| Graphitic carbon material has excellent physical and chemical characteristics including electronic and thermal conductivity,catalysis,energy storage,leading to its widely application in numerous fields such as energy resources,environmental protection and chemical engineering.Graphitic materials are mainly originated from natural graphite mines which are non-renewable resources with large amount of impurities.Thus,complicated physical and chemical purification is demanded,leading to high cost and heavy environmental pollution for the production of high-performance graphitic materials.Biomass materials have merits such as renewable,high carbon and low impurities containing,and controallable microstructures,making them ideal green candidates for producing graphitic materials.Nowadays,there are still lack of intensive study on the mechanism and precept of the carbonization-graphitization of biomass materials,causing slow progress of exploring biomass-based high-performance graphitic materials.As to this problem,in this work,the carbonization and catalytic graphitization processes of two main composites of biomass materials—cellulose,lignin,were thoroughly investigated,and graphitized products with high crystallinity and electronic conductivity could be obtained.Meanwhile,the mechanism of carbonization-graphitization of cellulose and lignin were intensively investigated;Photocatalyst composite based on cellulose-originated graphitized carbon was further prepared,being beneficial fordeveloping new application fields of biomass-based materials.The main contents are as follows:1.Study on the process and mechanism of carbonization-graphitization of lignocelluloseMicrocrystalline cellulose was taken as the raw material,of which the carbonization and catalytic graphitization under transition metals(Fe,Co,Ni,Mn)processes were investigated.The results showed that carbon microcrystallines were generated after carbonization;Furthermore,with the assistance of the optimal catalyst——Ni,the ratio of high-graphitic areas in the graphitic product was as high as 99.47%.Besides,the product had graphitic degree of62%,crystallinity as high as commercial graphite,annular graphitic structures with more than100 layers,and conductivityover 60 S/cm under pressure 20 MPa.It was discovered that due to the rigidity of the micro structure of carbon,the liquid catalyst particles could move without shackles,which made it easy to transfer rapidly to the ungraphitized areas,leading to the expanding of graphitized areas.This is the mechanism of the forming of graphitic product with excellent properties from cellulose-based char with the assistance of Ni.2.Study on the process and mechanism of carbonization-graphitization of ligninPurified base lignin was chosen as raw material,of which the process and mechanism of carbonization and graphitization were investigated.It was found that lignin melted during pyrolysis,and the product had no obvious carbon microcrystallines.Under the catalysis of Ni,the lignin-based graphitic product had graphitic degree of 36% and electronic conductivity of31 S/cm under pressure of 20 Mpa.The reason might be attributed to the embedding of catalyst particles by carbon,causing graphitizaion occured locally,and instead of large continueous graphitic areas,only a few isolated graphitic areas could be found.The effect of graphitization could be promoted by either increasing reaction temperature or Ni loading amount.Besides,it was observed that both thermal-plastic and thermal-setting phenolic resin had almost the same graphitization effect as lignin,further proved that the structure of lignin molecular was a negative effect for producing high-graphitic carbon materials.3.Study on the preparation of graphitic material from woody biomass materialsCellulose and lignin were mixed together with different weight ratios in order to simulate biomass materials.The graphitization of the simulated biomass materials and some woody biomass materials such as walnut shell and fir sawdust was investigated.The results illustrated that the graphitization effect of either simulated or real biomass materials the products were all between those of the graphitic products from cellulose and lignin.Large amount of obvious graphitic structures with annular shape existed in all biomass-based graphitic products,similar with the cellulose-based product;Cellulose and lignin were respectively extracted from the biomass materials,and the catalytic graphitization processes were also investigated.The results showed that the graphitization effect of extracted celluloses were almost as same as the raw materials,while that of the extracted lignins were similar as commercial base lignin.All the results proved that cellulose played a key role during the graphitization of biomass.4.Application of biomass-based graphitized carbon materials in photocatalysisAs the starting material,cellulose-based graphitized carbon was oxide,and the product with high hydrophilicity was defined as CGO.CGO and Ti O2 were further composited by in-situ deposition in distilled water,and the photocatalyst composite with high reactivity was achieved after heating.The photocatalytic reaction rates for degrading MO and reducing Cr(VI)over CGT were respectively 4.6 and 1.6 times higher than those over commercial Ti O2(P25).It had been concluded that the high photocatalytic reactivity was due to the thermal reduction of CGO to r CGO,during which the graphitic structure could be recovered,being beneficial for the transferring of photo-generated electrons,diminishing the recombination of photo-generated electrons and holes,and promoting their utilization ratios.Except cellulose,none of the composites synthesized from other biomass materials in the same procedure had such high photocatalytic reactivity,further illustrated that cellulose-based graphitized product had the best graphitization effect. |
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