Synthesis And Characterization Of Three Dimensional Porous Graphene Nanocomposited Materials

Graphene as a 2D hexagonal material occupied by sp2 carbon atoms has many outstanding mechanical, thermal and electronic properties because of its unique planar structure. The 2D structure, meanwhile, has limited the application of graphene in some degree. There exists very strong van der Waals’ force between layers as a consequence of both the weak interaction between graphene and solvent and the strong conjugated system between the interlayers of graphene. So it is easy for graphene to form the coalition with interlayer spacing of 0.34 nm, but meanwhile very difficult to disperse. This property brings great difficulties for further processing and application of graphene based materials. Graphene oxide(GO) prepared by oxidizing graphite powder not only can easily disperse in various solutions, but also can convert to graphene through reduction. Therefore GO becomes the one of graphene derivatives which has been most widely applied in experiment and in industry. Analogy to graphite, GO also has a layered structure, but the difference is that GO has many kinds of oxygen-containing functional groups such as hydroxyl, epoxy, carbonyl and carboxyl. The porous structure of GO gets well protected because the layered structure can easily disperse in solution. 3D graphene nanocomposite can be successfully obtained from 2D graphene-based material taking advantage of the unique properties of GO. These 3D graphene nanocomposites are expected to overcome the difficulty faced by 2D materials and therefore the research on 3D graphene nanocomposites are full of theoretical and application significance.The objective of this work is to provide new methods to synthesize different threedimension porous nano graphene composited materials,this thesis studied the following aspects:1. We reported detailed synthesis of a range of porous graphene oxide frameworks(GOFs) by reaction of graphene oxide(GO) sheets with various linear boronic acid pillaring units in a solvothermal reaction and synthesis of Li-doped GOF(GOF-4CBPBA@Li). The chemical structural changes were confirmed by means of SEM, BET, XRD and TGA analyses and the property for catalytic activity for the oxygen reduction reaction(ORR) and the kinetic reaction mechanism of the electron process were investigated through the Koutecky-Levich(K-L) plot and cyclic voltammogram. We had demonstrated that GOFs exhibit periodic layered structures with largely expanded interlayer spacing as characterized by SEM.The interlayer spacing increades 0.45 ? compared to GO. Furthermore, the strong boronate-ester bonds between GO layers result in improved thermal stability over the precursor GO. The frameworks provide highly increased specific surface area for nitrogen adsorption compared to GO alone, which indicates the GOFs have been synthesized successfully. Through electrochemical performance measurement, we demonstrated GOFs to be a highly active, cheap, and selective catalyst for the electrochemical synthesis of hydrogen peroxide.2. Several macroscopic graphene assemblies were prepared through proper assembly strategies in which graphene oxide as building blocks is operated via a serial of reactions: hydrothermal process, organic solvent replacement, freezing drying and plasma enhanced chemical vapor deposition(PECVD). The chemical structural changes and properties were tested by means of SEM, BET, XRD, TGA analyses and hydrogen storage measurement. The 3D graphene hydrogel, consisting of well-defined and cross-linked three dimensional porous structure, not only has high specific surface area(795 m2/g) but also exhibites a high hydrogen storage(5.5wt%).