Preparation And Application Of Nanocomposites Based On Molybdenum Disulfide And Nickel Sulfide

The energy crisis and ecological pollution problems with rapid economic development have emerged and are fast deteriorating.Therefore,developing appropriate materials for energy and environmental protection will promote the sustainable development of the whole society.Among the many materials,transition metal sulfide has become one of the most important materials all over the world because of its abundant sources,low production cost as well as excellent physical and chemical properties.The applications of the transition sulfide materials have covered numerous energy and environmental fields like sewage purification,battery,capacitor,electronic devices,electrocatalysis.To combine outstanding properties of the materials to prepare transition metal sulfide based composite materials will achieve obvious improvement in performance to meet the needs of the actual appliactions according to the synergistic effect of the components.There have been many methods developed for preparation of transition metal sulfide composite materials,among which hydrothermal method is commonly used with various advantages of easy regulation,high purity of products and so on.Therefore,in this thesis,several transition metal sulfide nanocomposites based on molybdenum disulfide and nickel sulfide,ie.MoS2/rGO,TiO2/MoS2/rGO,Ppy/Ni3S2@Ni foam were obtained mainly by the hydrothermal method,and the corresponding structure and performance were characterized and analysed.Their potential for adsorption,photocatalytic degradation and supercapacitor applications were also tested.Specific research work is as follows:Preparation of a porous MoS2-rGO composite and study on its high adsorption capacity for fast and preferential adsorption towards Congo redA porous MoS2-rGO composite was successfully prepared by a simple hydrothermal method without adding any surfactants.The microstructure and composition of the nanocomposite were carefully characterized by Scanning Electron Microscope(SEM),Transmission Electron Microscope(TEM),Raman spectroscopy and X-ray Diffraction(XRD).The results indicate that the as-prepared material consists of nemerous flower-like microspheres stacked by rGO and lamellar MoS2 nanosheets,both of which are evenly distributed.And these microspheres had a diameter of about 300 nm.The N2 adsorption-desorption measurement indicates that the composite material possesses a specific surface area of 44.4 m2/g and has a mean pore size of 35 nm.At the same time,the as-synthesized material was used as a adsorbent for the adsorption of Congo red and displays fast adsorption towards Congo red with maximum adsorption capacity reaching 440.9 mg/g at pH = 3.The adsorption kinetics and the adsorption thermodynamics were studied in depth by various models,and the analyses suggest that a preferential monolayer adsorption of Congo red onto the composite material according to the Langmuir isotherm,and the adsorption kinetics follows more likely to the Lagergren pseudo-first-order model.The charge sign of the nanocomposite was measured in order to understand the dependence of adsorption capacity on pH.According to the results,the π-π conjugation between the MoS2-rGO nanocomposite and Congo red plays a critical role on the adsorption.Finally,the adsorption performance of the abtained adsorbent towards several other anionic dyes and the selective adsorption behavior of the material in a mixed dye solution were also investigated.The nanocomposite was found to exhibit preferential adsorption towards Congo red and is considered to have practical application to remove or enrich Congo red.Fabrication of porous TiO2/MoS2/rGO composites by one-step method and their application research on photocatalytic degradation towards Rhodamine BTiO2 nanoparticles modified-MoS2/rGO composites were fabricated by one-step hydrothermal method,and the TiO2/MOS2/rGO composites with different ratio were obtained by adjusting the additive amount of TiO2.The SEM images indicate that,in the experimental range,with the increase of the amount of TiO2,they remained a good dispersion state in the composite.Meanwhile,the composite material maintains a favorable flaky porous structure.Subsequently,the as-prepared sample was used for the photocatalytic degradation of Rhodamine B.It was found that the TiO2/MoS2/rGO composite had a better performance of photocatalytic degradation toward Rhodamine B than MoS2/rGO,and the degradation rate of TiO2/MoS2/rGO-4 reached 90.5%as compared to MoS2/rGO(45.1%)after four-hour UV-irradiation.Moreover,the psreudo-first order kinetic model was applied to simulate the kinetics of the catalytic reaction.We further probed into the generation and quenching of the active species in the degradation process by means of UV-visible diffuse reflectance spectroscopy and fluorescence spectroscopy,and found that the light harvest and the recombination of the electron-hole pairs were both enhanced with the increase of TiO2,illustrating the light harvest has a more dominant influence on the photocatalytic process.Besides,the possible photocatalytic degradation mechanism was proposed as well.A Polypyrrole(Ppy)/Nickel sulfide(Ni3S2)composite with core-shell nanostructures on a nickel foam for supercapacitor device applicationA polypyrrole(Ppy)/Nickel sulfide(Ni3S2)composite with core-shell nanostructures on a nickel foam was synthesized by combining a facile hydrothermal method and a simple electrochemical-deposition process,and used as a binder-free electrode material for supercapacitor.As was seen from the electron microscopy,the diameter of the needle-rod-like Ni3S2 core is about 200 nm while the thickness of the polypyrrole shell is 300 nm or so.A series of Ppy/Ni3S2@Ni foam composites were obtained by changing the potentiostatic deposition time,and it was found that the content of the polypyrrole augmented with increasing the deposition time,resulting in mutual adhesion between the shells and formation of the dense layers,and thus changing the aforementioned well-defined core-shell structure.Futhermore,some electrochemical tests(Cyclic voltammetry(CV),Galvanostatic Charge/Discharge(GCD),and Electrochemical Impedence Spectroscopy(EIS))were carried on to investigate the electrochemical performance of the composites.The results show that the areal specific capacity of the Ppy/Ni3S2@Ni foam electrode obtained with the deposition time of 50s is 5 times higher than that of the Ni3S2@Ni foam electrode.What’s more,this special core-shell structure is able to maintain the stability of the structure while reducing the resistance between the interfaces,making the capacity retention rate of the material remain 93.6%after 500 times of the charge-discharge cycling measurement.