemical exfoliation and CO2 intercalation exfoliation have been developed.The graphene prepared by these methods still suffers from large differences in the consistency of graphene layers,many defects,and serious clustering of graphene powder,which limit the application of graphene.The ideal graphene preparation method should be low cost,high efficiency,tunable performance,and features such as morphology with few layers of graphene.Therefore,it is important to develop a new graphene powder synthesis route with simple operation,low cost,controllable number of layers,environmentally friendly,and scalable preparation.In this paper we propose a bottom-up strategy for the synthesis of graphene powders by a polymerization-pyrolysis process using bis-amino aromatic compounds as the carbon source and Na Cl microcrystals as the template,which can be scaled up to produce layer less,high quality graphene powders and can effectively achieve in situ doping of heteroatoms in graphene.And the specific applications of this graphene powder in the fields of lubrication and electromagnetic shielding are explored.The main contents are as follows:（1）A general preparation method for graphene powder using diaminoheterocyclic compounds from bottom up:graphene powders were synthesized via pyrolysis of self-polymerized compounds of aromatic molecules with bis-amino groups as carbon sources on Na Cl microcrystals as soluble templates.The key properties of graphene powders prepared by the method including the number of graphene layers,surface area and electronic conductivity can be effectively modulated by adjusting the mass ratio of monomer and Na Cl as well as pyrolysis temperature.As a typical example,graphene powders prepared using m-phenylenediamine as precursor with the various mass ratio of Na Cl at 1500℃process a high specific surface area from150 m²g^-1up to 545 m²g^-1with ignorable microspores,high powder conductivity(up to 1351 S m^-1at 20 MPa)and few numbers of graphene layers.Moreover,the bottom-up synthesis approach can also obtain high quality few layers graphene by using different precursors,and the doping of different elements（ie.,N,S）can be effectively regulated,providing an effective strategy for in-situ synthesis of graphene composites.Based on this,the experimental factors were optimized and the scale up of graphene preparation was achieved.（2）The bottom-up synthesis of graphene powder tribological properties:the graphene powder,mechanical exfoliation graphene,arc discharge method graphene as additives were added to the base lubricant,the preparation of different graphene lubricants,respectively,lubrication performance test,the results show that the prepared graphene powder compared to the other two graphene as additives added to the base oil tribological wear performance has been The results showed that the friction and wear performance of the prepared graphene powder was significantly improved compared with the other two graphene additives added to the base oil,with a 30%reduction in friction coefficient and 40%-48%reduction in wear compared with the base oil.The results indicate that the use of this type of graphene as a lubricant additive can effectively reduce frictional wear.（3）The bottom-up synthesis of the electromagnetic shielding properties of graphene powders:m-phenylenediamine was used as the precursor and sodium chloride as the template,and the precursor-sodium chloride mass ratio was adjusted to 1:60,and graphene powders with different degrees of graphitization were prepared by adjusting the carbonization temperature.The conductivity test revealed that the conductivity of graphene powder increased with the increase of carbonization temperature,and the conductivity was as high as 1400 S m-1 at1500℃,which can be used as an excellent electromagnetic shielding material.Due to the N-doping effect,the free electrons in the surface layer of graphene can easily form carriers under the action of electromagnetic waves and reflect most of the electromagnetic waves.In addition,functional groups such as C-N,C=O and holes act as polarization and scattering centers,and interfacial polarization and dipole polarization loss of electromagnetic waves occur.With only 20%filler,the average effective shielding of electromagnetic waves（8-18GHz）is as high as 86.4 d B,satisfying both civil and military applications.