Preparation And Properties Of MOF-Derived Magnetic/Carbon Composed Electromagnetic Wave Absorbing Materials

Electromagnetic wave radiation generated by electronic devices not only obstructs normal communication,but also deteriorates the human living environment.By converting unwanted electromagnetic energy into heat or other forms of energy,electromagnetic wave absorbing materials eliminate electromagnetic radiation.The ideal electromagnetic wave absorbing material should have the characteristics of light weight,strong absorption capacity,wide absorption band and thin matching thickness.Among the many widely studied electromagnetic wave absorbing materials,MOF-derived magnetic/carbon composite absorbers show great potential for electromagnetic wave absorbing applications due to their combination of magnetic and dielectric losses,as well as their low density,large specific surface area,high porosity and structural tunability.However,the absorption bands of many composite absorbing materials are mostly distributed in the high frequency band（8-18 GHz）,which cannot be satisfied for absorption of the low frequency band（2-8 GHz）involved in 5G networks.Meanwhile,the types of MOF precursors used for the derivative synthesis of magnetic/carbon matrix composites are limited.The development of MOF precursors with various structural designs is a tackle area for the preparation of composite electromagnetic wave absorbing materials.Base on the above,this work designs and synthesizes magnetic/carbon materials derived from mono-or bimetallic Ni-based MOFs and investigates the effects of components,microstructure and charge distribution on their electromagnetic wave absorption performance and a series of high-performance electromagnetic wave absorbing materials with excellent impedance matching and attenuation capabilities are obtained.The main contents are as follows:1,Using low-cost hexamethylenetetramine（HMT）as a ligand,Ni-modified three-dimensional nitrogen-doped porous carbon foam（Ni/NPC）was obtained through coordination assembly and calcination process.The prepared composite material Ni/NPC has a hierarchical porous structure,a large specific surface area,and a high content of heteroatom doping.These excellent structural features are beneficial to increase the effective absorption bandwidth.By changing the carbonization temperature,the microstructure of the material such as the size of metal particles,chemical valence state,degree of graphitization,and specific surface area can be effectively adjusted,which can effectively regulate the dielectric loss,ferromagnetic loss,and conductive loss,and optimize impedance matching.The composite material（Ni/NPC-600）prepared at 600℃exhibited the best absorption performance.At a frequency of 9.1 GHz（X-band）and a thickness of 3.11 mm,the minimum reflection loss was-53.0 d B.With the thickness of 2.50 mm,the effective absorption bandwidth（EAB）could reach 8.61 GHz,covering the entire Ku-band and most of the X-band.This work provides a valuable method for preparing broadband and highly efficient electromagnetic wave absorbing materials.2.A three-dimensional carbon nano sponge（Ni Zn/C）embedded with magnetic Ni and dielectric Ni₃Zn C_0.7 was synthesized via coordination assembly of bimetallic ions of Ni²⁺and Zn²⁺with HMT,followed by thermal decomposition.By adjusting the ratio of binary metal ions,the charge distribution,proportion,interface/dipole polarization of dielectric/magnetic materials can be regulated,thereby achieving controllable strong absorption performance in different frequency bands.Among them,the composite Ni Zn/C-7 exhibits excellent electromagnetic wave absorption performance from S-band to Ku-band.A minimum reflection loss of-52.5 d B is obtained with a thickness of 3.95 mm and a frequency of 5.1 GHz（C-band）.A minimum reflection loss of-33.7d B is achieved at a thickness of 5.00 mm and a frequency of 3.9 GHz（S-band）.The effective absorption bandwidth（EAB）reaches 4.08 GHz at a thickness of 1.44 mm.This work provides a reference strategy for solving the low-frequency electromagnetic pollution generated by 5G signals.