The stable dispersion of graphene flakes in an aqueous medium is highly desirable for the development of materials based on this two-dimensional carbon structure, but current production protocols ...that make use of a number of surfactants typically suffer from limitations regarding graphene concentration or the amount of surfactant required to colloidally stabilize the sheets. Here, we demonstrate that an innocuous and readily available derivative of vitamin B2, namely the sodium salt of flavin mononucleotide (FMNS), is a highly efficient dispersant in the preparation of aqueous dispersions of defect-free, few-layer graphene flakes. Most notably, graphene concentrations in water as high as ∼50 mg mL(-1) using low amounts of FMNS (FMNS/graphene mass ratios of about 0.04) could be attained, which facilitated the formation of free-standing graphene films displaying high electrical conductivity (∼52000 S m(-1)) without the need of carrying out thermal annealing or other types of post-treatment. The excellent performance of FMNS as a graphene dispersant could be attributed to the combined effect of strong adsorption on the sheets through the isoalloxazine moiety of the molecule and efficient colloidal stabilization provided by its negatively charged phosphate group. The FMNS-stabilized graphene sheets could be decorated with nanoparticles of several noble metals (Ag, Pd, and Pt), and the resulting hybrids exhibited a high catalytic activity in the reduction of nitroarenes and electroreduction of oxygen. Overall, the present results should expedite the processing and implementation of graphene in, e.g., conductive inks, composites, and hybrid materials with practical utility in a wide range of applications.
► Control of the reduction parameters on chemical reductions of graphene oxide (GO) leads to different deoxygenation degrees. ► Reduction proceeds by elimination of the most labile functional groups, ...mostly located on basal plane positions. ► GO sheets are composed of intermingled oxidized and non-oxidized regions, whose relative area depends on the reduction degree.
Chemical reduction of exfoliated graphite oxide (graphene oxide) has become one of the most promising routes for the mass production of graphene sheets. Nonetheless, the material obtained by this method exhibits considerable structural disorder and residual oxygen groups, and reports on their microscopic structure are quite scarce. We have investigated the structure and chemistry of graphene oxide samples reduced to different degrees using atomic force and scanning tunneling microscopy (AFM/STM) as well as X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD), respectively. TPD and XPS results indicate that reduction proceeds mainly by eliminating the most labile oxygen groups, which are ascribed to epoxides and hydroxyls on basal positions of the graphene plane. AFM/STM shows that the sheets are composed of buckled oxidized regions intermingled with flatter, non-oxidized ones, with the relative area of the latter increasing with the reduction degree.
The CORNISH project is the highest resolution radio continuum survey of the Galactic plane to date. It is the 5 GHz radio continuum part of a series of multi-wavelength surveys that focus on the ...northern GLIMPSE region (10degrees < l < 65degrees), observed by the Spitzer satellite in the mid-infrared. Observations with the Very Large Array in B and BnA configurations have yielded a 1".5 resolution Stokes I map with a root mean square noise level better than 0.4 mJy beam super(-1). Here we describe the data-processing methods and data characteristics, and present a new, uniform catalog of compact radio emission. This includes an implementation of automatic deconvolution that provides much more reliable imaging than standard CLEANing. A rigorous investigation of the noise characteristics and reliability of source detection has been carried out. We show that the survey is optimized to detect emission on size scales up to 14" and for unresolved sources the catalog is more than 90% complete at a flux density of 3.9 mJy. We have detected 3062 sources above a 7sigma detection limit and present their ensemble properties. The catalog is highly reliable away from regions containing poorly sampled extended emission, which comprise less than 2% of the survey area. Imaging problems have been mitigated by down-weighting the shortest spacings and potential artifacts flagged via a rigorous manual inspection with reference to the Spitzer infrared data. We present images of the most common source types found: H II regions, planetary nebulae, and radio galaxies. The CORNISH data and catalog are available online at http://cornish.leeds.ac.uk.
Detailed knowledge of the dispersion behavior of reduced graphene oxide (RGO) in solvents is important for its practical applications. Such behavior is expected to be different to that observed for ...pristine graphene, as a result of the chemically heterogeneous structure of RGO (patchwork of pristine and highly oxidized graphene domains). We have investigated the dispersibility of RGO in a wide range of solvents and analyzed the results on the basis of solvent surface energies and Hansen solubility parameters. Although RGO exhibited some features that are characteristic of pristine graphene, its dispersion behavior was dominated by its oxidized graphene domains, with alcohols being commonly the most successful solvents. Estimates of the effective Hansen parameters for RGO derived from the experimental data (δD≈16.9MPa1/2, δP≈10.7MPa1/2 and δH≈14.1MPa1/2) were consistent with this view and afforded the rational design of solvent mixtures that surpassed the best single-component solvents in terms of dispersed amount of RGO. RGO–polymer composites could then be readily prepared in the best performing solvents. Overall, the present results provide a guide to the processing of RGO in the liquid phase with practical utility in the preparation of different graphene-based materials.
Highly active antiretroviral therapy (HAART) results in potent and durable suppression of HIV-1 viremia. However, HIV-1 replication resumes if therapy is interrupted. Although it is generally ...believed that active replication has been halted in individuals on HAART, immune activation and inflammation continue at abnormal levels, suggesting continued, low-level viral replication. To assess whether active replication might be driving immune activation in HAART, we examined the impact of treatment intensification with the integrase inhibitor raltegravir on viral complementary DNA and immune activation parameters. In the presence of raltegravir, linear HIV-1 cDNA is prevented from integrating into chromatin and is subsequently converted to episomal cDNAs. Raltegravir intensification of a three-drug suppressive HAART regimen resulted in a specific and transient increase in episomal DNAs in a large percentage of HAART-suppressed subjects. Furthermore, in subjects with these episomal DNAs, immune activation was higher at baseline and was subsequently normalized after raltegravir intensification. These results suggest that, despite suppressive HAART, active replication persists in some infected individuals and drives immune activation. The ability of raltegravir intensification to perturb the reservoir that supports active replication has implications for therapeutic strategies aimed at achieving viral eradication.
We present optical spectroscopy of MWC 656 and MWC 148, the proposed optical counterparts of the γ-ray sources AGL J2241+4454 and HESS J0632+057, respectively. The main parameters of the Hα emission ...line equivalent width (EW), full width at half-maximum and centroid velocity in these stars are modulated on the proposed orbital periods of 60.37 and 321 d, respectively. These modulations are likely produced by the resonant interaction of the Be discs with compact stars in eccentric orbits. We also present radial velocity curves of the optical stars folded on the above periods and obtain the first orbital elements of the two γ-ray sources, thus confirming their binary nature. Our orbital solution supports eccentricities e∼ 0.4 and 0.83 ± 0.08 for MWC 656 and MWC 148, respectively. Furthermore, our orbital elements imply that the X-ray outbursts in HESS J0632+057/MWC 148 are delayed ∼0.3 orbital phases after periastron passage, similar to the case of LS I +61 303. In addition, the optical photometric light-curve maxima in AGL J2241+4454/MWC 656 occur ∼0.25 phases passed periastron, similar to what is seen in LS I +61 303. We also find that the orbital eccentricity is correlated with the orbital period for the known γ-ray binaries. This is explained by the fact that small stellar separations are required for the efficient triggering of very high energy radiation. Another correlation between the EW of Hα and orbital period is also observed, similar to the case of Be/X-ray binaries. These correlations are useful to provide estimates of the key orbital parameters P
orb and e from the Hα line in future Be γ-ray binary candidates.
The use of UV light to trigger different processes involving graphene oxide sheets suspended in aqueous medium at room temperature has been investigated. These processes include (1) deoxygenation of ...the sheets in the absence of photocatalysts, reducing agents and stabilizers, (2) selective nucleation and growth of metal nanoparticles on the sheets to yield graphene-based hybrids and (3) decomposition of the dye molecule rhodamine B in the presence of only graphene oxide. Photoinduced heating of the suspended graphene oxide sheets by intense UV irradiation (∼1
W
cm
−2 delivered at the surface of the dispersion) was interpreted to generate at high temperature and reactive environment strictly localized at the sheets and their immediate aqueous medium, which in turn brings about the mentioned processes. In addition to providing a simple route toward reduction of graphene oxide dispersions, the present results suggest that intense UV light can be used to promote reactions at ambient conditions with this material that would otherwise require high temperatures, chemical reactants and/or catalysts.
Strategies that improve the yield of graphene nanosheets in anodic exfoliation processes are desirable for the mass production of this material. Here, a simple pre-treatment of graphite foil with ...concentrated H2SO4 is demonstrated to be such an effective strategy, affording overall exfoliation yields up to ∼50 wt% under certain experimental conditions, compared with a baseline value of ∼10 wt% for untreated graphite. Filling of inner voids and interstices of the graphite foil with H2SO4 molecules was concluded to be responsible for the enhanced exfoliation performance. Additional approaches to further increase the anodic exfoliation yield are also proposed and discussed.
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