The Preparation Of Two-dimensional Transition Metal Dichalcogenides Quantum Dots And Their Photothermal Therapy Application

In recent years, two-dimensional（2D） layered transition metal dichalcogenides（TMDs） have become a hot research foucs, due to their unique physical and chemical properties. When the bulk forms of TMDs are exfoliated to single-layer or few-layer with the lateral dimension less than 10 nm, TMDs nanosheets exhibit novel electronic and optical properties due to quantum confinement effect and become a kind of new zero dimensional nanomaterials, named two-dimensional transition metal chalcogenide quantum dots（2D-TMD QDs）. Although some recent studies have shown their potential applications for catalysts, energy storage, biosensing, bioimaging and treatment, the related researches of 2D-TMD QDs are still very limited in material preparation, properties research and the application exploration.In this master’s thesis, we have expanded the preparation method of the 2D-TMD QDs. We have developed an ultrasonication-assisted liquid exfoliation method for the direct preparation of ultrasmall MSe₂ QDs（M=Mo, W） in aqueous solution and studied their photothermal properties. MoSe₂ QDs have been used as a novel and efficient photothermal therapy（PTT） agent in vitro cellular experiments for the first time. In order to solve some existing problems in Top-Down methods, such as the limitation of the prepared materials and low yield, we have developed an universal colloidal chemical synthesis method for controllable preparation of 2D-TMD QDs. The main contents are described as follows.Chapter 1: We summary the the structure, properties, preparation and applications of 2D-TMD QDs, and illustrate the topic basis, research ideas and research focus of this thesis.Chapter 2: We have developed an ultrasonication-assisted method for the preparation of MSe₂ QDs（M=Mo, W） in aqueous solution. MoSe₂ and WSe₂ quantum dots are prepared by ultrasonication-assisted liquid exfoliation method using F127 as the surfactant and water as solvent. And this method is simple, mild and universal. We use the transmission electron microscopy, atomic force microscopy, X-ray diffraction（XRD） and X-ray photoelectron spectroscopy（XPS） characterization techniques to study the morphology, size, thickness, structure and composition of MoSe₂ and WSe₂ quantum dots. The results show that the prepared MSe₂ quantum dots with ultrasmall size（2³ nm） have one to three layers（0.7².1 nm）, and have regular morphology, uniform size. The characterization results of XRD and XPS show that MSe₂ quantum dots still have the original 2H structure and composition, and the Mo, W and Se elements are not being oxidized during the preparation process.Chapter 3: We have studied the colloidal stability, photothermal property, toxicity and the effect of photothermal therapy on tumor cells of the as-prepared MoSe₂ QDs. The MoSe₂ QDs prepared by the ultrasonication-assisted liquid exfoliation have strong absorption of NIR light（17.4 Lg-1cm-1） and high photothermal conversion efficiency（⁴6.5%）. In vitro cellular experiments demonstrate that MoSe₂ QDs have low cytotoxicity and can efficiently kill human cervical cells（ HeLa cells） under NIR laser（785 nm） irradiation.Chapter 4: An universal colloidal chemical route is designed for controllable preparation of 2D-TMD QDs. We use trioctylphosphine as a coordinating solvent to dissolve selenium, tellurium solid powder acted as a non-metal source precursor solution. The mixture of metal hexacarbonyl compound and trioctylphosphine oxide are heated until full dissolution as a metal source precursor solution and octadecene as the reaction solvent. The MoSe₂, MoTe2, and WSe₂ quantum dots have been prepared under the fulled argon. By controlling the reaction time and the amount of ligand, the size of the quantum dots could be tuned. Since it can be used to prepare the two-dimensional transition metal selenide, and telluride quantum dots, this method is universal. The method has many other advantages including high yield, mild reaction conditions and simple preparation process, which make it conducive to mass production.