Abstract: Ultrathin graphene films find their use as advantageous support for nano- and biomaterials investigations. Thin film causes a very slight deterioration to measured signals, thus providing more details of the object's structure at nanoscale. The ultimate thinness of graphene works in the best way for this purpose. However, obtaining suspended thin film of a large-area, which is convenient for applications, is often a relatively complicated and time-consuming task. Here we present a one-step 1-min technique for synthesis of an extremely thin (about 1-2 nm) continuous film suspended over cells of a conventional copper grid (50-400 mu m mesh). This technique enables us to acquire a large-area film which is water-resistant, stable in organic solvents and can act as a support when studying nanoparticles or biomaterials. Moreover, the very mechanism of the film formation can be interesting from the point of view of other applications of ultrathin graphene oxide papers. (C) 2014 Elsevier Ltd. All rights reserved.

Abstract: Ultrathin two-dimensional (2D) nanosheets (NSs) possess extraordinary properties that are attractive for both fundamental studies and technological devices. Solution-based bottom-up methods are emerging as promising routes to produce free-standing NSs, but the synthesis of colloidal NSs with well-defined size and shape has remained a major challenge. In this work, we report a novel method that yields 2 nm thick colloidal Cu2-xS NSs with well-defined shape (triangular or hexagonal) and size (100 nm to 3 mu m). The key feature of our approach is the use of a synergistic interaction between halides (Br or Cl) and copper-thiolate metal-organic frameworks to create a template that imposes 2D constraints on the Cu-catalyzed C-S thermolysis, resulting in nucleation and growth of colloidal 2D Cu2-xS NSs. Moreover, the NS composition can be postsynthetically tailored by exploiting topotactic cation exchange reactions. This is illustrated by converting the Cu2-xS NSs into ZnS and CdS NSs while preserving their size and shape. The method presented here thus holds great promise as a route to solution-processable compositionally diverse ultrathin colloidal NSs with well-defined shape and size.

Abstract: We use a zero-dimensional reaction kinetics model to simulate CO2 conversion in microwave discharges where the excitation of the vibrational levels plays a significant role in the dissociation kinetics. The model includes a description of the CO2 vibrational kinetics, taking into account state-specific VT and VV relaxation reactions and the effect of vibrational excitation on other chemical reactions. The model is used to simulate a general tubular microwave reactor, where a stream of CO2 flows through a plasma column generated by microwave radiation. We study the effects of the internal plasma parameters, namely the reduced electric field, electron density and the total specific energy input, on the CO2 conversion and its energy efficiency. We report the highest energy efficiency (up to 30%) for a specific energy input in the range 0.41.0 eV/molecule and a reduced electric field in the range 50100 Td and for high values of the electron density (an ionization degree greater than 10−5). The energy efficiency is mainly limited by the VT relaxation which contributes dominantly to the vibrational energy losses and also contributes significantly to the heating of the reacting gas. The model analysis provides useful insight into the potential and limitations of CO2 conversion in microwave discharges.

Abstract: The Tomasch effect (TE) is due to quasiparticle interference (QPI) as induced by a nonuniform superconducting order parameter, which results in oscillations in the density of states (DOS) at energies above the superconducting gap. Quantum confinement in nanoscale superconductors leads to an inhomogenerous distribution of the Cooperpair condensate, which, as we found, triggers the manifestation of a new TE. We investigate the electronic structure of nanoscale superconductors by solving the Bogoliubov-de Gennes (BdG) equations self-consistently and describe the TE determined by two types of processes, involving two-or three-subband QPIs. Both types of QPIs result in additional BCS-like Bogoliubov-quasiparticles and BCS-like energy gaps leading to oscillations in the DOS and modulated wave patterns in the local density of states. These effects are strongly related to the symmetries of the system. A reduced 4 x 4 inter-subband BdG Hamiltonian is established in order to describe analytically the TE of two-subband QPIs. Our study is relevant to nanoscale superconductors, either nanowires or thin films, Bose-Einsten condensates, and confined systems such as two-dimensional electron gas interface superconductivity.

Abstract: Although Li-rich layered oxides (Li1+xNiyCozMn1−x−y−zO2 > 250 mAh g−1) are attractive electrode materials providing energy densities more than 15% higher than todays commercial Li-ion cells, they suffer from voltage decay on cycling. To elucidate the origin of this phenomenon, we employ chemical substitution in structurally related Li2RuO3 compounds. Li-rich layered Li2Ru1−yTiyO3 phases with capacities of ~240 mAh g−1 exhibit the characteristic voltage decay on cycling. A combination of transmission electron microscopy and X-ray photoelectron spectroscopy studies reveals that the migration of cations between metal layers and Li layers is an intrinsic feature of the chargedischarge process that increases the trapping of metal ions in interstitial tetrahedral sites. A correlation between these trapped ions and the voltage decay is established by expanding the study to both Li2Ru1−ySnyO3 and Li2RuO3; the slowest decay occurs for the cations with the largest ionic radii. This effect is robust, and the finding provides insights into new chemistry to be explored for developing high-capacity layered electrodes that evade voltage decay.

Abstract: The self-assembly of nanoparticles into clusters and the effect of the different parameters of the competing interaction potential on it are investigated. For a small number of particles, the structural organization of the clusters is almost unaffected by the attractive part of the potential, and for an intermediate number of particles the configuration strongly depends on the strength of it. The cluster size is controlled by the range of the interaction potential, and the structural arrangement is guided by the strength of the potential: i.e., the self-assembled cluster transforms from a faceted configuration at low strength to a spherical shell-like structure at high strength. Nonmonotonic behavior of the cluster size is found by increasing the interaction range. An approximate analytical expression is obtained that predicts the smallest cluster for a specific set of potential parameters. A Mendeleev-like table is constructed for different values of the strength and range of the attractive part of the potential in order to understand the structural ordering of the ground-state configuration of the self-assembled clusters.

Abstract: The photocatalytic oxidation of carbon black on TiO2 using nitric oxide as an oxidizing agent was investigated. Layer-wise deposited carbon and TiO2 powder was illuminated with UVA light in the presence of NO at parts per million concentrations in dry and hydrated carrier gas at a temperature of 150 degrees C. Carbon was photocatalytically converted mainly into CO2, and NO mainly into N-2. Carbon oxidation rates of 7.2 mu g/h/mgTiO(2) were achieved in the presence of 3000 ppm NO. Under these experimental conditions in the absence of molecular oxygen, formation of surface nitrates causing TiO2 photocatalyst deactivation is suppressed. Addition of water enhances surface nitrate formation and catalyst deactivation. NO and carbon particulate matter are air pollutants emitted by diesel engines. Elimination of soot collected on a diesel particulate filter through oxidation is a demanding reaction requiring temperatures in excess of 250 degrees C. The present study opens perspectives for a low-temperature regeneration strategy for the diesel particulate filter that simultaneously performs DeNO(x) reactions. (C) 2014 Elsevier B.V. All rights reserved.

Abstract: In this study a numerical groundwater reactive transport model of a shallow groundwater aquifer contaminated with volatile organic compounds is developed. In addition to advective-dispersive transport, the model includes contaminant release from source areas, natural attenuation, abiotic degradation by a permeable reactive barrier at the site, and dilution by infiltrating rain. Aquifer heterogeneity is parameterized using pilot points for hydraulic conductivity, specific yield and groundwater recharge. A methodology is developed and applied to estimate the large number of parameters from the limited data at the field site (groundwater levels, groundwater concentrations of multiple chemical species, point-scale measurements of soil hydraulic conductivity, and lab-scale derived information on chemical and biochemical reactions). The proposed methodology relies on pilot point parameterization of hydraulic parameters and groundwater recharge, a regularization procedure to reconcile the large number of spatially distributed model parameters with the limited field data, a step-wise approach for integrating the different data sets into the model, and high performance computing. The methodology was proven to be effective in reproducing multiple contaminant plumes and in reducing the prior parameter uncertainty of hydraulic conductivity and groundwater recharge. Our results further indicate that contaminant transport predictions are strongly affected by the choice of the groundwater recharge model and flow parameters should be identified using both head and concentration measurements. (C) 2014 Elsevier B.V. All rights reserved.

Abstract: The optimization of sample clean-up for the analysis of air particulate matter PAHs stable carbon isotope ratio using Solid Phase Extraction (SPE) cartridges is described in this paper. Various adsorbents, such as silica gel, alumina, florisil, commercially available for sample purification were compared. Best performance for the clean-up of 24-h air particulate matter samples was obtained with activated silica-gel columns in terms of selectivity and reproducibility. One step clean-up was optimized for concentration determination and in case of co-elutions, a second step was additionally used for carbon isotope ratio analysis. The method was subsequently validated with standard reference material and was checked for carbon isotope fractionation artefacts. No significant differences in δ13C values were found for unprocessed solutions of PAHs and solution subjected to the extraction and purification procedure. The procedure was tested on air particulate matter samples collected in three different locations in Belgium. Statistically significant differences in carbon isotope ratio of PAHs between Borgerhout location and Zelzate or Gent were noticed, confirming the differences in distribution and diagnostic ratios found during the concentration analyses and different PAH sources in these locations. The results, therefore, seem very promising for the use of δ13C of PAHs as an additional information helpful in source identification of these pollutants

Abstract: Using first-principles calculations and reactive force field molecular dynamics simulations, we study the structural properties and dynamics of a fluorine (F) atom, either adsorbed on the surface of single layer graphene (F/GE) or between the layers of AB stacked bilayer graphene (F@ bilayer graphene). It is found that the diffusion of the F atom is very different in those cases, and that the mobility of the F atom increases by about an order of magnitude when inserted between two graphene layers. The obtained diffusion constant for F/GE is twice larger than that experimentally found for gold adatom and theoretically found for C-60 molecule on graphene. Our study provides important physical insights into the dynamics of fluorine atoms between and on graphene layers and explains the mechanism behind the separation of graphite layers due to intercalation of F atoms.

Abstract: In recent years, it has been observed that Inconel X-750 spacers in CANDU reactors exhibits lower ductility with reduced load carrying capacity following irradiation in a reactor environment. The fracture behaviour of ex-service material was also found to be entirely intergranular at high doses. The thermalized flux spectrum in a CANDU reactor leads to transmutation of 58Ni to 59Ni. The 59Ni itself has unusually high thermal neutron reaction cross-sections of the type: (n, γ), (n, p), and (n, α). The latter two reactions, in particular, contribute to a significant enhancement of the atomic displacements in addition to creating high concentrations of hydrogen and helium within the material. Microstructural examinations by transmission electron microscopy (TEM) have confirmed the presence of helium bubbles in the matrix and aligned along grain boundaries and matrix–precipitate interfaces. Helium bubble size and density are found to be highly dependent on the irradiation temperature and material microstructure; the bubbles are larger within grain boundary precipitates. TEM specimens extracted from fracture surfaces and crack tips provide information that is consistent with crack propagation along grain boundaries due to the presence of He bubbles.

Abstract: The wide range of liquid-phase reactions required for the catalytic conversion of biomass compounds into new bioplatform molecules defines a new set of challenges for the development of active, selective, and stable catalysts. The potential of bifunctional Ru/H-USY catalysts for conversions in hot liquid water (HLW) is assessed in terms of physicochemical stability and long-term catalytic performance of acid sites and noble metal functionality, as probed by hydrolytic hydrogenation of cellulose. It is shown that zeolite desilication is the main zeolite degradation mechanism in HLW. USY zeolite stability depends on two main parameters, viz., framework and extra-framework aluminum content. The former protects the zeolite lattice by counteracting hydrolysis of framework bonds, and the latter, when located at the external crystal surface, prevents solubilization of the zeolite framework which is the result of its low water-solubility. Hence, the hot liquid water stability of commercial H-USY zeolites, in contrast to their steam stability, increased with decreasing Si/AI ratio. As a result, mildly steamed USY zeolites containing a high amount of both Al species exhibit the highest resistance to HLW. During an initial period of transformations, Al-rich zeolites form additional protective extra-framework Al species at the outer surface, self-stabilizing the framework. A critical bulk Si/AI ratio of 3 was determined whereby USY zeolites with a lower Si/AI ratio will self-stabilize over time. Besides, due to the initial transformation period, the accessibility of the catalytic active sites is extensively enhanced resulting in a material that is more stable and drastically more accessible to large substrates than the original zeolite. When these findings are applied in the hydrolytic hydrogenation of cellulose, unprecedented nearly quantitative hexitol yields were obtained with a stable catalytic system.

Abstract: Biomedical nanomagnetic carriers are getting a higher impact in therapy and diagnosis schemes while their constraints and prerequisites are more and more successfully confronted. Such particles should possess a well-defined size with minimum agglomeration and they should be synthesized in a facile and reproducible high-yield way together with a controllable response to an applied static or dynamic field tailored for the specific application. Here, we attempt to enhance the heating efficiency in magnetic particle hyperthermia treatment through the proper adjustment of the core-shell morphology in ferrite particles, by controlling exchange and dipolar magnetic interactions at the nanoscale. Thus, core-shell nanoparticles with mutual coupling of magnetically hard (CoFe2O4) and soft (MnFe2O4) components are synthesized with facile synthetic controls resulting in uniform size and shell thickness as evidenced by high resolution transmission electron microscopy imaging, excellent crystallinity and size monodispersity. Such a magnetic coupling enables the fine tuning of magnetic anisotropy and magnetic interactions without sparing the good structural, chemical and colloidal stability. Consequently, the magnetic heating efficiency of CoFe2O4. and MnFe2O4 core-shell nanoparticles is distinctively different horn that of their counterparts, even though all these nanocrystals were synthesized under similar conditions. For better understanding of the AC magnetic hyperthermia response and its correlation with magnetic-origin features we study the effect of the volume ratio of magnetic hard and soft phases in the bimagnetic core-shell nanocrystals. Eventually, such particles may be considered as novel heating carriers that under further biomedical functionalization may become adaptable multifunctional heat-triggered nanoplatforms. (C) 2014 Elsevier B.V. All rights reserved.

Abstract: A tight-binding approach based on the Chebyshev-Bogoliubov-de Gennes method is used to describe disordered single-layer graphene Josephson junctions. Scattering by vacancies, ripples, or charged impurities is included. We compute the Josephson current and investigate the nature of multiple Andreev reflections, which induce bound states appearing as peaks in the density of states for energies below the superconducting gap. In the presence of single-atom vacancies, we observe a strong suppression of the supercurrent, which is a consequence of strong intervalley scattering. Although lattice deformations should not induce intervalley scattering, we find that the supercurrent is still suppressed, which is due to the presence of pseudomagnetic barriers. For charged impurities, we consider two cases depending on whether the average doping is zero, i.e., existence of electron-hole puddles, or finite. In both cases, short-range impurities strongly affect the supercurrent, similar to the vacancies scenario.

Abstract: The bulk properties of elementary metals and copper based binary alloys have been investigated using automated first-principles simulations to evaluate their potential to replace copper and tungsten as interconnecting wires in the coming CMOS technology nodes. The intrinsic properties of the screened candidates based on their cohesive energy and on their electronic properties have been used as a metrics to reflect their resistivity and their sensitivity to electromigration. Using these values, the 'performances' of the alloys have been benchmarked with respect to the Cu and W ones. It turns out that for some systems, alloying Cu with another element leads to a reduced tendency to electromigration. This is however done at the expense of a decrease of the conductivity of the alloy with respect to the bulk metal. (C) 2014 The Electrochemical Society. All rights reserved.