The Preparation Of Functional Nanocomposites Based On Two-dimensional Transition-metal Dichalcogenides And Its Performance Research

Transition metal dichalcogenides (TMDs) are layered crystals with weak van der waals forcesenabling exfoliation into two-dimensional (2D) layers of single unit cell thickness, thetwo-dimensional layers of thin TMDs which are known as the inorganic analogues of graphemebecause of its unique crystal structure and electronic structure, its unique physical and chemicalproperties as well as graphene and the absence of carbon atoms. In recent years, study of TMDshave been reported on many articles in which has confirmed that2D TMDs show a great potentialapplication in optoelectronics, biotechnology, energy and other areas because of the existence ofbandgap and the unique properties similar as grapheme, thus causing great concern in academia. Asa prototypical compound of TMDs, MoS2is the layered compound with unique2D S-Mo-Sstructure in which the Mo atom layer is sandwiched between two S atom layers. It has beenextensively studied as solid lubricant, hydrodesulphurization catalyst, and been widely applied inthe field of optoelectronic devices emitting diodes, field effect transistors, memory due to theexistence of adjustable bandgap, significant progress has been made in the field of new energystorage, catalysis, etc. Because of this, it becomes the hotspot in the current2D nanomaterials.However, the present field such as optoelectronics, new energy and bio-sensing, has put forwordhigher requirements for the performance of MoS2, MoS2with single function are unable to meet therequirements, thus it is necessary to developing a method which is able to realize the prepation offunctional nanocomposites based on MoS2.In this thesis, the object for the study is Molybdenum disulphide (MoS2), and we explore itscontrollable preparation and electrochemical applications by conducting a series of experiments inorder to improve the preparation efficiency of single layer nanosheets, enhance the electrochemicalactivity and further explain the mechanism of enhancing the electrochemical activity. Contents ofthis paper divided into the following three aspects:Firstly, we prepare single layer MoS2nanosheets by a solvent stripping method (includingultrasound-assisted organic phase separation method and ultrasound-assisted aqueous phaseseparation method) and explore the effect of solvents, surfactants and reaction time on theexfoliation; we start with improving the efficiency of perparing few layers MoS2nanosheets, andwe optimize chemical intercalation to prepare a large number of few layers MoS2nanosheets. Theexperimental results show that:(1) the best organic solvent is N methylpyrrolidone, the best surfactant is didodecyldimethylammonium bromide, and with the increase of the reaction time, theexfoliation effect the better;(2) based on optimizing the chemical intercalation, we prepare a largenumber of monolayer MoS2nanosheets by using the best purification methods and comfirm that werealize the preparation of a large number of few-layers MoS2nanosheets successfully bycharacterization methods such as transmission electron microscopy, ultraviolet-visible absorptionspectra, X-ray diffraction and so on.Secondly, based on expanding the applications of monolayer MoS2nanosheets, we explore amicrowave-assisted aqueous phase method to prepare MoS2-noble metal (Au, Ag, Pd, Pt)nanocomposites. By using ascorbic acid as reducing agent and carboxymethyl cellulose as stabilizerin aqueous solution via microwave-assisted heating to prepare MoS2-noble metal (Au, Ag, Pd, Pt)nanocomposites, and we conduct a series of characterization of its structure and morphology,composition, the the characterization results show that the method used to achieve the preparationof the functional nanocomposites, the size of Pd nanoparticles loaded on the MoS2nanosheets isuniform and its dispersibility is very well. This method is more simple and quick, gentle, and areapplicable to other types of2D TMDs such as Molybdenum selenide (MoSe2), Tungsten sulfide(WS2), Tungsten selenide (WSe2) and so on.Thirdly, by using commercial catalyst Pd/C as a reference, we explore the electrochemicalcatalytic oxidation of methanol of the above successfully prepared Pd-MoS2nanocomposites inalkaline solution via cyclic voltammetry. The results show that Pd-MoS2nanocomposites haveenhanced catalytic activity with2.8-fold anodic peak current mass density compared to commercialPd/C catalyst, because that chemically exfoliated MoS2nanosheets are mainly metallic1T phasewith good conductivity, and because of its large surface area, greatly increase the electrochemicalcatalytic active sites, suggesting potential applications for direct methanol fuel cells (DMFCs).