Research On Preparation And Properties Of Reduced Graphene Oxide-based Absorbing Materials

Reduced graphene oxide（rGO）has unique two-dimensional layered structure,strong structural designability,excellent dielectric properties,oxidation resistance and corrosion resistance,and is often used in electronic components,batteries,sensors,capacitors,aerospace and other fields,especially in the field of electromagnetic wave absorption.However,rGO itself is prone to lamination,which seriously affects its performance,and it can not meet the high requirements of"strong absorption,light weight,thin coating and wide frequency band"for electromagnetic wave absorbing materials when it is used as an electrically lossy conductive filler alone.Therefore,it is usually modified by physical coating or chemical synthesis,such as designing multi-dimensional heterostructure,combining magnetic loss elements and designing three-dimensional electromagnetic wave absorbing materials of magnetic metal organic frame（MOFs）to increase dielectric loss,magnetic loss and interfacial polarization loss to meet the high requirements of rail transit,military and aerospace fields.However,when electromagnetic equipment is working,it is easy to cause fire hazards due to heat accumulation,which seriously threatens the normal operation of equipment and the safety of people’s lives and property.Based on this,this paper innovatively modified and reduced graphene oxide（GO）by one-pot method and self-assembly method,and prepared a series of high-performance rGO-based microwave-absorbing composites.Through microstructure design,the high-efficiency absorption of electromagnetic waves and the regulation of flame retardancy were realized,and the structure-activity relationship of material composition-structure-performance was found out,and the main research contents and results were as follows:（1）In order to design multi-dimensional heterostructure to increase interface loss or multiple reflection,carboxyl one-dimensional carbon nanotubes and two-dimensional MXene were bonded with oxygen-rich functional groups on the surface of GO by hydrogen bonding,and then graphene oxide foam（F-rGO）was reduced by hydrazine treatment,and a multi-dimensional heterostructure microwave absorber（CNT-MXene-F-rGO）was successfully prepared.The results show that when only 25wt%CNT-MXene-F-rGO is added to the paraffin matrix,the maximum reflection loss（RL）at 10.3GHz is-57.6d B and EAB is 3.3GHz,which meets the high requirements of"light weight,wide frequency and high efficiency"of electromagnetic wave absorbing materials.The microwave absorption mechanism shows that the interface polarization loss caused by multi-dimensional heterostructure,Maxwell-wagner（MWS）effect of phase difference caused by double hydrogen bonding network structure and conductive loss caused by high conductivity of carbon materials all work together to improve the electromagnetic wave absorption efficiency of CNT-MXene-F-rGO composites.In addition,the combustion behavior of CNT-MXene-F-rGO was also studied.When 10 wt%CNT-MXene-F-rGO was added to epoxy resin（EP）,the heat release amount（HRC）and peak heat release rate（PHRR）of EP composites decreased by 53.0%and 40.3%,respectively,showing excellent flame retardancy.（2）In order to further improve the absorbing rate of rGO-based absorbing materials,the interface polarization,impedance matching and magnetic loss capacity are increased by combining magnetic loss structures on the surface of rGO.RGO heterostructures（including zero-dimensional magnetic nanoparticles and two-dimensional RGO）containing Co,Ni and Fe OOH（100nm）were synthesized by coordination.The results show that in the paraffin ring with a content of only 20wt%and a thickness of 3.5mm,the RL value reaches the lowest-51.6d B,and the EAB exceeds 1GHz,thus achieving the purpose of high-efficiency electromagnetic wave absorption.The microwave absorption mechanism shows that excellent impedance matching and moderate dielectric weak magnetic loss in heterostructure are beneficial to improve its electromagnetic wave absorption efficiency.Subsequently,it was found that when the addition of CNFO@rGO was only 10wt%,its peak heat release（PHRR）and heat release rate（HRC）decreased by55.5%and 55.1%,which had excellent flame retardant effect.（3）In order to further improve the absorbing efficiency,a simple one-pot method was used to reduce graphene oxide in situ and grow a magnetic metal-organic framework（Fe-MOF）on the surface by solvothermal method.The results show that when 25 wt%Fe-MOF-rGO is added into paraffin matrix,the minimum RL value reaches-43.6d B and EAB exceeds 5.0GHz when the thickness is 2 mm,which further meets the goals of high efficiency,light weight and wide frequency band.According to the dielectric loss,magnetization loss and excellent resistance matching results,it is concluded that the electromagnetic absorption performance is determined by the conduction loss（excellent conductivity of rGO）,magnetic loss（magnetic resonance of Fe nanoparticles）and interfacial polarization loss（heterostructure of two-dimensional rGO and three-dimensional Fe-MOF）of Fe-MOF.In addition,when the addition of Fe-MOF-rGO was10wt%,the HRC and PHRR of EP decreased by 42.1%and 42.3%respectively,showing good flame retardancy.（4）Based on the above work,a bimetallic MOFs is constructed to study the influence of magnetic medium and three-dimensional structure on the microwave absorbing performance.The CNT-rGO-Co/Ni-MOF composite absorbing material was successfully prepared by constructing hydrogen bond self-assembly between carboxylated carbon nanotubes（CNT）and GO,then easily loading magnetic metal ions(Co²⁺,Ni²⁺)on the surface of GO,and coordinating with diaminoterephthalic acid.The results show that when only 25wt%CNT-rGO-Co/Ni-MOF is added to the paraffin matrix,the maximum RL value at 16.4GHz is-43.0d B,and EAB exceeds 4.0GHz,which meets the high requirements of light,broadband and efficient electromagnetic wave materials.The microwave absorption mechanism shows that the multi-interface polarization loss caused by multi-dimensional heterostructure,the resistance loss caused by excellent conductive network and the magnetic medium loss are the keys to the excellent electromagnetic wave absorption performance of CNT-rGO-Co/Ni-MOF composites.In addition,the combustion behavior of CNT-rGO-Co/Ni-MOF was also studied.When the mass fraction of CNT-rGO-Co/Ni-MOF was 10wt%,the HRC and PHRR of EP decreased by 59.2%and 52.6%,respectively,showing excellent flame retardancy.