| Chemically modified graphene is a kind of two-dimensional nanomaterial with a single-atom carbon layer,and includes graphene oxide(GO)and reduced graphene oxide(RGO).Reducing GO to prepare RGO is the most widely used method for producing graphene-based materials,and thus this process has important applications in the fields of structural materials,energy storage,biomedical materials,and so on.In this thesis,a systematic study was carried out on the reduction of GO.A new method of inhibiting the spontaneous reduction of GO in solution is developed,a new technique to improve the electrochemical reduction of GO for preparing RGO gel with high conductivity is designed,and a novel strategy to improve the compression elasticity of RGO aerogel by thermal reduction is devised.Also,the mechanisms ofthe above processes and methods are investigated and elucidated.The chemical structure of GO is in a metastable state,which leads to continuous spontaneous reduction reactions and the gradual evolution of physical and chemical properties of GO in both solid state and solution.To improve the long-term stability of GO is essential for its practical application.In this thesis,we find that low concentration of nitric acid can effectively inhibit GO reduction in solution.In the presence of 0.1 M nitric acid,the oxidation degree of GO did not decrease after 30 days at 80 ℃,and nitric acid did not affect the properties and performance of the RGO after reduction.Moreover,experiments also show that nitric acid does not maintain the oxidation degree of GO by directly oxidizing the reduction product.The possible mechanism is that the nitrate groups formed reversibly nitric esters with the hydroxyl group on GO under acidic conditions inhibit the spontaneous reduction reaction.The RGO hydrogels obtained by electrochemical reduction deposition of GO have high electrical conductivity.But this method suffers from a relatively slow deposition rate,so it can only be used to modify the electrode but is difficult to be applied to prepare bulk hydrogels.This thesis systematically studies the factors that control the electrochemical reduction deposition of GO.By controlling the chemical structure of the raw material GO,we confirm that the key factors affecting the electrodeposition rate are the adsorption of the GO sheet on the electrode surface and the diffusion rate of the sheet in the electrolyte.A new method for the preparation of RGO hydrogel by rapid electrochemical reduction deposition has been developed.By using the GO prepared by the low-temperature method as the raw material and introducing agitation,the highly conductive bulk RGO hydrogel is successfully prepared,whose electrical conductivity reaches up to 10000 S m-1.The RGO hydrogel exhibits excellent performance in conductive polymer composites and oil absorption.Self-assembled RGO aerogels with high compression elasticity are attractive materials because of their unique properties and broad applications,but there is a lack of guiding principles for the design of elastic RGO aerogels.In this thesis,the relationship between the elasticity of GO or RGO aerogels and the microstructure,surface functional groups had been systematically studied.We demonstrate that selfassembled GO and RGO aerogels have inherent compressive elasticity,but the water molecules adsorbed on their surface can cause the reversible transformation of the aerogel from elasticity to plasticity.Experimental data and molecular dynamics simulation show that hydrogen bond network is formed between the water molecules adsorbed on ultrathin pore wall surface of GO,which hindered the shape recovery of curved pore wall and made the aerogel plasticized.Therefore,a general method is proposed to remove the remaining oxygen-containing groups on the surface of RGO aerogel by thermal reduction at 400℃,so as to inhibit the adsorption of water and enhance its elasticity.This method can also effectively endow the RGO aerogel prepared by the conventional hydrothermal method with good compression elasticity. |
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