Preparation And Properties Of Lignin-based Conductive Carbon Materials

As a new type of carbon material,biomass conductive carbon has attracted extensive attention in recent years because of its excellent conductive properties and environmental protection properties.Biomass conductive carbon materials have the characteristics of high conductivity,low resistivity,good electrochemical performance and renewability.The high conductivity is due to the stability of covalent bonds between atoms in carbon materials,resulting in free conduction of electrons.The reason of low resistivity is that the carbon material has a very high electron density,which allows the current to be conducted well.Therefore,biomass conductive carbon materials have wide application prospects in energy,environmental protection,electronic devices and other fields.As a kind of new material with development potential,the excellent performance characteristics of biomass conductive carbon materials provide a broad space for its future development and application,and also provide a new idea for the high value-added utilization of biomass resources.In this paper,the lignin-based conductive carbon materials were prepared by liquid nitrogen freezing-vacuum thawing pretreatment,metal and non-metal catalysis,using enzymolytic lignin extracted from corn straw as raw material.The effects of different carbonization processes on the morphology,elemental composition and conductivity of lignin conductive carbon materials were characterized by SEM,XRD,XPS and infrared spectroscopy,and the prepared porous lignin conductive carbon materials were used as fillers for electromagnetic shielding materials to test their electromagnetic shielding properties.The main contents were as follows:(1)In order to solve the problem of low conductivity of carbon materials prepared under high temperature carbonization due to lignin structure,a new process of liquid nitrogen freezing and vacuum thawing for enzymatic hydrolysis of lignin was used to prepare lignin carbon materials(PLC)with high conductivity by high temperature carbonization.The effects of different carbonization temperature,carbonization holding time and liquid nitrogen freezing and vacuum thawing for lignin pretreatment time on the electrical conductivity of lignin carbon materials were investigated.When the pyrolysis temperature was 1000℃ and the carbonization time was 1h,the conductivity of lignin based carbon materials prepared by high temperature carbonization after liquid nitrogen freezing and vacuum thawing pretreatment could reach 8.93S/cm.With the increase of carbonization holding time,the order degree of lignin-based carbon materials decreased,and the conductivity and carbon materials yield decreased simultaneously.(2)In order to improve the conductivity of lignin conductive carbon materials.The conductive carbon PLC-Y-X(Y was a different kind of transition metal;X was the mass ratio)was prepared by using liquid nitrogen freezing-vacuum thawing pretreated enzymolysis lignin as raw material and transition metal(Fe,Co,Ni)as catalyst.The effects of transition metal types and mixed mass ratio with the enzymylated lignin on the structure,the conductivity and elemental composition of lignin conductive carbon materials were investigated.The Fe,Co and Ni could improve the conductivity of carbon materials at low doping ratio,and Fe had the best catalytic effect.The PLC-Fe-X was amorphous carbon,mainly containing C,O elements and a small amount of N elements.When the mass ratio of Fe-based catalyst to lignin was 2:5,the conductivity of lignin conductive carbon reached 13.89 S/cm,showing good conductivity.(3)In order to improve the conductivity and comprehensive properties of lignin conductive carbon,the PLC-Y/Z-X conductive carbon materiasl were prepared by introducing non-metallic elements(N,S,B)(Y was the type of metal elements,Z was the type of non-metallic element,X was the mass ratio).The effects that the types of nonmetallic elements and the mixed mass ratio of lignin had on the micromorphology,element composition and conductivity of lignin conductive carbon materials were systematically studied.The introduction of N element could effectively improve the conductivity of conductive carbon,and with the increase of the amount of N-based catalyst,the conductivity of the material was improved.When the mass ratio of N to raw material was 2:5,the conductivity of lignin conductive carbon was the highest,reaching 18.86 S /cm,showing good conductive property.Coaxial method was used to test the electromagnetic shielding properties of conductive carbon materials.With the gradual increase of the mass fraction of conductive carbon,the electromagnetic shielding properties of the materials would be improved.The mass fraction of conductive carbon was 70%,which could reach a maximum value of about 37 d B in Ku band,and met the requirements of common instruments for electromagnetic shielding materials.