Manipulation Of Surface Chemistry And Properties Of Graphene And Its Oxide

Graphene, single or few layered two dimensional sp2-hybridized carbon sheets, is a new rising star in the field of nanotechnology applications for its unique structure and promising physico-chemical properties. Controllable synthesis of graphene for targeted surface properties is of great importance for its versatile applications. Oxidation-reduction method is a cost-effective, high-throughput and versatile route to the synthesis of graphene, in which graphite oxide (GO) is an important precursor in graphene and its composites synthesis. In this thesis, the systematic study of the preparation parameters of GO via the modified Hummers method has been done, base on which, GO, graphene and Pt/graphene composites with varied surface chemistry and properties have been controllably synthesized. The main results of this work are summarized as follows:(1) The GO samples are prepared by the modified Hummers method, in which the oxidation time, temperature and oxidant/graphite weight ratio are tuned. The effect of the preparation condition on the structure and surface chemistry of GO has been studied. The results show that the increase of oxidant/graphite weight ratio, and the increase of oxidation time or temperature with the high oxidant/graphite weight ratio facilitate the introduction of the oxygen-containing groups on GO. The preparation temperature has been proved to have significant impact on the reaction rate of graphite oxidation. When GO are prepared with the high oxidant/graphite weight ratio, the types of the oxygen-containing groups on GO remain the same regardless of the reaction time and temperature, while their concentration distribution varies greatly. Adjusting the oxidant/graphite weight ratio can keep the oxidation under control during graphite oxidation in favor of observing the formation of the oxygen-containing groups on GO.(2) The GO samples are prepared with different amounts of oxidant to control the oxidation degree and characterized by XRD, FTIR,13C CPTOSS/MAS NMR, XPS and zeta potential measurement. When the amount of oxidant is below a critical value, the epoxy groups are dominant on the surfaces of GO, together with a relatively small amount of the hydroxyl and carbonyl groups. Further increasing the amount of oxidant leads to the formation and development of the carboxyl groups, which eventually reach a saturation level. In contrast to the GO prepared with the high oxidant/graphite ratio of5, the oxidation degree of the GO prepared with the low oxidant/graphite ratio of2reduce with the oxidation time increased. A possible mechanism for the formation of the oxygen-containing groups on GO has been proposed, which provides a guideline for the manipulation of the surface properties of GO.(3) The GO samples with good dispersibility and propensity to spontaneously exfoliate into graphene oxide but different surface states are used as the precursors for the synthesis of the graphene by using hydrazine hydrate as the reductant. With the increased oxidation degree of the precursor GO, more oxygen-containing groups are left on the as-prepared graphene, simultaneously, more nitrogen atoms and defects are introduced. The GO with a low oxidation degree and few carboxyl groups at the edges can be used as the precursor to prepare highly reduced graphene with a low content of defects and heteroatoms. While the GO with a low oxidation degree and abundant carboxyl groups at the edges can be used to synthesize dispersible graphene with the low defect density.(4) An eco-friendly, facile and scalable hydrothermal approach, in which the reduction and functionalization of graphite oxide are completed in one pot, is proposed for the synthesis of monolayer3-aminopropyltriethoxysilane (APTES)-functionalized graphenes (A-FGs). AFM, TEM and XRD analyses indicate that the as-synthesized A-FGs consist of only one or a few layered graphenes, while XPS, FTIR and TGA analyses reveal that APTES is bonded to graphene by the dehydration reaction between the Si-OH (produced by APTES hydration) and the-OH on the GO surface. As a result, free amino groups are left on the A-FGs. Moreover, A-FGs are highly dispersible in dimethylsulfoxide, APTES and ethylene glycol, and their solubilities are up to0.89,4.03and0.90mg/mL, respectively.(5) Parametric investigation of the polyol process for the preparation of Pt/graphene composites are carried out where Pt precursor and graphene oxide were in-situ reduced. It is found that the surface chemistry of the GO including the concentration of surface charge and functional groups and sp2domains, pH and the concentration of the precursor Pt salts play a vital role in controlling the size, loading and distribution of Pt nanoparticles on the graphene. The epoxy and/or hydroxyl groups are responsible for the nucleation and attachment of Pt. With the oxidation degree of GO increasing, the reduction degree of the graphene decreases, while the Pt size, distribution and loading do not vary in monotonic way. By adjusting the pH of the reaction system in the aging stage and as a result of enhanced the interaction between the Pt nanoparticles and graphene nanosheets, the Pt/graphene composite with a high Pt loading and a uniform size distribution is obtained when GO with a low or medium oxidation degree is used as the precursor.