Chemical Functionalization Of Graphene Oxide And Graphene-based Derivatives/nanocomposites: Preparations And Properties

Graphene is constructed as a single atomic sheet of conjugated sp2carbon atoms,which is the thinnest two-dimensional material. Graphene exhibits remarkablephysical phenomenas and excellent properties due to its special structure. As achemically exfoliated graphene derivative, graphene oxide (GO) is easy to bemodified and functionalized by introducing of abundantoxygen-containing functionalgroups on the surface and edges. Therefore, GO and GO-based materials haveattracted tremendous attention due to their exceptional electronic, optical, mechanicaland chemical properties, and have found potential applications in high-performanceelectrocatalytic and sensing devices. Graphene-based derivatives and nanocompositescan be obtained through the specific processing methods uaing GO as the startingmaterial. Tailoring and fictionalized GO is able to realize the particular properties forfurther expanding graphene-based derivatives. Despite the oxidation process disruptsthe highly conjugated structure, GO maintains the special high surface area and thelayered structure. This provides a hint that GO is an ideal and excellent supportor todisperse and anchor nanomaterials for applications in the fields of capacitors, fuelcells, biosensing, and so on. However, as a rising star of carbon materials, the basicissues and the applications of GO remain further exploration. First, it is essential tounderstand the differences of "internal situation" for GO, which is suitable for furtherinvestigations on practical applications after grading. Secondly, functionalized GOand discovering graphenederivatives are the research focus of scientists in recentyears. Finally, it is also the topic the researchers pursued to develop and expandgraphene-based nanocomposites. Hence, further investigations on the graphene-basedderivatives and nanocomposites are needed.Considering above research background, graphene-based derivatives and nanocomposites are preparared by a series of simple and effective approaches basedon functionalized graphene oxide. The main contents and results of this thesis aresummarized as following:1. A convenient and efficient preparation method for separation GO withwell-defined size distribution is developed using a centrifugation technique. Thegraded profile of GO nanosheets with narrow size distribution is effectively controlledby varying the centrifugation speed. The results show that the oxygen content of GOis highly dependent on their size distribution. The present work will be valuable forthe functionalization of graphene-based hybrids and the fabrication of graphenenanodevices.2. Two methods of modifying GO have been introduced. One is tailoring GO intonano-GO and graphene quantum dots (GQDs). The second is photochemicalreduction functionalization.(1) Nano-GO and GQDs are prepared by acid tailoring and hydrothermal cutting,respectively. We have demonstrated the differences in size, composition andphotoluminescence property between Nano-GO and GQDs. The quantum yield ofnano-GO is0.4%, while after hydrothermal treatment the quantum yield of GQDsincreases to1.6%. In addition, the fluorescence resonance energy transfer sensor havebeen developed using Nano-GO and GQDs as donors.(2) We have examined the surface enhanced Raman spectroscopy (SERS) of R6Gmolecules on photochemically reduced GO as a function of reduction time.Oxygenated groups on the reduced GO substrate that can significantly affect themolecular Raman signals have been identified. It is found that the reduced GO has thelargest enhancement because the distance between the molecular and graphene ismuch closer after partly removing of the oxygen-containing groups.3. Several approachs have been used to prepare and construct graphene-basednanocomposites, including self-assembly, in-situ photochemical method and chemicalreduction. Moreover, the properties of nanocomposites have also been investigated forapplications of SERS and electrochemical catalytic.(1) We develop a simple and cost-effective strategy to engineer a hybrid film ofAg nanoprisms and GO as the enhancer of SERS. The SERS property of the hybridfilm has been investigated by using R6G as molecule probe to explore the influence ofAg nanoprism and GO on SERS enhancement.(2) We introduce a photoinduced growth method into the fabrication of graphene-silve nanocomposite. In this strategy, the photochemical growth process iscarried out under alkaline environment in the absence of chemical reductant andsurfactant. Silver nanoparticles of several nanometers in size are well dispersed on thesurface of GO. The nanocomposite displayed better SERS activity as compared tosilver colloid and GO on the aspects of Raman enhancement and backgroundfluorescence suppression.(3) Ultrathin Au nanocrystals have been prepared with a uniform distribution viaa photo irradiation without the presence of chemical reductant and surfactant,accompanying by the deoxygenation of GO. In this system, GO sheets served asasubstrate and stabilizer and oxygen functional groups providedthe active sites for goldnucleation.More activated sites could capture more metal ions. Both photoirradiationand GO would provide electrons and take effect on theformation of Au particles.Besides, the redox reaction between GO and metalions precursors can spontaneouslyhappen. As-prepared RGO–Au nanocomposites exhibit high electrocatalytic activityand stability for methanol oxidation.(4) We have developed a facile and green strategy to prepare a3D CNT/graphenehybrid based on the van der Waals forces or π-π stacking by introducing adeoxygenation process between GO and acid-CNT under strongly alkaline condition.The3D RGO–CNT structure was designed by engineering1D CNT and2D GO, inwhich GO will prevent the irreversible integration of CNT and CNT will hinder therestacking of GO. This hybrid not only has a high surface area, but also exhibits agood electronic conductivity. This strategy for the preparation of3D electronmaterials is simple and low-cost, and the deoxygenation reaction between GO andacid-CNT under alkaline condition provide a new green route. The directelectrochemistry of GOD is obtained on the nano-hybrid modified electrode, whichshows good response for glucose sensing. This easy fabrication process couldpotentially be extended to detection of other biomolecules and bio-fuel cell.