Infrared studies on nitrogen oxides adsorbed on alkali metal ion-exchanged ZSM-5 zeolites

The adsorption of nitrogen oxides (NO_x) on a series of alkali metal ion-exchanged ZSM-5 zeolites at 226 K was investigated by in situ infrared spectroscopy. In the low NO pressure region, the main species found on each zeolites was an NO monomer linearly adsorbed onto the cation through an O atom (M⁺ ··· ON), but an M⁺ ··· NO species was not detected. On the other hand, a part of adsorbed NO disproportionated into N₂O and N₂O₃ under high NO pressures (higher than 1.3 kPa). The formation of N₂O₃ was enhanced at a high density of nitrogen oxides (NO_x) in the ZSM-5 pore.     

Ag and Dy doped zeolite as a broadband phosphor

Photoluminescence (PL) properties of silver (Ag) and dysprosium (Dy) codoped zeolites were investigated. It was found that PL from the ⁴F_9/2–⁶H_13/2 transition of Dy³⁺ ions at 575 nm is more than 50 times enhanced by the presence of Ag⁺ ions under ultraviolet excitation. The excitation wavelength dependence of the PL intensity coincided well with the absorption spectra of Ag⁺ ions, indicating that Dy³⁺ ions are excited by the energy transfer from Ag⁺ ions. In addition, by carefully optimizing annealing condition and Dy and Ag concentration, white light was realized due to the combination of blue emission of Ag⁺ ions, yellow emission of Dy³⁺ ions and red emission of Ag clusters.     

Metal-Containing Zeolites as Sorbents for Localization of Radioiodine and CsI Aerosols from Vapor-Air and Aqueous Phases

New sorbents for efficient sorption of radioiodine and radiocesium from the vapor-gas phase and aqueous solutions were prepared by treatment of Cu⁺- and Ag⁺-substituted NaX and NaA zeolites with acetylene in aqueous solution. The distribution factor K _d of radioiodine and radiocesium between the modified sorbents and aqueous solutions is higher than 10³-10⁴ ml g^{- 1}. Decontamination factor of the vapor-gas phase with respect to radioiodine and ¹³⁷CsI aerosols exceeds 10²-10³ and 10³, respectively. The sorption properties of the modified sorbents in both aqueous solutions and the vapor-gas phase are better than those of the initial sorbents. However, localization of radioiodine from the vapor-gas phase with the Cu⁺-containing sorbents is less efficient than with the Ag⁺-containing zeolites. At the same time, in aqueous solutions the sorption capacity of the Cu⁺-containing sorbents for radioiodine is appreciably higher than that of the Ag⁺-containing sorbents. The sorption properties of the modified sorbents were studied as influenced by various factors. Paracomplexes of univalent copper and silver with C₂H₂, H₂O, and anions present in the solution are probably formed during modification of the metal-containing zeolites. The dependence of K _d of radioiodine on the metal concentration in the sorbent, the free pore volume of the sorbent, and the anion nature was revealed.     

Catalyst preparation through ion-exchange of zeolite Cu-, Ni-, Pd-, CuNi- and CuPd-ZSM-5

Ion-exchanged zeolite ZSM-5 is the best known catalyst for direct NO_x decomposition and a viable candidate for NO_x reduction with methane. The preparation is crucial for the efficiency of the conversion and this paper describes the ion-exchange, with Cu²⁺, Ni²⁺ or Pd²⁺, and the dual exchange, with Cu²⁺/Ni²⁺ or Cu²⁺/Pd²⁺, under appropriate pH and ion concentrations for maximum dispersion.     

Metal clusters and nanoparticles assembled in zeolites: an example of stable materials with controllable particle size

An ion-exchangeable zeolite (mordenite) is used to control the formation of nanoparticles and clusters within the solid matrix by the hydrogen reduction of metal ions (Ag⁺, Cu²⁺, and Ni²⁺). SiO₂/Al₂O₃ molar ratio in mordenite appears to be an efficient tool to manage the reducibility of the metal ions. Few-atomic silver clusters in line with the larger silver nanoparticles were observed with DRS for the reduced Ag⁺-exchanged mordenites. Cu²⁺-exchanged ones produce the copper nanoparticles with different optical appearance, and Ni²⁺-exchanged mordenites are reduced up to complicated species with no explicit assignment of metal particles under the conditions studied.     

Interlayer coupling in peroxitonic model of superconductivity

The unusual ESR spectra of YBa₂Cu₃O_7−x is ascribed to a Cu²⁺ ion, whose one ligand in CuO₂ plane is involved in a peroxiton O⁻−Cu⁺−O⁻ bond. The analysis shows that the presence of a ligand in O⁻ substantially increases the energies ofd-hole orbitals. Since this increase for YBa₂Cu₃O_7\t-\gd, orbital is much larger than that ford ₃ z ²−r ² orbital, their separation is drastically reduced and there occurs a significant orthorhombic mixing between the two. This charge transfer from a planard _x ²− _r ² orbital to ad ₃ z ²−r ² orbital, which lies mainly perpendicular to the plane, provides a mechanism for interlayer coupling. The effect of this coupling on superconducting transition temperature is discussed.     

Tunable Color Temperatures and Efficient White Emission from Cs2Ag1−xNaxIn1−yBiyCl6 Double Perovskite Nanocrystals

Recently, Bi‐doped Cs₂Ag_0.6Na_0.4InCl₆ lead‐free double perovskites demonstrating efficient warm‐white emission have been reported. To enable the solution processing and enrich the application fields of this promising material, here a colloidal synthesis of Cs₂Ag_1?xNa_xIn_1?yBi_yCl₆ nanocrystals is further developed. Different from its bulk states, the emission color temperatures of the nanocrystal can be tuned from 9759.7 to 4429.2 K by Na⁺ and Bi³⁺ incorporation. Furthermore, the newly developed nanocrystals can break the wavefunction symmetry of the self‐trapped excitons by partial replacement of Ag⁺ ions with Na⁺ ions and consequently allow radiative recombination. Assisted with Bi³⁺ ions doping and ligand passivation, the photoluminescence quantum yield of the Cs₂Ag_0.17Na_0.83In_0.88Bi_0.12Cl₆ nanocrystals is further promoted to 64%, which is the highest value for lead‐free perovskite nanocrystals at present. The new colloidal nanocrystals with tunable color temperature and efficient photoluminescence are expected to greatly advance the research progress of lead‐free perovskites in single‐emitter‐based white emitting materials and devices.     

Effect of carbon monoxide and sulphur dioxide on the oxidation state of copper in zeolite

A study is made of the reduction and oxidation of Cu²⁺ in CuNaY zeolites by CO and SO₂, using electron spin resonance. It is observed that the Cu⁺ or Cu^o formed by the reduction of Cu²⁺ with CO can be reoxidized to Cu²⁺ by SO₂ at 400°C. SO₂ can also reduce a fraction of the Cu²⁺ sites in the Cu-exchanged zeolites. SO₂ decomposes and forms elemental S under experimental conditions on the zeolite.     

Al/Cu2O thermite compatibility studies by x-ray photoelectron and x-ray induced auger spectroscopy

The surface chemistry of Al/Cu₂O thermite in powdered mixtures and in pressed pellets was studied before and after accelerated agings with x-ray phThe Al₂O₃ film thicknesses on Al metal surfaces were deduced from signal intensity ratios of Al⁺³ and Al in XPS of Al 2s and from Al K-LL XStearic acid, the organic additive to Al powders, was detected by the C 1s signal. The CuO impurity in Cu₂O was observed in the Cu 2p _{$\text{3}\text{2}$} signal which was broadened by unpaired electron spin-spin interaction in the Cu⁺² d⁹ orbital; both impurities were removed du     

Intercalation of pyrographite by NO2+ and NO+ salts

BF₄^?, PF₆^? and SbF₆^? ions have been intercalated into pyrographite HOPG by chemical oxidation. The graphite is oxidized by NO₂⁺ (or NO⁺ in certain experiments) coming from NO₂BF₄, NO₂PF₆ and NO₂SbF₆ (or NOSbF₆) salts dissolved in dry nitromethane. X-ray diffraction allows us to determine the identity period along the $\text{c}$ axis leading to the stage n and the interpianar distance d_I. Relative weight change leads us to believe that the MF_x^? anions are solvated by the solvent. Chemical analyses confirm this hypothesis allowing us to give to these compounds the ideal formula C⁺_23nMF^?_x (CH₃NO₂)_y.     

Different effects of nickel and cobalt additions on the electronic conduction of copper tellurite glasses

Measurements of the d.c. electrical conductivity were made on 65TeO₂-(35-x)CuO-x(MO) (mol %) glasses wherex=0, 0.5, 1, 2, 3, 4 and M represents nickel or cobalt. A variation in the conductivity and activation energy of the glasses is observed as CuO is replaced by NiO and by CoO. It is found that withx=0.5 to 3 mol % of NiO, the conductivity increases and the activation energy decreases due to the decrease in effective electron hopping distance between the transition metal (TM) ions. The conductivity is found to decrease with the substitution of 4 mol % of NiO and 0.5 to 4 mol % of CoO and this is attributed to the decrease in relative concentration of hopping centres because of the decrease in the hopping transitions between ions of the same element (e.g. Cu⁺ and Cu²⁺ ions) and between the ions of different TM elements (e.g. Cu⁺ and Ni²⁺, Cu⁺ and Co²⁺). This decrease in conductivity has also been described due to the formation of Ni-O-Ni, Cu-O-Ni and Co-O-Co, Cu-O-Co bridge bonds in NiO-and CoO-doped glasses respectively. The CoO-doped glasses have been found to be of a more insulating nature.     

Synthesis of new sulphides of transition metal ions in presence of sun light

New sulphides of transition metal ions [M⁺ⁿ = Cu⁺¹, Cu⁺² and Zn⁺²] have been synthesised in sunlight. XRD patterns show that these compounds are not MxSy but are mercaptyl, hydroxyl metal sulphides [M(SH)(OH)(H₂O)₂] which is further ascertained by I.R. spectra showing bands due to T _d-symmetry. ESCA of compound of copper in solid state shows presence of Cu¹⁺ and Cu²⁺ ion. The presence of hydroxyl, mercaptyl, aqua and S^–2 groups has finally been confirmed with TGA, DTA and ESCA. Conductivity and Seebeck coefficient measurements show that compound of copper is p-type semiconductor and compound of zinc is n-type semiconductor. The production of these low cost materials opens an interesting area of research and development for their use in solar cell devices.     

Electrical conductivity and crystal structure of piperazinium 10-silver 12-iodide·4-dimethylformamide

Crystals of (C₄N₂H₁₂)Ag₁₀I₁₂·4C₃H₇NO contain channels formed by face-sharing iodide tetrahedra. These channels, parallel to the monoclinic $\text{c}$-axis, are isolated from each other by the (C₄N₂H₁₂)²⁺ ions and C₃H₇NO molecules. Electrical measurements along the $\text{c}$-axis of the crystals at 200 psig (argon) indicate that the material does not become a true solid electrolyte below 332 K, the decomposition temperature. Structural considerations show that despite the substantial ratio (3:1) of sites to Ag⁺ ions, the material is not expected to become a solid electrolyte, if it retains its room temperature structure, at any temperature or pressure.     

Ag-ZSM-5 zeolite as high-temperature water-vapor sensor material

The effect of the presence of water vapor in the gas stream on the absorption spectra of AgH-ZSM-5 zeolites at high temperatures was investigated using UV-Vis DR spectroscopy. Ag_mⁿ⁺ silver species exhibiting an absorption band at 37 700 cm^− 1 are formed in highly loaded AgH-ZSM-5 treated in an oxygen stream. The presence of water in the gas stream results in the fast erosion of the band at 37 700 cm^− 1 and the intensity of the band is fully recovered under water-free conditions. Ag_mⁿ⁺ silver species in the AgH-ZSM-5 zeolite and their optical properties are stable under high-temperature treatment of zeolite under various conditions. Thus, the preparation of chemically/thermally stable sensing material based on silicon-rich zeolites containing metal ion species suitable for sensor applications under sever conditions was demonstrated.     

Construction of Cuprous Oxide Electrodes Composed of 2D Single‐Crystalline Dendritic Nanosheets

An unusual anisotropic growth of Cu₂O is stabilized via the electrochemical synthesis of Cu₂O in the presence of Ag⁺ ions, which results in the formation of Cu₂O electrodes composed of 2D sheetlike crystals containing complex dendritic patterns. It is quite unusual for Cu₂O to form a 2D morphology since it has a 3D isotropic cubic crystal structure where the a, b, and c axes are equivalent. Each Cu₂O sheet is single‐crystalline in nature and is grown parallel to the {110} plane, which is rarely observed in Cu₂O crystal shapes. A various set of experiments are performed to understand the role of Ag⁺ ions on the 2D growth of Cu₂O. The results show that Ag⁺ ions are deposited as silver islands on already growing Cu₂O crystals and serve as nucleation sites for the new growth of Cu₂O crystals. As a result, the growth direction of the newly forming Cu₂O crystals is governed by the diffusion layer structure created by the pre‐existing Cu₂O crystals, which results in the formation of 2D dendritic patterns. The thin 2D crystal morphology can significantly increase the surface‐to‐volume ratio of Cu₂O crystals, which is beneficial for enhancing various electrochemical and photoelectrochemical properties of the electrodes. The photoelectrochemical properties of the Cu₂O electrodes composed of 2D dendritic crystals are investigated and compared to those of 3D dendritic crystals. This study provides a unique and effective route to maximize the {110} area per unit volume of Cu₂O, which will be beneficial for any catalytic/sensing abilities that can be anisotropically enhanced by the {110} planes of Cu₂O.     

Cactus‐Like Hollow Cu2‐xS@Ru Nanoplates as Excellent and Robust Electrocatalysts for the Alkaline Hydrogen Evolution Reaction

The development of Pt‐free electrocatalysts for the hydrogen evolution reaction (HER) recently is a focus of great interest. While several strategies are developed to control the structural properties of non‐Pt catalysts and boost their electrocatalytic activities for the HER, the generation of highly reactive defects or interfaces by combining a metal with other metals, or with metal oxides/sulfides, can lead to notably enhanced catalytic performance. Herein, the preparation of cactus‐like hollow Cu_2‐x S@Ru nanoplates (NPs) that contain metal/metal sulfide heterojunctions and show excellent catalytic activity and durability for the HER in alkaline media is reported. The initial formation of Ru islands on presynthesized Cu_1.94S NPs, via cation exchange between three Cu⁺ ions and one Ru³⁺, induces the growth of the Ru phase, which is concomitant with the dissolution of the Cu_1.94S nanotemplate, culminating in the formation of a hollow nanostructure with numerous thin Ru pillars. Hollow Cu_2‐x S@Ru NPs exhibit a small overpotential of 82 mV at a current density of ?10 mA cm^?2 and a low Tafel slope of 48 mV dec^?1 under alkaline conditions; this catalyst is among state‐of‐the‐art HER electrocatalysts in alkaline media. The excellent performance of hollow Cu_2‐x S@Ru NPs originates from the facile dissociation of water in the Volmer step.     

Structural,thermal and transport studies on Ag1 − x Cuxl (0.05 ⩽ x ⩽ 0.25) solid electrolyte

Preparation and characterization studies on polycrystalline samples of Ag_{1 – x}Cu_xl wherex=0.05, 0.1, 0.15, 0.2 and 0.25, respectively, have been reported. Samples were analysed using powder X-ray diffraction (XRD) and differential scanning calorimetric (DSC) techniques in order to identify the compositions and phase transition temperatures. A.c. electrical conductivity studies were carried out on pelleted specimens of various compositions in the frequency range 65.5 kHz to 1 Hz and over the temperature range 293–412 K. DSC results obtained in the temperature range 373–473 K have shown that the ß- to -phase transition temperature is enhanced from 426 K to 438 K whenx is increased from 0.05 to 0.25. XRD results have indicated that there is a shift ind-spacing when the Cul content is increased, suggesting changes in the crystal structure. Typical XRD patterns recorded for the composition Ag_0.95Cu_0.05l at three different temperatures (room temperature, 373 and 473 K, respectively) have confirmed that both face-centred cubic and hexagonal phases would be present at room temperature and at 373 K as well, whereas at 473 K the structure would be purely body-centred cubic in nature. A.c. impedance analysis of the above samples appears to suggest that their electrical conductivity, predominantly due to the migration of Ag⁺ ions, lies in the order of 10^–4S cm^–1 at room temperature.     

Carrier-Concentration and Magnetic-Field Effect on Mn2+ Luminescence in Bulk Zn1?x MnxTe Crystals

Measurements of photoluminescence, reflectance, and Hall effect as functions of the phosphorus doping level, temperature, and magnetic field in p-Zn_1–x Mn _x Te crystals are reported. The photoluminescence reveals two competing intra-Mn recombination channels. The first channel originates in the energy transfer from the photogenerated carriers to the internal Mn²⁺(3d⁵) states leading to the intra-Mn radiative recombination. The second one originates in the energy transfer from Mn ions to thermally activated carriers leading to intra-Mn nonradiative recombination. The Mn emission can be controlled either by changing the doping level with the phosphorus impurities or by varying the temperature and/or an external magnetic field.     

Electrochemical polymerization of benzene in the presence of Ag+, Pb2+ and Cu+ ions

Poly(p-phenylene) (PPP) films were synthesized by using benzene and fluorosulphonic acid (FSO₃H) as a strong acid containing Ag⁺, Pb²⁺ and Cu⁺ ions in methylene chloride (CH₂Cl₂) solution. Addition of Ag⁺ or Pb²⁺ ions into the polymerization medium improved the PPP films formation, but Cu⁺ ion did not have an effect on polymerization. PPP films were characterized by cyclic voltammetry, IR and TGA. Dry conductivities were measured by using four probe technique. Received: 18 September 2000 / Reviewed and accepted: 20 September 2000     

Preparation and characterization of zeolite framework stabilized cuprous oxide nanoparticles

Zeolite framework stabilized copper(I) oxide nanoparticles (4.8 ± 2.6 nm) were prepared for the first time by using a four step procedure: the ion exchange of Cu²⁺ ions with the extra framework Na⁺ ions in Zeolite-Y, the reduction of the Cu²⁺ ions within the cavities of zeolite with sodium borohydride in aqueous solution, the dehydration of Zeolite-Y with the copper(0) nanoclusters, and the oxidation of intrazeolite copper(0) nanoclusters by O₂ at room temperature. Zeolite stabilized copper(I) oxide nanoparticles were thoroughly characterized by ICP-OES, XRD, HR-TEM, Raman, XPS, UV-vis spectroscopy and N₂ adsorption-desorption technique.