Facile Synthesis And Property Study Of N-doped Graphene Aerogels

Graphene, as a flexible two-dimensional monolayer of sp2-hybridized carbon atoms, exhibits excellent carrier mobility(2×105 cm2 V-1 s-1), thermal conductivity(3000 W m-1 K-1), high fracture strength(110 GPa) and specific surface area(2630 m2 g-1). The electron transporting, optical coupling, electromagnetic, thermal and mechanical properties of graphene make it widely used in supercapacitor devices, lithium batteries, optical sensors, biosensing and adsorbent materials. What's more, nitrogen-doped graphene has attracted great attention due to incorporating nitrogen atoms into graphene could could alter the band structure and generate specific charge carriers(holes and electrons).Aerogels are a kind of porous materials with ultralow density, high porosity and large surface areas. They could be used in many fields including thermal insulation, hydrogen storage and adsorbents for toxic ionic or organics. Graphene aerogels permit the individual graphene sheets into three-dimensional(3D) porous skeleton, which would improve the feasibility of graphene for the absorption, catalytic, and electrochemical performance. So far, several approachs, such as sol-gel method, template method and hydrothermal method had been employed to prepare graphene aerogel. Among these methods, the hydrothermal method was a facial and efficient way to acquire the 3D graphene aerogels. Moreover, the controllability of the porous structure and the surface area of the N-doped graphene aerogel, could make obvious influences on its performance. Thus, it is desirable to choose suitable nitrogen dopant and investigate its effect on structure parameters of aerogels. Herein, we used the melamine as nitrogen-doped agent to fabricate the N-doped graphene aerogels(NGAs) via a self-assembly process by one-pot hydrothermal method. The achievements have made in this thesis are summarized as follows: 1. Facile Synthesis and structure characterization of N-doped graphene aerogels.NGAs were synthesized by using GO and melamine via the hydrothermal method and thermal-annealing process. They had a typical 3D network made up of flexible thin graphene nanosheets. SEM and bulk density observations demonstrated that melamine molecules could prevented GO sheets from self-stacking and allowed the sufficient assembly of GO sheets into the large volume. 2. Electrochemical performances of N-doped graphene aerogels.The electrochemical performances of NGAs were evaluated by cyclic voltammetry(CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy(EIS) techniques in three-electrodes system. The results revealed that the pore structure and capacitive performance of NGAs could be controlled by tuning the melamine/GO mass ratio. The enhanced electrochemical performance could be attributed to the synergistic effect of the doped-N level and the specific surface area, which was decided by the porous structure of NGAs. The synthesized NGA-3 showed a specific capacitance of 116 F g-1 and retained 92.5% of its initial capacitance after 5000 cycles. 3. The organic solvent adsorption capacities of N-doped graphene aerogel.Various organic solvents were used to evaluate adsorption capacities of the NGOA and NGA. After thermal-reduction, the NGA presented higher weight adsorption capacity for organic solvents up to 52.6-111.6 g g-1 along with high volume adsorption capacity up to 82.8-95.9% of its own volume, and maintained 96.5% of its initial capacity after 10 cycles. The results suggested that the NGA would offer great potential application for removal of organic contaminates in water.