Chemical Manipulation And Assembly Of Graphene Materials And Theirs Performances

Graphene oxide (GO) provides possible to prepare graphene based materials in large scale. Reduction of graphene oxide to reduced graphene oxide (rGO) is one important and challenging topic. In Chapter II, we studied the solvent thermal reduction of graphene oxide in mixture DMAc/H2O solvent under atmosphere press, both bath heating and microwave heating were employed, respectively. The reaction temperature is below160℃. FT-IR, XRD, AFM, XPS, Raman, and TGA measurements reveal that deoxygenation of GO occurs under the mild thermal conditions, yielding rGO. For micarowave as heating source, the reduction time is within10minutes, and the as-prepared rGO can be well dispersed in DMAc to form a stable suspension. The conductivity of reduced graphene paper was measured about200S/m,104times higher than that of GO paper.For a more high extent of reduction for graphene oxide, chemical reducing agents are used. In Chapter III, instead of hydrazine, sulfur-containing compounds such as NaHSO3, SOCl2and SO2et al. were used to reduce graphene oxide to chemical reduced graphene oxide. FT-IR, TGA, XPS et al. measurements confirmed the formation of rGO under chemical reduction at95℃. The results reveal that the reducing ability of NaHSO3is comparable to that of hydrazine. A possible mechanism of the reduction has been suggested. The electrical conductivity of the rGO paper prepared using a NaHSO3reducing agent is found to be6500Sm-1while it is observed to be5100Sm-1for hydrazine reduced graphene paper. These studies confirm that NaHSO3can be a good candidate as a reducing agent to compete with hydrazineHydrogenation of GO also may occur during its reduction at strong reducing conditions, forming C-H group in GO plane. In Chapter IV, we found a novel method to prepare hydrogenated graphene (HG) via a direct synchronal reduction and hydrogenation of graphene oxide (GO) in aqueous suspension under60Co gamma rays irradiation at room temperature. GO can be reduced by the aqueous electron (eaq-) while the hydrogenation takes place by the hydrogen radicals formed in-situ under irradiation. The maximum hydrogen content of the as-prepared highly hydrogenated graphene (HHG) is found to be5.27wt%with H/C=0.76. The yield of the target product is in gram scale and is promising for large scale prepartion. The as prepared HHG also shows high performance as anode materials for lithium ion batteries.It is important to assembly the micrometers size graphene sheets into macroscopic architechures for more applications. Three-dimensional (3D) architecture of graphene is significant important. In Chapter V, a mild method for preparation of3D architectures of graphene is developed via an in situ self-assembly of rGO nanosheets that were in-situ formed by a mild chemical reduction at95℃under atmosphere pressure without stirring. No chemical or physical cross-linkers and high press are required. Graphene aerogels can be prepared by freeze-drying of graphene hydrogels, and the shapes of the3D architectures can be controlled by changing the types of the reactors. The graphene hydrogel shows high specific capacitance(～160F/g) in supercapacitor. Graphene aerogels are in low density, high mechanical properties, thermal stability and high electrical conductivity.3D graphene architectures are good candidates for potential application in supercapacitors, oil sorbents and catalysts supports.The unique structure of3D graphene architectures comes from the building units-2D graphene sheets, providing extremely large area for combination with other components. Hybrid3D graphene architectures can be easily prepared during self-assembly in aqueous from the well dispersed GO sheets. In Chapter VI, electrical conductive magnetic graphene/Fe3O4aerogel has been successfully prepared by the one-step reduction and self-assembly of the mixture of GO in the present of Fe3O4nanoparticles, and the assembly process looks like the fishing process. The obtained gel is superparamagnetic, porous and light weight. Graphene/Fe3O4composite can be used as anode materials for LIBs, and it shows good electrochemical performance,1100mAh g-1after50cycles of charging/discharging. This study is a base for developing new3D graphene/nanoparticles for wide applications in near future.More different graphene architectures can be prepared if we control the porous structure of graphene aerogels. A simple and effective method for the fabrication of flexible macroporous3D graphene sponge using ice template is developed in Chapter Ⅶ. It is found that the porous structures of the3D graphene architecture depended on the rate of ice crystal formation. At a low cooling rate, the inner walls of the graphene hydrogel are re-assembled into hierarchical macroporous structure by the as-formed ice crystals, resulting in the formation of macroporous graphene sponge after freeze-drying. The as-prepared graphene sponge is flexible and can recover from a50%deformation. As the graphene sponge is used as the anode of a microbial fuel cell (MFC), the maximum power density reaches427.0W m-3, which is higher than that of the MFC fabricated using carbon felt as the anode material.Assembling micrometers size graphene oxide sheets into macroscopic film is another challenge for graphene fabrication. Foam film acts as template for ultrathin film fabrication if it is seen in a material view. In Chapter Ⅷ, we developed a novel method for the fabrication of macroscopic free-standing ultrathin films of GO through the route of the preparation dried foam films. The prepared GO thin film can be easily transferred to any substrates. After chemical or thermal reduction, the relative rGO film with highly electrical conductivity (920Ω□-1) was prepared, which has potential application as electrode materials to replace of ITO or FTO in flexible photoelectric devices. This method is also suitable for2D graphene-like material free-standing ultrathin films fabrication.Generally, the reduction of graphene oxide is conducted in heating condition, where energy is put-in. In fact, the reduction of GO in aqueous is a deoxygenation process with cost of electron and proton, during which GO plays the role of depolarizer. Can we out-put the energy during the reduction of GO? In Chapter IX, a primary battery has been fabricated, where Zn plate as anode and graphene oxide (GO) as cathode, and the electron-output has been achieved while a reduced graphene oxided (rGO) film was obtained synchronously. The output capacities of the batteries depend on the oxygenated degree and the amount of GO, and their specific capacity ranged from216to642mAh g-1while the average voltage is up0.6V. Electrochemical impedance spectroscopy (EIS) measurements reveal the decreasing resistance of Zn/GO cell during discharging process. And a domino-like process was observed during the discharging of GO film. A LED lamp can be ignited by the battery, indicating its potential for practical application.Inspired by the domino-like process during the chemical reduction of dried GO foam film in Zn-GO primary cell, we found electrochemical reduction method can be a general route for highly reduction of GO architectures in Chapter X. Point or line contacting can lead to the overall reduction of GO architectures for the moving three phase lines (3PIs), where face contact is not necessary. We fabricated1D graphene/cellulose line,2D graphene film/paper composite and3D graphene/sponge composite, and all showed excellent conductivity. The reduced graphene film gains conductivity of28200S/m, comparable with reduced by HI or thermal annealing, while this method is mild and green. We also prepared flexible graphene film on PET of large area, showing64%transparency with low resistance of1.8KΩ□-1.