Preparation And Properties Of Graphene Nanocomposites

Graphene is a two-dimensional carbon film that is composed of monolayers of sp2hybridized carbon. Due to its unique single atomic layer structure, large specific surface area, intriguing mechanical, thermal and electrical properties, graphene is considered as a promising supporting material for nanoparticles and an ideal conductive filler for polymer nanocomposites. Currently, the widely used method for large scale production of graphene is based on the exfoliation and reduction of graphite oxide. To improve the dispersibility, graphene needs to be functionalized with other organic molecules or polymers. But this oxidation-reduction-functionalization process is complicated and time-consuming. To realize the application of graphene composites, it is needed to develop more simple and effective methods for the preparation of graphene composites.This thesis focuses on two aspects:the controllable deposition of platinum nanoparticles on graphene and the preparation of polymer functionalized graphene using ultrasonication. The main results are summarized as follows:1. We propose a facile polyvinylpyrrolidone (PVP)-assisted hydrothermal method for the preparation of platinum (Pt) nanoparticles/graphene nanocomposites. PVP plays a crucial role in the stabilization of graphene and the deposition of Pt nanoparticles. Fourier transformed infrared spectroscopy (FTIR), Raman, X-ray diffraction (XRD) and atomic force microscope (AFM) results show PVP can effectively solubilizing graphene through the hydrophobic graphene-PVP interaction and preventing graphene from aggregation during the hydrothermal reduction process. Transmission electron microscopy (TEM), AFM and SEM results show that the Pt nanoparticles are uniformly distributed on the graphene surface. It is found that the Pt nanoparticle size varies with the amount of PVP. Cyclic voltammetry results indicate that the Pt/graphene nanocomposite has large electrochemical active surface area (ECS A), high catalytic activity and good durability. The ECS A of the prepared sample decreased by33%after6000CV cycles. This one-pot polymer-assisted hydrothermal synthesis approach is apparently promising for the preparation of nanoparticles/graphene composites.2. We prepared polystyrene (PS) functionalized graphene by ultrasonication of graphite in the PS solution and the resulting PS/graphene nanocomposites exhibit excellent conductive properties. In order to improve the exfoliation efficiency, we first prepare expanded graphite (EG) from the graphite intercalated compound (GIC). The intercalated graphite expanded nearly100times along the c axis in the expansion process. The SEM image shows that EG sheets are partially delaminated graphite nanoplatelets. The degradation of PS during ultrasonication is confirmed by the GPC result. The dispersibility experiment, Infrared and Raman spectroscopy results indicate that PS is successfully grafted onto the graphene surface. TGA result shows that the content of grafted PS is about8.9wt%. TEM, AFM and SEM are used to investigate the efficiency of exfoliation. The thickness of most PS functionalized graphene is less than10nm. The prepared PS/graphene nanocomposites exhibit excellent electrical property with a percolation threshold of about3wt%. This affords a novel method for developing polymer functionalized graphene through integrating the preparation and functionalization of graphene in one step using ultrsonication.