Graphene Electron Conductivity Research Articles

Evaluation of a graphene-covered dielectric microtube as a refractive-index sensor in the terahertz range

We studied the scattering and absorption of the H-polarized plane wave by a graphene-covered circular dielectric cylinder and a hollow tube with a graphene cover on the outer boundary in the terahertz range. The analytical solution of the wave-scattering problem was based on the Maxwell equations and the use of the separation of variables in the polar coordinates. We assumed the resistive boundary conditions on the zero-thickness graphene cover where the graphene electron conductivity was included as a parameter and was determined from the Kubo formalism. The computed spectra of the total scattering cross section and the absorption cross section displayed several types of resonances: the localized-surface-plasmon (LSP) resonances of the graphene cover and the resonances on the whispering-gallery modes of a dielectric cylinder or dielectric tube. The computed data can be useful for the design of graphene-based sensors of the changes in the refractive index of the host medium. For this purpose, the sensitivities and the figure-of-merit values of the LSP resonances were computed; their comparison demonstrated advantages of a thin-tube configuration.

A facile one-pot reduction method for the preparation of a SnO/SnO2/GNS composite for high performance lithium ion batteries

A SnO/SnO2/GNS composite with controlled oxidation states and composition has been prepared through simple one-pot reduction of an EG suspension of SnCl2 and graphene oxide. The as-prepared composite was characterized by XRD, FT-IR, XPS, SEM, TEM and BET. SnO and SnO2 nanoparticles are uniformly distributed on the surface of the graphene. Taking advantage of the high electron conductivity of graphene and the large theoretical capacity of SnO, this SnO/SnO2/GNS composite exhibits high charge/discharge capacity, good cycling stability and good rate capability. A specific discharge capacity of approximately 464.2 mA h g(-1) is retained after being charged/discharged at a current density of 1000 mA g(-1) for 30 cycles.

THz wave scattering by a graphene strip and a disk in the free space: integral equation analysis and surface plasmon resonances

The excitation of the surface plasmon resonances on a graphene strip and a disk in free space is studied numerically as a 2D and 3D electromagnetic wave-scattering problem, respectively. The associated mathematical model is based on the Maxwell equations with resistive boundary conditions on the surface of a zero-thickness strip or disk, where the graphene electron conductivity is included as a parameter and determined from the Kubo formalism. It is shown that plasmon resonance frequencies in the terahertz range shift with variation of the chemical potential of the graphene. Far-field and near-field patterns are plotted at several resonance frequencies.

A facile solvothermal method to produce ZnS quantum dots-decorated graphene nanosheets with superior photoactivity

Zinc sulfide–graphene (ZnS–GR) nanocomposites with a high degree of dispersion and high coverage of ZnS quantum dots (QDs) have been synthesized by a facile solvothermal method without any dispersant, during which the formation of ZnS nanoparticles and the reduction of graphene oxide (GO) occur simultaneously. ZnS–GR nanocomposites exhibit much higher photoactivity than nanoparticle crystal ZnS (NPC-ZnS) prepared in the absence of graphene (GR), as evaluated by degradation of methylene blue (MB) in the liquid phase under ultraviolet (UV) light. Among them, the ZnS–GR nanocomposite with a 5% mass fraction of GR prepared at 120 ° C has the highest photocatalytic activity. The conversion and mineralization over MB are 96.7% and 57.1% respectively, which is much higher than that of NPC-ZnS. The high photoactivity of ZnS–GR nanocomposites can be ascribed to the integrated effect of an extremely high specific surface area and the excellent electron conductivity of GR and its significant influence on the morphology and structure of the samples. Moreover, it is found that the oxidation of MB is driven mainly by the participation of ⋅OH radicals. Accordingly, a potential photocatalytic mechanism of ZnS–GR nanocomposites in the photocatalytic process has been proposed in this work. It is expected that our work could provide valuable information on the design of metal sulfide decorated GR with excellent properties.

Improving the photocatalytic performance of graphene–TiO2 nanocomposites via a combined strategy of decreasing defects of graphene and increasing interfacial contact

Incessant interest has been shown in the synthesis of graphene (GR)-semiconductor nanocomposites as photocatalysts aiming to utilize the excellent electron conductivity of GR to lengthen the lifetime of photoexcited charge carriers in the semiconductor and, hence, improve the photoactivity. However, research works focused on investigating how to make sufficient use of the unique electron conductivity of GR to design a more efficient GR-semiconductor photocatalyst have been quite lacking. Here, we show a proof-of-concept study on improving the photocatalytic performance of GR-TiO(2) nanocomposites via a combined strategy of decreasing defects of GR and improving the interfacial contact between GR and the semiconductor TiO(2). The GR-TiO(2) nanocomposite fabricated by this approach is able to make more sufficient use of the electron conductivity of GR, by which the lifetime and transfer of photoexcited charge carriers of GR-TiO(2) upon visible light irradiation will be improved more efficiently. This in turn leads to the enhancement of visible-light-driven photoactivity of GR-TiO(2) toward selective transformation of alcohols to corresponding aldehydes using molecular oxygen as a benign oxidant under ambient conditions. It is anticipated that our current work would inform ongoing efforts to exploit the rational design of smart, more efficient GR-semiconductor photocatalysts for conversion of solar to chemical energy by heterogeneous photocatalysis.