Functionalized Graphene: Preparation, Assembly And Their Applications

Graphene, a monolayer of graphite, has attracted huge research passionaround the world, due to its unique two-dimensional structure and excellentphysic-chemical properties. Graphene has shown enormous potentialapplications in various high-technique fields, such as optoelectronics, energyand catalysis as well as biomedicine. In this dissertation, we focus on theresearch of some key questions of materials chemistry of graphene, includingfunctionalization, assembly and their applications. The main results aresummarized as follows:Mildly oxidized graphene oxide (GO) with excellent aqueous dispersibilityand low lattice defect was prepared by chemical exfoliation of graphite througha modified Hummers' method. Chemical reduction of mildly oxidized GO byhydrazine and hydriodic acid produced highly conductive reduced GO (r-GO)sheets, whose conductivities reached169and405S/cm, respectively. Thesevalues are3times of those of the corresponding reduced products ofconventional GO via Hummers method, and comparable to the highest values ofr-GO obtained by high-temperature post-treatments.Non-covalent functionalization via Ï€-Ï€ interaction was applied to preparestable aqueous dispersion of r-GO. Vacuum filtration of the aqueous dispersionof r-GO could produce large-area flexible graphene films with layered structureand high conductivity and mechanical strength. The r-GO was further used tomodify the counter electrode of dye-sensitized solar cell by spin-coating itsaqueous dispersion and improve the photo-electron conversion efficiencysignificantly.Aqueous self-assembly was used to prepare complex of negatively chargedr-GO sheets and cationic5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin(TMPyP). It was observed and verified that the flattening of TMPyP moleculescould be induced by r-GO through electrostatic and Ï€-Ï€ stacking cooperativeinteractions. Furthermore, the coordination reaction between flattened TMPyPand Cd²⁺ions was greatly accelerated. On the basis of this phenomenon, we used the complex of TMPyP and r-GO as an optical probe for rapid and selectivedetection of Cd²⁺ions in aqueous media.Self-assembled r-GO hydrogel was prepared by one-step hydrothermalreduction of aqueous dispersion of GO. The formation of the hydrogel wasdriven by the three-dimensional stacking of r-GO sheets via Ï€-Ï€ interaction.Self-assembled r-GO hydrogel was not only electrically conductive,mechanically strong, and thermally stable but also exhibited a high specificcapacitance when used as electrode materials in supercapacitor.Self-assembled GO/DNA composite hydrogel was prepared by utilizing theprinciple of heat-induced DNA denaturation. The formation of the compositehydrogel was driven by bridging the adjacent GO sheets with single-strandedDNA via non-covalent interactions. The self-assembly GO/DNA compositehydrogel possessed high mechanical strength, environmental stability, anddye-loading capacity and exhibited a self-healing function.