Taloring And Functionalizing 3-D Carbon Materials And Studies Of Their Electrochemical Behaviors

Inexpensive carbon materials with good electrical and thermal properties are widely used in the field of electronic devices, energy storages, biosensors and catalysis. In these applications, high efficient electron transfers play a key role in the device performance. The properties of a carbon material are affected by the carbon sources, preparations, structures and functional groups. Three-dimensional hierarchical porous structure is skeletoned with inter-connected macro-pore or mesopores, and further comprises micropores（<2 nm） and mesopores（3-10 nm）. Charged ions and molecules with quick insertions and exertions are benefitted to the interconnected pores of this structure. Electron transfer and transport are greatly enhanced by the larger surfaces and the threedimension skeleton, respectively. Template method is often used to synthesize threedimensional porous carbon material because it provides a feasible way to tailor pores structure. Extensive works have been also conducted to modify carbon materials with hybrid atoms, molecules or other functional groups for unique electrochemical properties. However, either template approach or modification methods still face great challenges from high fabrication cost or tedious process.In this thesis, a facile template method is used to in situ fabricate hierarchical nanoporous carbon materials for delicately tailoring pore structures. Alkaline earth metal carbonate and carboxylate precursors are selected to mix with carbon sources for in-situ assembling templates by physical adsorption, followed by fabricating unique pore structures, in which the oxygen-containing alkaline earth metal salts as an oxidant can oxidize carbons to produce gases for introducing different pore structures. Modification approaches are used to prepare and functionalize carbon materials. Some special carbon sources containing functional groups are selected to functionalizing nonporous activated carbon when template-fabricating 3-D carbon structures. The factors affecting the electron transfer rate are discussed in detail. Results indicate that a unique three dimensional hierarchical carbon structures are produced, which can greatly enhance the mass transport such ion diffusion while retaining the good conductivity of carbon. This thesis work in more details are as follows.A hierarchical nanoporous carbon was synthesized by Ca CO₃ nanoparticlestemplating biomass extracted from fresh leaves by ethanol. It is the first report to have a functionalized active carbon containing plentiful functional groups including amine, amide,-SH directly from biomass by one-step fabrication, which are highly biocompatible and electrochemically active. In the experiment, commercial activated carbon and hierarchical nanoporous carbon originated from phenolic resin are used as controls for comparison. Results show that except-S- is detected, the commercial carbon has no other similar functional groups as that the biomass derived-nanostructured carbon has; the hierarchical nanoporous carbon originated from phenolic resin even has no any similar functional groups as that biomass-derived carbon possesses. The biomass derived hierarchical nanoporous carbon was further used to fabricate enzymatic glucose sensor, and demonstrated the highest electrochemical activity in comparison to the glucose sensors fabricated from phenolic resin-derived nanocarbon and the commercial nanocarbon. The work provides a new strategy to fabricate functionalized porous carbon and a high performance glucose oxidase biosensor, in which the functional groups play an essential role in the enhancement of biosensing.A three dimensional nanoporous graphene are fabricated by in situ assembled templates from mixing alkaline earth metal carbonate or carboxylate and carbon sources. After annealing, alkaline earth metal oxide nanoparticles decomposed from alkaline earth metal carboxylic are well-dispersed between graphene nanosheets, to embed on and separate graphene nanosheets. The formation mechanism of the 3-D nanoporous graphene was investigated by N₂ adsorption and desorption isothermal experiments, FSEM and TEM. It is confirmed that the three dimensional structure is due to the in-situ formed template by alkaline earth metal oxide work and gases like CO₂ and H₂ O by decomposition from alkaline earth metal organic during the fabrication. Results show that the as-prepared 3-D nanoporous graphene reaches a large capacitance of 225 F/g, which is one of the largest specific capacitance reported in the same electrolyts when the thesis is finished and the ion diffusion are benefitted from the mesopores on the 3-D nanoporous graphene.Ca（HCOO）₂ were used to tailor pore structures of three-dimensional graphene and the synthesized graphene was employed to construct micro H₂O₂ sensor. FESEM images show nanopores with diameters of several tens nanometer on the basal plane of graphene sheets. N₂ adsorption-desorption isotherm curve calculation shows that multipoint BET specific surface area of the graphene is up to 624.31 m²/g and pore size distribution is between 0.88 50 nm. The three dimensional graphene-based micro electrode was used to detect hydrogen peroxide. Results indicate that three-dimensional graphene-based micro-disk hydrogen peroxide sensor can offer good sensitivity and wide dynamic detection range due to the large reaction surface area and good catalytic activity of the electrode.In summary, by in situ introduced templates, oxidants and gases and choosing different carbon sources, hierarchical nanoporous carbon materials have been successfully tailored for delicate surface functional groups and pore structures. The optimized hierarchical nanoporous carbon can greatly enhance the ion diffusion rate by its macrosized pores while retaining good electron transport ability, and offers large surface area by its plentiful micropores. These unique materials were evaluated for their capacitive and sensing behaviors. Results demonstrate that hierarchical nanoporous carbon has excellent specific capacitance, and suitable pore size and functionalization for specific target molecules could enhance the specific capacitance and sensing performance.