Highly Efficient Ball-milling Preparation Of Two-Dimensional Transition Metal Dichalcogenide Nanosheets And Their Antibacterial Application

Two-dimensional?2D?transition metal dichalcogenides?TMDCs?with unique structures and optoelectrical properties have shown great potential in optoelectronics,energy,environment and biomedicine.2D TMDCs have layered structure and the layers interact each other by weak van der Waals force rather than strong chemical bonding,which makes it possible to exfoliate bulk 2D TMDCs into the nanosheets.As the 2D TMDCs decrease to single-layer or few-layer forms,or the lateral size of 2D TMDCs decrease to less than 10 nm,the electronic structure of TMDCs changes significantly and quantum confinement effect greatly affects their physical and chemical properties.For example,small-size TMDC nanosheets and TMDC nanodots have high specific surface area,numerous unsaturated coordinating sites,superior catalytic property,high fluorescence quenching ability,high biomolecules loading capability and good biocompatibility,which make them hot research topics in hydrogen evolution,biosensing,diagnostics and therapeutics.Until now,although several methods have been developed for the preparation of single-layer or few-layer TMDC nanosheets,including mechanical exfoliation,chemical vapor deposition,chemical exfoliation,sonication-assisted exfoliation,and colloidal chemistry,they usually have low efficiency,large size,and critical reaction conditions,which significantly hinders the study and application of small-size TMDC nanosheets and TMDC nanodots.In this thesis,we develop a highly efficient polymer-assisted ball milling method to prepare small-size TMDC nanosheets?<40 nm?.Based on this strategy,we further introduce inorganic salts to develop the polymer-salt assisted ball milling technique for the preparation of WSe₂ nanodots?<10nm?with 4 times yields compared to the polymer-assisted ball milling without salts.Subsequently,we studied the influence of size and surface modification to the antibacterial activity of WSe₂nanodots.1.By introducing polymer to improve the exfoliation of bulk TMDC materials by milling balls,we developed the polymer-assisted ball milling method and prepared series of small-size WSe₂nanosheets,explore the influence of polymer,grinding speed,and grinding time on effect of the exfoliation.WSe₂ nanosheets with uniform morphology,good dispersibility,and high yield?>60%?with average size among 7-40 nm can be efficiently prepared by this polymer-assisted ball milling method.2.Based on the preparation of WSe₂ nanosheets by polymer-assisted ball milling,we further studied the generality of this method,realized the efficient preparation of small-size TMDC nanosheets such as MoS₂,MoSe₂ and WS₂,and extended it to the exfoliation of other typical 2D layered materials such as graphite and boron nitride.3.In order to further improve the preparation efficiency of TMDC nanodots?<10 nm?,inorganic salts was added to the polymer-assisted ball milling system,and developed the binary polymer-salts assisted ball milling technique.The inorganic salts with high harness compared to polymer can break the TMDC into small fragments.The influence of the types of inorganic salts and feed ratio on the exfoliation of WSe₂ nanodots.Results show that the yield of WSe₂ nanodots can be improved 4 times.4.After investigating the colloid stability and cytotoxicity of WSe₂ nanosheets,we explore the influence of size and polymer modification on the antibacterial activity of WSe₂ nanosheets.