Research On Purification And Functional Modification Of Microcrystalline Graphite

The study of purification and functional modification processing technology of microcrystalline graphite from Chenzhou,Hunan Province was contained in this paper.On the basis of the mineralogical characteristics,high-purity microcrystalline graphite and high-purity microcrystalline graphene oxide?GO?aresimultaneouslyobtainedbythemeansof oxidation-centrifugation.By using purified GO as the precursor,nitrogen-doped and PEI-grafted microcrystalline were respectively prepared by hydrothermal method and sol-gel method,with NH₃·H₂O and Polyethylenimine?PEI?as nitrogen sources and organic modifiers,respectively.The effects of various variables on the purification and functionalization of microcrystalline graphene oxide were carefully investigated.The fixed carbon content,volatile matter and ash of purification samples were all tested according to GB/T 3521-2008.Besides,SEM?FT-IR?XPS?Surface Tension and Electrochemical Workstation,etc.were used to analyse the morphology features,crystal layer structure,supercapacitive performance and oil-water separation performance of the purified and modified products,so as to confirm optimal purification and modification process conditions and reveal the purification mechanism and structural changes in the modification process,simultaneously.The oxidation-centrifugation purification technology was studied with the microcrystalline graphite ore used as raw material,of which the fixed carbon content is 80.28%.Quartz in the raw ore is mostly embedded in fine veined,a small amount is embedded like small granules,and the size is quite fine.When grinding fineness reaches 200 mesh,high monomer dissociation degree still cannot be achieved.The oxidation process plays a role of chemical dissociation.The greater the amount of oxidant used,the higher the degree of monomer dissociation.LTGO-4 has the largest monomer cleavage rate,with a median particle size of 5.17?m.Centrifugation can remove the impurities dissociated from the oxidation process,and the centrifugal speed has a great influence on the purification effect and the purification yield.The best purification result of TCGO-4,the fixed carbon content is 98.8%,and the yield is 52.78%.The product obtained by this method not only maintains high purity,but also obtains finely dispersed.The microcrystalline graphene oxide,which contains oxygen functional groups such as carboxyl group,hydroxyl group and epoxy in the structure,can be used as a raw material for subsequent functional modification.The study of nitrogen doping modification processing technology was conducted with the nitrogen as nitrogen source and purified microcrystalline graphene oxide as raw material.The p H of the system has a direct relationship with the amount of NH₃·H₂O added.The p H value affects the dispersibility of the microcrystalline graphene oxide,while the amount of nitrogen source affects the nitrogen doping effect.The r NG12 has the best nitrogen doping effect.The reaction temperature plays an important role in the nitrogen doping process.Nitrogen-doped microcrystalline graphene could not be obtained at low temperature,and the samples after the reaction has different microstructures at different temperatures.The r NG12-170 has the best nitrogen-doping effect,and the microstructure exhibits a porous network with a large specific surface area.The reaction time has a great influence on the nitrogen doping rate,the nitrogen atom doping type and the microstructur e of the product.The r NG12-170-10 has a maximum nitrogen content of 11.9%,of which the highest pyridine nitrogen content is 58.69%of the total nitrogen content.The organic functional modification processing technology of GO was studied by sol-gel method with the purified GO as raw material and PEI as organic modifier.The p H of the system has a great influence on the organic functionalization.At low p H,no graft modification products can be formed,the layers combine with the electrostatic force to form large aggregates.When the p H is 10,there are amide bonds in the product.The amount of PEI has a great influence on the connection and overall morphology of the microcrystalline graphene oxide layers.The graphene layers in PEI10-4 samples are mainly covalently bonded,with disordered structures inside the stack and small specific surface area.The reaction temperature plays an important role in organic functionalization.When the reaction temperature is low,the system cannot be converted from a solution to a gel,and the graft modification cannot be performed.In PEI10-4-80,the GO pieces are connected by amide bonds to form a three-dimensional network structure with a large specific surface area and a good graft modification effect.The electrode and film samples were prepared by using r NG12-170-n?n=8,10,12?and PEI/GO as raw materials,and their electrochemical performance and oil-water separation performance were tested.The nitrogen-doped modified graphene r NG12-170-8 and r NG12-170-12 exhibit good double-layer properties,r NG12-170-8 and r NG12-170-10 have larger mass transfer resistance,r NG12-170-10 has the largest specific capacitance and its capacity reaches 231.4 F·g^-1.All of them show good application prospects.The PEI/GO film has a contact angle of 0°with water in the air and exhibits super-hydrophilicity.While in water,the oil droplets have a contact angle o f 153°on the surface of the PEI/GO film,exhibiting super-oleophobicity.Therefore,we can conclude that PEI/GO membrane has super-hydrophilicity and super-oleophobicity.The removal efficiencies of toluene and n-hexane in toluene emulsions and n-hexane emulsions of PEI/GO membranes reached 71.84%and 69.37%,and the fluxes were 588L/m²·h and 138L/m²·h,respectively.Thus,the oil-water separation membrane prepared by PEI modified GO has a good application prospect.The research in this paper has a certain theore tical reference value and production guidance for it provides relevant data support for the purification and functional modification of microcrystalline graphite,and reveals the mechanism of oxidation and centrifugal purification of microcrystalline graph ite,as well.