Preparation And Electromagnetic Properties Of NiFe-LDH Derivative Based Composites

In recent years,layered double hydroxides(LDHs)have attracted much more attention by researchers in the field of electromagnetic wave(EMW)absorbing materials due to their unique lamellar structure and magnetic metal nanoparticles formed on the lamellae after high temperature calcination.Graphene,a delicate two-dimensional crystal with excellent conductivity,large specific surface area and low density,has attracted much attention in the field of absorbing materials.However,the EMW loss mechanisms of the above two materials both have advantages and disadvantages.Here,the new EMW absorbing materials with excellent electromagnetic properties,high absorption efficiency,ultra-wide absorption bandwidth and light weight are obtained by hydrothermal method.The Ni_xFe_y-LDH derivatives named Ni_xFe_y-MO with different relative molar ratios of Ni and Fe were firstly prepared and then compounded with reduced graphene oxide(rGO).After that,Ni/NFO-rGO(NF-rGO)and NiO/NFO@N-rGA(NNGA)were successfully obtained.The EMW absorbing properties of the two composites were systematically investigated.The work not only combines the advantages of the two materials,but also overcomes the shortcomings of graphene’s disadvantage of easy stacking.The specific work is as follows:(1)NiFe-LDH with different Ni and Fe ratios was prepared by hydrothermal method,and then Ni_xFe_y-MO were obtained after annealing.The results show that when the relative molar ratio of Ni is large,the prepared Ni_xFe_y-MO has a rich hierarchical pore structure.When the filling ratio of Ni_xFe_y-MO in paraffin is 50 wt%,the minimum reflection loss(RLmin)of Ni1Fe7-MO is-46.3 d B at 5.1 GHz with the matching thickness of 4.89 mm.The effective absorption bandwidth(EAB)is 3.2 GHz.It can be seen from the analysis that Ni_xFe_y-MO has good magnetic loss capability,but shows impedance mismatch due to poor dielectric loss capability limits its EMW absorbing performance.(2)NiFe-LDH@rGO composites with different amounts of graphene were synthesized by hydrothermal method,and then NF-rGO composites were obtained by high-temperature calcination process.The results show that NF-RGO-3 exhibits excellent EMW absorption property when the concentration of GO solution is 1.125 mg/m L and the filling ratio of NFrGO-3 in paraffin wax is 15 wt%.When the matching thickness is 2.52 mm,the RLmin reaches-57.2 d B at 11.5 GHz,and the EAB is 5.1 GHz.The NF-rGO composites overcomes the defects of the single material to a certain extent and improves the impedance matching characteristics.(3)An ultralight composite(NNGA)formed by flower-like NiFe LDH derivatives(NiO/NFO)and graphene aerogel was prepared by hydrothermal method.Based on DFT,the strongest total Cartesian polarization on the z-axis of N-rGO has been confirmed,demonstrating the importance of nitrogen doping on EMW absorbing properties.The results show that when the molar ratio of NiO/NFO to rGA is 1:2.5 and the filling ratio of NNGA in paraffin is 15 wt%,the RLmin of NNGA-2 is-57.4 d B at 10.6 GHz with the matching thickness is 1.97 mm,and the EAB reaches 6.6 GHz.The three-dimensional porous structure formed by the NNGA composites not only slow down the stacking trend of graphene sheets,but also induces a variety of loss mechanisms,which improves the attenuation and loss of electromagnetic waves.impedance matching characteristics.