Controlled Inorganic And Organic Functionalization Of Graphene

Graphene, a new type of two-dimensional monolayer of carbon nano-materials, has received tremendous attentions and become the focus of research in the field of physics, chemistry and materials since its discovery in 2004 due to its unique combination of structrual, electrical, thermal, optical and mechanical properties. However, its lack of surface functional groups and poor dispersibility in solvents strongly limit the application of graphene in many fields. There have been some reports about the modification or functionalization of graphene or graphene oxide by various methods in recent years, including organic and inorganic functionalization. But the funcationalization of graphene still needs to be improved in some aspects, such as the amelioration of funcationazation methods, the enhancement of the dispersibility of functionalized graphene, and so forth. In this thesis, we study both the organic and inorganic functionalization of graphene and synthesize various functionalized graphene via facile and efficient approaches in order to overcome the existed problems in this area. The main contributions are as follows:1. A novel multifunctional magnetic nanopartilces functionalized graphene was prepared. The graphene nanosheets were coated uniformly by a layer of monodisperse and highly crystalline Fe3O4 magnetic nanoparticles via a high-temperature solution-phase hydrolysis method. Many instrumental measurements, such as atomic force microscopy, transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and near-edge X-ray absorption fine structure spectroscopy were used to characterize the structure and properties of the products. A series of control experiments and mechanism study show that the size and magnetization of the nanoparticles on graphene can be adjusted by varying the reaction conditions, which reveals that this method is well controllable. The resulting product shows strong supraparamagnetism (saturated magnetization is up to 44 emu/g) and electrical conductivity (conductivity is 0.7 S/m), and can be further chemically modified on its surface. It also has excellent dispersibility in solvents and processability, and novel magnetic and conductive graphene-polymer composites can be effortlessly fabricated by solution-processing with polymers.2. Pd, Pt, Au and Ag nanoparticles functionalized graphene was prepared. The nano-sized noble metal crystals were generated on graphene by a solution reduction method. The observations of transmission electron microscopy and scanning electron microscopy show that the surfaces of graphene are evenly decorated with metal nanopartcles. The resulting products have good dispersibility in solvents. Raman spectroscopy, X-ray diffraction, and energy dispersive X-ray spectroscopy measurements confirm the presence of metal nanocrystals on the reduced graphene. The weight contents of the metal elements of Pd, Pt, Au and Ag are up to 38.6%, 17.5%, 18.2% and 18.3%, respectively.3. Graphene was functionalized by an organic method based on nitrene chemistry. The synthesis method is convenient and efficient, and has excellent versatility, allowing various functional groups and polymers covalently connect onto the surfaces of graphene. Atomic force microscopy, transmission electron microscopy, scanning electron microscopy, thermal gravimetric analysis, X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy were employed to characterize the resulting products. The results demonstrate the successful introduction of various organic moieties on graphene, such as hydroxyl, carboxyl, amino, bromine, long alkyl chain, polyethylene glycol, and polystyrene. The reactive functional groups still retain their chemical reactiviy, and could be further modified by different chemical reactions, including surface-initiated polymerization, amidation, and reduction of metal ions. The resuling functionalized graphene nanosheets remain to be separated individual single layers, and are have excellent conductivity, dispersibility and processability in solvents. This general strategy to functionalize graphene can be extended to prepare many other distinctive types of functionalized graphene, opening a whole new horizon in the field of functional graphene materials.