Design,Preparation And Microwave Absorption Performance Of MoS₂ Based Integrated Nanostructures

With the rapid development of wireless communication and gigahertz electronic devices,electromagnetic pollution has led to a series of problems which disturbs proper operations of electrical equipments and even causes radiative damage to living species.To deal with these problems,searching for high-performance microwave absorbing materials(MAMs)has attracted wide attention.Based on these requirements,a variety of materials have been intensively researched from traditionally MAMs like magnetic metals and ferrites to nanosized dielectric or magnetic materials with different nanostructure.Recently,two-dimensional materials have been adopted for microwave absorption(MA)applications(e.g.graphene,reduced graphene oxide,MoS2,MXenes,etc.).Their high specific surface area with abundant functional groups and defects give rise to polarization loss.The decreased thickness increases conductive paths which improves conductivity loss.Similar efforts have been made in MoS2,which has been proved to be an efficient MA material.However,some problems were found in bare MoS2 including comparatively high density and intrinsic low conductivity loss,which hinder further practical applications for microwave absorption.In this dissertation,we have successfully synthesized MoS2 based integrated nanostructures to deal with the problem which this new MAM have faced.Among our results,the MoS2 based heterostructures not only exhibited excellent microwave absorbing abilities,but also possessed interface-induced controllable electromagnetic wave attenuation performances.The main research results are summarized as follows:1.We developed an efficient method utilizing chemical vapor deposition technique to integrate 2D MoS2,OD Ni nanoparticles with ID CNTs.With the help of Ni nanoparticles as catalysts,CNTs were grown in situ on the surface of MoS2,forming a novel 201-MoS2-Ni-CNTs nanostructure.More importantly,excellent absorption ability was achieved in this 201 nanocomposite.The minimum reflection loss value of 201-MoS2-Ni-CNTs composites reached-50.08 dB.The maximum effective microwave absorption bandwidth(RL<-10 dB)of 6.04 GHz was obtained.The efficient microwave absorption performance originates from 3 aspects:1)Appropriate impedance matching ratio by adjusting the amount of CNTs within the controlled CVD process;2)Strong dielectric loss generated by enhanced conductivity loss(comes from high conductive CNTs)and interfacial polarization loss;3)Large surface area arose from the formation of network-like CNTs.Thus,this method could be extended to other low-dimensional materials,proving to be an efficient and promising strategy for high microwave absorption performance.2.We systematically synthesized 3 different MoS2 based mixed-dimensional van der Waals heterostructures with excellent and controllable MA performances.To our best knowledge,our work is the first systematic study of electromagnetic properties in mixed-dimensional vdWs heterostructures.The optimal reflection loss and effective absorbing bandwidth(reflection loss<-10 dB)are that:(i)for 2-0 type(2D MoS2/OD Ni nanoparticles),-19.7 dB and 2.92 GHz;(ii)for 2-1 type(2D MoS2/ID carbon nanotubes),-47.9 dB and 5.60 GHz;and(iii)for 2-3 type(2D MoS2/3D carbon layers),-69.2 dB and 4.88 GHz.Due to the better-defined interfaces generated in mixed-dimensional van der Waals heterostructures,larger interfacial dipole polarization loss can be reached by means of increasing interfacial contacts between 2D MoS2 and 0D,ID,and 3D building blocks.Accordingly,the microwave absorption performance was enhanced.Thus,our results suggested that the clean interfaces generated in mixed-dimensional vdWs heterostructures provided a better platform to push the investigations in microwave absorption performance.3.We developed a novel approach to fabricate Chevrel phase Mo6S8 without using the second metal(M)which was believed to be necessary in ordinary preparation through leaching M from MxMo6Ss.The novel synthesis method involved only one heating step of exfoliated MoS2 at 900? under Ar/H2 atmosphere.The as-prepared Mo6S8 is purity-phase and of great crystallinity.The electromagnetic properties and microwave attenuation performances of Chevrel phase Mo6S8 and its heterostructures with MoS2 were investigated.Results illustrated that considerable microwave absorptions were achieved in Mo6S8 and Mo6S8/MoS2 hybrid structure which possessed suitable impedance matching ratio and strong dielectric loss.The minimum reflection loss reached-38.1 dB for Mo6S8 and-47.5 dB for Mo6S8/MoS2 heterostructure,which opens a new pathway for Chevrel phase in microwave absorption.