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.     

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.     

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.     

Aerosol source (biomass,traffic and coal emission) apportionment in Lithuania using stable carbon and radiocarbon analysis*

In the present study, a combination of the stable carbon isotope ratio (¹³C/¹²C) with radiocarbon data (¹⁴C) allowed us to perform the aerosol source apportionment. Filter samples of PM₁ were collected during the warm and cold periods in rural and urban sites in Lithuania. The ¹⁴C/¹²C ratio of total carbon (TC) was measured using the single stage accelerator mass spectrometer quantifying of fossil and non-fossil derived aerosol emissions. The δ¹³C value was measured using an elemental analyser interfaced with an isotope ratio mass spectrometer. We have found that the highest fraction of contemporary carbon (f_c?=?0.82) was measured during a warm period in a rural location. A higher fraction of fossil fuel-derived carbon was observed for air masses transported from highly industrialized Western European regions during both seasons. Isotope mass balance calculations revealed that the traffic emissions composed 15 and 25?% in rural and urban sites, respectively, and did not change during either season. Input from coal-derived aerosol particles was estimated to be 15?% at an urban site during the cold period. The combination of the stable carbon isotope ratio with the radiocarbon data allowed us to distinguish coal, liquid fossil fuel combustion, and non-fossil derived aerosol particle emissions.     

Horse heart cytochrome c entrapped into the hydrated liquid-crystalline phases of phytantriol: X-ray diffraction and Raman spectroscopic characterization

Small angle X-ray diffraction (SAXD), resonance Raman (RR) spectroscopy with 413 nm excitation, and non-resonance Raman technique with 785 nm excitation were used to probe the influence of entrapped cytochrome c (Cyt c) on the structure of hydrated phytantriol (Phyt) liquid-crystalline phases as well as conformational changes of heme group and secondary structure of the protein. SAXD measurements indicated that incorporation of Cyt c affects both nanostructure dimensions and type of liquid-crystalline phases of hydrated Phyt. The unit cell dimensions decrease with increasing Cyt c concentration for all phases. In addition, protein perturbs the nanostructure of Q(230) and Q(224) liquid-crystalline phases of hydrated Phyt to such an extent that they transform into the Q(229) phase with the Im3m space group. RR data revealed that entrapment of oxidized Cyt c into the Q(230) phase at 1 wt.% content results in near complete reduction of central iron ion of the heme group, while its low-spin state and six-ligand coordination configuration are preserved. Based on the analysis of heme out-of-plane folding vibration near 568 cm(-1) (γ(21)) and ν(48) mode at 633 cm(-1), it was demonstrated that the protein matrix tension on the heme group is relaxed upon incorporation of protein into Q(230) phase. Non-resonant Raman bands of difference spectra showed the preservation of α-helix secondary structure of Cyt c in the liquid-crystalline phase at relatively high (5 wt.%) content. The Cyt c induced spectroscopic changes of Phyt bands were found to be similar as decrease in temperature.     

Hydrogen yield from water radiolysis in the presence of zeolites

This paper reports a study of the decomposition of water by gamma radiolysis in the presence of zeolites ZSM-5, SAPO-5, and MOR. The irradiation is performed using ⁶⁰Co as a source with 1.12×10¹⁵ Bq activity at a 8.3 kGy/h dose rate. The stable products of radiolysis as well as the other chemical species are measured by mass spectrometry. The calculated radiation yield (G_{H 2}) generally decreases in the order: H-ZSM-5>Na-ZSM-5>H-SAPO-5>MOR under the given experimental conditions; the yield is higher in the presence of these catalysts than in their absence.     

Light trapping effect in silicon wafers with anodically etched surfaces

Received: 10 May 1996/Accepted: 19 November 1996