Novel Two-dimensional Mo₂TiC₂T_x-based Composites For Enhanced Microwave Absorption Properties

With the rapid development of technology,electromagnetic wave interference and pollution are becoming prominent issues.There is an increasing demand for new wave-absorbing materials with light weight,wide frequency and strong absorption in the military and civilian fields.Two-dimensional transition metal carbide materials（MXenes）with large specific surface area,abundant chemically active sites and functional groups have shown great potentials for applications as wave-absorbing materials.In this study,a series of MXene-based composite absorbers with"thin,light,wide,and strong"were obtained by adjusting the acid etching conditions,annealing treatment temperature,and the shape of the loaded magnetic material.The related research and results are as follows:（1）The Mo₂Ti Al C₂ ceramic powder was firstly acidly etched by using Li F/HCl or HF.Li F/HCl used as etchant we obtained the porous skeletonized morphology instead of typical layered MXene structure due to excessive etching.In contrast,the etchant of high concentration of HF was benefit in successfully obtaining Mo₂TiC₂T_xMXene,and the pure HF-etched sample S3 has the largest interlayer space and exhibits excellent electromagnetic wave absorption（EMA）performance.The minimum reflection loss(RL_min)value reached-25.39 d B（17.04 GHz）with an effective absorption bandwidth（EAB）of 3.2 GHz at a thickness of 1.6 mm.The mechanism was analyzed as follows:Mo₂TiC₂T_x etched with high HF concentration has abundant functional groups and defects as polarization centers,which can enhance the dielectric loss.This study expands the application of 2D MXene material family in the field of electromagnetic wave absorption.（2）Based on the above research,Mo O₃/Ti O₂/Mo₂TiC₂T_x composites with different oxidation degrees were prepared through annealing treatment.As the temperature increased,it was found a widened Mo₂TiC₂T_x layer spacing and uniform delamination.In addition,Mo O₃ and Ti O₂ oxide spheres with gradually increasing size uniformly distributed between the Mo₂TiC₂T_x layers and on the surface.When the annealing temperature is 300℃,the RL_min value of Mo O₃/Ti O₂/Mo₂TiC₂T_x composite reaches-30.76 d B（2.3 mm）at 10.18 GHz with an EAB of 8.6 GHz（1.8 mm）,which greatly broadens the absorption bandwidth of Mo₂TiC₂T_x.The in-situ introduction of Mo O₃ and Ti O₂ optimizes the impedance matching of Mo₂TiC₂T_x,generates a large number of defects and heterogeneous interfaces,and strengthens the dipole polarization and interfacial polarization behavior,thus enhancing the dielectric loss.（3）The single dielectric loss mechanism of MXene cannot be fully qualified as new wave absorbing materials.In addition,magnetic loss is crucial for the improvement of wave absorption performance.In this section,Ni/Mo₂TiC₂T_xcomposites were prepared by intercalation treatment of multilayer Mo₂TiC₂T_x to obtain delaminated Mo₂TiC₂T_x（d-Mo₂TiC₂T_x）nanosheets,and then Ni/Mo₂TiC₂T_xcomposites were prepared by loading Ni magnetic materials with different morphologies（spherical and flake）on delaminated MXene through the solvent thermal reduction route.It was shown that the abundant functional groups on the MXene surface and the restricted interlayer space could reduce the size of Ni and promote the distribution.In addition,the flower-like Ni-loaded MXene（NM-2）exhibits the optimum absorption performance:the RL_min is-50.36 d B（13.28 GHz）and the EAB is3.04 GHz at a thickness of 1.4 mm.The synergistic effect of dielectric and magnetic losses generated after loading Ni greatly enhances the electromagnetic wave loss capability.In addition,the absorption performance is further enhanced by the proper impedance matching and multiple scattering and reflection.