Preparation Of Transition Metal Sulfide （MoS₂、WS₂） Nanosheets And Study Of Their Performance

At present,atomic layer thickness of molybdenum disulfide（MoS₂）and（WS₂）nanosheets,due to their special dimension effect,make them of optics,catalysis,energy storage performance significantly,and gradually become a hot spot in the every fields.Their structural characteristics:the band gap increased with atomic layer decreased gradually.In the end,their indirect band gaps convert to a direct band gap.At the same time,atomic layer thickness of nanosheets has high electron mobility,which is advantage to the electron transfer.These structure characteristics make it has the function of optical modulation,optical and electrical catalytic properties,and the energy storage performance.However,researchers have not found the effective stripping preparation method of MoS₂ and WS₂ nanosheets,and the study of the optics,catalysis and energy storage is still in the initial stage.Therefore,in this thesis,we first introduce the background and the main contents of 2D MoS₂ and WS₂ nanosheets in the first chapter;Secondly,in the second chapter,we propose a method for the preparation of two-dimensional MoS₂ and WS₂ nanosheets by weathering method,and study the laser modulation properties of them;in the third chapter,a new method is proposed to prepare MoS₂/G heterostructure,which is used in the optical,catalytic,and energy storage;In the fourth chapter,we mainly talked about how to design a kind of rotary ultrasonic stripping block material based on the principle of ultrasonic theory.The feasibility of this method was demonstrated by the experiments of MoS₂ and WS₂ nanosheets prepared by exfoliation.The universality of the method and the thermal catalytic properties of the films were investigated.In the fifth chapter,we studied the photocatalytic water splitting properties of MoS₂ nanosheets doped with polycrystalline black phosphorus nanosheets;at last,the sixth chapter summarized the full text of the research and innovation,and prospects for the future work.In this paper,the main contents and and conclusions are as follows:1.Inspired by the natural weathering exfoliation of seaside rocks,we propose a"chemical weathering" method for exfoliating monolayer MoS₂ and WS₂ from their bulk counterparts.SEM,TEM,AFM,XRD and other instruments were used to characterize the morphology,structure,lattice and thickness of the prepared samples.In the theory,it is feasible to analyze the block material by weathering stripping.For the first time,it is found that the band gap of MoS₂ and WS₂ nanosheets with sulfur vacancy defects is in accordance with the requirements of laser saturation absorption.At the same time,the laser modulation performance test on MoS₂ and WS₂ nanosheets absorber in solid state lasers.It is the first time to realize the laser mode locking of MoS₂ nanosheets,and the first step is to realize the laser tuning Q and mode locking of WS₂ nanosheets.The experimental results show that the locking effect of WS₂ nanosheets is better than that of MoS₂ nano films.The first step is to realize the femtosecond mode locking of WS₂ nanosheets in solid state lasers after further processing of WS₂ nanosheets.This is a major breakthrough in the application of two-dimensional materials in solid state lasers.2.We use graphene oxide（GO）inserted into the edge of block MoS₂.Through ultrasonic power,monolayer GO is used as a lever to pry MoS₂ block into layered nanosheets.Next,two-dimensional MoS₂/G heterostructure was obtained by the reduction of graphene oxide.This kind of heterostructure is used as a saturable absorber to modulate the laser in a solid state laser.At the same time,the photocatalytic degradation properties of the two dimensional MoS₂/G heterostructure were studied.In addition,the energy storage performance of MoS₂/G as anode material in lithium ion batteries was studied.The experimental results show that the two-dimensional MoS₂/G heterostructure is a very good optical,catalytic and energy storage material.3.Starting from the force analysis of two-dimensional materials ultrasonic stripping,we put forward and designed a kind of rotary ultrasonic stripping two-dimensional material equipment.The experimental results show that the device is effective and practical in the stripping process of two-dimensional materials（MoS₂ and WS₂）.The thickness of the prepared MoS₂ and WS₂ nanosheets was lower than 1 nm.In addition,the stripping method not only for the block of molybdenum disulfide（MoS₂）and two tungsten sulfide（WS₂）,but also can be used for stripping other two-dimensional materials,such as graphite and block six boron nitride（h-BN）,and the yield is up to more than 95%.The experimental results show the universality of this method.4.A catalyst（P/MoS₂）was designed from the composite of MoS₂ nanosheets and polycrystalline black phosphorus nanosheets.First of all,the theoretical study and the preparation of polycrystalline black phosphorus nanosheets by liquid phase method.Secondly,the photocatalytic properties of P/MoS₂ were studied.The experimental results show that the addition of MoS₂ nanosheets into the polycrystalline black phosphorescent catalyst can not only replace the noble metal Pt during photocatalytic hydrogen production.Moreover,the catalyst is free from the bondage of the sacrificial agent,and the catalyst has the well effect of water splitting.