Complete oxidation of acetaldehyde on Pt/CeO2-ZrO2-Bi2O3 catalysts

Pt/CeO₂-ZrO₂-Bi₂O₃ catalysts for catalytic combustion of acetaldehyde, which is one of volatile organic compounds (VOCs), were prepared by a wet impregnation method in the presence of polyvinylpyrrolidone K25 (PVP). The addition of PVP in the preparation process was effective to enhance the specific surface area and the Pt²⁺ ratio on the surface. Additionally, the pore volume and size of the catalysts were modified by the PVP addition. The Pt/CeO₂-ZrO₂-Bi₂O₃ catalysts are specific for the total acetaldehyde oxidation and CO and any acetaldehyde-derivative compounds were not observed as by-products. The catalytic activity of the Pt/CeO₂-ZrO₂-Bi₂O₃ catalysts was significantly promoted by the PVP addition and the total oxidation temperature decreased. By the optimization of the amount of platinum, the complete oxidation of acetaldehyde was realized at a temperature as low as 140 °C on a 10 wt%Pt/CeO₂-ZrO₂-Bi₂O₃ catalyst.     

CO2 absorption and desorption of Bi2O3-La2O3 powders prepared by mechanical synthesis

In order to obtain CO₂-absorbents to eliminate CO₂ concentration locally, Bi₂O₃-La₂O₃ mixed powders were prepared by mechanical alloying (MA) method using a planetary ball-milling machine. CO₂-absorption and desorption properties were checked by TG-DTA for the obtained powder samples. As a result, the sample shown by (Bi₂O₃)_1−x(La₂O₃)_x [x≤0.50] was found to form α-Bi₂O₃-solid solution with repeated CO₂-adsorption and desorption around 400- 500 °C. Absorbed and desorbed CO₂ contents varied with MA time: the 72 h MA’ed sample had a larger CO₂ content than the 24 h MA’ed sample. The performance depended on the sample composition, and (Bi₂O₃)_0.70(La₂O₃)_0.30 was found to have the highest performance in the present system.     

New substitutions and novel derivatives of the Aurivillius phases, Bi5TiNbWO15 and Bi4Ti3O12

We investigated isomorphous substitution of several metal atoms in the Aurivillius structures, Bi₅TiNbWO₁₅ and Bi₄Ti₃O₁₂, in an effort to understand structure-property correlations. Our investigations have led to the synthesis of new derivatives, Bi₄LnTiMWO₁₅ (Ln = La, Pr; M = Nb, Ta), as well as Bi₄PbNb₂WO₁₅ and Bi₃LaPbNb₂WO₁₅, that largely retain the Aurivillius (n = 1) + (n = 2) intergrowth structure of the parent oxide Bi₅TiNbWO₁₅, but characteristically tend toward a centrosymmetric/tetragonal structure for the Ln-substituted derivatives. On the other hand, coupled substitution, 2Ti^IV → M^V + Fe^III in Bi₄Ti₃O₁₂, yields new Aurivillius phases, Bi₄Ti_3−2xNb_xFe_xO₁₂ (x = 0.25, 0.50) and Bi₄Ti_3−2xTa_xFe_xO₁₂ (x = 0.25) that retain the orthorhombic noncentrosymmetric structure of the parent Bi₄Ti₃O₁₂. Two new members of this family, Bi₂Sr₂Nb₂RuO₁₂ and Bi₂SrNaNb₂RuO₁₂ that are analogous to Bi₂Sr₂Nb₂TiO₁₂, possessing tetragonal (I4/mmm) Aurivillius structure have also been synthesized.     

Temperature-dependent oxygen release, intercalation behaviour and catalytic properties of V2O5·xNb2O5 compounds

In order to investigate the catalytic properties, V_2,38Nb_10,7O_32,7, VNb₉O₂₅ and solid solutions of V₂O₅ in TT-Nb₂O₅ were prepared by thermal decomposition of freeze-dried oxalate precursors. The samples were characterised by X-ray diffraction and surface area determination. The crystalline samples are capable of the intercalation of sodium and lithium ions from solution. Above a temperature of about 500 °C, in dependence on the oxygen partial pressure a reversible release and uptake of oxygen without a structural variation takes place. The catalytic properties have been evaluated for the oxidative dehydrogenation (ODH) of propane and propene. There are only small differences in the catalytic activity of the different crystalline samples. Because of the relative high starting temperature, a selective catalytic oxidation of propane to propene is hardly observed.     

Structural characterization and photocatalytic properties of novel Bi2YVO8

Bi₂YVO₈ was prepared by solid-state reaction for the first time. The structural and photocatalytic properties of Bi₂YVO₈ were studied. The results showed that this compound has the tetragonal crystal system with space group I4/mmm. The band gap of Bi₂YVO₈ was estimated to be about 2.09 eV by plotting (αhν)² versus hν and obtaining the hν axis intercept value according to Tauc's equation. For the photocatalytic water splitting reaction, H₂ or O₂ evolution was observed from pure water with Bi₂YVO₈ as the photocatalyst under ultraviolet light irradiation (wavelength = 390 nm). Degradation of aqueous methylene blue photocatalyzed by this compound was investigated under visible light irradiation. Bi₂YVO₈ showed higher photocatalytic activity compared to Bi₂YTaO₇, Bi₂InTaO₇ or TiO₂ (P-25). Complete removal of aqueous methylene blue was achieved after visible light irradiation for 170 min. The decrease of the total organic carbon and the formation of inorganic products such as SO₄²⁻ and NO₃⁻ revealed the continuous mineralization of aqueous methylene blue during photocatalytic reaction.     

Hydrothermal synthesis and study of an inorganic-organic hybrid vanadate of a nickel(II) coordination complex with pyrazine, Ni3(C4H4N2)3(V8O23)

The three-dimensional hybrid compound Ni₃(C₄H₄N₂)₃(V₈O₂₃) has been synthesized by mild hydrothermal methods under autogenous pressure at 170 °C. The structure of the phase is stable until 380 °C. The removal of the pyrazine molecules from the structure induces its collapse. The IR spectrum shows the vibration modes of the pyrazine molecule and those of the [VO₄]³⁻ groups. A UV-visible spectrum shows the characteristic bands of the Ni(II) d⁸-high-spin cation in a slightly distorted octahedral coordination. Magnetic measurements indicate the existence of antiferromagnetic interactions that can be fitted with a chain model to give g = 2.31, J/k = −5.3, and zJ′/k = −5.5.     

Design of magnetic and fluorescent Mg-Al layered double hydroxides by introducing Fe3O4 nanoparticles and Eu ions for intercalation of glycine

We describe a novel route for the preparation of magnetic and fluorescent magnesium-aluminum layered double hydroxides by introducing Fe₃O₄ nanoparticles and Eu³⁺ ions. From the powder X-ray diffraction results, it was found that the Fe₃O₄ nanoparticles were highly dispersed in the inner void of octahedral lattice, and the Eu³⁺ ions substituted for the Al³⁺ ions and entered into hydrotalcite lattice through isomorphous replacement. Moderate introduction of Fe₃O₄ nanoparticles and Eu³⁺ ions did not change the lamellar structure of magnesium-aluminum layered double hydroxides. Glycine can also be intercalated into this magnetic and fluorescent layered double hydroxides by ion-exchange method. After intercalation of glycine, the basal spacing of magnetic and fluorescent layered double hydroxides increased from 7.6 to 8.8 Å, indicating that glycine was successfully intercalated into the interlayer space of layered double hydroxides. Magnetic measurements reveal that these novel layered double hydroxides possess paramagnetic property at room temperature, and the emission and excitation spectra indicate the layered double hydroxides exhibit fluorescent property.     

Preparation of KNbO3 by hydrothermal reaction

Perovskite-type KNbO₃ powder was prepared by hydrothermal reaction using Nb₂O₅ in KOH solution. A single phase of KNbO₃ was obtained when the molar ratio of KOH/Nb₂O₅ was above 20 and the reaction temperature was above 160 °C. Three types of KNbO₃ powder with the orthorhombic, tetragonal and cubic symmetries were obtained, depending on the reaction temperature and the ratio of KOH/Nb₂O₅. The molar ratios of K/Nb in the cubic and tetragonal phases were 0.91 and 0.94, respectively and that of the orthorhombic one was 0.98, and the mass loss was observed in the TG curves of tetragonal and cubic phases. The tetragonal and cubic phases were stabilized by OH⁻ and adsorbed water.     

Acidity characterization of a titanium and sulfate modified vermiculite

A natural vermiculite has been modified with titanium and sulfated by the intercalation and impregnation method in order to optimize the acidity of the clay mineral, and characterization of samples were analyzed by X-ray fluorescence (XRF), X-ray diffraction (XRD), nitrogen adsorption isotherms, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature programmed desorption with ammonia (TPD-NH₃). All the modified solids have a significantly higher number of acidic sites with respect to the parent material and in all of these, Brönsted as well as Lewis acidity are identified. The presence of sulfate appears not to increase the number of acidic centers in the modified clay. For the materials sulfated with the intercalation method, it is observed that the strength of the acidic sites found in the material increases with the nominal sulfate/metal ratio. Nevertheless, when elevated quantities of sulfur are deposited, diffusion problems in the heptane reaction appear.     

Synthesis and crystal structure of [3,5-(CH3O)2C6H3NH3]4P4O12·4H2O

The chemical preparation and crystal structure are given for a new organic-cation cyclotetraphosphate. This compound is triclinic P-1 with the following unit cell parameters: a=7.857(1) Å, b=8.877(2) Å, c=17.271(3) Å, α=93.94(1)°, β=101.75(2)°, γ=103.72(1)° V=1137.0(4) Å³, Z=1 and ρ_cal=1.467 g cm⁻³. The crystal structure has been determined and refined to R=0.037, using 6291 independent reflections. The atomic arrangement can be described by inorganic layers parallel to the (0 0 1) planes, between which the organic entities are located.     

Preparation of hexagonal WO3 from hexagonal ammonium tungsten bronze for sensing NH3

Hexagonal tungsten oxide (h-WO₃) was prepared by annealing hexagonal ammonium tungsten bronze, (NH₄)_0.07(NH₃)_0.04(H₂O)_0.09WO_2.95. The structure, composition and morphology of h-WO₃ were studied by XRD, XPS, Raman, ¹H MAS (magic angle spinning) NMR, scanning electron microscopy (SEM), and BET-N₂ specific surface area measurement, while its thermal stability was investigated by in situ XRD. The h-WO₃ sample was built up by 50-100 nm particles, had an average specific surface area of 8.3 m²/g and was thermally stable up to 450 °C. Gas sensing tests showed that h-WO₃ was sensitive to various levels (10-50 ppm) of NH₃, with the shortest response and recovery times (1.3 and 3.8 min, respectively) to 50 ppm NH₃. To this NH₃ concentration, the sensor had significantly higher sensitivity than h-WO₃ samples prepared by wet chemical methods.     

High rate performances of the cathode material LiNi1/3Co1/3Mn1/3O2 synthesized using low temperature hydroxide precipitation

A low-temperature reaction route is introduced based on hydroxide precipitation method to synthesize the cathode material LiNi_1/3Co_1/3Mn_1/3O₂. The crystal structure and morphology of the prepared powder have been characterized by X-ray diffraction and Scan electron microscope, respectively. The charge–discharge tests were performed between 2.5 and 4.5 V. The discharge capacity of the material is strongly impacted by the reaction temperature. The powders sintered at 850 °C show the best electrochemical performance and the initial discharge capacity is about 160 mAh g⁻¹ at 5 C. Powder X-ray diffraction and Scan electron microscope results reveal that the excellent electrochemical performances should be ascribed to the lower precursor reaction temperature, the lower degree of cation mixing and analogous spherical small particles, which can improve the transfer of Li ions and electrons. All these results indicate that this material has potential application in lithium-ion batteries.     

Development of perovskite in Fe-substituted Pb(Zn1/3Ta2/3)O3 and dielectric characteristics

Pb(Zn_1/3Ta_2/3)O₃ ceramics, compositionally modified by the incorporation of Fe to the octahedral lattice sites, were prepared and characterized in terms of perovskite development, dielectric properties, as well as microstructure evolution. The powders of the B-site precursor compositions were synthesized separately and reacted with PbO to form Pb[(Zn_1/3Ta_2/3),(Fe_1/2Ta_1/2)]O₃. The perovskite contents increased continuously with the Fe concentration. The maximum dielectric constant values of the ceramics increased tremendously with the fraction of Fe, whereas the dielectric maximum temperatures were rather insensitive to the compositional change.     

Fabrication of TiO2 hollow fibers with surface nanostructure

Polyvinyl alcohol-TiO₂ (PVA-TiO₂) core sheath nanofibers were fabricated by electrospinning an aqueous solution of PVA and introducing the thread-like droplets directly into a titanium tetraisopropoxide (TTIP)/hexane solution. Rod-like and sheet-like structures of lepidocrocite-type layered titanate formed on the surface of the TiO₂ sheath of the nanofibers by alkaline treatment in 1 mol L⁻¹ aqueous NaOH solution at 363 K. The nanofibers were converted to hollow TiO₂ nanofibers with surface nanostructure and anatase crystallinity by acid treatment to remove sodium ions and heat treatment at 773 K. The surface nanostructures enhanced the crystallinity and external surface area of the nanofiber and contributed to the improvement of photocatalytic oxidation activity.     

Optimization of reaction conditions in selective oxidation of styrene over fine crystallite spinel-type CaFe2O4 complex oxide catalyst

The CaFe₂O₄ spinel-type catalyst was synthesized by citrate gel method and well characterized by thermogravimetric analysis, atomic absorption spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction and transmission electron microscopy. The crystallization temperature of the spinel particle prepared by citrate gel method was 600 °C which was lower than that of ferrite prepared by other methods. CaFe₂O₄ catalysts prepared by citrate gel method show better activity for styrene oxidation in the presence of dilute H₂O₂ (30%) as an oxidizing agent. In this reaction the oxidative cleavage of carbon-carbon double bond of styrene takes place selectively with 38 ± 2 mol% conversion. The major product of the reaction is benzaldehyde up to 91 ± 2 mol% and minor product phenyl acetaldehyde up to 9 ± 2 mol%, respectively. The products obtained in the styrene oxidation reaction were analyzed by gas chromatography and mass spectroscopy. The influence of the catalyst, reaction time, temperature, amount of catalyst, styrene/H₂O₂ molar ratio and solvents on the conversion and product distribution were studied.     

A powder X-ray diffraction refinement of the BaNd2Ti3O10 structure

The structure parameters of BaNd₂Ti₃O₁₀ were refined based on Olsen’s model. This material has a monoclinic unit cell with space group P2₁/m. The unit cell parameters are: a=7.73030(14) Å, b=7.62578(14) Å, c=14.23174(31) Å, β=97.832(6)°. The structure can be considered as a layered perovskite-like structure, in which the perovskite block shows distortion. The various layers link in the order of (Ba_1/2O)-(Ba_1/2TiO₃)-(NdTiO₃)-(NdTiO₃).     

Synthesis by an ionic liquid-assisted method and optical properties of nanoflower Y2O3

Flower-like Y₂O₃ nano-/microstructured phosphors without metal activators have successfully been fabricated by an ionic liquid (IL)-assisted method involving temperature (600 °C) annealing. In this paper, the effect of IL concentration on the morphology of the product has been investigated. The IL plays a crucial role in the formation of various morphologies of Y₂O₃. The structural and morphological features of the obtained samples have been characterized by means of X-ray powder diffraction (XRD) analysis, photoluminescence spectra (PL), Fourier-transform infrared (FT-IR) spectra and X-ray photoelectron spectra (XPS). The photoluminescence spectra of the products exhibit an intense bluish-white emission (ranging from 405 to 430 nm and centered at 418 nm). The luminescent mechanisms have been ascribed to the carbon impurities in the Y₂O₃ host. The effect of the ILs cation and the counter anions on the Y₂O₃ morphology of these nanostructures was studied experimentally. It was observed that Y₂O₃ morphology and PL of these nanostructures were strongly influenced by the type of cation and anion. As the length of the subsidiary chain of cation section of IL (imidaziole ione) reduces, the thickness of the nano-sheets increases. It is expected that the present method may easily be extended to similar nano-/microstructures of other oxide materials. Such investigations are currently underway.     

High temperature thermopower and electrical resistivity studies in the transparent conducting oxide Sn doped MgIn2O4

Sn doping in an n-type transparent conducting oxide MgIn₂O₄ is carried out and its effect on the high temperature transport properties viz. thermopower and electrical resistivity is studied. A solid solution exists in the composition window Mg_1+xIn_2−2xSn_xO₄ for 0 < x ≤ 0.4. The band gap as well as the transport properties increases with increasing Sn concentration. The high temperature resistivity properties indicate degenerate semiconducting behavior for all the compositions. The highest figure of merit obtained is 0.12 × 10⁻⁴ K⁻¹ for the parent compound at 600 K.     

Topotactic route for new layered perovskite oxides containing fluorine: Ln1.2Sr1.8Mn2O7F2 (Ln = Pr, Nd, Sm, Eu, and Gd)

A series of fluorine intercalated Ruddlesden-Popper layered perovskites, Ln_1.2Sr_1.8Mn₂O₇F₂ (Ln = La, Pr, Nd, Sm, Eu, and Gd) were synthesized from the parent oxides, Ln_1.2Sr_1.8Mn₂O₇, with the organic reagent, poly(vinylidene fluoride), as the fluorine source. Oxidative intercalation readily occurred by decomposition of the organic fluoride immediately adjacent to the parents.     

Structural properties of Al2O3-La2O3 binary oxides prepared by sol-gel

The structural properties of La₂O₃ and Al₂O₃-La₂O₃ binary oxides prepared by sol-gel were studied by XRD, HRTEM and UV-vis. The binary oxides with high lanthana contents show an amorphous structure after calcination at 650 °C. At calcination temperatures higher than 1000 °C there is a phase transformation from the amorphous state to the crystalline LaAlO₃ with a perovskite structure. The structure of La₂O₃ is consistent with the hexagonal system; however, some crystalline microdomains with a monoclinic structure were detected by HRTEM. Islands of La₂O₃ and LaAl₁₁O₁₈ phases were detected at high lanthana concentration in the binary oxide. The modification in the coordination shell of the Al³⁺ cations due to the interaction with La³⁺ cations confirms the formation of phases with a perovskite structure and the presence of islands of the LaAl₁₁O₁₈ phase.