Preparation and electrochemical behavior of methylene blue intercalated into layered niobate K<Subscript>4</Subscript>Nb<Subscript>6</Subscript>O<Subscript>17</Subscript>

K₄Nb₆O₁₇ nano-layered compound was obtained by solid-phase synthesis and then methylene blue (MB) was intercalated into layered niobate K₄Nb₆O₁₇ interlayer I by a two-step guest-guest exchange method using the intercalation compound, methyl viologen (MV²⁺)–K₄Nb₆O₁₇, as precursor. The optically transparent MB⁺–K₄Nb₆O₁₇ nanocomposite thin film has been characterized by XRD, IR, TGA, elemental analysis, UV, and electrochemical measurements. It was estimated that the intercalated MB⁺ ions are mainly aggregated. The cyclic voltammogram of the MB⁺–K₄Nb₆O₁₇ nanocomposite thin film exhibited a fine diffusion-controlled cathodic process, which hints the possibility of being utilized as an electrode modifying material.     

Preparation,thermostability, and spectroscopic properties of Rhodamine 6G intercalated titanoniobate nanocomposite

Rhodamine 6G (R6G), a well-known fluorescent dye, has been intercalated into layered potassium titanoniobate (KTiNbO₅) through a guest–guest exchange method by using propylammonium titanoniobate (PrNH₃ ⁺-TiNbO₅) as a precursor. The synthesis process, the structure and morphology characterizations for lamellar nanocomposite have been investigated by means of XRD, FTIR, and SEM. The thermostability of R6G⁺-TiNbO₅ nanocomposite is discussed on the basis of thermogravimetric and calorimetric techniques. Absorption and fluorescence techniques are applied to study the photoresponse of R6G in hybrid film. The results indicate that R6G⁺ cations in thin film are highly fluorescent even at a high dye concentration, which may be due to the formation of J-dimers within the confined galleries.     

A study on electrodeposited Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloys

Zn_1−x Fe _x alloys were electrochemically deposited on AISI 4140 steel substrates from sulfate bath. The bath was consisted of 40 g dm⁻³ ZnSO₄·7H₂O, 20–40 g dm⁻³ FeSO₄·7H₂O_, 25 g dm⁻³ Na₃C₆H₅O₇, and 16 g dm⁻³ H₃BO_3. The effect of bath composition on the electrical resistivity, the phase structure, and the corrosion behavior were investigated by the current–voltage measurements versus temperature, the X-ray diffraction (XRD) analysis, the atomic absorption spectrometry analysis, and the polarization measurements, respectively. Iron content was shown to strongly affect the structure, the electrical resistivity and the corrosion stability of Zn–Fe alloys.     

Combustion synthesis and structural characterization of Li–Ti mixed nanoferrites

Polycrystalline samples of the mixed nanoferrites, Li_{0·5 + 0·5x} Ti _x Fe_{2·5 − 1·5x} O₄ (0·02 ≤ x ≤ 0·1), were prepared by combustion method at lower temperatures compared to the conventional high temperature sintering for the first time at low temperatures, using PEG which acts as a new fuel and oxidant. XRD patterns reveal a single-phase cubic spinel structure. The as synthesized Li–Ti ferrites are in nanocrystalline phase. The crystallite size was found to be in the range 16–27 nm. SEM images reveal rod-like morphology in all the samples with a discontinuous grain growth. The B–H loops have been traced using VSM technique, for all the compositions, at room temperature and the hysteresis parameters are calculated. Saturation magnetization decreases with increase in Ti content due to the fact that the Ti^4 + ion, which is a non-magnetic ion, replaces a magnetic Fe^3 + ion. The hysteresis loops show clear saturation at an applied field of ±10 kOe and the loops are highly symmetric in nature. The cation distribution is known indirectly by using saturation magnetization values.     

LaCrO3–VO x –YSZ anode material for solid oxide fuel cells operating on H2S-containing syngas

The perovskite type lanthanum chromite LaCrO₃ has been synthesized by nitrate-citrate combustion method. Phase transformations have been studied by using simultaneous differential scanning calorimetry and thermogravimetric analysis. The bulk structure of LaCrO₃ as well as the catalyst have been examined by X-ray diffraction (XRD). The cell was made using LaCrO₃–VO _x –YSZ anode. Impedance measurements showed that the polarization resistance was much smaller when the fuel changed from pure H₂ to 5000 ppm H₂S balance H₂. The performance for 5000 ppm H₂S balance H₂ was much better than with pure H₂ as a result of a lower polarization resistance. At 900 °C the maximum power density was 463 mW cm⁻² when using H₂S-containing H₂ as fuel. The presence of H₂S in the syngas significantly decreased the polarization resistance and improved the fuel cell performance. At 900 °C the achieved power density was 214 mW cm⁻² for H₂S (5000 ppm)-containing syngas (40% CO + 60% H₂).     

Synthesis and photoluminescence of Eu-doped Zn/Al layered double hydroxides

Eu-doped ZnAl-layered double hydroxides (ZnAl–LDHs) with various Zn²⁺/(Al³⁺+Eu³⁺) molar ratios from 1:1, 2:1, 3:1, to 4:1 were first synthesized by the coprecipitation method at room temperature and the Eu³⁺/Al³⁺ molar ratio of 0.06 was almost maintained. The obtained solids were characterized by powder X-ray diffraction (XRD), photoluminescent spectrum (PL), scanning electron microscope (SEM), infrared spectroscopy (IR), and thermogravimetric (TG) analysis. XRD results show that the crystallinity of the Eu-doped products gradually was improved when the Zn²⁺/(Al³⁺+Eu³⁺) molar ratio was higher than 2. The photoluminescent spectra of the Eu-doped ZnAl–LDHs are described by the well-known ⁵ D ₀–⁷ F _J transition (J = 1, 2, 3, 4) of Eu³⁺ ions with the strongest emission for J = 2.     

Effect of cobalt substitution on magnetic and transport properties of Nd0·5Sr0·5Mn1?xCoxO3 (x = 0·1, 0·3 and 0·5)

The magnetic and transport properties of the compounds Nd_0·5Sr_0·5Mn_1-x_{{\rm 1}-{x}}Co_x_{{x}}O₃ (x = 0·1, 0·3 and 0·5), synthesized by citrate–gel route have been investigated. The spin transition in cobaltates at low temperatures affects the magnetic as well as transport properties. The irreversibility behaviour between the zero-field cooled (ZFC) and field cooled (FC) magnetization as a function of temperature becomes stronger with increasing Co content. This is understood on the basis of glassy behaviour, which becomes more robust with increasing Co substitution. The non-saturating M–H behaviour indicates strong magnetic inhomogeneities which may cause the magnetic phase separation at the nanoscopic length scale. The double exchange interaction is stronger between Mn^3 +–O^2 −–Mn^4 + as compared to Co^3 +–O^2 −–Co^4 + pairs. Co-substitution suppresses the double exchange which will lead to cluster/spin glass like behaviour as well as semiconducting features due to localization of charge carriers (mobile e_g{e}_{\rm g} electrons).     

Frequency-dependent dielectric and electric modulus properties of Li–Ni–Sm–Fe–O spinel embedded in conducting polymer

Conducting polymeric nanocomposite containing Li–Ni–Sm–Fe–O spinel was synthesized by the chemical oxidizing of aniline in the presence of LiNi_0.5Sm_0.08Fe_1.92O₄ particles. The dielectric and electric modulus properties of the as-prepared samples were investigated over a frequency range from 10⁶ to 10⁹ Hz. The dielectric constant (ε′), dielectric loss (ε″) and dissipation factor (tan δ) for all samples presented relatively high values at low frequency and were found to decrease with the frequency. The values of ε′, ε″ and tan δ of the nanocomposite were lower than that of the pristine PANI. Electric modulus analysis had been carried out to understand the electrical relaxation process. The dielectric relaxation time for the nanocomposite became longer due to the introduction of LiNi_0.5Sm_0.08Fe_1.92O₄ particles lowering the crystallinity of PANI.     

Entropy Flow of Chemical Oscillating Reactions Involving Amino Acids

Variations of H⁺, Mn²⁺, and BrO₃^-{{\rm BrO}_3^-} during chemical oscillating reactions involving amino acids were investigated using H₂SO₄–BrO₃^-{{\rm BrO}_3^{-}} –Mn²⁺–acetone as an oscillator, and the thermodynamic functions (ΔS, ΔH, and ΔG) were calculated. The results indicated that the oscillating reaction is a process from disorder to order. In the oscillating system, the heat provided by the environment is used to increase the internal energy and entropy. When external positive entropy flow could make the system reach negative entropy flow, the system starts to oscillate and to maintain oscillations by a stable entropy.     

Fracture strength of ion-exchange silicate-containing dental glass ceramics

Dental glass ceramics with the composition of (0.2K, 0.8Na)₂O–xAl₂O₃–ySiO₂ (x = 0.4–0.8, y = 4–6) were studied for their mechanical properties. Different ion-exchange practices were used to modify the sub-surface concentration distributions of K⁺, Na⁺, and H⁺ of these glass ceramics. Specimens were heat-treated in molten KNO₃, and NaNO₃ + KNO₃ salt baths at 350–450 °C for the ion exchanges of K⁺ and Na⁺, or in the 4% acetic aqueous solution at 85 °C for a hydration treatment. Some glass ceramics contained a feldspar crystalline phase, which was not affected by different ion-exchange practices. Specimens with a single ion-exchange process or with the hydration treatment had higher flexural strength than those without either of these two treatments. For double ion-exchange specimens, the flexural strength increased with decreasing ion-exchange temperature. The double ion-exchange specimens had flexural strength up to 280 MPa, which was slightly lower than that of the single ion-exchange specimens, but much higher than that of the as-annealed specimens. However, the Weibull modulus of these double ion-exchange specimens was 5–8 because of the presence of large defects. For further increasing mechanical reliability, silicate-containing dental glass ceramics were required to have appropriate flaw controls and ion-exchange processes.     

Reduction of Np(V) with Fe(II) in weakly acidic solutions containing H<Subscript>2</Subscript>C<Subscript>2</Subscript>O<Subscript>4</Subscript>

The kinetics of the reaction of Np(V) with Fe(II) in dilute perchloric and nitric acid solutions containing H₂C₂O₄ was studied by spectrophotometry. In the range pH 1–2, the reaction rate is described by the equation d[Np(V)]/dt = k[Np(V)][Fe(II)][H₂C₂O₄]²[H⁺]^−1.6, k = 182 mol^−1.4 l^1.4 s⁻¹. The activation energy in the range 25–45°C is 26 kJ mol⁻¹. The reaction mechanism involves formation of Fe(II) and Np(V) oxalate complexes, followed by their reaction with the participation of the H⁺ ion.     

Synthesis,characterization and catalytic activity of Au supported on functionalized SBA-15 for low temperature CO oxidation

SBA-15 functionalization with 3-mercaptopropyltrimethoxysilane was used to prepare a supported gold catalyst for the low temperature CO oxidation reaction. Catalytic runs were performed at atmospheric pressure and T = 40–150 °C and the influence of different thermal treatments of the sample prior to reaction was studied. The modifications induced by the pre-treatments in the physico-chemical properties of both the carrier and the disperse phase were investigated by chemical analysis, CHS elemental analysis, N₂ adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), solid state cross-polarization magic-angle-spinning nuclear magnetic resonance spectroscopy (CPMAS NMR) of ²⁹Si and ¹³C and Fourier transform infrared spectroscopy (FTIR). The pre-treatment conditions were found to strongly affect both the gold particle size and the nature of the Au surface species. An appreciable catalytic activity was found on samples treated at 600 °C in H₂/He atmosphere, provided that the functionalizing agent had been completely removed by a previous high-temperature calcination.     

Influence of conditions on the potential of the couple of nonoxygenated U5+/U4+ ions bound in complexes with the P2W17O 6110? and SiW11O 398? anions

The formal potential of the couple of nonoxygenated U⁵⁺/U⁴⁺ ions bound in complexes with unsaturated heteropoly anions (HPAs) P₂W₁₇O₆₁¹⁰⁻ (I) and SiW_{11 O39}⁸⁻ (II) in 0–1 M NaNO₃ and 1 M (NaCl + HCl) in the range of pH 0.7–4.7 was measured. In 1 M NaNO₃ solutions at pH 4.7–3.0 for I and 4.3–3.9 for II, the formal potentials are constant: 0.820 and 0.730 V, respectively. They preserve approximately the same value with a decrease in pH to 0.7 in 1 M (NaCl + HCl). The potential noticeably decreases with a decrease in the NaNO₃ or NaCl concentration from 1 M to 0 (pH 4.1–4.7): to 0.09 and 0.05–0.06 V for I and II, respectively. Approximate constancy of the potential of the U⁵⁺/U⁴⁺ couple with a decrease in pH to 1 and lower distinguishes this couple from the M⁴⁺/M³⁺ couples (M = Ce, Am, Bk) whose potential appreciably grows with increasing acidity. This is due to the fact that the U⁵⁺ and M⁴⁺ ions in acid solutions remain in the form of complexes with the ratio M: HPA = 1: 2, whereas the M³⁺ ions pass into the form of 1: 1 complexes. Thus, variation of the formal potentials of all the M ^{n + 1}/M ⁿ⁺ couples in the presence of H⁺ and Na⁺ ions is associated with variation of the stability constants of the complexes M(HPA)₂, which, in turn, is caused by interaction of single-charged ions with HPA. However, the H⁺ and Na⁺ ions interact with HPA by different mechanisms and therefore affect the potential of the U⁵⁺/U⁴⁺ couple differently. Original Russian Text ? V.P. Shilov, A.B. Yusov, A.M. Fedoseev, Ph. Moisy, 2008, published in Radiokhimiya, 2008, Vol. 50, No. 5, pp. 393–396.     

Composition and stability constants of Np(V) fluoride complexes in chloride-fluoride melts

The absorption spectra of the NpO₂⁺ ion in the region of the ³ H ₅← ³ H ₄ magnetic dipole transition (∼1650 nm) in chloride-fluoride melts based on the eutectics NaCl-KCl-CsCl, NaCl-CsCl, and RbCl-CsCl at 650–750°C were recorded. The equilibrium concentrations of neptunium fluoride complexes in these melts were determined from the relative intensities of the NpO₂⁺ absorption bands. Existence of the complexes [NpO₂Cl₃F]³⁻ and [NpO₂Cl₂F₂]³⁻ was established, and the step stability constants of these complexes in melts of various cationic compositions were calculated.     

Fine-grained high-T c superconducting YBa2Cu3O7−δ powders through a modified citrate method

Synthesis and thermal decomposition characteristics of acetate-modified citrate precursor have been investigated. The intermediates of thermal decomposition exhibit enhanced reactivity. Quantitative estimation of the intermediate phases above 1125 K has been carried out and a directed reaction between Y₂Cu₂O₅ and BaCuO₂ phases is postulated for the formation of pure 1–2–3 phase. Isothermal calcination of the precursor at 1175 K for 9 h is sufficient for the complete conversion of the intermediate phases to SmBa₂Cu₃O_7−δ. The particles thus obtained are nearly spherical and monosized to give a BET surface area of 3 m²/g. The oxygenated powder showsT _c onset at 97 K for magnetic susceptibility and a narrow hysteresis for magnetization withH _c1 andJ _c values of 105Oe and 6×10⁴ A/cm² respectively at 77 K. EPR and EDAX techniques confirm the phase purity. Electron diffraction studies confirm XRD results. For oxygenated powder the excess charge (p ⁺) on square planar copper site [Cu-O] ^p * is estimated to be 0.28.     

Effect of CdS nanoparticles on photoluminescence spectra of Tb<Superscript>3 + </Superscript> in sol–gel-derived silica glasses

CdS nanoparticles doped with Tb^3 + were synthesized by sol–gel technique. The influence of CdS on the Tb^3 + glass was studied by UV-Visible and luminescence spectroscopy. The luminescence intensity of the glasses increased significantly in the presence of CdS nanoparticles. Terbium ions excited into the ⁵ D ₃ level have a rich emission spectrum in the 400–700 nm range decaying to different ⁷ F _J levels. The intensity of violet and blue luminescence from ⁵ D ₃ level is highly dependent on Tb^3 + concentration, on presence of CdS co-dopant and annealing conditions.     

Transport Properties under Magnetic Field and J c (H) Peak Effect on Single-Crystal Bi-2212 Whiskers

In this study, 50 nm–18 mm in length superconducting single-crystal Bi-2212 whiskers have been fabricated using glass-ceramic BSCCO material. The microstructure, transport and magnetic properties were characterized by XRD, SEM-EDX, R–T, I–V and M–H analysis. Highly c-axis oriented single-crystal whiskers were produced without any grain boundaries in any crystallographic direction. T _c and T _zero were obtained to be 94.8 K and 92.8 K, respectively, and decreased with increasing the magnetic field. Magnetic properties, M–H curves of the whiskers, were investigated at 3 different constant temperatures up to 5 T. Symmetric hysteresis loops for all temperature and field cases were obtained and maximum J _c ^mag value was calculated to be 4.58×10⁶ A cm⁻² at 10 K for 0 T but dropped to 1.61×10⁶ A cm⁻² at 30 K for 0 T. Transport critical current density, J _c ^trans, of the whiskers in low magnetic field (between 0 and 270 Oe) and in a wide temperature region (5–75 K) was investigated. It was obtained that initially J _c ^trans increased with increasing the magnetic field but then started to decrease with further increase on the magnetic field at all temperature values. We have investigated this problem in terms of the Bulk pinning model, the Geometrical barrier model and the Bean–Livingston surface barrier model. We have noticed that all these models were not fitted well to our data. However, we have modified the Bean–Livingstone model by adding a new parameter. It was found that this modified formula fitted well to the data obtained in this work and can give successful explanations to the other results obtained by other groups.     

Fabrication and ferroelectric properties of sol–gel derived 1–1 intergrowth-superlattice-structured Bi<Subscript>3</Subscript>TiNbO<Subscript>9</Subscript>-Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films

1–1 intergrowth-superlattice-structured Bi₃TiNbO₉–Bi₄Ti₃O₁₂ (BTN–BIT) ferroelectric thin films have been prepared on p-Si substrates by sol-gel processing. The precursor films are crystallized in the desired intergrown BTN–BIT superlattice structures by optimizing the processing conditions. Synthesized BTN–BIT thin films annealed below 750 °C are polycrystalline, uniform and crack-free, no pyrochlore phase or other second phase, and exhibited good ferroelectric properties. As the annealing temperature increases from 600 to 700 °C, both remanent polarization P _r and coercive electric field E _c of BTN–BIT thin films increase, but the pyrochlore phase in BTN–BIT films annealed above 750 °C will impair the ferroelectric properties. The BTN–BIT thin films annealed at 700 °C have a P _r value ~19.1μC/cm² and an E _c value ~135 kV/cm.     

Ion-selective properties of nanostructured alkali-metal-doped vanadium oxide

We have studied thin-film electrodes based on nanoparticulate vanadium oxide doped with alkalimetal cations. The hydrogen function of the electrodes manifests itself in the pH range 2–5, with a slope of 55, 54, and 54 ± 2 mV/pH for M _x V₂O₅·nH₂O with M = Li, Na, and K, respectively. Their sensitivity range is 10⁻⁴ to 10⁻¹ mol/l. The electrode potential as a function of concentration follows the Nernst equation with a slope of 55, 55, and 57 ± 2 mV/pC for M = Li, Na, and K, respectively. The Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ selectivity coefficients of the electrodes are determined.     

Spectroscopic characterization of tungstated zirconia prepared by equilibrium adsorption from hydrogen peroxide solutions of tungsten(VI) precursors

Two series of WO _x /ZrO₂ samples are prepared by equilibrium adsorption from H₂O₂ solutions at pH 1.8 containing two different precursor anions, [W₂O₃(O₂)₄(H₂O)₂]²⁻ and [H₂W₁₂O₄₀]⁶⁻. The starting material is amorphous zirconium oxyhydroxide. The maximum W densities obtained are larger than that reported in the literature for systems synthesized by the same method using aqueous non-peroxide solutions. In the case of the metatungstate precursor, this increase is attributed to the generation of additional anchoring sites by interaction between the amorphous support and H₂O₂. The high uptake achieved when the peroxo complex is used as a precursor is a result of both the ZrO _x (OH)_4-2x –H₂O₂ interaction and low nuclearity of the adsorbing anion. The materials are characterized by XRD, DR–UV–vis, Micro-Raman and FT-IR spectroscopy. The surface acidities of samples with identical W loading prepared by equilibrium adsorption from the [H₂W₁₂O₄₀]⁶⁻–H₂O₂ system and by impregnation with aqueous solution of ammonium metatungstate are investigated by FT-IR spectroscopy of CO adsorbed at 80 K.