Sol-gel preparation and characterization of non-substituted and Sr-substituted lanthanum cobaltates

This paper reports on the results concerning the sol-gel preparation and characterization of Sr-substituted perovskite lanthanum cobaltates La_1−xSr_xCoO_3−δ (x = 0.0, 0.25, 0.5 and 0.75). The metal ions, generated by dissolving starting materials in diluted acetic acid were complexed by 1,2-ethanediol to obtain the precursors for the non-substituted and Sr-substituted LaCoO₃. The influence of the synthesis temperature, heating time and the amount of substituent on the phase purity of La_1−xSr_xCoO_3−δ were investigated. The phase transformations, composition and micro-structural features in the gels and polycrystalline samples were studied by thermal analysis (TG/DTA), infrared spectroscopy (IR), powder X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM).      

The binary system PbO - BiVO4

Phase equilibria established in the PbO - BiVO₄ system over the whole component concentration range up to 1000°C have been investigated. A phase diagram has been constructed using DTA and XRD.      

Methylcellulose/SiO<Subscript>2</Subscript> hybrids: sol-gel preparation and characterization by XRD,FTIR and AFM

Methylcellulose (MC) / SiO₂ organic / inorganic hybrid materials have been prepared from MC and methyltriethoxysilane or ethyltrimethoxysilane, and characterized by XRD, FTIR and AFM. XRD showed peak shifts. FTIR shows intermolecular hydrogen bonding between MC and SiO₂. AFM depicts surface roughness which depends on the silica precursor and MC content.      

Low temperature synthesis and characterization of Mn3O4 nanoparticles

Heating hydrous manganese (II) hydroxide gel at 85 °C for 12 hours produces Mn₃O₄ nanoparticles. They were characterized by X-ray powder diffraction (XRD) and infrared spectroscopy (FTIR). The particle size estimated from the SEM and X-ray peak broadening is approximately 32 nm, showing them to be nanocrystalline. EPR measurements confirm a typical Mn²⁺signal with a highly resolved hyperfine structure.      

Ceramic materials made of CdTe and Cd-Zn-Te nanocrystalline powders

In the present study newly produced semiconductor ceramic nanopowder materials made of CdTe and Cd_1−xZn_xTe (CZT) are considered. Common features and differences in microstructures, phase transformations, grain growth and properties of the ceramic materials of the binary and ternary compositions are studied.      

Sol-gel bioactive glass-ceramics Part I: Calcium phosphate silicate/wollastonite glass-ceramics

In this work we present experimental results about synthesis, structure evolution and in vitro bioactivity of new calcium phosphate silicate/wollastonite (CPS/W) glass-ceramics. The samples obtained were synthesized via polystep sol-gel process with different Ca/P+Si molar ratio (R). The structure of the materials obtained was studied by XRD, FTIR spectroscopy and SEM. XRD showed the presence of Ca₁₅(PO₄)₂(SiO₄)₆, β-CaSiO₃ and α-CaSiO₃ for the sample with R=1.89 after thermal treatment at 1200°C/2h. The XRD results are in good agreement with FTIR analysis. SEM denotes that apatite formation can be observed after soaking in simulated body fluid (SBF).      

2-pyrrolidone - capped Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocrystals

Water-soluble Mn₃O₄ nanocrystals have been prepared through thermal decomposition in a high temperature boiling solvent, 2-pyrrolidone. The final product was characterized with XRD, SEM, TEM, FTIR and Zeta Potential measurements. Average crystallite size was calculated as ∼15 nm using XRD peak broadening. TEM analysis revealed spherical nanoparticles with an average diameter of 14±0.4 nm. FTIR analysis indicated that 2-pyrrolidone coordinates with the Mn₃O₄ nanocrystals only via O from the carbonyl group, thus confining their growth and protecting their surfaces from interaction with neighboring particles.      

The effect of calcium substitution on the afterglow of Eu2+/Dy3+ doped Sr4Al14O25

The effect of calcium substitution on the afterglow of tetrastrontium aluminate phosphors (Sr₄Al₁₄O₂₅:Eu²⁺, Dy³⁺) was investigated. A series of (Sr₁-_xCa_x)O⊎nAl₂O₃:Eu²⁺(1%), Dy³⁺(0.5%), with variation of calcium content (x = 0 − 1), were synthesized by a high temperature solid state reaction in a reducing atmosphere. The photoluminescence, persistent luminescence (afterglow), and lumen equivalents of these materials were studied and compared. It turned out that the afterglow properties of the phosphors were strongly dependent on the Sr/Ca ratio. As the Ca content increased, a phase transition and blue shift in emission spectra were observed.      

Comparison of the efficacy of sulfurization agents in decreasing the sheet resistance of polyamide and polyethylene with copper sulfide layers and influence of their compositions

The process of obtaining semiconductive and electrical conductive layers of copper sulfides by the sorption — diffusion method on polymers (polyamide 6 and low density polyethylene) using solutions of potassium pentathionate, K₂S₅O₆, and higher polythionic acids, H₂S _n O₆ (n = 21, 33), was investigated. The layers were characterized for compositional and electrical properties by X-ray diffraction (XRD) analysis and sheet resistance measurements. The thickness of copper sulfides layers on polyamide and polyethylene increased with increasing time of polymer sulfurization and varied from 10 to 43 μm. The variations of the sheet resistance of copper sulfides layers formed on the surface of polymers on sulfurization agent used, the conditions of sulfurization, chemical and phase composition of the obtained layers were established. Sheet resistance of copper sulfides layers decreases with increasing time of the duration of sulfurization and the number of sulfur atoms in the polythionate anion. The sheet resistance values for copper sulfide layers formed on the polyamide surface are much lower than those of Cu _x S formed on the polyethylene surface. XRD showed the predomination of Cu _x S phases with low x values.      

Surfactant-assisted polyol preparation of nickel powders with different morphologies

Sub-micrometer nickel powders of controlled size and morphology were produced by a surfactant-assisted polyol method, using ethylene glycol (EG) as solvent and reductant in the presence of sodium dodecyl sulfate (SDS) surfactant and NaOH. The resultant Ni powders were characterized by XRD, SEM, EDS, and FTIR. Spherical, hexagonal, and triangular fcc Ni powders from 0.30 to 0.60 μm were obtained in the presence of SDS; irregular spherical fcc Ni powders were obtained in its absence. The concentrations of SDS, NaOH and Ni(CH₃COO)₂·4H₂O greatly influence the product morphology and size.      

Structural properties and magnetic interactions in Al3+ and Cr3+ co-substituted CoFe2O4 ferrite

A series of CoAl_xCr_xFe_2−2xO₄ systems (x = 0.1 to 0.5 in steps of x = 0.1) spinel ferrites have been synthesized successfully using wet chemical co-precipitation technique. The samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR) and magnetization measurements. The powder XRD patterns confirm the single phase spinel structure for the materials synthesized. X -ray diffraction measurements were performed to yield the lattice constant as function of the amount x corresponding to Al-Cr substitution. Lattice parameters, X-ray density, bulk density and particle size decrease whereas porosity increases with the increase in Al-Cr content, ‘x’. Infrared studies show two absorption bands at about 400 cm⁻¹ and 600 cm⁻¹ for octahedral and tetrahedral sites, respectively. Saturation magnetization decreases with the increase in Al-Cr content x. AC magnetic susceptibility measurements were carried out as a function of temperature to measure the Curie temperature, which was found to decrease with Al-Cr content x. The decrease of Curie temperature has been explained by A-B interaction.      

A green chemical route for the synthesis of Mn3O4 nanoparticles

A novel environmental friendly, room temperature route using an ionic liquid 1-n-butyl-3-methylimidazolium hydroxide ([BMIM]OH) for the synthesis of Mn₃O₄ nanoparticles is presented. The product was characterized using Fourier transform infrared spectroscopy, X-ray powder diffraction, and transmission electron microscopy. Phase purity was confirmed by XRD, and X-ray line profile fitting determined a crystallite size of 42 ± 11 nm. TEM analysis revealed various morphologies. EPR measurements have indicated the existence of long-range interactions, due to the wide range of particle sizes and morphologies observed.      

ZrOCl<Subscript>2</Subscript> · 8H<Subscript>2</Subscript>O: An efficient catalyst for rapid one-pot synthesis of 3-carboxycoumarins under ultrasound irradiation in water

In this report, a rapid, efficient and environmental friendly synthesis of 3-carboxycoumarins under ultrasound irradiation in water media is described. The Knoevenagel condensation of Meldrum’s acid with substituted benzaldehydes in the presence of zirconium oxide chloride (ZrOCl₂·8H₂O) and ultrasonic irradiation in water gave the corresponding 3-carboxycoumarins in good to excellent yields.      

Microwave-induced combustion synthesis and characterization of NixCo1−xFe2O4 nanocrystals (x = 0.0, 0.4, 0.6, 0.8, 1.0)

A series of Ni-doped cobalt ferrites Ni_xCo1_−xFe₂O₄ (x = 0.0, 0.4, 0.6, 0.8, and 1.0) were prepared using microwave-induced combustion. Nickel, cobalt, and ferric nitrates were used as starting materials and glycine as fuel. The influence of Ni content on the lattice parameter, stretching vibrations, and magnetization was studied. XRD, FTIR, and SEM were used for structure, composition, and morphology investigation. A porous network structure was observed with average particle size 60–67 nm. All samples had a cubic spinel structure. The unit cell parameter “a” decreases linearly with nickel concentration due to the smaller ionic radius of nickel. Magnetization measurements showed that coercivity decreased as Ni content increased; it increased with decreasing temperature.      

Photocatalytic properties of Ru-doped titania prepared by homogeneous hydrolysis

Nanocrystalline titania particles doped with ruthenium oxide have been prepared by the homogenous hydrolysis of TiOSO₄ in aqueous solutions in the presence of urea. The synthesized particles were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), Selected Area Electron Diffraction (SAED) and Nitrogen adsorption-desorption was used for surface area (BET) and porosity determination (BJH). The photocatalytic activity of the Ru-doped titania samples were determined by photocatalytic decomposition of Orange II dye in an aqueous slurry during irradiation at 365 nm and 400 nm wavelengths.      

Catalytic reduction of NO by CO over Pd — doped Perovskite-type catalysts

The perovskite type oxides (nominal formula LaTi_0.5Mg_0.5O₃) with addition of Pd were prepared by annealing the ethanol solution of precursors in nitrogen flow at 1200°C and characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption of NO (NO-TPD). Their activity was evaluated for NO reduction by CO under stoichiometric and oxidizing conditions and for direct decomposition of NO. Pd substituted samples exhibited high NO reduction activity and selectivity towards N₂. Nearly complete elimination of NO was achieved at 200°C. Two simultaneous reactions, NO reduction by CO and direct decomposition of NO as well as two forms of NO adsorption were observed on the surface of Pd substituted perovskite samples. The distribution of Pd in different catalytically active sites or complexes on at the catalyst surface may be responsible for the proceeding of two reactions: NO reduction with CO and direct NO decomposition.      

Copper-cobalt ferrites as catalysts for methanol decomposition

Copper-cobalt ferrites with composition Cu_1?xCo_xFe₂O₄, where x= 0.2 and 0.8 were prepared by thermal treatment of co-precipitated precursor. The obtained materials were characterized by TG-DSC, XRD, Transmission and Conversion Electron Mössbauer spectroscopy and temperature programmed reduction with hydrogen. The catalytic properties of ferrites were tested in methanol decomposition to CO and hydrogen.      

Ionic liquid promoted synthesis of bis(indolyl) methanes

1-benzyl-3-methyl imidazolium hydrogen sulphate [bnmim][HSO₄] was found to be an effective catalyst for the condensation reaction of indoles and derivatives with benzaldehydes in microwave irradiation with lower reaction time and higher yields to give bis(indolyl) methanes.      

Equilibrium and kinetic study of the proton transfer reactions between nitroalkanes and strong organic bases — phosphazenes in tetrahydrofuran solvent

Proton transfer reactions rates between carbon acids 1-nitro-1-(4-nitrophenyl)ethane (NPNE), 2-methyl-1-nitro-1-(4-nitrophenyl)propane (MNPNP)) and phosphazenes (BEMP, BTPP, P₁-t-Oct) in tetrahydrofuran have been measured, and the activation parameters were determined. The results are compared with those previously obtained for P₁-t-Bu phosphazene, guanidines and amidines.      

Characterization of sorption gels used for determination of mercury in aquatic environment by diffusive gradients in thin films technique

The influence of pH, ionic strength and selected natural ligands on the measurement of mercury by the diffusive gradients in thin films technique (DGT) using recently introduced sorption gels was determined. Sorption gels containing Chelex 100, Spheron-Thiol, Duolite GT73 and modified Iontosorb AV resins were investigated, with the sorption capacity determined for all used sorption gels. The minimum DGT measurable concentrations were calculated from 3 times the standard deviation of mercury amount in unexposed sorption gels.