Preparation Of 1T-MoS₂ And 1T-WS₂ And Relative Properties

Transition metal disulfide MX2(M=Mo,W;X=S)is a typical two-dimensional material.Several types of crystal strucutres have been observed in these materials,and the common two types are 2H phase and 1T phase.The difference in lattice structure results in distinct physical properties of the two phases.For example,compared to 2H-MoS2 and 2H-WS2,1T-MoS2 and 1T-WS2 has higher conductivity,higher hydrophilicity,and larger interlayer distance.These advantages make it have broad applications such as electrochemical energy storage,catalysis and microwave absorption.However,thermodynamic studies have shown that the 1T phase is a metastable phase and it is difficult to synthesize and stabilize.Therefore,how to obtain a 1T phase MoS2 and WS2,with high stability is remained as a challenge.As a special extreme condition,a high magnetic field can transfer high-intensity energy without contact to the atomic scale of matter,thus affecting the nucleation and growth of materials.Presently,the synthesis and processing of materials under high magnetic fields has gradually become a new important technical route to improve the physical properties of materials.In this dissertation,high magnetic fields are used to realize the phase controlled synthesis of MoS2 and WS2 two-dimensional nanosheets.Stable,high-purity 1T phase MoS2 and WS2 and 1T@2H heterojunction with different 1T phase contents can be obtained,and then the microwave absorption and sodium ion battery performance of MoS2 and WS2 with different crystal phases are studied.The main research contents are as follows:1)Phase modulation induces an increase in WS2 microwave absorption performance.The results show that the introduction of 1T phase can improve the complex permittivity of WS2,and greatly improve the microwave absorption performance of WS2.The maximum microwave absorption intensity of 1T@2H WS2 can reach 47.1 dB when the content is 35 wt%,which is 15 times of the pure 2H phase WS2 The corresponding effective absorption bandwidth is 5.2 GHz(10.7-15.9 GHz).The research results will provide experimental data for the developments of new absorbing materials by phase regulation to improve the microwave absorption properties of materials.2)Preparation of 1T phase WS2 under strong magnetic field and its microwave absorption properties.The results show that pure and high stability 1T phase WS2 two-dimensional nanostructure can be successfully prepared by hydrothermal reaction under high magnetic fields.The pure 1T phase WS2 has a larger complex permittivity and better microwave absorption performance than the 1T@2H WS2.The highest microwave absorption intensity can reach-41 dB when the percentage is 30 wt%,and the corresponding effective absorption bandwidth is 4.2 GHz.The experimental results show that the hydrothermal reaction under magnetic fields can be used as an effective route to achieve metastable phase.The controllable synthesis of 1T phase WS2 further proves that the introduction of 1T phase helps to improve the microwave absorption performance of WS2.3)Controllable synthesis of MoS2 under high magnetic fields and their microwave absorption properties.The results show that the phase-controlled synthesis of MoS2 can be achieved by hydrothermal reaction under high magnetic fields.The 1T@2H planar heterostructure MoS2 with different 1T phase content can be successfully prepared under different magnetic field strengths.Pure and stable 1T phase MoS2 two-dimensional nanostructures could be produced under 9T high magnetic field.Compared with the 2H phase MoS2,the pure 1T phase of MoS2 has a higher complex permittivity and more excellent microwave absorption performance,with a mass percentage of 60 wt%the microwave absorption intensity can reach-53 dB.The above results prove that magnetic field can be used as an effective route to achieve controllable synthesis of metastable 1T phase MoS2,and the microwave absorption performance of MoS2 can be effectively improved by crystal phase modulation.4)Studies on the phase modulation to improve the performance of MoS2 sodium ion batteries.The results show that 1T,MoS2 has excellent electrochemical performance as an anode electrode material for sodium ion batteries,and its specific capacity is 224 mAh g-1 at high current density of 8 A g-1.Electrochemical Impedance Spectroscopy(EIS),Galvanostatic Intermittent Titration Technique(GITT),and Scanning Transmission Electron Microscopy(STEM)measurements prove that the excellent electricity chemical energy is resulted from the enhanced electronic and ionic transport dynamics and stable 1T octahedral coordination.The above results demonstrate that hydrothermal synthesis under magnetic fields can provide a simple and clear way for synthesis of 1T-MX2 materials.