Low temperature synthesis of porous copper/zinc oxide

A two-step urea aqueous solution process at a low temperature (90 °C) was employed for the preparation of a copper/zinc oxide material. Well defined porous spherical particles with average sizes of around 5 μm in diameter were prepared first and then used as a support for further copper-zinc precipitation. It was found that the particle composition and shape were changed with applied stirring speed (100 rpm or 200 rpm) and that particle size is inversely proportional to the copper content in the particles. The particles preserved their size and shape after the heat treatment. Prepared Cu/ZnO samples showed catalytic activity for the reaction of steam reforming of methane. Samples were characterized by scanning field emission electron microscopy, energy dispersive X-ray analyses, X-ray powder diffraction, surface area analyses, and atomic absorption spectroscopy.     

The zinc ferrite obtained by oxidative precipitation method as a catalyst in n-butanol conversion

This paper presents the results of catalytic properties of n-butanol conversion of the zinc ferrite obtained by oxidative precipitation method. The zinc ferrite showed good dehydrogenating activity but also catalyzed consecutive bimolecular condensation of emerged aldehyde particles into symmetrical ketone. The zinc-iron oxide of spinel structure was prepared from ferrous sulfate, which forms as a waste during the titanium dioxide production.The X-ray diffraction methods (XRD, XRF) were used in determining the structure and composition of obtained zinc ferrite, while thermogravimetry (TG-DTG), and differential thermal analysis (DTA) were used in the study of thermal transformations of zinc spinel in air.     

Novel solar light driven photocatalyst, zinc indium vanadate for photodegradation of aqueous phenol

In the present investigation, we have demonstrated the synthesis of novel photocatalyst, zinc indium vanadate (ZIV) by solid-solid state route using respective oxides of zinc, indium and vanadium. This novel photocatalyst was characterized using XRD, FESEM, UV-DRS and FTIR in order to investigate its structural, morphological and optical properties. XRD clearly shows the formation of phase pure ZIV of triclinic crystal structure with good crystallinity. FESEM micrographs showed the clustered morphology having particle size between 0.5 and 1 μm. Since, optical study showed the band gap around 2.8 eV, i.e. in visible region, we have performed the photocatalytic activity of phenol degradation under visible light irradiation. The photodecomposition of phenol by ZIV is studied for the first time and an excellent photocatalytic activity was obtained using this novel photocatalyst. Considering the band gap of zinc indium vanadate in visible region, it will also be the potential candidate for water splitting.     

Influence of acid precursors on physicochemical properties of nanosized titania synthesized by thermal-hydrolysis method

The influence of nature and concentration of acid species on surface morphology and physicochemical properties of titania particles synthesized by direct thermal hydrolysis of titanium tetrachloride was investigated. The acids used were hydrochloric acid, nitric acid, sulfuric acid, and perchloric acid with a concentration of 3 M. Thermal hydrolysis of titanium tetrachloride in hydrochloric acid and perchloric acid with molar ratios of [H⁺]/[Ti⁴⁺] = 0.5, 1.0, 1.5, and 2.0, respectively, was used to study the effect of acid concentration. The synthesized materials were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, dynamic light scattering, and thermogravimetric analysis. Characterization of the samples by X-ray diffraction studies revealed the influence of acid species on the phase transformation of titania. Samples prepared by hydrochloric acid, nitric acid, and perchloric acid formed rutile phase with rhombus primary particles, while sulfuric acid resulted in anatase phase with flake-shaped primary particles. Transmission electron microscopy and dynamic light scattering results confirmed the nanosized titania particles and the agglomeration of primary particles to form secondary particles in spherical shape. The particle size of titania prepared using perchloric acid was smaller than those prepared with other acid sources. A direct correlation between [H⁺]/[Ti⁴⁺] ratio and particle size of titania was observed.     

Photocatalytic properties of BiVO4 prepared by the co-precipitation method: Degradation of rhodamine B and possible reaction mechanisms under visible irradiation

Bismuth vanadate (BiVO₄) was synthesized by the co-precipitation method at 200 °C. The photocatalytic activity of the oxide was tested for the photodegradation of rhodamine B under visible light irradiation. The analysis of the total organic carbon showed that the mineralization of rhodamine B over a BiVO₄ photocatalyst (∼40% after 100 h of irradiation) is feasible. In the same way, a gas chromatography analysis coupled with mass spectroscopy revealed the existence of organic intermediates during the photodegradation process such as ethylbenzene, o-xylene, m-xylene, and phthalic anhydride. The modification of variables such as dispersion pH, amount of dissolved O₂, and irradiation source was studied in order to know the details about the photodegradation mechanism.     

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.     

Novel hydroxide precursors for low temperature synthesis of selected ternary oxides

A novel method of using hydroxide precursors to reduce the synthesis temperature for few selected ternary oxides has been presented here. This technique is very useful and advantageous when the ternary oxides contain an alkaline earth element. The selected compositions for this method are BaCeO₃ (BC), BaBiO₃ (BB), La_0.7Sr_0.3CoO₃ (LSCO) and BaBi₂Nb₂O₉ (BBN). Commercially purchased strontium (or barium) hydroxide and freshly prepared lanthanum, cobalt, bismuth and niobium hydroxides were mixed thoroughly in stoichiometric ratio and heated at different temperatures ranging from 100 to 700 °C for 10 h for corresponding compositions. The sequence of the reaction and evolution of the product phase were studied by the X-ray diffraction (XRD) studies. The phase purity and lattice parameters were also determined by XRD investigations. All the product phases in each case were formed at relatively low temperature than when they were prepared by co-precipitation or solid state method. The morphology and average particle size of these powders were investigated by scanning electron microscopy (SEM).     

Precursor, base concentration and solvent behavior on the formation of zinc silicate

Zinc silicate was synthesized hydrothermally from zinc acetate and tetraethyl orthosilicate or sodium silicate. The possible lowest synthetic temperature and reaction parameters determining the morphology of the products were discussed. High base concentration favors the rod formation. XRD, TEM were used to characterized the products. Green and red photoluminescence were observed by the doping of Mn²⁺ or Eu³⁺, respectively.     

Ligand-assisted hydrothermal synthesis of ZnWO4 rods and their photocatalytic activities

ZnWO₄ rods were prepared using a ligand-assisted hydrothermal method with ZnCl₂ and Na₂WO₄ in the presence of various amines as ligands for zinc ions. The choice of ligand was found to play an important role in the formation of ZnWO₄ rods. The aspect ratio of the ZnWO₄ rods increased with increasing ligand strength. XRD and HRTEM confirmed that the ZnWO₄ rods grow along the [1 0 0] direction. The photochemical activities of the ZnWO₄ rods for the decomposition of Rhodamine 6G were examined. The photocatalytic activity was found to depend on the aspect ratio of the ZnWO₄ rods.     

TiO2 supported on rod-like mesoporous silica SBA-15: Preparation, characterization and photocatalytic behaviour

TiO₂ nanoparticles have been successfully incorporated in the pores of mesoporous silica SBA-15 with different morphologies by a wet impregnation method. The composites were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma (ICP) emission spectroscopy, transmission electron microscopy (TEM), N₂-sorption and UV-Vis diffuse reflectance spectroscopy. The photodegradation of methyl orange (MO) was used to study their photocatalytic property. It is indicated that the morphology of SBA-15 had a great influence on the photocatalytic activity of the composites. When TiO₂/SBA-15 composite was prepared by loading TiO₂ nanoparticles on uniform rod-like SBA-15 of 1 μm length, it showed higher photocatalytic degradation rate than that on less regular but much larger SBA-15 support. This difference was rationalized in terms of the homogeneously distributed and shorter channels of rod-like SBA-15, which favored mass transport and improved the efficient utilization of the pore surface.     

Properties of TiO2 prepared by acid treatment of BaTiO3

TiO₃ powders were prepared by acid treatment of BaTiO₃ and their properties were investigated. The BaTiO₃ powder was subjected to HNO₃ in concentrations ranging from 10⁻³ to 8 M at 90 °C for 0.5-6 h. Dissolution of BaTiO₃ and precipitation of TiO₂ occurred at acid concentrations of 2-5 M. BaTiO₃ dissolves completely to form a clear solution at reaction times of 0.5-1 h, but a rutile precipitate is formed after 2 h of acid treatment. By contrast, anatase is precipitated by adjusting the pH of the clear solution to 2-3 using NaOH or NH₄OH solution. The rutile crystals were small and rod-shaped, consisting of many small coherent domains connected by grain boundaries with small inclination angles and edge dislocations, giving them a high specific surface area (S_BET). With increasing HNO₃ concentration, the S_BET value increased from 100 to 170 m²/g while the crystallite size decreased from 25 to 11 nm. The anatase crystals obtained here were very small equi-axial particles with a smaller crystallite size than the rutile and S_BET values of about 270 m²/g (higher than the rutile samples). The photocatalytic activity of these TiO₂ was determined from the decomposition rate of Methylene Blue under ultraviolet irradiation. Higher decomposition rates were obtained with larger crystallite sizes resulting from heat treatment. The maximum decomposition rates were obtained in samples heated at 500-600 °C. The photocatalytic activity of the TiO₂ was found to depend more strongly on the sample crystallite size than on S_BET.     

Phase selection and visible light photo-catalytic activity of Fe-doped TiO2 prepared by the hydrothermal method

It is necessary to extend the absorption range of TiO₂ based materials from the ultraviolet to the visible light region for most photo-catalytic applications of TiO₂ under solar irradiance or indoor lighting. Also, the ability to control the structural evolution, particularly the competition and transformation between different phases (anatase or rutile), is extremely important for the preparation of high efficiency TiO₂ based photo-catalysts. In this work, we have systematically studied the effects of various processing factors on the phase selection process/outcome of nanocrystalline Fe-doped TiO₂, which includes the level of doping ions, annealing temperature, solution pH and the addition of acidic anions, using a low temperature hydrothermal method. Both Fe-doped rutile and anatase TiO₂ phases were obtained via varying the processing conditions. The visible-light photo-catalytic activity of doped materials was significantly improved over that of the pure TiO₂ nanopowders, which was demonstrated by effective degradation of methylene blue under visible light.     

Proton transport and structural relations in hydroxyl-bearing BaTiO3 and its doped compositions synthesised by wet-chemical methods

Hydrothermally synthesised powders of BaTiO₃ and its Fe- or Nd-doped analogues contain hydroxyl groups in the lattice substitutional to oxide ion, as confirmed from TGA/DTA, IR spectral analysis of D₂O-treated powders, EGA-MS, the contraction in lattice constant with heat treatment by XRD and surface examination by XPS. Electrical resistivity measurements were carried out on the pellets from 298 to 1000 K by ac impedance spectroscopy and dc methods in dry or moist air and 8% H₂+Ar environments. The electrical conductivity observed for unsintered pellets between 298 and 500 K, is in the range of 10⁻³ to 10⁻⁷ S/cm and can be attributed to the extrinsic hydroxyls in BaTiO₃. The acceptor-doped composition, BaTi_0.9Fe_0.1O_3−δ: 2δ(OH) exhibits higher electrical conductivity than BaTiO₃ or the donor-doped Ba_0.9Nd_0.1TiO_3−δ: 2δ(OH) in moist air. The hydrothermally prepared powders heat treated below 1000 K having cubic symmetry at room temperature, possess higher proton conductivity and reabsorption capability for hydroxyls on exposure to moisture than the powders sintered at 1673 K (tetragonal symmetry). The conductivity at 298-500 K is due to the mobility of proton along OHO octahedra in the perovskite lattice. The conduction at 550-1000 K is a combined effect of proton as well as oxygen vacancy mobility in BaTiO₃ and Ba_0.9Nd_0.1TiO₃; electron hole (Ti⁴⁺, Ti³⁺, Fe³⁺, Fe²⁺) participation is the additional contribution in acceptor-doped composition in this temperature range.     

Preparation of MgO nano-rods with strong catalytic activity via hydrated basic magnesium carbonates

MgO nano-rods of several microns in length and 50–100 nm in width were prepared by calcining nesquehonite phase, obtained by simple precipitation using (NH₄)₂CO₃ under ambient condition. The MgO nano-rod with reasonably high surface area (75–120 m² g⁻¹) exhibits strong activity in solvent-free base catalyzed Claisen-Schmidt condensation giving 99% conversion in 2 h and is easily recyclable with no significant change in catalytic activity. Presence of numerous basic sites of different strengths (surface hydroxyl groups, low coordinate O²⁻ sites) is attributed to the observed effect.     

Catalytic activity and magnetic properties of barium hexaferrite prepared from barite ore

Barium hexaferrite (BaFe₁₂O₁₉) has traditionally been used in permanent magnets and more recently used for high density magnetic recording. The classical ceramic method for the preparation of barium hexaferrite consists of firing mixture of chemical grade iron oxide and barium carbonate at high temperature. In this paper a mixture of chemical grade hematite, barium oxide and predetermined mixtures of iron oxide ore and barite ore containing variable amounts of coke were used to prepare barium hexaferrite (BaFe₁₂O₁₉) as a permanent magnetic material. The mixtures were mixed in a ball mill and fired for 20 h in a tube furnace at different temperatures (1100, 1150, 1200 and 1250 °C). XRD, magnetic properties, porosity measurements and catalytic activity were used for characterization of the produced ferrite. The results of experiments showed that the optimum conditions for the preparation of barium hexaferrite are found at 1200 °C for the mixture of chemical grade hematite and barium oxide. It was also found that the barium hexaferrite can be prepared from the iron and barite ores at 1200 °C. The addition of coke enhanced the yield of barium hexaferrite and improved its physicochemical properties. Samples prepared from ores with coke% = 0 show the most acidic active sites, they show a higher catalytic activity towards H₂O₂ decomposition. With addition of coke the catalytic activity decreases due to the poisoning effect of carbon on the available active site.     

Synthesis, structure and oxygen-storage capacity of Pr1−xZrxO2−δ and Pr1−x−yPdyZrxO2−δ

Nanocrystalline Pr_1−xZr_xO_2−δ (0 ≤ x ≤ 1) and Pr_1−x−yPd_yZr_xO_2−δ (x = 0.50, y = 0.02) solid solutions have been synthesized by a single step solution combustion method. The whole range of solid solution compositions crystallize in cubic fluorite structure. The lattice parameter ‘a’ linearly varied up to x = 1.0. Oxygen-storage capacity (OSC) and redox properties of Pr_1−xZr_xO_2−δ (0.0 ≤ x ≤ 0.8) solid solutions have been investigated by temperature-programmed reduction (TPR) and are compared with those of Ce_1−xZr_xO₂. Pr_1−xZr_xO_2−δ exhibited H₂ uptake and CO oxidation at a lower temperature than Ce_1−xZr_xO₂. Small amount of Pd ion (y = 0.02) substitution was found to bring down the temperature of oxygen release-storage significantly.     

Synthesis of perovskite-type (La1−xCax)FeO3 (0 ≤ x ≤ 0.2) at low temperature

Gel formation was realized by adding citric acid to a solution of La(NO₃)₃·5H₂O, Ca(NO₃)₂·4H₂O, and Fe(NO₃)₂·9H₂O. Perovskite-type (La_1−xCa_x)FeO₃ (0 ≤ x ≤ 0.2) was synthesized by firing the gel at 500 °C in air for 1 h. The crystallite size (D_1 2 1) decreased with increasing x, while the specific surface area was 6.8-9.4 m²/g and independent of x. The XPS measurement of the (La_1−xCa_x)FeO₃ surface indicated that the Ca²⁺ ion content increased with increasing x, while the Fe ion content was independent of x. Catalytic activity for CO oxidation increased with increasing x.     

Solution combustion synthesis of γ(L)-Bi2MoO6 and photocatalytic activity under solar radiation

The facile method of solution combustion was used to synthesize γ(L)-Bi₂MoO₆. The material was crystallized in a purely crystalline orthorhombic phase with sizes varying from 300 to 500 nm. Because the band gap was 2.51 eV, the degradation of wide variety of cationic and anionic dyes was investigated under solar radiation. Despite the low surface area (<1 m²/g) of the synthesized material, γ(L)-Bi₂MoO₆ showed high photocatalytic activity under solar radiation due to its electronic and morphological properties.     

Photoluminescence of nanocrystalline SrMgF4 prepared by a solution chemical route

SrMgF₄ was prepared by precipitation in aqueous solution. Alkaline earth metal acetates and ammonium fluoride were used as precursors. After drying and annealing the samples at different temperatures and times, single phase SrMgF₄ was obtained. By varying the annealing conditions, the mean crystallite size could be adjusted. Furthermore, the thermally treated samples displayed UV-excited intensive broad band luminescence in the visible region. The emissions colour and intensity can be adjusted by the tempering conditions. X-Ray diffraction, TEM-microscopy, fluorescence and IR-spectroscopy were used for analysis.