Diverse morphologies of zinc oxide nanoparticles and their electrocatalytic performance in hydrogen production

Hydrogen is considered an attractive alternative to fossil fuels,but only a small amount of it is produced from renewable energy,making it not such a clean energy carrier after all.Producing hydrogen through water electrolysis is promising,but using a cost-effective and high-performing catalyst that has longterm stability is still a challenge.This study exploits,for the first time,the potential of zinc oxide nanoparticles with diverse morphologies as catalysts for the electrocatalytic production of hydrogen from water.The morphology of the nanoparticles(wires,cuboids,spheres)was easily regulated by changing the concentration of sodium hydroxide,used as the shape controlling agent,during the synthesis.The spherical morphology exhibited the highest electrocatalytic activity at the lowest potential voltage.These spherical nanoparticles had the highest number of oxygen vacancies and lowest particle size compared to the other two morphologies,features directly linked to high catalytic activity.However,the nanowires were much more stable with repeated scans.Density-functional theory showed that the presence of oxygen vacancies in all three morphologies led to diminished band gaps,which is of catalytic interest.     

Catalyst and substituent effects on the rhodium(II)-catalysed intramolecular Buchner reaction

Intramolecular rhodium(II)-catalysed aromatic addition (Buchner) reactions of a range of α- and β-substituted α-diazoketones are reported. Both steric and electronic effects are evident for the aromatic additions investigated. In general, highly efficient aromatic addition is achieved through use of rhodium carboxylates bearing electronegative ligands, such as rhodium trifluoroacetate, while aromatic addition employing rhodium catalysts with more electron-donating ligands, such as rhodium caprolactam, is less efficient. Excellent levels of diastereoselectivity are possible for this process in the presence of rhodium acetate and rhodium caprolactam, however, a reduction in diastereocontrol is generally associated with use of the more reactive, electronegative catalysts. Interestingly, these catalyst effects can be overcome through the steric effects of the substituents on the α-diazoketone substrates, with the presence of sterically bulky substituents at the 2- or 3-position rendering the aromatic addition essentially catalyst independent in terms of efficiency and diastereocontrol.     

Reactions of Charged Substrates. 6. The Methoxymethyl Carbenium Ion Problem. 1. A Semiempirical Study of the Kinetic and Thermodynamic Stabilities of Linear and Cyclic Oxo- and Thiocarbenium Ions Generated from Pyridinium and Dimethylanilinium Ions

AM1-calculated energy profiles for dissociation of (methoxymethyl)pyridinium and dimethylanilinium ion substrates show that the methoxymethyl carbenium ion is not sufficiently stable to exist as an intermediate on the reaction coordinate for this model reaction. [(Thiomethoxy)methyl]pyridinium ion, however, has a distinct transition state because of the stability of the resulting ion-neutral complex. The complete potential energy surfaces for water displacement on the methoxymethyl substrate with either pyridine or dimethylaniline as the leaving group show distinct transition states and very flat surfaces for the ion-neutral complexes in which interaction of the carbenium ion with both leaving group and nucleophile is stabilizing. Secondary systems studied, including linear methoxy and thiomethoxy substrates, 5- and 6-membered cyclic oxo and thio substrates, and ribosyl-, xylopyranosyl-, and glucopyranosylpyridinium ions yield ion-neutral complexes with sufficient intrinsic stability to exist as intermediates. Comparison with solution data, primarily activation entropy and Br?nsted coefficients, suggests that the sugar oxocarbenium ions, either as distinct, solvent-equilibrated intermediates or elements of ion-neutral complexes, are formed by unimolecular dissociation of the respective substrates in solution.     

Regenerating a symmetry in asymmetric dark matter

Asymmetric dark matter theories generically allow for mass terms that lead to particle-antiparticle mixing. Over the age of the Universe, dark matter can thus oscillate from a purely asymmetric configuration into a symmetric mix of particles and antiparticles, allowing for pair-annihilation processes. Additionally, requiring efficient depletion of the primordial thermal (symmetric) component generically entails large annihilation rates. We show that unless some symmetry completely forbids dark matter particle-antiparticle mixing, asymmetric dark matter is effectively ruled out for a large range of masses, for almost any oscillation time scale shorter than the age of the Universe.     

Use of the surfactant 3-(3-cholamidopropyl)-dimethyl-ammoniopropane sulfonate in hydrophobic interaction chromatography of proteins

Isocratic hydrophobic interaction chromatography of five proteins has been carried out using mobile phases containing the surfactant 3-(3-cholamidopropyl)-dimethylammoniopropane sulfonate (CHAPS). Linear relationships were found between log k' and ammonium sulfate concentrations for all the proteins with CHAPS in the submicellar concentration range. The slope of such a plot decreases monotonically as CHAPS concentration is increased. To a first approximation, the effect of CHAPS on protein retention can be explained in terms of a competitive binding model. However, CHAPS does show differential effects on the elution of proteins, substantially altering selectivity. The use of a normalized capacity factor, k'/k'o, proves useful for comparing retention times of different proteins as a function of CHAPS concentration. The magnitudes of k'/k'o were found to be inversely correlated with the slopes of plots of log k' vs. ammonium sulfate concentration in the absence of CHAPS. Adsorption isotherms for CHAPS were determined over the working range of ammonium sulfate. The binding of CHAPS to the SynChropak Propyl stationary phase and its effects on retention were found to be readily reversible. For each protein, plots of k'/k'o vs. surface concentration of CHAPS were superposable for data obtained at different salt concentrations. These findings support a competitive binding model. A simple geometric argument for stationary phase occupancy provides a qualitative explanation for the observed surfactant selectivity.     

A small angle neutron scattering and electrochemical impedance spectroscopy study of the nanostructure of the iron chalcogenide glass ion-selective electrode

This paper presents a preliminary structural and interfacial study of the iron chalcogenide glass [i.e., Fe_x(Ge₂₈Sb₁₂Se₆₀)_100−x] ion-selective electrode (ISE) using small angle neutron scattering (SANS) and electrochemical impedance spectroscopy (EIS). SANS detected variations in the neutron scattering as a function of iron content in the chalcogenide glass. Furthermore, a change in the chalcogenide glass structure was observed at elevated iron dopant levels. Conversely, EIS was used to show that the iron chalcogenide membrane comprises various time constants, and the interfacial charge transfer reaction depends on the membrane iron content. Equivalent circuit modeling revealed that the charge transfer resistance decreases at elevated iron levels, and this may be related to the presence of iron defects in the glass. It is proposed that the iron chalcogenide membrane comprises an iron nanostructural network embedded in the amorphous matrix, and this directly influences the electrical conductivity and concomitant electrochemical reactivity of the glass.     

Solid targets for 99mTc production on medical cyclotrons

Recent disruptions in the molybdenum-technetium generator supply chain prompted a review of non-reactor based production methods for both ⁹⁹Mo and ^99mTc. Small medical cyclotrons (E _p ~ 16–24 MeV) are capable of producing Curie quantities of ^99mTc from isotopically enriched ¹⁰⁰Mo using the ¹⁰⁰Mo(p,2n)^99mTc reaction. Unlike most other metallic target materials for routine production of medical radioisotopes, molybdenum cannot be deposited by reductive electroplating from aqueous salt solutions. To overcome this issue, we developed a new process for solid molybdenum targets based on the electrophoretic deposition of fine ¹⁰⁰Mo powder onto a tantalum plate, followed by high temperature sintering. The targets obtained were mechanically robust and thermally stable when irradiated with protons at high power density.     

Spectral Interferences in Light Element Analysis

 Interferences (overlaps) occurring when lines of other elements affect either peak or background measurements can cause errors in quantitative WD analysis, but may be minimised by suitable choices of analysis conditions such as spectrometer crystal, background offsets, and pulse-height analyser settings. Computer spectrum-simulation is much more effective than reference to wavelength tables for investigating interferences. The ‘Virtual WDS’ simulation program developed by the present authors, hitherto applied only to ‘ordinary’ elements (Z ≥ 11), has been extended to light elements for which evaporated multilayers are used in place of true crystals. ‘Virtual WDS’ utilises experimentally recorded light-element K spectra and L and M spectra of heavier elements in the same wavelength range. It is impractical to record all high-order peaks, so computed line profiles are used, with widths and intensities interpolated from a limited set of observations. The relative positions of first and higher order peaks are affected significantly by the refractive index of the multilayer, requiring modification of the Bragg equation. Suppression of high orders by pulse-height analysis is less effective than for ‘normal’ wavelengths, owing to the breadth of the pulse-height distribution for low X-ray energies. Simulation using a Gaussian expression aids optimisation of threshold and window-width settings.