Study On The Microwave Synthesis And Electrochemical Properties Of Graphene Materials From Bottom - Up

Graphene is a two dimensional and one atom layer carbon material that carbon atoms connect with sp² hybrid form six-carbon atoms ring stretch out in all directions in the plane. Due to the specific structure of carbon atom in graphene that endow it many excellent physical and chemical properties, such as quantum hall effect, high carrier mobility（15000 cm²/（V?s））, high light transmission（97.7%）, high thermal conductivity（3000-5000W/m/K）, high mechanical strength（the tensile modulus is about 1 TPa） and the biggest theory specific area（2630 m²/g）. Furthermore, it has good chemical stability in the chemical reaction. Therefore, graphene, as a multi-functional material, has received wide research attention since it was successfully prepared.Currently, the approaches for preparing graphene material include top-down and bottom-up method. For the top-down method, stripping method, oxidation-reduction method and zipping carbon nanotubes method are involed; for the bottom-up method, chemical vapor deposition method（CVD）, epitaxial growth method and other methods are involed. Each method has the advantages and the disadvantages toward different application fields.Doping can effectively open the zero band gap of pure graphene material. Doping in the graphene includes adsorption doping and lattice doping. The lattice doping methods include CVD method, ball milling method, thermal annealing method, wet chemical method, bottom-up synthesis method, plasma method, photo-chemistry method and arc-discharge method. N, S, B, F, Cl, Br, I dopant atoms or co-dopants are usually introduced into the graphene materials.As the world’s energy crisis and environmental pollution is increasingly serious, searching for renewable clean energy, developing high quality and reliable energy storage devices and looking for an efficient treatment technology to alleviate the environmental pollution has become the research focus to solve the above mentioned major issues. For example, fuel cells, super capacitors and photocatalytic technologies have become the hot topics. Fuel cell is an effective device that can convert chemical energy into electrical energy, featuring the advantages of clean and high energy conversion efficacy. With the utilization of new energy, efficient energy storage devices have become the necessary facilities. Among the, super capacitors have the advantages of quick charging, long service life, high power and wide using temperature rather than traditional capacitor. For the environment pollution problem, photocatalysis is an effective technology. Under the light irradiation, the photo-excited electrons and holes could be used in the reduction and oxidation reaction for removing pollutants in air, water disinfection and hydrogen production. In this paper, we applied the microwave synthesis technology to synthesize the graphene, doped graphene materials, graphene/CNTs composites and graphene/photocatalyst composites involing small organic molecules as the starting material and sodium metal as the catalyst. And we evaluated the electrocatalytic oxygen reduction activity over the pure graphene and doped graphene catalysts. For the graphene/CNTs composites, the electric double layer capacitor performance was evaluated. And we obtanied the photocatalytic activity of NO removal over the graphene composite photocatalysts.The paper has been divided into four parts:1. The pure graphene materials were synthesized by the bottom-up microwave synthesis technology involving methanol as a carbon source and metal sodium as a catalyst. The products were characterized by XRD, SEM, TEM, RM, FTIR, AFM, XPS and BET. We confirmed the synthesis of pure graphene materials by studying the morphology, defects, surface groups, thickness, specific surface area and the bonding stucture of carbon atoms. Furthermore, ethanol, ethylene glycol, glycerin and isopropyl alcohol were used as the starting material, and we obtained graphene materils with different morphologies, indicating the generality of this method.. Supported by the literature results and experimental data, the microwave induced reaction mechanism for the synthesis of graphene materials was proposed. The oxygen reduction performance of graphene materials synthesized via methanol as the carbon source was evaluated. The results demonstrate this material has a good performance of oxygen reduction response, anti-methanol poisoning and cycle stability. Through K-L equation we calculated the electro-catalytic process is a one step and four electron involved dynamic processes.We took N containing N, N-dimethyl formamide and triethanolamine and S containing dimethyl sulfoxide as the starting material to fabricate the N-doped graphene and S-doped graphene, using the microwave synthesis technology. Furthermore, we synthesized B-doped graphene using ethanol as the carbon source and B₂O₃ as the B source. They were characterized by XPS to konw the doping amount and the bonding structure of the impurity atom. We evaluated the electro-catalytic oxygen performance over various doped graphene material. The results show they exhibit a good oxygen reduction response and methanol resistance.The K-L equation calculationindicates the electro-catalytic process is a one step and four electron processes.We in-situ synthesized the CNT/graphene composites involving carbon nanotube as the hard template, methanol and triethanolamine as the carbon source, respectively. The composite materials were well characterized and the electric double layer capacitance were evaluated. The optimized amount of CNT were determined based on the capacitance performance.We developed a microwave-assisted route to fabricate the titanium oxide/graphene composites involing ethanol as the carbon source and isopropyl titanate as the titanium source. From the TEM results, we found that the titanium oxides was present at the edge or surface of the graphene. We evaluated the photocatalytic activity of NO removal. The results show the composite materials have an excellent removal efficiency under visible light irradiation（λ>420 nm）.