Study On The Preparation, Characterization And Properties Of Cd（cu）s And Cu₂O Semiconductor/graphene Nanocomposites

In this thesis, GO was prepared from pristine graphite according to Hummers method and then combined with various nano-materials for yielding a series of rGO nanocomposites. Microstructures were characterized by SEM and XRD, etc. The electrochemical properties and photocatalytic performance were also investigated. And then we studied the energy band and electron structures of composites by first principles. The main research contents and results are drawn as follows:（1） Graphite oxide was prepared by flake graphite via modified Hummers method and then was reduced to grapheme through the hydrothermal and solvothermal reduction methods. The component and microstructure for the graphene were analyzed by SEM, TEM, FT-IR, SEM, XPS and TG-DSC. The results indicate that the layer spacing of GO was larger than that of graphite and GO is a typical two-dimensional layered nanomaterial with plenty of groups, such as hydroxyl, carboxyl and carbonyl groups, on its sruface. However, the grapheme oxide was reduced more completed by solvothermal method than by hydrothermal method.（2） CdS/rGO nanocomposite was prepared by solvothermal method using different surfactants and were characterized by a series of tests. The results indicate that when the surfactant is CTAB, a homogeneous distribution of spherical CdS nanocrystals on the graphene nanosheets can be occured. Moreover, electrochemical performances of the composite were tested by cyclic voltammetry（CV） tests, electrochemical impedance spectroscopy（EIS） and galvanostatic charge/discharge tests. The results show that the composite electrode has a good electrochemical reversibility and capacitance performance. The visible photocatalytic activity of the composite is tested using Rhodamine B（RhB） as the model contaminant when the wavelength of visible light was bigger than or equal to 420 nm. Compared with the GO and CdS, CdS/rGO nanocomposite demonstrates the best photocatalytic efficiency for RhB dye under visible light. The addition of graphene promoted the adsorption of RhB on the composites and decreased the recombination efficiency of electron-hole pairs. Thus, the photocatalytic activity for RhB dye was increased.（3） The CuS/rGO nanocomposite with uniform morphology was successfully prepared by solvothermal method with GO and cupric chloride as materials, thioacetamide as reactants and glycol as solvent. The electrochemical properties and the photocatalytic performance of the prepared products were tested. The results indicate that the reduction of GO and a homogeneous distribution of CuS nanocrystals on the graphene nanosheets occurs simultaneously. Moreover, the morphology of CuS nanoparticles is similar to that of "red blood cells" with the size of 100 nm. The electrochemical performances of the composite were tested by cyclic voltammetry（CV） and galvanostatic charge/discharge tests. By comparison with the GO and CuS, the CuS/rGO nanocomposite displays distinctly enhanced specific capacitance. The visible photocatalytic activity of the composite was tested using Rhodamine B（RhB） as the model contaminant when the wavelength of visible light bigger than or equal to 420 nm. Compared with the corresponding bare GO and CdS, CdS/rGO nanocomposite demonstrated improved photocatalytic efficiency for RhB dye under visible light.（4） The Cu₂O/rGO nanocomposite was synthetised by hydrothermal method. The optimal fabrication conditions is at 160 ℃ for 6 h, and the pH value is 11. After hydrothermal reaction, most of the functional groups of GO disappear and rGO show a shape of folds, while the shape of Cu2 O particles is spherical with the particle diameter of about 200 nm. The electrochemical performances of the composite were tested by cyclic voltammetry（CV） and galvanostatic charge/discharge tests. The CV curve of Cu₂O/rGO has a strong redox peak, which should be generated by the redox reaction of Cu2+/Cu+. According to the charge/discharge curve of Cu₂O/rGO nanocomposite, its voltage varied linearly with time, which shows that the electrode material has an ideal capacitance characteristic in the range of the test potential. The visible photocatalytic activity of the composite was tested using Rhodamine B（RhB） as the model contaminant when the wavelength of visible light bigger than or equal to 420 nm. Compared with the corresponding bare GO and Cu2 O, Cu₂O/rGO nanocomposite demonstrated improved photocatalytic efficiency for RhB dye under visible light.（5） The surface adsorption models of CdS, CuS and Cu2 O with a single C atom were constructed. The results show that the pure bulk materials exhibit semiconducting properties, while the band gap of the surface structure adsorbed C atoms decreased, which reduced the energy required to excite electrons. Meanwhile, the excite electrons can transfer from the atom of Cd and Cu to C and S, which reduce the chance of the electron-hole recombination in the structure, improved the photocatalytic efficiency. A single C atom adsorption usually does not affect the type of band gap of Cu₂O（111） plane. Due to the impurity level and the adjustment of the periodic potential field, the positions of top of valence band and bottom of the conduction band change, and the width of band gap is decreased, which lead to the enhanced photocatalytic efficiency.