The Functionalization Of Two-dimensional Nanomaterials ?MoS₂,WS₂,BN? With Green Chemistry Approach And Its Application

The past decade has witnessed an extraordinary increase in research progress on two-dimensional?2D?nanomaterials in the fields of photoelectrocatalysis,biology,electronics,energy storage and so on.Single-layer molybdenum disulfide,tungsten disulfide and boron nitride nanosheets,as graphene-analogous materials,can make up the drawback of graphene to some extent,which have guaranteed numerous promising applications and attract our interests.The metallic 1T phase Mo S₂ and WS₂has higher photoelectrocatalytic activity,and are mainly produced by alkali metal ion interlayer,wet chemical synthesis,electron radiation,etc.However,there are some shortcomings in the preparation and application.Therefore,it is still a major challenge to find a highly efficient,simple and green phase transformation method.Boron nitride,a structural analogue of graphene,has attracted much attention due to the favorable high mechanical strength,high thermal conductivity and good chemical stability.Functionalization is an important way to endow materials with new features and applications.Novel properties of functionalized BN materials,such as high water solubility,excellent biocompatibility,tunable surface affinities,good processibility,adjustable band gaps,large specific surface area etc.,have guaranteed wide applications in biomedical,electronic,composite,environmental and‘‘green”energy-related fields.The preparation and modification of BN,improving the dispersion of BN and the interface interaction between BN and polymer are of great importance.In this work,our purpose is to find an efficient,simple and green method to achieve the transformation of 2H to 1T phase of transition metal disulfide?MoS₂,WS₂?and achieve better electrochemical catalytic performance,and to functionalize the BN nanosheets to be more watersoluble.The supercritical carbon dioxide?SC CO₂?system is a green solvent system.Introducing surfactants or nanoparticles into the SC CO₂-water interface can built the emulsion environment,and the emulsion properties and the interfacial phase behavior can be controlled by changing the temperature and pressure.Our works are focus on these questions.We innovatively use the special emulsion environment built by supercritical CO₂ to realize the phase transition of MS₂?M=Mo,W?and the functionalization of BN nanosheets,we studied the phase transition mechanism and electrochemical application and expand the application of BN in polymer composite materials.The main research contents are as follows:?1?Supercritical CO₂-assisted reverse-micelle induced phase transformation from 2H to 1T phase of transition metal disulfide?MoS₂,WS₂?and their application in hydrogen evolution reaction.In this study,we report a two-step process for synthesizing stable two-dimensional?2D?metallic 1T phase MS₂ nanosheets in the reverse-micelle induced emulsion microenvironment with the assistance of supercritical CO₂.TEM,Raman and XPS characterizations demonstrate that the asprepared MoS₂ nanosheets consist of 1T-and 2H-phase,and the content of 1T phase is more than 90%.The obtained 1T-MoS₂ exhibits excellent stability and good activity for the hydrogen evolution reaction.TEM and UV-vis spectrum characterizations also testify that we have obtained 1T-WS₂.Compared with the reported method,this method is efficient,green,simple,mild and safe.?2?SC CO₂-assisted the functionalization of BN nanosheets and their application in the traditional chemical crosslinking?OR?hydrogelIn this work,we firstly use the microemulsion system composed of PVP/ethanol/H₂O₂ constructed by SC CO₂ to realize effective functionalization?-OH,-NH?of BN nanosheets,and explained the mechanism.Then we prepared the conventional organic crosslinked hydrogels using the obtained functionalized BN nanosheets?f-BNNS?and Ethyleneglycol dimethacrylate?EGDMA?as chemical crosslinkers.Besides,there are hydrogen bonding interaction between clay,f-BNNS,and polymer molecular chain.Thus,hydrogel have chemical crosslinkers and physical crosslinkers.We also explored the role of f-BNNS in composite materials.We enhanced the mechanical properties and thermal performance of the hydrogel,and endow the gel with self-healing performance.?3?Physically linked multi-functional f-BNNS/clay/PNIPAM nanocomposite?NC?hydrogels.In this work,inspired by nature,we build a type of physically linked peculiar 3D hierarchical f-BNNS/clay/PNIPAM ternary networks?TN?nanocomposite hydrogel by introducing of readily reformable noncovalent bonds as cross-linkers and sacrificial bonds.We don't add chemical crosslinkers.The vital innovative point of our material design is the incorporation of f-BNNS,guaranteeing the enhancement of mechanical strength and simultaneously the mobility of polymer molecular chains can be also retained.Hence,the hydrogel owns high mechanical properties,automatically self-healing ability and adhesiveness.What's more,the hydrogel is conductive.