Oxidation of Np(IV) with hydrogen peroxide in carbonate solutions

Oxidation of Np(IV) with hydrogen peroxide in NaHCO₃-Na₂CO₃ solutions was studied by spectrophotometry. In NaHCO₃ solution, Np(IV) is oxidized to Np(V) and partially to Np(VI). It follows from the electronic absorption spectra that Np(IV) in 1 M Na₂CO₃ forms with H₂O₂ a mixed peroxide-carbonate complex. Its stability constant β is estimated at 25–30. The Np(IV) bound in the mixed complex disappears in a first-order reaction with respect to [Np(IV)]. The first-order rate constant k’ is proportional to [H₂O₂] in the H₂O₂ concentration range 2.5–11 mM, but further increase in [H₂O₂] leads to a decrease in k′. The bimolecular rate constant k = k′/[H₂O₂] in solutions containing up to 11 mM H₂O₂ increases in going from 1 M NaHCO₃ to 1 M Na₂CO₃ and significantly decreases with a further increase in the carbonate content. The activated complex is formed from Np(IV) peroxide-carbonate and carbonate complexes. Synchronous or successive electron transfer leads to the oxidation of Np(IV) to Np(V). Large excess of H₂O₂ oxidizes Np(V) to Np(VI), which is then slowly reduced. As a result, Np(V) is formed in carbonate solutions at any Np(IV) and H₂O₂ concentrations.     

A Cascade Enzyme System Integrating Peroxidase Mimic with Catalase for Linear Range Expansion of H2O2 Assay: A Mechanism and Application Study

Peroxidase (POD) Nanozyme-based hydrogen peroxide (H₂O₂) detection is popular, but hardly adapt to high concentration of H₂O₂ owing to narrow linear range (LR) and low LR maximum. Here, a solution of combining POD and catalase (CAT) is raised to expand the LR of H₂O₂ assay via decomposing part of H₂O₂. As a proof of concept, a cascade enzyme system (rGRC) is constructed by integrating ruthenium nanoparticles (RuNPs), CAT and graphene together. The rGRC-based sensor does perform an expanded LR and higher LR maximum for H₂O₂ detection. Meanwhile, it is confirmed that LR expansion is closely associated with apparent K_m of rGRC, which is determined by the relative enzyme activity between CAT and POD both in theory and in experiment. At last, rGRC is successfully used to detect high concentration of H₂O₂ (up to 10 mm ) in contact lens care solution, which performs higher assay accuracy (close to 100% recovery at 10 mm of H₂O₂) than traditional POD nanozymes. This study brings up a kind of POD/CAT cascade enzyme system and provides a new concept for accurate and facile H₂O₂ detection. Additionally, it replenishes a new enzyme-substrate model of achieving the same pattern with competitive inhibition in enzyme reactions.     

The influence of calcium chloride deicing salt on phase changes and damage development in cementitious materials

The conventional CaCl₂–H₂O phase diagram is often used to describe how calcium chloride behaves when it is used on a concrete pavement undergoing freeze-thaw damage. However, the chemistry of the concrete can alter the appropriateness of using the CaCl₂–H₂O phase diagram. This study shows that the Ca(OH)₂ present in a hydrated portland cement can interact with CaCl₂ solution creating a behavior that is similar to that observed in isoplethal sections of a ternary phase diagram for a Ca(OH)₂–CaCl₂–H₂O system. As such, it is suggested that such isoplethal sections provide a reasonable model that can be used to describe the behavior of concrete exposed to CaCl₂ solution as the temperature changes. Specifically, the Ca(OH)₂ can react with CaCl₂ and H₂O resulting in the formation of calcium oxychloride. The formation of the calcium oxychloride is expansive and can produce damage in concrete at temperatures above freezing. Its formation can also cause a significant decrease in fluid ingress into concrete. For solutions with CaCl₂ concentrations greater than about 11.3% (by mass), it is found that calcium oxychloride forms rapidly and is stable at room temperature (23 °C).     

Oxidation of Am(III) to Am(IV) with ozone in solutions of heteropolyanions

Oxidation of Am(III) in the presence of K₁₀P2W₁₇O₆₁ and K₈SiW₁₁O₃₉ (L) at 20dGC was studied by spectrophotometry. Am(III) is oxidized with ozone to Am(IV) only in the pH range 3.5–1.0. In the case of formation of a complex with Am: L = 1: 1, the reaction is approximately first-order with respect to the metal, and its rate decreases with a decrease in pH from 3.5 to 1.0. Am(IV) in solution in the presence of ozone is slowly reduced with products of water α-ray radiolysis, predominantly with ?₂?₂. The rate constant of the reaction of Am(IV) with ?₂?₂ was estimated.     

Effect of strain on the frequency-independent parameters of the equivalent circuit of island gold films

This paper deals with the outcome of a follow-up of our earlier work on the effect of strain on the frequency-dependent resistance (r_p) of island gold films whose mass thicknesses in nm were 0.5, 1.2, 2.4, 3.5, 5 and 10. The frequency-independent parameters of the equivalent circuit of island metal films are R_b, R_g and C_g where R_b is the macroscopic resistance that associates the conduction within the interior (bulk) of islands, R_g is the macroscopic resistance that accompanies the conduction across the gaps among islands and C_g is the macroscopic capacitance of the film that results from the islands and gaps. We deduced the least-square values of R_b,R_g and C_g for our films by inserting the experimental values of r_p and the corresponding angular frequencies (ω) into the known equation that relates r_p to both of ω and the frequency independent parameters; this deduction was done via a computerized analysis. We found that: (1) For the tensional longitudinal strain, an increase in its magnitude is associated with an increase in R_g and a decrease in C_g. (2) For the compressional longitudinal strain, an increase in its value is accompanied by a decrease in R_g and an increase in C_g. (3) R_b is nearly invariant with strain. (4) The increase in the mass thickness of the island gold films is associated with: (i) a decrease in R_b,R_g and an increase in C_g. (ii) a decrease in the gauge factor of the studied films.     

New Results for Superconductivity in κ-(BEDT-TTF)2Cu(NCS)2 When an Applied Magnetic Field is Aligned Parallel to the Conducting Planes

Using a Tunnel Diode Oscillator technique, we have measured the effect of a parallel magnetic field on the in-plane rf penetration depths in organic [α- (BEDT-TTF)₂NH₄Hg(SCN)₄ and κ-(BEDT-TTF)₂Cu(NCS)₂] and heavy fermion (CeCoIn₅) superconductors. We show that in this particular ge- ometry, the effects due to vortex activity are minimized. The penetration depth is then governed by the density of superconducting carriers. It is shown in many experiments including rf penetration depth measurement that α-(BEDT-TTF)₂NH₄Hg(SCN)₄ and CeCoIn₅ have s-wave and d-wave pairing symmetries, respectively. The pairing symmetry of κ-(BEDT-TTF)₂-Cu(NCS)₂, however, is still an unsolved matter, showing inconsistent results. In this paper, the penetration depth of κ-(BEDT-TTF)₂Cu(NCS)₂ is shown to be more similar to α-(BEDT-TTF)₂NH₄Hg(SCN)₄ than to CeCoIn₅, suggesting the pairing is nodeless.     

Orientation and growth behavior of CaHfO3 thin films on non-oxide substrates

The growth behavior of CaHfO₃ on (001) Ni and Ge substrates was examined. CaHfO₃ is a perovskite insulator that is suitable for applications as a buffer layer or gate dielectric. The tendency for CaHfO₃ growth on both (001) Ni and (001) Ge substrates is to orient with the CaHfO₃ (200) + (121) planes parallel to the surface, which corresponds to the (110) orientation in the pseudo-cubic geometry. This differs from that of CaHfO₃ on perovskites, such as (001) LaAlO₃, where a pseudo-cube-on-cube orientation is observed.     

Kinetics of redox processes in manganese oxides

The redox processes in ceramic and powder samples of α-Mn₂O₃ (kurnakite) and β-Mn₃O₄ (hausmannite) have been studied in the temperature range 20–1000°C. The results demonstrate that the conversion of α-Mn₂O₃ to β-Mn₃O₄ in the binary system Mn-O is essentially irreversible, even if there are nucleation centers in the form of the higher oxide α-Mn₂O₃ during the oxidation of hausmannite. It is shown that the high reactivity of hausmannite ground in a WC mill is not due to a mechanochemical effect. Grinding-induced contamination has a significant effect on the oxidation behavior of the system: the impurities incorporated into the sample during grinding in a mill favor complete (WC contamination) or partial (Fe contamination) conversion of hausmannite to kurnakite. Hausmannite contaminated with tungsten carbide oxidizes by a catalytic mechanism. In the case of Fe impurities, oxidation follows a solid-state mechanism, through the formation of restricted Fe_xMn_2?x O₃ solid solutions.     

First principles study of isotope effect in hydrogen-bonded K3H(SO4)2: I — stable structures

The first principles calculations for K₃H(SO₄)₂ (KHS) system are performed in order to determine its stable structure in the presence of the hydrogen or the deuterium in its hydrogen bond, and to discuss the origin of the large isotope effect in the KHS system. As a result, a reasonable value of the antiferroelectric interaction energy is obtained. It is also found that the position of the hydrogen is closer to the center of the hydrogen bond than that of the deuterium, based on the calculated results of the proton-position dependence of the oxygen–oxygen distance and on the experimental fact that the oxygen-oxygen distance in K₃D(SO₄)₂ (DKHS) is larger than that in KHS.     

Le conducteur ionique (LaO)AgS. observation en microscopie electronique de la migration de l'argent

(LaO)AgS is prepared by reaction of Ag₂S on La₂O₂S. It has a compound of tetragonal symmetry; the structure is formed by alternating (LaO)_n and (AgS)_n sheets. It is also a good ionic conductor. In an electron microscope it decomposes, with metallic silver being separated out to form filament whiskers or droplets. La₂O₂S₂, which is also formed, is unstable in the electron beam, and is quickly transformed into the oxysulfate (LaO)₂SO₄.     

Photosensitizing Metasurface Empowered by Enhanced Magnetic Field of Toroidal Dipole Resonance

Photochemical reaction exploiting an excited triplet state (T₁) of a molecule requires two steps for the excitation, i.e., electronic transition from the ground (S₀) to singlet excited (S₁) states and intersystem crossing to the T₁ state. A dielectric metasurface coupled with photosensitizer that enables energy efficient photochemical reaction via the enhanced S₀→T₁ magnetic dipole transition is developed. In the direct S₀→T₁ transition, the photon energy of several hundreds of meV is saved compared to the conventional S₀→ S₁→T₁ transition. To maximize the magnetic field intensity on the surface, a silicon (Si) nanodisk array metasurface with toroidal dipole resonances is designed. The surface of the metasurface is functionalized with ruthenium (Ru(II)) complexes that work as a photosensitizer for singlet oxygen generation. In the coupled system, the rate of the direct S₀→T₁ transition of Ru(II) complexes is 41-fold enhanced at the toroidal dipole resonance of a Si nanodisk array. The enhancement of a singlet oxygen generation rate is observed when the toroidal dipole resonance of a Si nanodisk array is matched with the direct S₀→T₁ transition wavelength of Ru(II) complexes.     

Annealing behavior of TiO<Subscript>2</Subscript>-sheathed Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

TiO₂-sheathed Ga₂O₃ one-dimensional (1D) nanostructures were synthesized by thermal evaporation of GaN powders and then sputter-deposition of TiO₂. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis results indicate that the Ga₂O₃ cores are of a single crystal nature with a monoclinic structure while the TiO₂ shells are amorphous. Photoluminescence (PL) emission is slightly decreased in intensity by TiO₂ coating, but it is significantly increased by thermal annealing in an oxygen atmosphere. The emission peak is also shifted from ~500 to ~550 nm by oxygen annealing. The increase in the green emission is due to the increase in the concentration of the Ga vacancies in the cores by the inflow of oxygen during oxygen annealing. On the other hand, annealing in a nitrogen atmosphere leads to a red shift of the emission to ~700 nm originating from nitrogen doping.     

Damage in cement pastes exposed to MgCl<Subscript>2</Subscript> solutions

Magnesium chloride (MgCl₂) reacts with cement pastes resulting in calcium leaching and the formation of calcium oxychloride, which can cause damage. This paper examines the damage in different cement pastes exposed to MgCl₂ solutions. Volume change measurement and low temperature differential scanning calorimetry are used to characterize the formation of calcium oxychloride. Thermogravimetric analysis and X-ray fluorescence are used to quantify calcium leaching from Ca(OH)₂ and C-S-H. The ball-on-three-balls test is used to quantify the flexural strength reduction. Calcium oxychloride can form in cement pastes exposed to MgCl₂ solutions with a (Ca(OH)₂/MgCl₂) molar ratio larger than 1. As the MgCl₂ concentration increases, two-stages of flexural strength reduction are observed in the plain cement pastes, with the initial reduction primarily due to calcium leaching from Ca(OH)₂ and the additional reduction due to the calcium leaching from C-S-H (at MgCl₂ concentrations above 17.5 wt%). For the cement pastes containing fly ash, there is a smaller reduction in flexural strength as less Ca(OH)₂ is leached, while no additional reduction is observed at high MgCl₂ concentrations due to the greater stability of C-S-H with a lower Ca/Si ratio. The addition of fly ash can mitigate damage in the presence of MgCl₂ solutions.     

On the orthorhombic phase in ZrO2-based alloys

During TEM observation, a tetragonal (t) to orthorhombic (o) phase transformation often occurs in thin portions of ZrO₂-containing foils. This transformation is stress-induced and in some senses artefactual, in that the reaction product is actually a high-pressure phase, relative to monoclinic (m) ZrO₂, that can form from metastable t-ZrO₂ in the TEM because its density is intermediate between t- and m-ZrO₂. Examples of the formation of o-ZrO₂ in a number of different systems are given.     

Regulating Bulk‐Heterojunction Molecular Orientations through Surface Free Energy Control of Hole‐Transporting Layers for High‐Performance Organic Solar Cells

Interface properties are of critical importance for high‐performance bulk‐heterojunction (BHJ) organic solar cells (OSCs). Here, a universal interface approach to tune the surface free energy (γ_S) of hole‐transporting layers (HTLs) in a wide range through introducing poly(styrene sulfonic acid) sodium salts or nickel formate dihydrate into poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is reported. Based on the optimal γ_S of HTLs and thus improved face‐on molecular ordering in BHJs, enhanced fill factor and power conversion efficiencies in both fullerene and nonfullerene OSCs are achieved, which is attributed to the increased charge carrier mobility and sweepout with reduced recombination. It is found that the face‐on orientation‐preferred BHJs (PBDB‐TF:PC₇₁BM, PBDB‐T:PC₇₁BM, and PBDB‐TF:IT‐4F) favor HTLs with higher γ_S while the edge‐on orientation‐preferred BHJs (PDCDT:PC₇₁BM, P3HT:PC₇₁BM and PDCBT:ITIC) are partial to HTLs with lower γ_S. Based on the surface property–morphology–device performance correlations, a suggestion to select a suitable HTL in terms of γ_S for a specific BHJ with favored molecular arrangement is provided. This work enriches the fundamental understandings on the interface characteristics and morphological control toward high‐efficiency OSCs based on a wide range of BHJ materials.     

Oxidation of U(III) with water in the course of precipitation of its solid compounds from aqueous solutions

U(III) was precipitated from solution as a yellowish-brown precipitate under the action of NH₄OH or Na₂B₄O₇ solutions at pH ～7.5. The electronic spectra showed the presence of substantial amounts of U(OH)₃ in the precipitate, decreasing within a few minutes. Therefore, pure U(OH)₃ can hardly be obtained. A brown precipitate is formed when a U(III) solution is added to an NH₄F solution. An X-ray phase analysis shows that anhydrous UF₃ is the only crystalline compound in the precipitate. The synthesis of U(III) phosphate was unsuccessful, because uranium was completely oxidized to U(IV). Thus, preparation of U(III) phosphate compounds from aqueous solutions is hardly possible.     

Heterostructures Built in Metal Hydrides for Advanced Hydrogen Storage Reversibility

Hydrogen storage is a vital technology for developing on-board hydrogen fuel cells. While Mg(BH₄)₂ is widely regarded as a promising hydrogen storage material owing to its extremely high gravimetric and volumetric capacity, its poor reversibility poses a major bottleneck inhibiting its practical applications. Herein, a facile strategy to effectively improve the reversible hydrogen storage performance of Mg(BH₄)₂ via building heterostructures uniformly inside MgH₂ nanoparticles is reported. The in situ reaction between MgH₂ nanoparticles and B₂H₆ not only forms homogeneous heterostructures with controllable particle size but also simultaneously decreases the particle size of the MgH₂ nanoparticles inside, which effectively reduces the kinetic barrier that inhibits the reversible hydrogen storage in both Mg(BH₄)₂ and MgH₂. More importantly, density functional theory coupled with ab initio molecular dynamics calculations clearly demonstrates that MgH₂ in this heterostructure can act as a hydrogen pump, which drastically changes the enthalpy for the initial formation of B H bonds by breaking stable B B bonds from endothermic to exothermic and hence thermodynamically improves the reversibility of Mg(BH₄)₂. It is believed that building heterostructures provides a window of opportunity for discovering high-performance hydrogen storage materials for on-board applications.     

Hysteresis in Transport Critical-Current Measurements of Oxide Superconductors

We have investigated magnetic hysteresis in transport critical-current (I_c) measurements of Ag-matrix (Bi,Pb)₂Sr₂Ca₂Cu₃O_10–x (Bi-2223) and AgMg-matrix Bi₂Sr₂CaCu₂O_8+x (Bi-2212) tapes. The effect of magnetic hysteresis on the measured critical current of high temperature superconductors is a very important consideration for every measurement procedure that involves more than one sweep of magnetic field, changes in field angle, or changes in temperature at a given field. The existence of this hysteresis is well known; however, the implications for a measurement standard or interlaboratory comparisons are often ignored and the measurements are often made in the most expedient way. A key finding is that I_c at a given angle, determined by sweeping the angles in a given magnetic field, can be 17 % different from the I_c determined after the angle was fixed in zero field and the magnet then ramped to the given field. Which value is correct is addressed in the context that the proper sequence of measurement conditions reflects the application conditions. The hysteresis in angle-sweep and temperature-sweep data is related to the hysteresis observed when the field is swept up and down at constant angle and temperature. The necessity of heating a specimen to near its transition temperature to reset it to an initial state between measurements at different angles and temperatures is discussed.     

Full Wafer In Situ Deposition of Thallium Lead Superconductors

Thin films of (Tl,Pb)Sr₂Ca_0.8Y_0.2Cu₂O₇, and (Tl,Pb)Sr₂CuO₅ can be grown in a single step process which involves sputter deposition from a mixed oxide target and simultaneous thermal evaporation of Tl₂O. The use of a radiant heater has allowed extension of this in situ deposition process to full LaAlO₃ and NdGaO₃ wafers. Variations in the composition of the deposited film is < 4% across a 50 mm wafer while the thickness uniformity is ? 8%. The highest transition temperature for a (Tl,Pb)Sr₂Ca_0.8Y_0.2 Cu₂O₇ film thus far is 83 K. The RMS surface roughness of (Tl,Pb)Sr₂CuO₅ films is uniform across the wafer and approximately 1% of the film thickness for films 20 to 100 nm thick.     

Full Wafer In Situ Deposition of Thallium Lead Superconductors

Thin films of (Tl,Pb)Sr₂Ca_0.8Y_0.2Cu₂O₇, and (Tl,Pb)Sr₂CuO₅ can be grown in a single step process which involves sputter deposition from a mixed oxide target and simultaneous thermal evaporation of Tl₂O. The use of a radiant heater has allowed extension of this in situ deposition process to full LaAlO₃ and NdGaO₃ wafers. Variations in the composition of the deposited film is < 4% across a 50 mm wafer while the thickness uniformity is 8%. The highest transition temperature for a (Tl,Pb)Sr₂Ca_0.8Y_0.2 Cu₂O₇ film thus far is 83 K. The RMS surface roughness of (Tl,Pb)Sr₂CuO₅ films is uniform across the wafer and approximately 1% of the film thickness for films 20 to 100 nm thick.