Supercritical Carbon Dioxide-Assisted Deposition Of Pt Nanoparticles On Graphene And Dispersion Of Carbon Nanotubes Via Rapid Expansion Of Supercritical Suspensions

In this thesis, we utilized rapid expansion of supercritical suspension to disperse carbon nanotubes and graphene and used supercritical carbon-dioxide as a dissolving medium to solvent to achieve deposition of Pt nanoparticles on carbon nanotubes and graphene sheetsWe firstly synthesized graphite oxide by Hummers method with some modification, and reduced graphite oxide to graphene sheets through thermal expansion reduction at high temperature. By electron microscopy (SEM, TEM, AFM), Fourier infrared (FT-IR), Thermo-gravimetric curve (TGA) analysis, we confirmed the oxidation of the graphite and graphite oxide was reduced at high temperature.Supercritical carbon dioxide deposition technique was used to disperse Pt metal on the surface of graphene sheets or carbon nanotubes to obtain composites with more functions, which is valuable in theoretical research and practical application. Using PtMe2COD as the Pt precursor, we prepared Pt/GS and Pt/MWCNT composites with the aid of supercritical carbon dioxide. The morphology of Pt metal nanoparticles on supports was probed by TEM. XRD and XPS analysis confirmed that the Pt nanoparticles were successfully loaded on graphene. To compare the catalytic activity of Pt/GS, Pt/MWCNT and commercial Pt/C (Vulcan XC-72carbon black), cyclic voltammetry and chronoamperometry were used to measure their catalytic performance formethanol electro-oxidation.We attempted to promote the dispersion of carbon nanotubes with the rapid expansion of supercritical solution (RESS) technology. About10MPa,40℃were chosen as experimental conditions, and then carbon nanotubes were stirred for2h at25mL autoclave. The Nozzle was axial annulus gap nozzle with a diameter of50μm. Dispersed carbon nanotubes were easily reagglomerated even after RESS. Emission to aqueous dispersant solution could prevent carbon nanotubes from reagglomeration, but the presence of dispersants would obviously impact the performance of resultant composite material, thus not suited for the preparation of nanocomposites. To prevent reagglomeration, we designed three methods to address this issue. In the first method, dimethyl isophthalate could precipitate with a steep fall pressure in RESS because the oversaturation, thus coating carbon nanotubes during rapid expansion, thus preventing carbon nanotubes from reagglomeration; In the second method, carbon nanotubes were embedded within polymer chains(PMMA) after rapid expansion in a very short time by taking advantage of joule cooling effect. The polymer matrix hindered carbon nanotubes from reagglomeration. In the third method, layered structure of graphite could be exfoliated during rapid expansion, but graphene sheets would reagglomerate. Therefore, we dispersed carbon nanotubes and graphene sheets at the same time, thus separating the carbon species and preventing their reagglomeration. SEM was used as primary tool to assess the dispersion. The dispersion states of the carbon species before and after these treatments are compared, thus the effectiveness of preventing reagglomeration could be determined.