Preparation, Structures And Properties Of Graphene(Oxide)/Silver And Graphene/PMMA Nanocomposites

In the present dissertation, we have summarized the recent research progress of graphene and its nanocomposites. Three kinds of graphene-based nanocomposites including graphehe oxide (GO)/silver, graphene/silver and graphene/poly(methyl methacrylate)(PMMA) have been successfully fabricated by the optimal methodologies, and their nanostructures and properties have been carefully investigated.Silver nanoparticles (Ag NPs) have been homogeneously deposited onto GO nanosheets by an optimal method, in which N, N-dimethylformamide (DMF) as a co-dispersant of GO and reductant of sliver ions is added to an aqueous suspension of GO and AgN03. GO nanosheets are uniformly covered by AgNPs with a narrow size distribution and inter-particle gap. Raman signals of GO are greatly enhanced after deposition owing to the charge transfer interaction of GO with Ag NPs. The GO/Ag composite can be further utilized as an effective surface-enhanced Raman scattering (SERS) active substrate. Several new Raman bands and frequency shifts are clearly observed in using4-aminothiophenolas a Raman probe on GO/Ag compared to the normal Raman spectrum of solid4-ATP. The Raman enhancement arises from a major electromagnetic effect and a minor chemical effect.Reduced graphene oxide/silver composites (RGO/Ag) have been prepared by chemical reduciong of GO/Ag with sodium borohydride (NaBH4). The coverage density of Ag NPs on RGO was effectively adjusted by controlling the feed ratio of AgNO3to GO in weight. The as-prepared RGO/Ag composites can accelerate the catalytic reduction of methylene blue in the presence of NaBH4, and they also show high electrocatalytic activity for hydrazine oxidation.Chemical reduction of GO to produce graphene nanosheets often results in irreversible agglomeration and precipitation. Herein, stable well-dispersed graphene sheets in solvents were obtained by simultaneous functionalization and reduction of GO under alkaline conditions, in the presence of sodium borohydride and imidazolium ionic liquids (Imi-ILs) containing two vinyl-benzyl groups. In this case, positively charged imidazolium groups of Imi-ILs underwent ion-exchange with negatively charged GO sheets and were linked to their edges, while Imi-ILs were non-covalently attached onto the large surfaces of graphene through π-π and/or cation-π stacking interactions. The vinyl-benzyl reactive sites were then copolymerized in situ with MMA to fabricate graphene/PMMA nanocomposites. Functionalized graphene sheets were uniformly dispersed in the PMMA matrix and contributed to large increases in storage modulus (+58.3%) and glass transition temperature (+19.2℃) at2.08vol%loading. High electrical conductivity was also achieved (ca.13.37Sm-1at1.0vol%) with a low percolation threshold (0.25vol%) for the composites. Hence, a general methodology which facilitates the development of a multifunctional advanced material has been successfully established. This can be extended to other vinyl polymer-based composites containing graphene.