Structure-controlled Synthesis And Performance Studies Of The Graphene Based Composite Aerogels

Aerogel, a novel kind of mesoporous materials, is recognized by quite low density, large open pore, high speci?c surface area, etc. Graphene aerogels exhibit not only the properties of traditional aerogels but also the characteristics of graphene, such as high conductivity, excellent mechanical property, and possess potential applications in the ?elds of energy storage/conversion, catalysis, environmental remediation, sensing devices, etc. This dissertation focuses on structure-controlled synthesis and performances study of the graphene-based composite aerogels. By using graphene oxide synthesized via Hummers method as the starting material, we have successfully regulated and controlled the structure and constitution of the graphene-based composite aerogels utilizing spontaneous assembly, phase transfer and organic-inorganic nitrogen co-doping approaches. Physical properties and practical performances of the graphene based composite aerogels have also been investigated in detail. The main results are summarized as follows:Reduced graphene oxide-polypyrrole(r GO-PPy) hydrogels were successful synthesized through the spontaneous assembly between graphene oxide and pyrrole at room temperature without addition of any other oxidants as well as reductants. Supercritical carbon dioxide drying process was used to get the corresponding aerogel. FT-IR, Raman, XPS and XRD measurements were employed to investigate the mechanism of the hydrogel formation. The results revealed that the interaction between graphene oxide and polypyrrole results in the spontaneous assembly. SEM, TEM and N2 sorption-desorption measurements showed that PPy in the form of plate-like nanoparticles with different sizes disorderedly anchored onto r GO nanosheets and the aerogels possesse porous structures with high specific surface area. In addition, PPy acts as ―adhesive‖ for r GO sheets, which leads to the high mechanical property of r GO-PPy composite aerogel with storage modulus as high as 12 MPa. When used as electrode materials of supercapacitor, r GO-PPy composite aerogel manifested high specific capacitance(304 F/g at current density of 0.5 A/g).Graphene based composite aerogels were prepared by phase transfer strategy. Graphene oxide(GO) was used as surfactant to replace the surfactant on the surface of low dimensional nano-materials during the phase transfer process to get the dispersion of GO and low dimensional nano-materials. Different graphene based composite aerogels were obtained after reduction treatment of dispersion and supercritical CO2 drying in sequence. The low dimensional nano-materials in the composite aerogels ranged from zero dimensional nanparticle(PPy NPs), one dimensional nanowires(Ag NWs, W18O49 NWs) to two dimensional nanosheets(Mo S2 Ss). The phase transfer process was confirmed by UV-Vis, Micro-IR spectroscopy and Zeta potential measurements. SEM, TEM and N2 sorption-desorption tests were used to investigate the microtopography and porous structure of the resulting composite aerogels. The graphene-Ag NWs composite aerogel was used as the Surface Enhanced Raman Scattering(SERS) substrate to detect Rhodamine B as the probe molecule, which exhibited the detection limit as low as 1.0×10-8 mol/L and good repeatability.Nitrogen doped graphene aeorgels(N-G-NH3) was prepared by organic(ethanolamine, EOA)-inorganic(NH3) nitrogen source doping method. For comparison, nitrogen doped graphene(N-G-N2) aerogel was also synthesized by organic nitrogen source(EOA) doping method. SEM and nitrogen sorption-desorption tests showed that N-G-NH3 aerogel possess porous structure with high specific surface area. EDX and XPS were employed to investigate the content and doping form of nitrogen in the aerogels. The results demonstrated that organic-inorganic nitrogen source co-doping method not only increased the content of nitrogen, but also regulated the ratio between the nitrogen in different doping form. The conductivity of N-G-N2 aerogel(143.1 S/m) is lower than that of N-G-NH3 aerogel(154.2 S/m). The N-G-NH3 aerogel manifested detection limit 5.61×10-6 mol/L(S/N=3) and linear range 1.0×10-5 mol/L ~ 8.5×10-4 mol/L when it was used for modifying glass electrode to detect hydroquinone.