Fabrication And Properties Of Lightweight And Multifunctional Porous Carbon Materials

The porous carbon material is a three-dimensional porous carbon material composed of a carbon matrix material,and has many advantages such as low density,large specific surface area and good biocompatibility.Therefore,it is excellent in electronic devices,energy storage,environmental protection,and thermal management.However,three-diemsional(3D)carbon sponges still have problems in the process of research and application,such as single function,poor structural strength and unordered microstructures.In this paper,different biomass materials and graphene were studied as precursors and templates for the preparation of carbon materials.Three-dimensional carbon sponges were prepared by controlling the microstructure effectively,and the macroscopic mechanical properties and functional properties of the materials were achieved.The systematic study of the mechanical,thermal and electromagnetic properties of bulk materials has laid a solid theoretical foundation for its further application in related fields.The main contents of this paper are as follows:The starch was used as the carbon source,through the environment-friendly "fermentation method",the starch motifs were constructed into three-dimensional macroscopic precursors with porous structure.Through the continuous temperature field control,three-dimensional carbon sponge with adjustable pore structure was obtained.The three-dimensional carbon sponge consists of amorphous carbons obtained by carbonization of starch in the form of chemical bonds to form a porous wall.The morphology and pore size of the pore structure are controlled through the regulation of the yeast content,the water content,and the proportion of starch in the "fermentation" process,so that the sponge structure and function are integrated.Specimens with different porosities have different specific surface area,the maximum specific surface area can reach 988 m2/g.When the density is 0.27 g/cm3,the compressive strength is 3.68 MPa,the specific compressive strength is 13.49 MPa?cm3?g-1 and the compressive modulus is 121.92 MPa.Due to its rich porous structure,the carbon monolith can effectively block the heat flow.The thermal conductivity is only 0.06 W?m-1?K-1 at a density of 0.08 g/cm3.The unique porous structure of the carbon sponge also gives it excellent electromagnetic shielding and sound absorption properties.When the thickness is 5 mm,the electromagnetic shielding effectiveness reaches 17.2 d B.We also designed another carbon sponge with the carbonized lignin and cellulose as a three-dimensional framework prepared by direct carbonization.The composite carbon sponge is a three-dimensional structure(wood)composed of lignin and cellulose as a template,which is immersed in a urea solution and dried,and then the surface of the composite sponge was covered with nitrogen-doped graphene sheets through a high-temperature carbonization reaction.The composite sponge has a remarkable anisotropic pore structure and thus exhibits corresponding anisotropic characteristics in terms of mechanics and heat transfer.When the density is 0.148 g/cm3,the lateral compressive strength of the composite sponge is 0.86 MPa and the crush strength is 3.3 MPa.When the density is 0.127 g/cm3,the radial thermal conductivity is 0.088 W?m-1?K-1,the axial thermal conductivity is 0.135 W?m-1?K-1.Meanwhile,the excellent conductivity,anisotropic pores and the of nitrogen-doped graphene sheets,making it high performance in the field of electromagnetic shielding.When the thickness of the sponge is only 1.5 mm,the mean value of the electromagnetic shielding effectiveness in the X band is close to 40 d B,and the highest value can be 60 d B.Also,the specific electromagnetic shielding effectiveness is 465.1 d B?cm3?g-1.Finally,we learned from nature and inspired from the honeycomb structure.The honeycomb structure made up with aramid paper was used as the template and the graphene oxide solution was as a raw material.Then the specimen was prepared by a following carbonization and freezing drying process.After that,a carbon monolith with a periodic cell structure in the horizontal direction,and a unique laminated graphene foam structure perpendicular to the honeycomb wall in the cell was obtained.When the density of the composite sponge is only 0.061 g/cm3,the crush strength reaches 2.1 MPa,and the specific compressive strength reaches 34.4 MPa?g-1?cm3,which is much larger than the reported graphene sponge.At a density of 0.041 g/cm3,the thermal conductivity is only 0.045 W?m-1?K-1.The unique structure and material properties of the composite sponge also offer an excellent electromagnetic shielding effectiveness.When t the density is 0.061 g/cm3,the mean value of electromagnetic shielding effectiveness reached 40 d B.Also,the specific electromagnetic shielding effectiveness is 655.7 d B?cm3?g-1,this value is much higher than that value of most reported shielding materials.