Liquid-phase synthesis and physicochemical properties of xerogels,nanopowders and thin films of the CeO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Low-agglomerated xerogels, ultrafine oxide powders with particle sizes of 12–20 nm, and uniform thin films with particle sizes of 8–14 nm are prepared in the CeO₂–Y₂O₃ system using liquid-phase low-temperature methods, namely via coprecipitation of hydroxides and cocrystallization of salts, sol—gel technology. A comparative characterization of the prepared xerogels and nanopowders is performed using a set of physicochemical analytical methods. A dependence of phase composition, microstructure, and particle size on synthetic parameters is elucidated.     

The character of interactions of CO,H<Subscript>2</Subscript>, and CH<Subscript>3</Subscript>OH with the surface of γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Cu-Zn oxide catalyst

The thermal desorption of CO, H₂, and CH₃OH from the surface of Katalco-58 industrial catalyst for the synthesis of methanol and γ-Al₂O₃ was studied. Weak interaction of the gases with the surface of samples was observed over the temperature range 75–400°C. The desorption of the gases obeyed the second-order Wigner-Polyani equation. The desorption energies of the gases were calculated. The mechanism of dimethyl ether synthesis was studied.     

Kinetics and thermodynamics of thermal decomposition of NH<Subscript>4</Subscript>NiPO<Subscript>4</Subscript>·6H<Subscript>2</Subscript>O

The single phase NH₄NiPO₄·6H₂O was synthesized by solid-state reaction at room temperature using NiSO₄·6H₂O and (NH₄)₃PO₄·3H₂O as raw materials. XRD analysis showed that NH₄NiPO₄·6H₂O was a compound with orthorhombic structure. The thermal process of NH₄NiPO₄·6H₂O experienced three steps, which involves the dehydration of the five crystal water molecules at first, and then deamination, dehydration of the one crystal water, intramolecular dehydration of the protonated phosphate groups together, at last crystallization of Ni₂P₂O₇. In the DTA curve, the two endothermic peaks and an exothermic peak, respectively, corresponding to the first two steps’ mass loss of NH₄NiPO₄·6H₂O and crystallization of Ni₂P₂O₇. Based on Flynn–Wall–Ozawa equation, and Kissinger equation, the average values of the activation energies associated with the thermal decomposition of NH₄NiPO₄·6H₂O, and crystallization of Ni₂P₂O₇ were determined to be 47.81, 90.18, and 640.09 kJ mol⁻¹, respectively. Dehydration of the five crystal water molecules of NH₄NiPO₄·6H₂O, and deamination, dehydration of the crystal water of NH₄NiPO₄·H₂O, intramolecular dehydration of the protonated phosphate group from NiHPO₄ together could be multi-step reaction mechanisms. Besides, the thermodynamic parameters (ΔH ^≠, ΔG ^≠, and ΔS ^≠) of the decomposition reaction of NH₄NiPO₄·6H₂O were determined.     

Sol–gel synthesis and characterization of polycrystalline GdFeO<Subscript>3</Subscript> and Gd<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> thin films

Thin films of the perovskite and garnet structured gadolinium ferrites GdFeO₃ and Gd₃Fe₅O₁₂ have been synthesized by a sol–gel method, based on stoichiometric mixtures of acetyl acetone chelated Gd³⁺ and Fe³⁺ dissolved in 2-methoxy ethanol. After spin coating onto Si wafers, and heating in air at 700 °C for 20 h, neatly grown essentially single phase films were obtained. From X-ray photoelectron spectroscopy an iron deficiency is observed in the uppermost layer of both films, implying that the crystallites preferably end in planes rich in Gd and O but not in Fe. The films were also characterized by X-ray powder diffraction, scanning electron microscopy, infrared spectroscopy, and magnetic measurements.     

Synthesis and examination of antimicrobial properties of aminomethylated derivatives C<Subscript>6</Subscript>–C<Subscript>7</Subscript> of alicyclic diols

Synthesis of C₆–C₇ alicyclic diols was studied by a catalytic oxidation of cyclohexene, norbornene and their methyl derivatives in the presence of heterogenized molybdenum-containing catalysts. By a triple condensation of the diols with formaldehyde and secondary amines a synthesis of their aminomethylated derivatives with various substituents at nitrogen atom was examined. Antimicrobial properties of the synthesized amino alcohols in M-10 oil as additives with fungicidal and bactericidal activities were studied.     

Synthesis and photocatalytic activity of mesoporous SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>

Mesoporous SiO₂–TiO₂ was synthesized by the sol–gel method using Si(OC₂H₅)₄, Ti(OC₂H₅)₄, and stearyltrimethylammonium chloride. By using acetylacetone as the capping agent of Ti(OC₂H₅)₄, homogeneous SiO₂–TiO₂ composite was obtained. Spherical mesoporous SiO₂–TiO₂ was also synthesized by the sol–gel method using W/O emulsion under microwave irradiation. The specific surface area of these mesoporous SiO₂–TiO₂ materials decreased when the Ti/Si molar ratio was higher than 0.1, which indicated that Ti was homogeneously distributed in mesoporous SiO₂ matrix at Ti/Si ≦ 0.1. The photocatalytic activity of mesoporous SiO₂–TiO₂ materials was investigated by the degradation of methylene-blue in water under UV light irradiation. Mesoporous SiO₂–TiO₂ was effective for the adsorption–decomposition of methylene-blue.     

Ionic mobility and electrophysical properties of solid solutions in PbF<Subscript>2</Subscript>–SbF<Subscript>3</Subscript> and PbF<Subscript>2</Subscript>–SnF<Subscript>2</Subscript>–SbF<Subscript>3</Subscript> systems

Ionic mobility and electrical conductivity of solid solutions with fluorite structure, obtained with solid-state approach in PbF₂–SbF₃ and PbF₂–SnF₂–SbF₃ systems, are studied by 19F NMR and electrochemical impedance spectroscopy methods. The 19F NMR spectra parameters, types of ion motions in the fluoride sublattice, and the ionic conductivity magnitude are shown to be determined by the temperature and fluoride concentration in the solid solutions. The solid solution specific conductivity in the PbF₂–SbF₃ and PbF₂–SnF₂–SbF₃ systems at 420–450 K is as high as ~10^–2 S/cm, which allows accounting the solid solutions as a base for preparation of functional materials.     

Synthesis and characterization of Pd nanoparticle-modified magnetic Sm<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> as effective multifunctional catalyst for reduction of 2-nitrophenol and degradation of organic dyes

In this study, Pd nanoparticle-modified magnetic Sm₂O₃–ZrO₂ material (Pd–Fe₃O₄–Sm₂O₃–ZrO₂) as multifunctional catalyst was fabricated and used for catalytic reduction of 2-nitrophenol compound, degradation of methylene blue and rhodamine B dyes, which are toxic pollutants. The magnetic material was used for the first time as a catalyst for the reduction and degradation studies. Pd nanoparticle-modified magnetic Sm₂O₃–ZrO₂ catalyst was prepared using the deposition–precipitation methods and were characterized by X-ray diffraction, scanning electron microscopy, atomic absorption spectrometry, Raman spectroscopy and BET surface analyzer. The Pd nanoparticle-modified magnetic Sm₂O₃–ZrO₂ material can lead to high catalytic activity for the reduction of 2-nitrophenol and degradation of rhodamine B and methylene blue with >?95% conversion within ~?2 and 80 s even when the content of Pd in it is as low as 5.8 wt%.     

Synthesis of nanopowders and physicochemical properties of ceramic matrices of the LaPO<Subscript>4</Subscript>–YPO<Subscript>4</Subscript>–(H<Subscript>2</Subscript>O) and LaPO<Subscript>4</Subscript>–HoPO<Subscript>4</Subscript>–(H<Subscript>2</Subscript>O) systems

Sol-gel method was used to synthesize nanosize powders in the LaPO₄–YPO₄–(H₂O) and LaPO₄–HoPO₄–(H₂O) systems. Dense ceramic samples with high microhardness (up to 25 GPa) were formed from these powders by sintering at temperatures of up to 1600°C. The isomorphic capacity of the monoclinic LaPO₄ matrix for the second component (yttrium or holmium) simulating radioactive nuclides of the actinide-rare-earth fraction was found to be high. The composites are stable in aqueous solutions, which is indicated by the low concentration of lanthanum and yttrium ions during leaching test (~10^–7 g L^–1). The results obtained in the study can be used to develop new high-efficiency ceramic matrices for solidification of the actinide-rare-earth fraction of liquid wastes formed in processing of the spent nuclear fuel.     

Gel decomposition and formation of MgFe<Subscript>1.6</Subscript>Ga<Subscript>0.4</Subscript>О<Subscript>4</Subscript> powders

The thermal behavior of the gels that are formed in the synthesis of MgFe_1.6Ga_0.4О₄ powders was studied by differential scanning calorimetry and thermogravimetry (DSC–TG). The combustion temperatures of the gels in flowing air and flowing argon were determined from experimental data and thermodynamic calculations. The calculations of combustion temperatures from the heat flow of reaction versus time are shown to be a reliable tool to determine the parameters of gel combustion.     

Photoresist Modification of Sol–Gel Solutions for Texturing of Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> and Bi<Subscript>3</Subscript>TiNbO<Subscript>9</Subscript> Thin Films

Bismuth titanate (Bi₄Ti₃O₁₂) and bismuth titanium niobate (Bi₃TiNbO₉) c-axis textured thin films were fabricated using the sol–gel processing technique. Chemical modification of precursor solutions was performed using a proprietary photosensitive chemical (photoresist). Increases in crystallinity and texture of resulting films were seen over films that were made from unmodified solutions. Analysis by X-ray diffraction (XRD) revealed c-axis orientation factors for Bi₄Ti₃O₁₂ near 88% and Bi₃TiNbO₉ near 63% in “modified” films. Atomic force microscopy images of films show microstructural improvement between “modified” and “unmodified” films. Images generally show smaller randomly oriented grains in “unmodified” films, and larger oriented platelet structures related to growth due to crystal habit in “modified” films. Light scattering experiments show the addition of photoresist to the precursor solution initiates accelerated particle growth. AFM imaging of soft-baked films also suggests an enhancement of texture.     

Effects of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> on the crystallization and structure of CaO–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> glass ceramics

Radiation-induced degradation of the weakly and strongly 4-vinylpyridine basic ion exchange resins by gamma radiolysis was investigated in the presence of air and liquid water. This study is focused on evaluating the radiolytic gases (H₂, CO, CO₂ and CH₄) and liquid products (water-solute TOC and NH₄ ⁺). The weakly basic resin yielded lower amounts of H₂ and CO and higher amounts of CO₂ than those of the strongly basic resin. Moreover, the strong basic resin tended to yield greater amounts of NH₄ ⁺. Resins were characterized by the FTIR spectroscopy technique and the results showed that the resins structures are relatively stable.     

Impedance Study of the Conductivity of Solid Oxide Electrolyte Films SrZr<Subscript>0.95</Subscript>Y<Subscript>0.05</Subscript>O<Subscript>3–δ</Subscript> and CaZr<Subscript>0.9</Subscript>Y<Subscript>0.1</Subscript>O<Subscript>3–δ</Subscript>

Information on the across-plane conductivity of films of solid-oxide electrolytes SrZr_0.95Y_0.05O_3–δ and CaZr_0.9Y_0.1O_3–δ deposited on ion-conducting supports is acquired by the impedance method. It is shown that the support/film interface and the intergrain boundaries considerably affect the across-plane charge transfer in the film. The effect of the crystallographic orientation of the YSZ support on the microstructure and conductivity of the CaZr_0.9Y_0.1O_3–δ electrolyte film is demonstrated.     

Non-empirical investigation of the geometrical structure and energy stability of dimers of yttrium β-diketonates Y<Subscript>2</Subscript>(MDA)<Subscript>6</Subscript> and Y<Subscript>2</Subscript>(HFA)<Subscript>6</Subscript>

The structure of tris-complexes Y(MDA)₃, Y(HFA)₃ and their dimeric forms of Y₂(MDA)₆ and Y₂(HFA)₆ (MDA = C₃O₂H₃; HFA = C₅O₂F₆H) are investigated by the non-empirical Hartree-Fock method and also taking into account the correlation of electrons in the context of density functional theory (DFT/B3LYP) using effective pseudopotentials to describe the atomic core and double-exponential valence basis sets supplemented with polarization functions. For the first time the structure of Y(HFA)₃, Y₂(MDA)₆, and Y₂(HFA)₆ molecules has been studied in this work. The equilibrium configuration of Y(HFA)₃ monomer is a structure with a coordination polyhedron of [YO₆] that has the form of a distorted octahedron with planar chelate fragments and CF₃ substituents in which the C-F bond screens the C-C bond in the chelate fragment. The barrier of the internal rotation of one CF₃ group is ～3.0 kJ/mole (DFT/B3LYP). It is shown that rotations of CF₃ groups in Y(HFA)₃ molecule could be considered as mutually independent. The structures of C ₁ and C ₂ symmetry are the equilibrium configurations of Y₂(MDA)₆ and Y₂(HFA)₆ dimers respectively (DFT/B3LYP). The structure of the coordination polyhedron of [Y₂O₁₂] in C ₁ and C ₂ symmetry configurations can be represented as a combination of eight-and seven-coordinated polyhedra or two seven-coordinated polyhedra respectively. The energy stability of dimeric complexes is studied. According to DFT/B3LYP data, the dimerization energy equals ?80.8 kJ/mole and ?62.3 kJ/mole for Y₂(MDA)₆ and Y₂(HFA)₆ respectively. The force fields and frequencies of normal vibrations are calculated for the equilibrium configurations. The trends of changes in the vibrational spectra in Y(MDA)₃→Y(HFA)₃ and monomer→dimer transitions are discussed. The comparison with available experimental data is made.     

Influence of synthesis route on morphology and conduction behavior of BaCe<Subscript>0.8</Subscript>Y<Subscript>0.2</Subscript>O<Subscript>3−δ</Subscript>

In this article, the role of the preparation route and calcinations temperature on the thermal expansion and conductivity of BaCe_0.8Y_0.2O_3−δ (BCY) has been studied. In particular, the samples were synthesized by means of the solid-state reaction and by a sol–gel route. BCY has been suggested as proton conducting electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Proton conductivity strongly depends on the densification of the material as well as the crystal structure, which is generally influenced by the preparation procedure. It was found that a single phase material could be achieved at 1000 °C for the samples prepared through the sol–gel route with ~96% packing density. In case of ceramic route, single phase could be obtained at higher temperatures (1200 °C) and does not lead to good density values. The ceramic synthesis produces BCY material in cubic symmetry where as the gel–citrate complexation route leads to homogenous orthorhombic BCY. The conductivity measurements of sample synthesized by two different routes were investigated by means of impedance spectroscopy and electron microscopy. A comparative study of thermal expansion behavior of BCY synthesized by different route was carried out.     

Fragmentation Reactions of b<Subscript>5</Subscript> and a<Subscript>5</Subscript> Ions Containing Proline—The Structures of a<Subscript>5</Subscript> Ions

A detailed study has been made of the b₅ and a₅ ions derived from the amides H-Ala-Ala-Ala-Ala-Pro-NH₂, H-Ala-Ala-Ala-Pro-Ala-NH₂, and H-Ala-Ala-Pro-Ala-Ala-NH₂. From quasi-MS³ experiments it is shown that the product ion mass spectra of the three b₅ ions are essentially identical, indicating macrocyclization/reopening to produce a common mixture of intermediates prior to fragmentation. This is in agreement with numerous recent studies of sequence scrambling in b ions. By contrast, the product ion mass spectra for the a₅ ions show substantial differences, indicating significant differences in the mixture of structures undergoing fragmentation for these three species. The results are interpreted in terms of a mixture of classical substituted iminium ions as well as protonated C-terminal amides formed by cyclization/rearrangement as reported recently for a₄ ions (Bythell, Maître , Paizs, J . Am. Chem. Soc. 2010, 132, 14761–14779). Novel fragment ions observed upon fragmentation of the a₅ ions are protonated H-Pro-NH₂ and H-Pro-Ala-NH₂ which arise by fragmentation of the amides. The observation of these products provides strong experimental evidence for the cyclization/rearrangement reaction to form amides and shows that it also applies to a₅ ions.     

Solubility and stability of (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>SO<Subscript>4</Subscript>·H<Subscript>2</Subscript>O<Subscript>2</Subscript> in organic and aqueous-organic media

Solubility and stability of (NH₄)₂SO₄·H₂O₂ in organic solvents (glycerol, ethylene glycol, TOSOL-A40 OM antifreeze), in mixtures of an organic solvent and water, and in pure water was studied. Crystallographic properties of the ammonium sulfate precipitating from aqueous-organic solvents and aqueous solutions in various time intervals and differing from ordinary (NH₄)₂SO₄ in solubility and one of crystallographic parameters were analyzed.     

Effect of ZrO<Subscript>2</Subscript> on Catalyst Structure and Catalytic Sulfur-Resistant Methanation Performance of MoO<Subscript>3</Subscript>/ZrO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts

A series of MoO₃/ZrO₂–Al₂O₃ catalysts was prepared and investigated in the sulfur-resistant methanation aimed at production of synthetic natural gas. Different methods including impregnation, deposition precipitation, and co-precipitation were used for preparing ZrO₂–Al₂O₃ composite supports. These composite supports and their corresponding Mo-based catalysts were investigated in the sulfur-resistant methanation, and characterized by N₂ adsorption–desorption, XRD and H₂-TPR. The results indicated that adding ZrO₂ promoted MoO3dispersion and decreased the interaction between Mo species and support in the MoO₃/ZrO₂–Al₂O₃ catalysts. The co-precipitation method was favorable for obtaining smaller ZrO₂ particle size and improving textural properties of support, such as better MoO₃ dispersion and increased concentration of Mo⁶⁺ species in octahedral coordination to oxygen. It was found that the MoO₃/ZrO₂–Al₂O₃ catalyst with ZrO₂Al₂O₃ composite support prepared by co-precipitation method exhibited the best catalytic activity. The ZrO₂ content in the ZrO₂Al₂O₃ composite support was further optimized. The MoO₃/ZrO₂–Al₂O₃ with 15 wt % ZrO₂ loading exhibited the highest sulfur-resistant CO methanation activity, and excess ZrO₂ reduced the specific surface area and enhanced the interaction between Mo species and support. The N₂ adsorption-desorption results indicated that the presence of ZrO₂ in excessive amounts decreased the specific surface area since some amounts of ZrO₂ form aggregates on the surface of the support. The XRD and H₂-TPR results showed that with the increasing ZrO₂ content, ZrO₂ particle size increased. These led to the formation of coordinated tetrahedrally Mo⁶⁺(T) species and crystalline MoO₃, and this development was unfavorable for improving the sulfur-resistant methanation performance of MoO₃/ZrO₂–Al₂O₃ catalyst.