Papers by Keyword: Graphen

Abstract: The use of graphene-based transparent conductive electrodes critically depends upon the enhancement of electrical conductivity with a negligible loss of optical transmittance of graphene. Hence, the hybridization of graphene and metal nanostructures has been intensively investigated to improve electrical conductivity. Here we demonstrate clusterization of PtCl2 on graphene by a facile method, MeV electron-beam irradiation (MEBI) under ambient conditions, as characterized by scanning electron microscopy, transmittance electron microscopy, and resonant Raman spectroscopy. The workfunction difference between PtCl2 nanoclusters and graphene results in p-type doping of graphene, to achieve a reduced sheet resistance of 69.1 % with respect to that of pristine graphene while maintaining transmittance of 91.7 %. The mechanism of formation of PtCl2 nanoclusters on graphene is likely to be defect-mediated clusterization due to the high energy electron-beam.

Abstract: A monolayer of carbon is called graphene. It exhibits unusual properties in the Hall effect and in the cyclotron resonance. It is found that it exhibits fractional charge in the Hall effect. The interactions amongst electrons almost become constant at low temperatures. Hence, the Kohn's theorem, which shows that the interactions do not play much role in determining the cyclotron resonance, becomes operative at low temperatures. The experiments on graphene do not depend on the wave vector dependence of the frequency. Hence whether the dispersion depends on k2 or on k does not matter. The Hubbard model has been very successful in explaining the ground state of several electron systems. We consider a triangle with three vortices. Each vortex can be occupied by two electrons. By using the spin in a particular way, we can obtain new features in the Hubbard model. There is a doubling in the Peierls-Luttinger phase factor and eigen values acquire higher multiplicities than are known for the usual treatment of spin. The flux is distributed on the area of the triangle. The graphene consists of hexagons of carbon atoms but the Hall effect shows that there are defects on which electrons form clusters so that there is spin wave type behaviour. A cluster of electrons shows spin-waves leading to "spin deviation" of several per cent.

Abstract: Carbon nanotubes (CNTs) were unique nanostructured materials composed of single or multiple rolled graphene sheet which usually need expensive sources as a starting material in its preparation. In this paper, new approach of starting material was expected to be commercialized due to its cheaper and renewable properties. Fermented glutinous rice would be optimized before it can be used as starting material in the CNTs preparation. In optimizing the process, a few parameters were considered. One of the important parameters was the amount of inoculums; known as ‘ragi’. This paper showed the effect of inoculums using Fourier Transmission Infrared Spectroscopy (FTIR). The amount was varies depending on percentage of glutinous rice used in the process. The optimum amount of inoculums for nanotechnology application was 3.0% (w/w) of glutinous rice due to the most favorable level of glucose and alcohol after 3 days fermentation. The glucose level decreased whereas alcohol yield was raised when higher inoculums amount were used. The result suggested that sample with inoculums amount of 3.0% (w/w) glutinous rice was the best starting material for nanotechnology application.

Abstract: The geometrical and electronic structures of pure graphene and S-doped graphene have been investigated using plane wave pseudopotential method with generalized gradient approximation based on the density functional theory. The local structure change, Mulliken population, density of states, and electron density difference of S-doped graphene have been calculated. It can be observed that the Fermi level shifts towards the conduction band after the doping of sulfur atom. The results also suggest that there are chemical bonds formed between the sulfur and carbon atoms, and the charges transfer from the doped sulfur atom to graphene.

Abstract: Selecting graphene oxide (GO) and the Degussa P25 TiO₂ (80% anatase and 20% rutile) as raw materials, the composites of graphene/TiO₂ nano-tubes were simply and quickly prepared under the conditions of a concentrated solution of sodium hydroxide. The as-obtained composites’ phase structure was analyzed and characterized by powder X-ray diffraction (XRD), their morphologies were also observed and cross-confirmed under the Transmission Electron Microscopy (TEM). The measurements showed that the composites prepared in this work have a remarkable structure, and compared to the seperate TiO₂ nano-tubes, the agglomeration of TiO₂ nano-tubes covered on the surface of the graphene is apparently not so serious. In view of this, we preliminary tested the composites’ photo-catalytic performance with the visible light irradiation, and also made a comparison with TiO₂ nano-tubes.

Abstract: Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional 2D honeycomb lattice. The graphene sheets in graphite interact with each other through van der Waals forces to form layered structure. The first graphene sheets were obtained by extracting monolayer sheets from the three-dimensional graphite using a technique called micromechanical cleavage in 2004 [. There are numerous attempts in the literature to produce monolayer graphene sheets by the treatment of graphite. The first work was conducted by Brodie in 1859 and GO was prepared by repeated treatment of Ceylon graphite with an oxidation mixture consisting of potassium chlorate and fuming nitric acid [. Then, in 1898, Staudenmaier produced graphite oxide (GO) by the oxidation of graphite in concentrated sulfuric acid and nitric acid with potassium chlorate [. However, this method was time consuming and hazardous. Hummers and Offeman found a rapid and safer method for the preparation of GO and in this method graphite was oxidized in water free mixture of sulfuric acid, sodium nitrate and potassium permanganate [.

Abstract: Graphene nanosheet (GNS)/ Al₂O₃ composite powder with homogeneously distributed GNSs has been fabricated from wet ball milled expanded graphite and Al₂O₃, and then followed by the rotary evaporator at relatively low temperature to dry the mixture and the residual solvent was removed in atmosphere-vacuum pipe-type furnace accessing mixed gases of Argon and Hydrogen at 600 for 6h. During the process, homogeneously dispersed and mixed GNS/ Al₂O₃ composite powders with quite few damage of GNSs structure and properties have been obtained. The microstructures and grain sizes of GNS/ Al₂O₃ composite powders have been investigated. The results showed that the addition of GNSs had diminished the size of Al₂O₃ particles and also the as-prepared GNSs/ Al₂O₃ composite powders can be dispersed and mixed more homogeneously remarkably with the presence of GNSs.

Abstract: In this paper graphene is used to improve absorption rate of nano-titanium dioxide under visible light, meanwhile titanium dioxide is doped with superparamagnetism nano-powder of γ-Fe2O3 to modify the recovery of the photocatalyst. Gradually the increasing content of grapheme promotes the removal efficiency and correspondingly. Excitation condition is reduced and the photocatalysis property under visible light is improved and recycle rate of the titanium dioxide is effective promoted after the dispose. The effect of photocatalytic degradation of methylene blue is used to evaluate the photocatalytic activity. The methylene blue degradation rate raised from 53.4% to 85.9% with the increasing graphene load from 5% to 20% under visible light. The degradation efficiency of methylene blue decreased to 15% without the graphene load. The recovery rate of the photocatalyst can achieve 95% above. Graphene oxide works as the electron acceptor and photosensitizer to efficiently enhance the dye photodecomposition.

Abstract: Abstract. The surface plasmon resonance photocatalysts of Ag-AgBr/RGO were synthesized by chemical precipitation and photochemical reduction method. The samples were characterized by X-ray diffraction and UV-Vis absorption spectroscopy. The photocatalytic activities of catalysts were studied using the photocatalytic degradation of helianthine as a probe reaction. The results showed that the degradation rate of 10 mg/L helianthine reached 95% after 60 min of visible light irradiation.

Abstract: The evolution of SiC surface morphology during graphene growth process has been studied through the comparison of substrate surface step structure after in-situ etching and graphene growth in vacuum. Influence of in-situ substrate surface preparation on the properties of graphene was studied through the comparison of graphene layers on etched and un-etched substrates grown under same conditions.