Flame Aerosol Synthesis of Metal Decorated Reduced Graphene Oxide Nanocomposites
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Three dimensional (3D) graphene-based materials have garnered attention over the past decade in both academia and industry due to their unique structures with high surface area, superior mechanical strength, and useful thermal and electronic properties. In this thesis, we report a one-step aerosol flame-based synthesis of metal- (palladium, cobalt, nickel, and silver) decorated crumpled reduced graphene oxide nanocomposites using the High Temperature Reducing Jet (HTRJ) Reactor technology. In this process, an aqueous precursor containing dispersed graphene oxide and dissolved metal nitrate salts is injected into the throat of a converging-diverging nozzle. The hot combustion products of a fuel-rich hydrogen-oxygen flame flow through the nozzle, rapidly heating the aqueous precursor, leading to the evaporation and decomposition of the metal salts into gas phase species. Meanwhile, droplet evaporation crumples the graphene oxide sheets and hot hydrogen reduces oxygen-containing functional groups. The gas phase species react to nucleate and grow nanoparticles that are attached the reduced graphene oxide sheets. Finally, the metal-decorated crumpled reduced graphene oxide nanocomposites are cooled by dilution with nitrogen then collected on a filter membrane. The excess hydrogen reduces the metal oxides into pure metals and nitrogen quenches the process and stops further growth of the nanoparticles. Detailed characterization of the graphene oxide precursor, reduced graphene oxide, and these nanocomposites was carried out using Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) with elemental mapping by Energy-Dispersive X-ray Spectroscopy (EDS), Fourier-Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopy to see the crumpled structure, deposition of the metal on the crumpled balls and to study any chemical interactions between the metals and the crumpled graphene balls. The XRD patterns matched those of the respective metals and did not indicate formation of oxides. TEM imaging showed that the metal was uniformly distributed on the surface of the crumpled graphene oxide. For our standard synthesis conditions, the metal nanoparticles were roughly 2-7nm in size. SEM images showed that the crumpled structure of the reduced graphene oxide did not change upon decoration with metal. FTIR showed no evidence of chemical bonding between the metal and the reduced graphene oxide, as there were no new peaks in the FTIR spectra. The metals decorated on the crumpled reduced graphene oxide can provide electronic and catalytic properties that could be valuable in applications including catalysis, lithium-ion batteries, fuel cells, and sensors.