Research On Fluorescence And Electrochemical Properties Of Low-dimensional Transition Metal Compounds

Zero-dimensional quantum dots have many unique advantages in the fields of solar energy conversion,luminescence,display devices,molecular and cell markers,and biological imaging due to their quantum confining effect,size effect,surface effect and other physical effects.However,because the traditional cadmium-based(II-VI group)and lead-based(Ⅳ-Ⅵ group)quantum dots have heavy metals toxicity.The quantum dots that do not contain heavy metals,non-toxic and more environmentally friendly have been widespread attention in recent years,such as zinc oxide(ZnO)quantum dots and transition metal dichalcogenides(TMDs)quantum dots derived by two-dimensional layered transition metal dichalcogenides become the important target of the study of the scientific research workers.ZnO quantum dots have many advantages,such as a variety of preparation methods,easy access to raw materials and relatively low cost.ZnO quantum dots have rich defect types and two fluorescence emission bands located in the ultraviolet and visible regions,in which the fluorescence emission colors in the visible range include yellow,green,blue and other wavelengths.The usual synthesis methods of TMDs quantum dots can be divided into two categories:Top down and bottom up.The former belongs to the physical method while the latter belongs to the chemical method,and each of them has different advantages and disadvantages,so it is suitable for different fields.In general,TMDs quantum dots are easy to functionalize,have different surface states and a large number of electrochemically active sites,which make TMDs quantum dots have great application potential in the field of LED devices,supercapacitors,and sensors and so on.In this thesis,ZnO quantum dots and various TMDs quantum dots and their composite structures were prepared by simple and feasible synthesis methods.For this purpose,we have designed and pioneered a variety of synthetic methods.For example,by combining organic polymer resin materials with inorganic ZnO quantum dots,multi-color photoluminescence emission of ZnO quantum dots composites in solid state has been successfully realized.The photoluminescence regulation of MoS2 quantum dots with different surface passivation by different solvent was studied.In addition,the possibility of application of WTe2 quantum dots in lithium ion battery was explored.The specific content of each chapter in this thesis is as follows:In the first chapter,the concept and characteristics of quantum dots are systematically introduced,and the fluorescence mechanism and application of ZnO quantum dots are emphatically introduced.Then,the synthetic methods and application of TMDs quantum dots are introduced.Finally,the topic selection background and research content of this paper are briefly summarized.In the second chapter,we summarize the drugs used in the experiment,and then briefly introduces the experimental equipment and instruments.In addition,the experiment and characterization methods are also introduced.In the third chapter,ZnO quantum dots were prepared by sol-gel method and mixed with prepolymer solution of melamine-formaldehyde resin,after thermal curing,solid phosphors powder was obtained by grinding.The polychromatic solid photoluminescence properties and possible polychromatic photoluminescence mechanism of the obtained phosphors were studied by various characterization methods.In addition,the most luminous blue ZnO quantum dot phosphors powder coated with melamine-formaldehyde resin was applied to light-emitting diode devices.The possibility of further practical application of the solid ZnO quantum dot phosphors powder synthesized was preliminary confirmed.The fourth chapter of thesis focuses on MoS2 quantum dots of TMDs quantum dots.MoS2 quantum dots were prepared by a simple top-down ultrasonic crushing assisted hydrothermal/solvothermal method.MoS2 quantum dots passivated with different surface functional groups were obtained by changing the solvent.The photoluminescence characteristics of MoS2 quantum dots passivated by different functional groups were studied through a series of characterization.The photoluminescence regulation mechanism of the electron-sucking functional group/electron-donating functional group on the passivated MoS2 quantum dots was mainly studied and explained.In the chapter five of thesis,the WTe2 quantum dots in TMDs quantum dots and the anode materials of NiSe in lithium ion battery are studied.Fluorescent WTe2 quantum dots were prepared by ultrasonic-assisted solvothermal method,and WTe2 powders were obtained by high temperature solid-state reaction.The nanowire structure was obtained by combining WTe2 quantum dots with Ni containing metal salt by electrospinning process.After the subsequent high temperature selenization process,WTe2 quantum dots doped NiSe/C composite nanowires were obtained.The lithium ion storage properties of WTe2 quantum dots doped NiSe/C nanowires were compared with those of non WTe2 quantum dots doped NiSe/C nanowires,which were used as self-supporting anode materials.The results show that the doping of WTe2 quantum dots can greatly improve the lithium ion storage performance of NiSe/C nanowires,and the possible mechanism of this effect is studied.The sixth chapter gives a summary of the content of this paper,and then analyzes some problems existing in the current work and the possible future research directions.