Harnessing the Liquid‐Phase Exfoliation of Graphene Using Aliphatic Compounds: A Supramolecular Approach

The technological exploitation of the extraordinary properties of graphene relies on the ability to achieve full control over the production of a high‐quality material and its processing by up‐scalable approaches in order to fabricate large‐area films with single‐layer or a few atomic‐layer thickness, which might be integrated in working devices. A simple method is reported for producing homogenous dispersions of unfunctionalized and non‐oxidized graphene nanosheets in N‐methyl‐2‐pyrrolidone (NMP) by using simple molecular modules, which act as dispersion‐stabilizing compounds during the liquid‐phase exfoliation (LPE) process, leading to an increase in the concentration of graphene in dispersions. The LPE‐processed graphene dispersion was shown to be a conductive ink. This approach opens up new avenues for the technological applications of this graphene ink as low‐cost electrodes and conducting nanocomposite for electronics.     

Temperature effect over structure and photochemical properties of nanostructured SnO<Subscript>2</Subscript> powders

We successfully synthesized tin dioxide nanoparticles with polyhedral morphology via an ethylene glycol assisted sol-gel approach. The structural characteristics of three tin dioxide samples were investigated after being thermally treated at 400°C, 600°C and 800°C. X-ray diffraction (XRD) patterns clearly show the formation of single phase tin dioxide nanoparticles, with crystallite size of 6–20 nm, in good correlation with Fourier transform infrared (FTIR) spectra. Transmission electron microscopy (TEM) analysis confirms the formation of 6nm polyhedral nanoparticles for the 400°C sample. Ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectra suggest a high concentration of oxygen vacancies. The oxygen vacancy concentration increases with temperature, due to the combined action of the formation of V_O and the energetic O compensation. X-ray photoelectron spectroscopy (XPS) analysis also confirms the formation of single phase tin dioxide and the presence of oxygen vacancies in good agreement with UV-VIS and PL data.

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Synthesis and characterization of ZnO nanostructures obtained in mixtures of ionic liquids with organic solvents

ZnO nanoparticles were synthesized in mixtures of ionic liquids based on imidazolium cation with organic solvents (dimethyl sulfoxide and ethylene glycol) by a simple, one-step solution route at low temperature. The effect of these mixtures on the morphology, size and properties of as obtained ZnO nanopowders was investigated. The obtained nanopowders have been characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), UV-Vis absorption spectroscopy (UV-Vis) and photoluminescence (PL). The effect of the ionic liquid mixture on the photocatalytic degradation of methylene blue has been analysed. The XRD studies confirmed the hexagonal wurtzite structure of the obtained ZnO powder. The UV-Vis absorption spectra present the typical shape for ZnO, with a broad band situated in the UV region, with the maximum around 360 nm. The calculated band-gap energy is in interval 3.25–3.28 eV. The synthesized ZnO nanopowders have high photocatalytic activity against methylene blue, the best results being obtained when 1-ethyl-3-methylimidazolium tetrafluoroborate was used as the solvent.

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Ground level ozone (O3) associated with radon (222Rn) and particulate matter (PM) concentrations in Bucharest metropolitan area and adverse health effects

The aim of this paper is to contribute with new information in the application of ground based radon (²²²Rn) observations to atmospheric research, namely its relation with air pollution due to ground-level ozone (O₃) and particle matter in two size fractions (PM10 and PM2.5) for Bucharest metropolitan area in Romania. During January 1–December 31, 2011, ground levels of radon, ozone and particulate matter (PM) have been continuously monitored in synergy with the main meteorological parameters (air temperature, humidity and pressure), and daily global air quality indices. A systematic analysis of surface ozone observations of ground level radon, ozone and PM is presented. Observational results indicate the following yearly daily mean ground level concentrations: 40.26 ± 7.54 Bq/m³ for radon, 90.51 μg/m³ for ozone, 35.96 μg/m³ for PM2.5, and 40.91 μg/m³ for PM10. The assessment of the results showed the influence of local and meteorological conditions on the daily mean radon, ozone and PM concentrations. However, in densely populated metropolitan area of Bucharest the mean daily values of ozone, PM2.5, PM10, and attached ²²²Rn are sometimes higher than European Community limit values leading to serious public concern during the last years. Due to the high risk of increased levels of O₃, PM2.5, PM10, and attached ²²²Rn on human health respiratory function (especially for children and older persons), and urban green, the results are very useful for atmospheric, radiological protection, epidemiological and environmental studies.     

In situ study of electrochromic properties of self-assembled TiO2 nanotubes

Electrochromical properties of anodic self-assembled nanotubes were investigated. It was found that amorphous titania nanotubes were able to insert H⁺ ions in a highly reversible manner. Coloration of the TiO₂ nanotubes occurred at potentials below ?0.5 V vs. Ag/AgCl in 1M (NH₄)₂SO₄ aqueous solution. The proton insertion reaction probably leads to the formation of a Ti³⁺/Ti⁴⁺ solid solution in the amorphous titania electrode, as was shown by the analysis of the derivative curve. The nanotubular titania electrode shows reasonable color efficiency when compared with other electrochromic materials and it is a promising candidate for the fabrication of low-cost interdigitated electrochromic devices.     

Super-energy and Killing-Yano tensors

In this paper we investigate a class of basic super-energy tensors, namely those constructed from Killing-Yano tensors, and give a generalization of super-energy tensors for cases when we start not with a single tensor, but with a pair of tensors.     

Whole‐Cell‐Catalyzed Multiple Regio‐ and Stereoselective Functionalizations in Cascade Reactions Enabled by Directed Evolution

Biocatalytic cascade reactions using isolated stereoselective enzymes or whole cells in one‐pot processes lead to value‐added chiral products in a single workup. The concept has been restricted mainly to starting materials and intermediate products that are accepted by the respective wild‐type enzymes. In the present study, we exploited directed evolution as a means to create E. coli whole cells for regio‐ and stereoselective cascade sequences that are not possible using man‐made catalysts. The approach is illustrated using P450‐BM3 in combination with appropriate alcohol dehydrogenases as catalysts in either two‐, three‐, or four‐step cascade reactions starting from cyclohexane, cyclohexanol, or cyclohexanone, respectively, leading to either (R,R)‐, (S,S)‐, or meso‐cyclohexane‐1,2‐diol. The one‐pot conversion of cyclohexane into (R)‐ or (S)‐2‐hydroxycyclohexanone in the absence of ADH is also described.