Synthesis And Properties Of Metal Oxide And Sulfide Nanocomposites

Metal oxides, such as ZnO and ZnFe2O4, and metal sulfides, such as CuS, have a wide range of applications in photocatalyst, photoelectrochemistry and Li-ion batteries, and other fields, due to their unique physical and chemical properties. Graphene, as one of the special structures of carbon consisting of monolayers of hybridized carbon atoms arranged in a honeycombed network with six-membered rings, has been used as an excellent substrate to host active nanomaterials owing to its prominent thermal stability, superior electronic conductivity, remarkable structural flexibility, high specific surface area, and widespread potential applications in nanoscience and nanotechnology. In this paper, we have studied the preparation and property of different metal oxides and metal sulfides and their nanocomposites. Particularly, their preparation process and photocatalytic performance, photoelectrochemical response and electrochemical performance as anode for Li-ion batteries have been investigated. The main research content includes the following aspects:1. Sonochemical synthesis of CuS/reduced graphene oxide nanocomposites with enhanced absorption and photocatalytic performanceThe CuS nanoparticle-decorated reduced graphene oxide (CuS/rGO) composites have been successfully prepared via a sonochemical method. X-ray diffraction and electron microscopy observations confirm that CuS nanoparticles of 10-25 nm are well distributed on the rGO nanosheets. Ultraviolet-visible spectroscopy reveals the CuS/rGO nonocomposites show a strong and broad light absorption. Photo-catalytic performance of the CuS/rGO nanocomposites is evaluated by measuring the decomposition of methylene blue solution under natural light. The experimental results reveal that the as-prepared nanocomposites show remarkably enhanced photocatalytic activity compared with pure CuS. This can be attributed to the enhanced light adsorption, strong dyestuff absorption, and efficient charge transport after the introduction of rGO.2. Hierarchical ZnO hollow microspheres with strong violet emission and enhanced photoelectrochemical responseHierarchical ZnO hollow microsphereswere prepared via a carbon microspheres-templated approach, and their microstructures were analyzed by X-ray diffraction, scanning electron microscopy,and transmission electron microscopy. The as-prepared ZnO products show well-defined hollow spherical morphology with a size of 2-4 mm. The thickness of ZnO shells is around 100nm, and they are assembled by numerous nanoparticles of 30-50 nm. The optical properties of the ZnO hollow microspheres were studied, and they exhibit a narrowed band gap (2.96eV) and a sharp violet emission at 434nm. Moreover, the ZnO hollow microspheres show a stable and greatly enhanced photocurrent response to visible light, which can be attributed to the hierarchical structures and the narrowed band gap resulted from the carbothermic process.3. Graphene anchored with porous ZnFe2O4 nanospheres as a good-performance anode material for Li-ion batteriesWe report a facile one-pot solvothermal route for synthesizing the ZnFe2O4-graphene nanocomposites using FeCl3 Zn(Ac)2-2H2O and NaAc as raw materials and absolute ethylene glycol as solvent. The structure and morphology were characterized by XRD, SEM and TEM. The electrochemical performance was measured by cyclic voltammetry (CV), galvanostatic charge and discharge measurements and AC impedance test. The results revealed that the ZnFe2O4 nanospheres are uniformly dispersed on the graphene nanosheets with a size of about 100nm. The nanocomposites show highly improved electrochemical performance as anode for Li-ion batteries (LIBs). The ZnFe2O4-graphene nanocomposites deliver a first discharge capacity of 1400 mAh g-1 and remain a reversible capacity up to 704.2 mAh g-1 after 50 cycles at a current of 100 mA g-1. Contrarily, the pure ZnFe2O4 nanospheres show only a reversible capacity of 121.7 mA g-1 after 50 cycles. The ZnFe2O4-graphene nanocomposites also exhibit ameliorative rate capacity of 271.8 mAh g-1 at the current of 800 mA g-1, which is much higher than the pure ZnFe2O4 electrode (26.6 mAh g-1), and recovers to 814 mAh g-1 when the current density is reduced back to 100 mA g-1. The enhanced electrochemical performances of the nanocomposites are ascribed to the confining and conducting effects of graphene and the synergistic effects between the conductive graphene and porous ZnFe2O4 nanocomposites.