| The transition metal chalcogenide?TMDs?has a layered structure similar to graphene.With Molybdenum disulfide?Mo S2?as an example,the molybdenum atoms in the layer are bound to the sulfur atoms by covalent bond,and inter-sheets interaction is via van der Waals bonding.TMDs nanosheets are composed of one or several monolayers,and their transverse dimensions range from tens of nanometers to several microns.Transverse dimensions of TMDs quantum dots are less than 10 nanometers.Compared with the bulk,TMDs nanosheets and quantum dots exhibit unique and excellent physical and chemical properties,such as band gap structure that can be adjusted with the number of layers,and are widely used in the fields of energy,catalysis and electronic devices.However,large-scale,environment-friendly production of high quality TMDs nanosheets is still a big challenge.Liquid-phase shear mixing is one of the most promising methods at present.However,the existing liquid-phase shear mixing methods often use toxic and high-boiling solvents,or prolonged ultrasound that consumes energy.Therefore,it is still an important topic to develop a simple and environmental-friendly method for preparing Mo S2 nanosheets.In this thesis,a simple method for preparing TMDs nanosheets and quantum dots with Mo S2 as an example is presented.Production of semiconducting 2H pure phase,few layers and large size Mo S2 nanosheets were successfully realized by shear mixing using commercial Mo S2 as raw material,using 1-pyrene butyric acid as edge intercalation and stabilizer.Through a series of characterization methods such as HRTEM,AFM,UV-vis and Raman,the exfoliated Mo S2 nanosheets were characterized,and the effects of different process parameters on the experimental results were discussed and analyzed.The results show that the average size of the prepared Mo S2nanosheets is 1.8?m,the thickness of most nanosheets is 2-4 layers,and it has a pure 2H phase.When exfoliated speed was 6000 rpm,the optimal preparation conditions were identified as raw Mo S2 was 4.5g for 300 m L water and 200 mg 1-pyrene butyric acid and shear time was 1 h.The method has been shown to be equally applicable to the preparation of WS2 and Mo Se2 nanosheets.Mo S2 quantum dots were prepared by solvent-thermal method from commercial bulk Mo S2.Through characterization,it was found that the average size of quantum dots was 6 nm,and most quantum dots was of only 1-2 layers.The obtained Mo S2 quantum dots exhibit blue fluorescence at 365 nm and have photoluminescence properties.Moreover,with the increase of excitation wavelength,the emission wavelength of the quantum dots appears red shift.After repeated experiments,we have also obtained WS2 quantum dots and Mo Se2 quantum dots,that showed blue fluorescence under 365 nm light.Compared with Mo S2 quantum dots,the size of WS2 quantum dots and Mo Se2 quantum dots were slightly different. |
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