Controlled Synthesis And Properties Studies Of Graphene-Metal Sulfide Semiconductor Composites

Graphene, as an entirely new class of carbon with two-dimensional (2-D), is an important and exciting discovery after carbon nanotube and fullerene. It is a basic structural unit for graphitic materials of other dimensionalities, which can be wrapped up into0-D fullerenes, rolled into1-D nanotube and stacked into3-D graphite. Owing to its unique2-D structure, graphene shows excellent optical, electrical, mechanical, themlal performance, and becomes a hot research topic in the field of materials science, physics and chemistry.Graphene based composite is an important way for holding promise for many applications, such as catalysis, optics, electronics, magnetic, biomedicine, sensors, energy storage etc. In this dissertation, a series of graphene-metal sulfide semiconductor composites were designed and prepared by different methods, and investigate their optical properties, adsorption properties, photocatalytic performance under visible light irradiation and electrochemical performances. The main contents of this thesis are discussed as follows:1. The design, preparation, characterization and optical properties of Ag2S/Graphene composite.Graphene oxide is a widely used graphene derivatives with rich oxygen-containing groups. Ag2S/Graphene composite was prepared by sol-thermal method, using a single-source molecular (silver diethyldithiocarbamate) as precursor or carbon disulfide, ethylenediamine and silver nitrate as raw materials, and graphene sheets as a support material. The crystal phase and morphology of the composite have been characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectra (XPS), Raman spectroscopy etc. The results show that the graphene and Ag2S composite can effectively control the morphology, size and dispersion of Ag2S particles. Simultaneously, the influences of the reaction conditions were discussed and a possible mechanism for the formation of Ag2S/Graphene composite was proposed. Moreover, Ag2S/Graphene composite shows surface-enhanced Raman scattering activity for graphene oxide, and it also reveals relatively better fluorescence property compared with pure Ag2S.2. The synthesis, characterization, adsorption properties and photocatalytic performance study of CdS/Graphene composite.CdS/Graphene composite was synthesized using two different chemical reagents and graphene oxide as starting materials. The composite was characterized by various analyzing measures. A possible mechanism for the formation of CdS/Graphene composite was proposed. To study the adsorption of CdS/Graphene composite, the dye methyl orange was selected as the model compound. Analysis showed that CdS/Graphene composite have an effective absorbent for removing methyl orange in water, due to its high adsorption capacity. At room temperature, the adsorption approached to equilibrium in2.5h. The adsorption kinetics data is in good agreement with pseudo-second-order kinetic model. Furthermore, the photocatalytic activity measurements demonstrate that the CdS/Graphene photocatalysts show superior photoactivity in degradation of methyl orange under visible light irradiation. The significant enhancement in photoactivity under visible light irradiation may be due to the remarkable synergistic effect of the combination of graphene sheets and CdS nanopartices, leading to the efficient separation of photogenerated electrons and holes in the composite.3. The preparation, adsorption and electrochemical properties of Ni3S2/Graphene composite.Potassium alkyldithiocarbonatio complexes was easily produced at35℃for3h, using cyclohexanol, potassium hydroxide, carbon disulfide and acetonitrile as source materials. And than nickel(II) alkyldithiocarbonatio complexes was synthesized from potassium alkyldithiocarbonatio and nickel nitrate. Nickel sulfide was prepared from molecular precursors (nickel(II) alkyldithiocarbonatio) under sol-thermal conditions. The influences of the reaction conditions are discussed, such as surfactant, reaction time, reaction temperature.By using single-source molecular precursors, Ni3S2/Graphene composite was easily synthesized by employing graphene oxide both as starting materials, under sol-thermal conditions. The composite was characterized by various analyzing measures. Methyl orange was selected as the model compound to study the adsorption of Ni3S?/Graphene composite. The results suggested that Ni3S2/Graphene composite have an effective absorbent for removing methyl orange in water, due to its high adsorption capacity. At room temperature, the adsorption approached to equilibrium in4.5h. The pseudo-second-order kinetic model can well-describe the adsorption kinetics of methyl orange on Ni3S2/Graphene. Results of the electrochemical test show Ni3S2/Graphene composite have a higher specific capacitance and a relatively good electrochemcal stability, which is due to the remarkable synergistic effectt between Ni3S2and graphene nanosheets.4. The preparation and optical properties study of ZnS/Graphene composite.A ZnS/Graphene composite was prepared by hydrothermal method. The composite was characterized by XRD, XPS, TEM, FTIR, Raman spectra and fluorescence spectroscopy. The results show that a great number of ZnS particles were attached onto the graphene sheets with the particle diameter is about4.5-15nm. Furthermore, Raman and fluorescence properties of the composite were observed. ZnS/Graphene composite displays surface-enhanced Raman scattering activity for pure ZnS and graphene oxide, and fluorescence enhancement property compared with pure ZnS and ZnS/graphene oxide samples. Moreover, possible reasons were discussed to the change of optical properties in the composite.5. The preparation and electrochemical properties of MxSy/Graphene composite.Metal sulfides (MxSy, M=Bi, Co) were produced from molecular precursors (xanthate) by sol-thermal method. The inferences of different reaction time, reaction temperature and surfactants (gelatin, β-cyclodextrin, ethylenediamine tetraacetic acid disodium salt) were discussed. The sample was characterized by XRD, TEM, SEM etc.MxSy/Graphene composites were designed and successfully prepared by sol-thermal method, using molecular precursors (xanthate) and graphene oxide as the raw materials. The sample was characterized by various analyzing measures. Furthermore, electrochemical properties of Co9S8and Co9S8/Graphene were studied. Test results show the introduction of graphene can effectively improve electrochemical performance of Co9S8.