Preparation And Photoelectrochemical Performance Of Graphene/Semiconductor Nanocomposites

Graphene is a single layer of carbon atoms in a closely packed honeycombtwo-dimensional (2D) lattice. Due to its excellent properties, graphene and thegraphene-based functional materials has attracted great attention all over the worldfor its potential applications, especially in catalysis and energy-storage devices.In this work, Graphene oxide (GO) was firstly produced by a modifiedHummers’ method and several kinds of graphene/semiconductor nanocompositeswere then successfully synthesized by different methods, respectively. Thephotocatalytic activities and electrochemical performance were evaluated.Furthermore, the effects resulted from the presence of graphene in thenanocomposites have been also investigated. The main contents are as follows:1. Synthesis and characte rization of GOGraphene oxide (GO) was systhesized from graphite powder based onmodified Hummer’s method. Experimental results demonstrated that the exfoliatedGO was almost transparent, and had one or few layer2D sheet structure with someobvious wrinkles which indicated the fact that the2D sheet structure becomesthermodynamically stable during bending. On the other side, the resulting GO sheetswith carboxylic acid, hydroxyl and epoxide groups were full of disordered, highlyoxidised sp3domains as well as defects of carbon vacancies.2. Synthesis and photocatalytic pe rformance of Graphene/SemiconductornanocompositesCombining semiconductors and graphene to form composite materials isexpected to enhance the effeciency of photocatalytic degradation to a certain extent,so these photocatalytic materials are worth exploring.(1) GO and P25nanoparticles (commercial TiO2) were used as raw materialsto synthesize TiO2-graphene (TiO2-GE) nanocomposites by using the solvothermalmethod. Experimental results clearly showed that TiO2-GE nanocomposites exhibitedTiO2(B) crystalline phase structure. TiO2nanomaterials (the size of about15~20nm)were distributed well onto the2D graphene sheets, indicating the formation ofTiO2-GE nanocomposites. Meanwhile, it was demonstrated from the methylene blue (MB) photodegradation results that TiO2-GE nanocomposites possessed excellentphotocatalytic activities. This may due to the introducing of graphene sheets couldextend optical absorption range and enhance the absorbance of UV-vis light.(2) Graphene-wrapped ZnO spheres were successfully prepared by lyophilizingmethod, using graphene oxide (GO) as a precursor of graphene, ZnO spheresobtained via refluxing their acetate precursors in diethylene glycol (DEG) medium asbuilding blocks. ZnO clustered spheres with the size of about100~400nm, whichwas composed of numerous nanocrystals with hexagonal wurtzite structure, werewell separated from each other and wrapped with transparent graphene sheets.Furthermore, the ZnO-coated graphene nanocomposites showed a significantenhancement in the photodegradation of methylene blue compared to that of ZnOspheres. Such improved photocatalytic properties may in terms of the fact that theintroducing of graphene sheets could increase the adsorptivity of pollutants, extendlight absorption range and facile charge transportation and separation.3. Synthesis and Electrochemical lithium storage performance ofGraphene/Semiconductor nanocompositesThe unique properties of graphene make it an excellent active matrix for thepreparation of graphene-based nanocomposites to improve the electrochemicalperformance of anode materials.(1) Si/graphene nanocomposites with different weight ratios were successfullyprepared by ball-milling of commercially available Si nanoparticles and graphene oxide(GO) nanosheets. It was demonstrated that Si nanoparticles within the Si/graphenenanocomposites were well distributed onto the flexible graphene nanosheets. Comparedto the pristine Si nanoparticles anode, the Si/graphene composite anodes showed anenhanced reversible capacity and cyclic performance, highlighting the advantages ofanchoring Si nanoparticles on graphene sheets. The enhancement on electrochemicalperformance could be ascribed to the fact that graphene nanosheets within theSi/graphene nanocomposites could act as a flexible conductive scaffold network tomaintain excellent electronic contact, improve ionic conductivity and charge transfer aswell as accommodate the large volume change of Si during the lithiation/delithiation process.(2) The3D structure TiO2nanotubes-graphenen (GE) nanocomposites withdifferent weight ratios as the anode materials were designed and synthesized throughhydrothermal process without use any reducing agents and surfactants. Theelectrochemical performance of TiO2-GE nanocomposites was further investigated.The characteristic results demonstrated the TiO2-GE nanocomposites with anataseTiO2nanotubes well dispersed and interlaced and incorporated graphene showed theexcellent rate capability and cycling stability, especially the TiO2-5%GE, which dueto the introduction of2D graphene with high surface area and good conductancefacilitating the storage of Li+in TiO2.