Pressure‐Tuneable Visible‐Range Band Gap in the Ionic Spinel Tin Nitride

The application of pressure allows systematic tuning of the charge density of a material cleanly, that is, without changes to the chemical composition via dopants, and exploratory high‐pressure experiments can inform the design of bulk syntheses of materials that benefit from their properties under compression. The electronic and structural response of semiconducting tin nitride Sn₃N₄ under compression is now reported. A continuous opening of the optical band gap was observed from 1.3 eV to 3.0 eV over a range of 100 GPa, a 540 nm blue‐shift spanning the entire visible spectrum. The pressure‐mediated band gap opening is general to this material across numerous high‐density polymorphs, implicating the predominant ionic bonding in the material as the cause. The rate of decompression to ambient conditions permits access to recoverable metastable states with varying band gaps energies, opening the possibility of pressure‐tuneable electronic properties for future applications.     

Nickel surface anodic oxidation and electrocatalysis of oxygen evolution

The processes of nickel surface anodic oxidation taking place within the range of potentials preceding oxygen evolution reaction (OER) in the solutions of 1 M KOH, 0.5 M K₂SO₄, and 0.5 M H₂SO₄ have been analyzed in the present paper. Metallic nickel, thermally oxidized nickel, and black nickel coating were used as Ni electrodes. The methods of cyclic voltammetry and X-ray photoelectron spectroscopy were employed. The study was undertaken with a view to find the evidence of peroxide-type nickel surface compounds formation in the course of OER on the Ni electrode surface. On the basis of experimental results and literature data, it has been suggested that in alkaline solution at E ≈ 1.5 V (RHE) reversible electrochemical formation of Ni(IV) peroxide takes place according to the reaction as follows: This reaction accounts for both the underpotential (with respect to ) formation of O₂ from NiOO₂ peroxide and also small experimental values of dE/dlgi slope (<60 mV) at low anodic current densities, which are characteristic for the two-electron transfer process. It has been inferred that the composition of the γ-NiOOH phase, indicated in the Bode and revised Pourbaix diagrams, should be ∼5/6 NiOOH + ∼1/6 NiOO₂. The schemes demonstrating potential-dependent transitions between Ni surface oxygen compounds are presented, and the electrocatalytic mechanisms of OER in alkaline, acid, and neutral medium have been proposed.     

Femtosecond real-time probing of transition state dynamics in a surface photoreaction: methyl desorption from CH3I on MgO(100)

A novel experimental approach to the investigation of surface adsorbate reaction dynamics is presented. The direct time-resolved monitoring of the surface reaction transition state and product formation dynamics were accomplished via pump-probe mass spectrometry. As an example, methyl iodide molecules adsorbed at submonolayer coverage on an ultrathin magnesia film on Mo(100) were photoexcited to the A-band by ultrafast laser pulse irradiation. Employing time-delayed multiphoton ionization the dynamics of the dissociative methyl iodide transition state and of the emerging methyl photoproduct could be detected with femtosecond resolution. The reaction times deduced from the temporal evolution of the methyl ion mass signal indicate a strong interaction of the methyl fragment with the substrate surface prior to desorption.     

Prussian Blue Modified Amperometric Hg2+ Ion Biosensor Based on Glucose Oxidase Inhibition

In this research a Hg²⁺ ion biosensor was developed by combining Prussian blue (PB) with glucose oxidase (GOx) – an enzyme that can be inhibited by Hg²⁺ ions. An application of PB in the design of Hg²⁺ ion biosensor enabled detecting changes in hydrogen peroxide reduction current at low operational potential of 0.2 vs Ag|AgCl,KCl_sat. The described Hg²⁺ ion biosensor exhibited wide linear range from 27 μM to 247 μM of Hg²⁺ and higher maximal detectable concentration of Hg²⁺ than other GOx inhibition-based biosensors, making it convenient for the analysis of samples with high concentration of Hg²⁺ ions.     

Experimental and theoretical study of the OH vibrational spectra and overtone chemistry of gas-phase vinylacetic acid

In this study we present the gas-phase vibrational spectrum of vinylacetic acid with a focus on the nu = 1-5 vibrational states of the OH stretching transitions. Cross sections for nu = 1, 2, 4 and 5 of the OH stretching vibrational transitions are derived on the basis of the vapor pressure data obtained for vinylacetic acid. Ab initio calculations are used to assist in the band assignments of the experimental spectra, and to determine the threshold for the decarboxylation of vinylacetic acid. When compared to the theoretical energy barrier to decarboxylation, it is found that the nu OH = 4 transition with thermal excitation of low frequency modes or rotational motion and nu OH = 5 transitions have sufficient energy for the reaction to proceed following overtone excitation.     

Platinum–tin complexes as catalysts for the anodic oxidation of borohydride

Platinum–tin complexes were prepared by the reduction of Pt(IV) with Sn(II) in HCl media and studied by light absorption spectrometry, X-ray photoelectron spectroscopy (XPS), and electron microscopy. The formation of three complexes, H₃[Pt(SnCl₃)₅], H₂[Pt(SnCl₃)₂Cl₂], and H₂[Pt₃(SnCl₃)₈], depending on HCl and SnCl₂ concentrations, has been shown. The glassy carbon (GC) electrode modified in the complexes solutions was found to be an electrocatalyst for borohydride oxidation in a 1.0-M NaOH solution. Comparison of BH₄ ⁻ electrooxidation on Pt and on GC modified with platinum–tin complexes has shown that catalytic hydrolysis of BH₄ ⁻ did not proceed in the latter case in contrast to its oxidation on the Pt electrode, and only direct BH₄ ⁻ oxidation has been observed in the positive potentials scan. The activity of Pt–Sn complexes for BH₄ ⁻ oxidation changes with time and eventually decreases due to Sn(II), bound in the complex with Pt(II), oxidation by atmospheric oxygen. The complexes may be renewed by addition of missing amounts of SnCl₂ and HCl.     

Comparison of the efficacy of sulfurization agents in decreasing the sheet resistance of polyamide and polyethylene with copper sulfide layers and influence of their compositions

The process of obtaining semiconductive and electrical conductive layers of copper sulfides by the sorption — diffusion method on polymers (polyamide 6 and low density polyethylene) using solutions of potassium pentathionate, K₂S₅O₆, and higher polythionic acids, H₂S _n O₆ (n = 21, 33), was investigated. The layers were characterized for compositional and electrical properties by X-ray diffraction (XRD) analysis and sheet resistance measurements. The thickness of copper sulfides layers on polyamide and polyethylene increased with increasing time of polymer sulfurization and varied from 10 to 43 μm. The variations of the sheet resistance of copper sulfides layers formed on the surface of polymers on sulfurization agent used, the conditions of sulfurization, chemical and phase composition of the obtained layers were established. Sheet resistance of copper sulfides layers decreases with increasing time of the duration of sulfurization and the number of sulfur atoms in the polythionate anion. The sheet resistance values for copper sulfide layers formed on the polyamide surface are much lower than those of Cu _x S formed on the polyethylene surface. XRD showed the predomination of Cu _x S phases with low x values.      

A joint universality theorem for periodic Hurwitz zeta-functions. II

We obtain a joint universality theorem for periodic Hurwitz zeta-functions under weaker hypotheses than those in the previous papers of the first author.