Preparation Of Cerium-based Composite Materials And Research On Their Microwave Absorption Propertie

With the proliferation of electronic communication devices,it is inevitable that serious electromagnetic（EM）pollution will be generated.Increasingly more prominent than physical hazards,EM interference not only limits the performance of advanced electronic devices and can lead to serious economic losses,but also constrains the development of emerging fields,thus making research into broadband and high attenuation capability electromagnetic wave（EMW）absorbing materials imminent.However,some conventional absorbing materials are generally not capable of solving existing EMW pollution,so the design and preparation of new multi-requirement high-performance absorbing materials has become a major research direction.Cerium dioxide materials are considered to be promising candidates for EMW absorption due to their chemical stability,ease of synthesis,low cost,tunable dielectric properties and the presence of oxygen vacancy defects.However,the impedance mismatch of cerium dioxide materials does not lead to excellent EMW performance.Therefore,we have carried out structural modulation and component optimisation of cerium dioxide materials to improve the impedance matching of cerium-based materials and give them more attenuation loss mechanisms to enhance the absorbing ability of cerium dioxide materials,so that they can better meet the requirements of practical applications.The specific research content and conclusions are as follows:（1）Component optimisation of cerium dioxide materials:Three-dimensional porous carbon materials were successfully prepared using pine towers as a biomass carbon source,the KOH pine tower activation technique and a subsequent high-temperature carbonisation process.A series of Ce O₂/porous carbon materials were then prepared using a simple solvothermal reaction by adjusting the addition of cerium salts.The 3D conductive network formed by the porous carbon improved the EMW loss capability of the cerium-based materials.The results show that the Ce O₂/porous carbon composites display enhanced EMW absorption properties.At a cerium salt content of 0.6 mmol,the composite has a minimum reflection loss(RL_min)of-56.04 d B at a low thickness of 1.9 mm and a maximum effective absorption bandwidth(EAB_max)of 5.28 GHz at a thickness of 2.1 mm.The excellent EMW absorption performance is attributed to the porous carbon conductive framework network,the multi-interface polarisation at the heterogeneous interface and the The excellent EMW absorption performance is attributed to a combination of the porous carbon conducting framework network,multi-interface polarisation at the heterogeneous interface and dipole polarisation due to oxygen vacancy defects caused by the unique structure of Ce O₂.（2）Structural design of cerium dioxide materials:Ni Ce O_x-modified carbon nanotube（CNTs）composites were prepared by hydrothermal methods.By adjusting the addition ratio of nickel and cerium salts,Ni Ce O_x with different morphologies can be formed,and CNTs are introduced in the subsequent synthesis process,which on the one hand can effectively prevent the aggregation of Ni Ce O_x nanosheets,and on the other hand the 3D network formed by the interweaving of CNTs is beneficial to improve the conduction loss.In addition,the heterogeneous interface between CNTs and Ni Ce O_x and within Ni Ce O_xgenerates a large amount of interfacial polarisation when placed in the EM field,and the functional groups such as carboxyl groups generated by the acidification of CNTs and the oxygen vacancy defects of Ce O₂ can act as polarisation centres leading to dipole polarization.Due to the improved impedance matching and the creation of multiple loss mechanisms,the Ni Ce O_x/CNTs composite achieves excellent EMW absorption performance,with a RL_min of-53.2 d B at a matched thickness of only 1.9 mm,and a EAB_maxof 5.04 GHz at a thickness of 2.3 mm.（3）Enrichment of loss mechanisms in Ce O₂ materials with synergistic magnetic and dielectric losses:We report the structural evolution of a synthetic Ce-Co PBA mediated by a solvent at room temperature.By adjusting the solvent ratio,the Ce-Co PBA was gradually transformed from a hexagonal bipyramidal structure to a dendritic structure,followed by high temperature annealing of Ce-Co PBA to prepare porous dendritic Ce O₂/Co@CNT composites.The generation of CNT promotes the generation of conductive networks,while the generation of graphitic carbon introduces a large number of defects as polarisation centres,further compensating for the lack of dielectric loss capability of the cerium-based material.The aggregation of positive and negative charges on both sides of the heterogeneous interfaces gives the material an outstanding interfacial polarisation effect.In addition,the generation of magnetic Co particles also compensates for the lack of magnetic loss capability of cerium-based materials and greatly enriches the loss mechanism of cerium-based materials.As a result,a RL_min of-51.68 d B is achieved at 2.5 mm and an EAB_max of 7.76 GHz can be achieved with the help of the excellent dielectric synergy.