R Esearch On Improving Microwave Absorption Property Of Porphyra-Derived Porous Carbon And Its Absorbing Mechanism

The electromagnetic radiation has been a threat to human healthand social production,w hich leads to the research of electromagnetic absorbing materials plays an important role in both civilian and military fields.Therefore,great efforts are still on the w ay to obtain thin thickness,light w eight,w ide bandw idth and strong absorption microw ave absorption material.Biomass is abundant resource present around the w orld w hich used as raw materials to derived porous carbon materials have the characteristics of high specific surface area,rich pore structure and good electrical conductivity,especially their unique microstructure,w hich has attracted extensive attention in the field of electromagnetic w ave absorption.In order to improve the impedance matching of biomass-porous carbon materials,porphyra w as used as the carbon source,and the composite w ith MnO ₂,NiCo₂O ₄ and activation temperature w ere used to improve the impedance matching of the materials.The structure,composition and properties of the samples w ere characterized by XRD,Raman,F E SE M,HRTE M,BE T,XPSand VNA,and the absorbing mechanism w ere discussed.The research indicates that:(1)The biomass porous carbon(BPC)w as fabricated via a facile pre-carbonization and subsequent KOH activation-carbonization procedure at 650?using porphyra as carbon precursor.D ue to its high dielectric constant and impedance mismatch,the absorption performance is poor,and the reflection loss(RL)in the range of 2-18 GHzare all higher than-10 d B,due to the poor impedance matching performance due to their high dielectric constant.(2)MnO ₂/BPC composites w as prepared by hydrothermal method using K MnO ₄,MnSO ₄and prepared BPC as raw materials.Rod MnO ₂w ith a degree of about 1?m and a diameter of 200 nm grew on the porous skeleton of BPC.W hen the content of MnO ₂increases from 25 w t%to 35 w t%,the dielectric constant of the composite decreases from 10.56 to 4.11.W hen the mass ratio of MnO ₂to BPC is 30%,the minimum RL value of MnO ₂/BPC composite material can reach-40.16 d B and the effective absorption bandw idth(E AB)is 5.12 GHzw hen the matching thickness is 5.5 mm and the frequency is 2.42 GHz.The enhanced absorbing performance is attributed to the porous structure and the increased interfacial polarization caused by the introduction of Mn O 2.(3)Using Ni(NO₃)₂,Co(NO₃)₂,CH₄N₂O and prepared BPC as raw materials,and cetyltrimethylammonium bromide(CTAB)as surface chemical agent,NiCo₂O₄/BPC composites w ere prepared by hydrothermal method and high temperature calcination?The dielectric constant of the sample decreases w ith the increase of the content of NiO₂O₄.W hen the mass ratio of NiCo₂O₄ to BPC is 10%,the minimum RL value of the sample can reach-43.20 d B w hen the matching thickness of NiCo₂O₄/BPC is 5.5mm and the frequency is 6.24 GHz,and the E AB is 2.64 GHz.The interface polarization caused by abundant interfaces in NiCo₂O₄/BPC composites can effectively improve the impedance matching conditions and enhance the w ave absorption performance of the materials.(4)W hen the activation temperature increases from 650 ? to 800 ?,the pore structure of BPC material becomes more abundant,and the specific surface area of BPC material increases from 1145.42 m2·g-1 to 1376.04 m2·g-1.The biomass porous carbon obtained at 750 ? constituted of three-dimensional honey comb-like pore structure possesses large specific surface area of 1330.59 m2·g-1,w hich are advantageous for the absorption of microw ave.E specially,the optimal reflection loss can obtain-57.75 d B at 9.68 GHzw ith E AB of 7.6 GHzvia the thickness to only 3.5mm.Higher porosity leads to larger specific surface area and more interfaces,w hich enhance the attenuation and absorption of electromagnetic w aves of the material and enhance the w ave absorption performance.The activation temperature has an effect on the graphitization degree,surface morphology and pore structure of the BPC material,w hich can improve the impedance matching of the material,and has a significant impact on the electromagnetic w ave absorption performance.