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Synthesis And Characterization Of Graphene-based Materials

Posted on:2011-02-08Degree:DoctorType:Dissertation
Country:ChinaCandidate:C XuFull Text:PDF
GTID:1101360302498785Subject:Materials Science and Engineering
Abstract/Summary:PDF Full Text Request
Graphene, a monolayer of carbon atoms packed into a dense honeycomb crystal structure, has attracted tremendous attention from both the experimental and theoretical scientific communities since it was found in 2004. Due to the unique nanostructure and extraordinary properties, graphene based materials have shown promising applications in electronics, optics, magnetics, biomedicine, catalysis, sensors, energy storage etc. In this dissertation, the chemical modified graphene-graphene oxide was used as precursor to prepare graphene based derivants and composites, and certain properties of these products were also analyzed. Furthermore, the special functions of graphene based sheets on synthesis of particles were also investigated. The dissertation is mainly focused on:1. Surface modification of graphene oxide. Amphiphilic oligoester was grafted onto the surface of graphene oxide after utilization of toluene-2,4-diisocyanate as a coupling agent, which contained two isocyanate groups. One remarkable result after modification was that the obtained graphene was dispersed stably in both aqueous and organic solutions.2. Preparation of graphene. Graphene oxide was selective reduced using ethanol and ethylene glycol as reductants through solvothermal and polyol methods, respectively. Only the epoxy groups on graphene oxides were reduced by alcohols, while those groups such as hydroxyl and carboxyl groups were maintained. Due to the partial reduction, the degree of re-graphitization of alcohol reduced graphene oxide was lower than that of hydrazine reduced, and the conductivity also fell into an intermediate stage between that of graphene oxide and its deeply reduced counterparts.3. Graphene based nanoparticle composites.(1) Graphene oxide-Co3O4 nanocomposites were synthesized through the in situ decomposition of cobalt nitrate and crystal growth of CO3O4 on the surface of graphene oxide sheets in n-hexanol solvent. Probably due to the concert effect of graphene oxide and CO3O4 on the catalysis of ammonium perchlorate, the addition of graphene oxide-Co3O4 composites not only brought down the decomposition temperature, but also increased the exothermic heat of ammonium perchlorate.(2) Graphene-metal nanoparticle (Au, Pt and Pd) composites were synthesized using graphene oxide sheets as precursor and metal nanoparticles as building blocks in the water-ethylene glycol system. In this system, the metal nanoparticles formed first and were adsorbed onto the surface of carbon sheets. Then these particles played a pivotal role in catalytic reduction of graphene oxide with ethylene glycol under low temperature, leading to the formation of graphene-metal particle nanocomposites consequently. The graphene-Pt composite was used as a model to test the applicability in direct methanol fuel cells through cyclic voltammograms analyses. And results indicated that such composite possessed good catalysis activity and cyclability.(3) Graphene-TiO2 composites were prepared using solvothermal progress. At 160℃, the tetrabutyl titanate decomposed into TiO2 nanoparticles and adsorbed onto the alcohol reduced graphene sheets, forming composite consequently. The densities of TiO2 nanoparticles on graphene sheets were altered easily just through controlling the usage of tetrabutyl titanate.4. Graphene oxide sheets had been used as the nanoscale substrates for the formation of quasi-two-dimensional silver nanoparticle films. These silver nanoparticle films assembled on graphene oxide sheets were flexible and formed stable suspensions in aqueous solutions. And the obtained suspensions were easily processed into macroscopic films with high reflectivity. Raman signals of graphene oxide in such hybrid films were increased by the attached silver nanoparticles and the degree of enhancement could be adjusted by varying the quantity of silver nanoparticles on the graphene oxide sheets.5. The special functions of graphene-based sheets on the particle synthesis.(1) Graphene-cuprous oxide (CU2O) composites were prepared using copper acetate pre-adsorbed graphene oxide sheets as precursors. Results showed that cubic CU2O particles with an edge length of~200 nm formed in the present of graphene oxide, while ruleless and hard aggregated CU2O particles were obtained without graphene oxide. Such results indicated that in our system the carbon sheets might play a role as a template which made Cu2O crystals grow along certain directions, forming cube-like crystals. A preliminary study on the electrochemical behavior of the graphene-Cu2O composite used as anode material for lithium ion batteries was carried out. The capacity of such sample was high in the first charge-discharge cycle. Nevertheless, such electrode showed a poor cyclability.(2) A modified silver mirror reaction was used to investigate the affection of graphene oxide on the silver particle size. Results confirmed that addition of graphene oxide could lead to forming small silver nanoparticles. Meanwhile, the reaction conditions such as pre-heated time, temperature, the usage of silver salt and graphene oxide also affected the size of silver nanoparticles. Under certain conditions, the as-synthesized aqueous silver particle colloids were much stable, which were mixed discretionarily with some organic solvents, such as methanol, ethanol, acetone,1-propanol. etc.. and kept stability.
Keywords/Search Tags:Graphene, graphene oxide, surface modification, selective reduction, composites
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