Shape-controlled synthesis of manganese oxide nanoplates by a polyol-based precursor route

Manganese oxide nanoplates with different shapes have been prepared based on an ethylene glycol-mediated route. The first step consists of precipitating manganese alkoxide precursor in a polyol process from the reaction of manganese acetate with ethylene glycol. During this process, the morphologies of the prepared precursor could be tuned from disc-shaped to hexagonal nanoplates by introducing different organic additives. The second step involves the treatment of the precursor under different conditions. Crystalline Mn₂O₃ with the same morphology was readily obtained by calcination of the manganese alkoxide precursor. Furthermore, Mn₃O₄ nanoplates could be obtained by immersing the precursor into the deionized water.     

A novel single-step synthesis of N-doped TiO2 via a sonochemical method

A novel single-step synthetic method for the preparation of anatase N-doped TiO₂ nanocrystalline at low temperature has been devoleped. The N-doped anatase TiO₂ nanoparticles were synthesized by sonication of the solution of tetraisopropyl titanium and urea in water and isopropyl alcohol at 80 °C for 150 min. The as-prepared sample was characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and UV–vis absorption spectrum. The product structure depends on the reaction temperature and reaction time. The photocatalytic activity of the as-prepared photocatalyst was evaluated via the photodegradation of an azo dye direct sky blue 5B. The results show that the N-doped TiO₂ nanocrystalline prepared via sonication exhibit an excellent photocatalytic activity under UV light and simulated sunlight.     

Chitosan as template for the synthesis of ceria nanoparticles

Cerium oxide (CeO₂), nanoparticles were prepared using chitosan as template, cerium nitrate as a starting material and sodium hydroxide as a precipitating agent. The resultant ceria–chitosan spheres were calcined at 350 °C. The synthesized powders were characterized by, XRD, HRTEM, UV–vis, FTIR, and TG-DTA. The average size of the nanoparticles obtained was ∼4 nm and BET specific surface area ∼105 m² g⁻¹. Blueshifts in the ultraviolet absorption spectra have been observed in cerium oxide nanocrystallites. The band-gap was found to be 4.5 eV. The blueshifts are well explained for diameters down to less than a few nanometers by the change in the electronic band structure.     

Citrate gel route for synthesis of dense pyrochlores

The solid solution of pyrochlore oxides, Nd₂Zr_xTi_2−xO₇ (x = 0.2, 0.4, 0.6, 0.8 and 1.0) was synthesized by citrate gel method and the conventional ceramic method. The results indicate that the citrate gel method gives pyrochlore phase formation at a much lower temperature and better morphology of the product oxides as compared with the ceramic method. The dc conductivity study was carried out on some samples to understand the defects, if any, in the lattice of the solid solution Nd₂Ti_xZr_2−xO₇ (x = 0.2, 0.4, 0.6, 0.8 and 1.0) on substitution of Zr by Ti. The formation of defects in the lattice on substitution of Zr by Ti, was explained on the basis of XPS studies.     

Low temperature synthesis and characterization of SnTa2O6

Sn(II)Ta₂O₆ is well known as the mineral Thoreaulite, but attempts to prepare it by direct combination of SnO and Ta₂O₅ fail. SnTa₂O₆ has now been synthesized by reacting SnCl₂ with KTaO₃ at 673 K under an inert atmosphere. Although a reported structure determination of SnTa₂O₆ indicated an acentric space group, our second harmonic generation (SHG) studies indicate that SnTa₂O₆ is centrosymmetric as is the case for isostructural SnNb₂O₆.     

Combustion synthesis of CuFe2O4

Metallic ferrites are investigated as prospective materials for different applications especially as anodes in extractive metallurgy. CuFe₂O₄, one of the important ferrites, is envisaged for substituting the carbon anode in Hall-Heroult cells. A single step combustion process has been used for the synthesis of CuFe₂O₄ powder from cupric nitrate, ferric nitrate and urea. The experimental conditions for maximum conversion efficiency of the precursor powders have been optimized. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) have confirmed the formation, structure and homogeneity of the as-prepared powders. The detailed physical, electrical and structural characterization of the materials have been carried out for the specimens obtained on sintering at different temperatures up to 1000 °C.     

Formation and control of mechanism for the preparation of ultra-fine barium strontium titanate powders by the citrate precursor method

A modified citrate precursor method, combining the advantages of the nitrate autocombustion method by introducing the nitric acid, was successfully used to synthesize ultrafine Ba_0.70Sr_0.30TiO₃ powders. Slight agglomerated and homogenized BST powders, with an average particle size of 20 nm, were obtained at 800 °C. Combining the results of TG/DTA and XRD, it can be concluded that the formation of BST powders takes place via two reaction mechanisms: decomposition of an intermediate oxycarbonate mechanism (DIOm) at low temperature, and solid-state reaction mechanism (SSRm) between nanocrystalline carbonates and amorphous TiO₂ at high temperature. TEM shows higher amount of CA led to BST powders of better quality in morphology. Based on results of chemical analysis, it is suggested that higher amount of CA drives the mechanism to tend to DIOm. By simply adjusting the ratio of reagents, the reaction mechanism can be dominated and we can greatly control the final morphology of the powders.     

Chromium doped barium titanyl oxalate nano-sandwich particles: A facile synthesis and structure enhanced electrorheological properties

Chromium doped barium titanyl oxalate (BCTO) particles with sandwich-like morphologies were synthesized via a facile chemical co-precipitation method in the presence of acrylamide. The morphologies, structures as well as dielectric and electrorheological (ER) properties of the as-synthesized BCTO particles were studied as functions of the concentration of acrylamide. The results show that with increasing the concentration of acrylamide used in the chemical co-precipitation process, the morphologies of the as-synthesized products change from an irregular shape via sandwich-like structure to congeries of blocks, at the same time, the crystallinity and the BET surface area (S_BET) exhibit maximal values. All these phenomena are reasonably explained in terms of the interaction between acrylamide and BCTO. Among the as-synthesized products with various morphologies, the BCTO sandwich-like particles show the strongest interfacial polarization and ER effect, which originate from their peculiar morphology and S_BET.     

Ba3ZnTa2−xNbxO9 and Ba3MgTa2−xNbxO9 (0≤x≤1): synthesis, structure and dielectric properties

Oxides belonging to the families Ba₃ZnTa_2−xNb_xO₉ and Ba₃MgTa_2−xNb_xO₉ were synthesized by the solid state reaction route. Sintering temperatures of 1300°C led to oxides with disordered (cubic) perovskite structure. However, on sintering at 1425°C hexagonally ordered structures were obtained for Ba₃MgTa_2−xNb_xO₉ over the entire range (0≤x≤1) of composition, while for Ba₃ZnTa_2−xNb_xO₉ the ordered structure exists in a limited range (0≤x≤0.5). The dielectric constant is close to 30 for the Ba₃ZnTa_2−xNb_xO₉ family of oxides while the Mg analogues have lower dielectric constant of ∼18 in the range 50 Hz to 500 kHz. At microwave frequencies (5-7 GHz) dielectric constant increases with increase in niobium concentration (22-26) for Ba₃ZnTa_2−xNb_xO₉; for Ba₃MgTa_2−xNb_xO₉ it varies between 12 and 14. The “Zn” compounds have much higher quality factors and lower temperature coefficient of resonant frequency compared to the “Mg” analogues.     

Synthesis of barium titanate nanoparticles via a novel electrochemical route

An electrochemical route from Ti metal plate in KOH and Ba(OH)₂ electrolyte at room temperature is first established for the synthesis of BaTiO₃ nanoparticles. Anodic sparks play a key role, and KOH concentration is one of the most significant factors which affect the appearance of anodic sparks in this method. XRD patterns show that the powder obtained in our study is a pure perovskite phase BaTiO₃ with a cubic structure, whose size and morphology are subsequently studied by TEM. The mean diameter of the particles is 13.8 nm and the standard deviation (S.D.) fitted is 6.26 nm. It is also found that the mean size of the obtained nanoparticles increase from 13.8 nm to 168.0 nm, when 60 vol.% absolute ethanol is replaced by distilled water as the solvent of the electrolyte.     

Low temperature synthesis of nanocrystalline lithium ferrite by a modified citrate gel precursor method

Single phase nanocrystalline lithium ferrite is synthesized by a modified citrate gel precursor technique. Ferrite nanoparticles of average size of 8 nm, obtained after calcination of the citrate gel made by the usual method at 450 °C, show superparamagnetic behavior. However, small amounts of -Fe₂O₃ is formed as an impurity phase due to the initial formation of some -Fe₂O₃ phase. On the other hand, when the pH of the mixed solution is increased to 7 after the addition of ammonia solution, a lower calcination temperature of 200 °C is sufficient for the formation of single phase lithium ferrite nanoparticles of size 30 nm. No impurity phases are detected when the nanocrystalline powders are calcined at higher temperatures. The magnetic properties of the ferrite nanoparticles of different sizes obtained by calcining the powders at different temperatures are studied.     

A novel route to the synthesis of nanosized metallic molybdenum at moderate temperature and its catalytic properties

Nanosized metallic molybdenum could be synthesized from MoO₃ and KBH₄ by solid-state reaction at moderate temperature. The crystallinity, morphology, surface properties of as-synthesized metallic molybdenum were investigated by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectral (XPS). The results of its catalytic activity test show that the as-synthesized nanosized metallic molybdenum is superior to the noble metal catalyst 0.3% Pd/Al₂O₃ for the selective hydrogenation of alkadienes at higher temperature and pressure.     

Synthesis of bismuth titanate by citrate method

A simple citrate gel route was adopted for the preparation of bismuth titanate (Bi₄Ti₃O₁₂) powders. Stoichiometric quantities of BiCl₃ and TiOCl₂ were mixed with required amount of citric acid, and the mixture was heated on a water bath. This leads to formation of gel, which was decomposed at 673 K. Formation of bismuth titanate was observed on calcining powders at 973 K by X-ray diffraction studies. The average particle size is found to be 20 nm by microscopy. The room temperature dielectric constant is found to be 175 at 1 kHz. The hysteresis loop parameters were also obtained by home built Sawer-Tower circuit.     

Dielectric characteristics of bismuth-modified lead magnesium niobate ceramics

Aliovalent Bi was substituted for Pb in Pb(Mg_1/3Nb_2/3)O₃ with required alteration in the Mg/Nb ratio. Resultant changes in the perovskite developments, lattice parameters as well as dielectric characteristics were investigated. Powders were prepared via a two-step B-site precursor route to enhance the perovskite formation. The perovskite structure persisted up to the range of 30 mol% Bi(Mg_2/3Nb_1/3)O₃ substitution. Values of the maximum dielectric constant decreased drastically, while the dielectric maximum temperatures changed only moderately. Meanwhile, the diffuseness exponent values decreased continuously with the Bi modification.     

New dielectric material system of x(Mg0.95Zn0.05Ti)O3-(1 − x)Ca0.8Sm0.4/3TiO3 at microwave frequency

The microstructures and the microwave dielectric properties of the x(Mg_0.95Zn_0.05)TiO₃-(1 − x) Ca_0.8Sm_0.4/3TiO₃ ceramic system were investigated. In order to achieve a temperature-stable material, we studied a method of combining a positive temperature coefficient material with a negative one. Ca_0.8Sm_0.4/3TiO₃ has dielectric properties of dielectric constant ε_r ~ 120, Q × f value ~ 13,800 GHz and a large positive τ_f value ~ 400 ppm/°C. (Mg_0.95Zn_0.05)TiO₃ possesses high dielectric constant (ε_r ~ 16.21), high quality factor (Q × f value ~ 210,000 at 9 GHz) and negative τ_f value (− 59 ppm/°C). Sintering at 1300 °C with x = 0.9, 0.9(Mg_0.95Zn_0.05Ti)O₃ − 0.1 Ca_0.8Sm_0.4/3TiO₃ has a dielectric constant (ε_r) of 22.7, a Q × f value of 124,000 GHz and a temperature coefficient of resonant frequency (τ_f) of − 6.3 ppm/°C.     

Nickel permanganate as a precursor in the synthesis of a NiMn2O4 spinel

The present study describes the preparation, characterization, and thermal decomposition of the compound Ni(MnO₄)₂·xH₂O, which was synthesized by a coprecipitation method at a low temperature. The role of this compound as a precursor in the synthesis of a Ni-Mn spinel was determined via X-ray, TG-DTA, electron diffraction, and EDAX measurements.     

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.     

Solution combustion synthesis of MgAl2O4 using fuel mixtures

The paper reveals a new perspective concerning the rational fuel selection and the logical elaboration of the recipes for the MgAl₂O₄ solution combustion synthesis. It was shown that Mg(NO₃)₂·6H₂O and Al(NO₃)₃·9H₂O exhibit different behavior with respect to urea, glycine and β-alanine. Urea proved to be the most adequate fuel for Al(NO₃)₃·9H₂O, while β-alanine proved to be the most appropriate fuel for Mg(NO₃)₂·6H₂O. Considering that there is a predilection of metal nitrates with respect to these fuels, in the case of MgAl₂O₄ combustion synthesis best results were achieved when fuel mixtures (urea and β-alanine, urea and glycine) were used. The use of fuel mixtures allowed the formation of pure, nanocrystalline MgAl₂O₄ directly from the combustion reaction, without any subsequent annealing step. The use of a single fuel (urea, glycine or β-alanine) led to the formation of an amorphous powder, which required further annealing in order to achieve the formation of crystalline MgAl₂O₄.     

A novel method to low temperature synthesis of nanocrystalline forsterite

Nanocrystalline forsterite (Mg₂SiO₄) powder was synthesized using sucrose as a chelating agent and template material from an aqueous solution of magnesium nitrate and colloidal silica. The synthesized powders were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), simultaneous thermal analysis (STA), and scanning electron microscopy (SEM). The synthesized nano-powder had particle size smaller than 200 nm and average crystallite size of powders calcined at 800 °C for 3 h was in the range of 10-30 nm. Also the effect of addition 2 and 4 wt.% forsterite seed on nucleation temperature and crystallite size of forsterite was investigated. The presence of small amounts of Mg₂SiO₄ as seed obviously accelerated the crystallization of forsterite. According to DTA results the inceptive formation temperature of Mg₂SiO₄ without any seed was 760 °C, while this temperature for the specimen containing 4 wt.% seed was 700 °C.     

Hydrothermal synthesis attempts of dawsonite-type hydroxymetalocarbonate precursor compounds for catalytic Ho, Sm, and La oxides

Chemical interactions in mixed, aqueous solutions of NH₄HCO₃ and M(NO₃)₃·9H₂O, where M stands for Ho, Sm, or La, were facilitated under various hydrothermal treatment conditions (pH 8-12 and temperature = 75-135 °C). The solution chemistry established did not make available necessary concentrations of soluble HCO₃⁻ and MO(OH)₂⁻ species for the formation of dawsonite-type ammonium hydroxymetalocarbonates, NH₄M(CO₃)(OH)₂, but, alternatively, high concentrations of soluble CO₃²⁻, and M(H₂O)_n³⁺ or M(H₂O)_n−1(OH)²⁺ facilitating, respectively, precipitation of corresponding hydrated carbonate, M₂(CO₃)₂·2H₂O, or carbonate hydroxide, MCO₃(OH). X-ray powder diffractometry, infrared spectroscopy, and thermal analyses proved alternative formation of Ho₂(CO₃)₃·2H₂O or LaCO₃(OH) under the whole set of hydrothermal treatment conditions probed, and Sm₂(CO₃)₃·2H₂O at pH < 10 or SmCO₃(OH) at pH ≥ 10, thus implying dependence of the composition of the product carbonate compound on the hydrolysability of the initial M(H₂O)_n³⁺ species and, hence, the metal ionic size (La > Sm > Ho). Calcination of the various hydrothermal treatment products at ≥600 °C resulted in the thermal genesis of the corresponding sesqui-oxides (M₂O₃). Bulk and surface characterization studies of the product oxides, employing N₂ sorptiometry and scanning electron microscopy, in addition to the above analytical techniques, revealed overall strong crystallinity, large average crystallite size, and well-defined particle morphology. They revealed, moreover, surfaces, though of limited accessibilities (≤13 m²/g), exposing OH groups of various coordination symmetries and, hence, acid-base properties, thus furnishing promising surface catalytic attributes.