Preparation And Microwave Absorption Properties Of Two-dimensional Ti₂CT_X MXene And Its Composites

The development of wireless communication technology in recent years,has diverted the social economic interest into the application of electromagnetic wave in various fields.However,a series of problems such as electromagnetic information leakage,electromagnetic environment pollution,signal crosstalk and electromagnetic interference generated in the application process have seriously damaged the safety of equipment,its operation and human health as well.In order to solve these problems,it is urgent to develop absorbent materials with better microwave absorption performance and lighter weight.The new two-dimensional MXene material has a stable layered structure,high conductivity and abundant surface functional groups.It has a great prospect in the field of microwave absorption,but there are still problems such as poor impedance matching,effective band width and low reflection loss intensity.Therefore,the wave-absorbing performance of the composite material can be improved by combining with new wave-absorbing materials.Ti₂CT_x,which belongs to the MXene family,has a thinner crystal thickness,a larger specific surface area,and a lower density,showing a promising future in the field of lightweight microwave absorbent materials.It can be combined with MoS₂,that also possess the characteristics of light weight and excellent wave-absorbing performance.Since,through the synergistic effect of heterogeneous structure,the impedance matching can be optimized to enhance the dissipation of incident microwave,forming the Ti₂CT_x and MoS₂ composite materials with characteristics of"thin,light,wide and strong".The main contents and research results are as follows:（1）The high purity Ti₂AlC material was obtained by the non-pressure sintering method with simple operation and equipment,following the molar ratio of n（Ti C）:n（Ti）:n（Al）=1:1.2:2.2.The raw material was weighed and kept in argon atmosphere at 1300℃for 180min.A more green and safe mixture of HCl and Li F was used as etching agent,and HF was synthesized in situ to etch the self-made Ti₂AlC.Ti₂CT_x material with complete layered structure,complete etching and rich functional groups on the surface was obtained.The microwave response characteristics of Ti₂CT_x were studied at the frequency of 2～18 GHz,concluding that the Ti₂CT_x is a wave-absorbing material with dielectric loss.Because of high conductivity,impedance matching performance was poor,indicating that at the filling ratio of 70 wt%,the RL_min could reach-39.45 d B,with 1.41 mm thickness,and effective bandwidth of 2.10 GHz（13.89～11.79 GHz）.The conductivity loss caused by the laminar structure of Ti₂CT_x material provide the transmission channel.with the generation of dipole polarization by Ti₂CT_x internal defects and surface functional groups.Since,the multiple reflections caused by repeated reflection and scattering of electromagnetic waves between layers.The layered structure of Ti₂CT_x lead to the formation of interlayer polarization.（2）In order to solve the problems of poor impedance matching and narrow effective band width of Ti₂CT_x material,using（NH₄）₆Mo₇O₂₄·4H₂O,CS（NH₂）₂ and Ti₂CT_x as raw materials,the heterogeneous structure of MoS₂/TiO₂/Ti₂CT_x composite was prepared by traditional hydrothermal method.Moreover,the effects of different proportions of Ti₂CT_xand MoS₂ on the wave-absorbing properties of the composites were studied.It was concluded that when the mass ratio of MoS₂ and Ti₂CT_x was 1:2,the composites with excellent wave-absorbing properties were obtained.When the filling ratio of MoS₂/TiO₂/Ti₂CT_x（MoS₂:Ti₂CT_x=1:2）composite was 70 wt%,the minimum reflection loss value of-54.70 d B was obtained at 7.59 GHz,with the corresponding thickness of 3.39mm,and the effective bandwidth of 2.28 GHz（8.74～6.36 GHz）.When the thickness is adjusted to2 mm,the effective bandwidth can be expanded to 4 GHz（15.73～11.73 GHz）.The absorbing mechanism of MoS₂/TiO₂/Ti₂CT_x composite was also analyzed.The synergistic effect of MoS₂ phase,TiO₂ phase and Ti₂CT_x phase resulted in the excellent wave-absorbing performance.The excellent absorbing performance of MoS₂/TiO₂/Ti₂CT_x composite was mainly derived from two aspects:On the one hand,the optimization of impedance matching enables more electromagnetic waves to enter the material;On the other hand,the electromagnetic wave is dissipated by the material through multiple reflection,polarization loss and conductance loss.（3）In order to solve the shortcomings of traditional hydrothermal method,such as low efficiency and small yield,as well as the large amount of TiO₂ produced by oxidation of Ti₂CT_x during the reaction process affecting the microwave absorption performance,Ti₂CT_xand MoS₂ composites were prepared by microwave solvothermal method.The heterogeneous MoS₂/Ti₂CT_x composites were successfully prepared by mixing Ti₂CT_x and MoS₂ in different proportions,heating with microwave reaction device,using polyethylene glycol 200 as reaction solvent and holding at 200℃for 30 min.In this paper,the phase composition,surface morphology and microwave absorption properties of the composites were investigated.MoS₂ of MoS₂/Ti₂CT_x composite grows uniformly on the Ti₂CT_x layer,and the Ti₂CT_x matrix has no obvious oxidation state,which is due to two advantages:One is that microwave heating has high efficiency,and the product is uniform;The other is that polyethylene glycol is used as the reaction solvent to reduce the reaction boiling point.Through the study and analysis of the electromagnetic parameters of the composites,it was concluded that RLmin can reach-53.26 d B（frequency 15.5 GHz）and EAB up to 4.11 GHz（15.85～12.84 GHz,12.28～11.18 GHz）at the thickness of 3.14mm microwave,using hydrothermal preparation of MoS₂/Ti₂CT_x（MoS₂:Ti₂CT_x=8:1）at the filling ratio of 70 wt%,thus indicating the characteristics of light,thin and strong microwave absorbing material.The wave-absorbing mechanism of MoS₂/Ti₂CT_x composite was also analyzed.Different from the hydrothermal synthesis of MoS₂/TiO₂/Ti₂CT_x composites,MoS₂/Ti₂CT_x composites mainly rely on the synergistic action of MoS₂ phase and Ti₂CT_x phase to achieve excellent wave absorption performance.