Thermal,XRD, and magnetization studies on ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript> and NiAl<Subscript>2</Subscript>O<Subscript>4</Subscript> spinels,synthesized by citrate precursor method and annealed at 450 and 650 °C

Two aluminate spinel materials (ZnAl₂O₄ and NiAl₂O₄) were synthesized by the citrate precursor method. The citrate precursors consisting of coprecipitated citrates of Zn²⁺ or Ni²⁺ and aluminum were first subjected to thermal analysis (TG-DSC) for determining the optimum temperature for annealing. Two step decomposition was observed incorporating dehydration and formation of the aluminate. The second step gives an endo peak (−2937 J/g) at 356 °C in the DSC curve of the coprecipitated nickel(II) citrate–aluminum citrate gel in O₂ atmosphere. Kinetic/mechanistic analysis of the TG data has also been carried out and values of E _a, ΔS ^#, ΔG ^#, and A were approximated. On the basis of the findings, 450 °C has been chosen for annealing of the gels. Annealing has also been done at 650 °C for 1 h in muffle furnace in an attempt to obtain nanometric particles of aluminates (MAl₂O₄) {M = Ni, Zn} and to find out their magnetic properties which could render them useful for chemical sensing applications, etc. The TG-DSC curves of various powders which were obtained on annealing at the two temperatures did exhibit thermal instability when carried out in N₂ atmosphere. NiAl₂O₄ and ZnAl₂O₄ spinels (particle size 17 and 34 nm, respectively) are obtained in pure crystalline phase at 650 °C. ZnAl₂O₄ prepared this way shows coercivity values of 470 and 58.37 G and NiAl₂O₄, 107 and 23.24 G when annealed at 450 and 650 °C, respectively. ZnAl₂O₄ prepared by a polymer precursor method and annealed at 1000 °C, has earlier been reported to have coercivity value of 469 G. Thus, the citrate precursor method is good for the synthesis of ZnAl₂O₄, producing single phase nanocrystalline powder of high quality and crystallinity. The value of magnetization was found to be small in the present case for the NiAl₂O₄ spinel obtained at 450 °C.     

Thermal analysis of hydrotalcite synthesised from aluminate solutions

The aluminate hydrotalcites are proposed to have either of the following formulas: Mg₄Al₂(OH)₁₂(CO₃ ²⁻)·xH₂O or Mg₄Al₂(OH)₁₂(CO₃ ²⁻, SO₄ ²⁻)·xH₂O. A pure hydrotalcite phase forms when magnesium chloride and aluminate solutions are mixed at a 1:1 volumetric ratio at pH 14. The synthesis of the aluminate hydrotalcites using seawater results in the formation of an impurity phase bayerite. Two decomposition steps have been identified for the aluminate hydrotalcites: (1) removal of interlayer water (230 °C) and (2) simultaneous dehydroxylation and decarbonation (330 °C). The dehydration of bayerite was observed at 250 °C. X-ray diffraction techniques determined that the synthesis of aluminate hydrotalcite with seawater and a volumetric ratio of 4.5 results in very disordered structures. This was shown by a reduction in the mass loss associated with the removal of interlayer water due to the reduction of interlayer sites caused by the misalignment of the metal-hydroxyl layers.     

Influence of the thermal treatment in the crystallization of NiWO4 and ZnWO4

NiWO₄ and ZnWO₄ were synthesized by the polymeric precursor method at low temperatures with zinc or nickel carbonate as secondary phase. The materials were characterized by thermal analysis (TG/DTA), infrared spectroscopy, UV–Vis spectroscopy and X-ray diffraction. NiWO₄ was crystalline after calcination at 350 °C/12 h while ZnWO₄ only crystallized after calcination at 400 °C for 2 h. Thermal decomposition of the powder precursor of NiWO₄ heat treated for 12 h had one exothermic transition, while the precursor heat treated for 24 h had one more step between 600 and 800 °C with a small mass gain. Powder precursor of ZnWO₄ presented three exothermic transitions, with peak temperatures and mass losses higher than NiWO₄ has indicating that nickel made carbon elimination easier.     

Thermal analysis applied in the crystallization study of SrSnO3

SrSnO₃ was synthesized by the polymeric precursor method with elimination of carbon in oxygen atmosphere at 250 °C for 24 h. The powder precursors were characterized by TG/DTA and high temperature X-ray diffraction (HTXRD). After calcination at 500, 600 and 700 °C for 2 h, samples were evaluated by X-ray diffraction (XRD), infrared spectroscopy (IR) and Rietveld refinement of the XRD patterns for samples calcined at 900, 1,000 and 1,100 °C. During thermal treatment of the powder precursor ester combustion was followed by carbonate decomposition and perovskite crystallization. No phase transition was observed as usually presented in literature for SrSnO₃ that had only a rearrangement of SnO₆ polyhedra.     

The influence of precursor temperature on strontium sulphide doped silver for optoelectronic application

This research aims at the study of strontium sulphide doped silver using 0.1 mol of strontium chloride hexahydrate (SrCl2.6H2O), Thioacetamide (C₂H₅NS), and 0.01 mol of silver nitrate (AgNO3) as the cationic, anionic, and dopant concentrations via electrochemical deposition technique. The film had a strong peak at (111) and (211) which corresponds to 2theta values of 26.69° and 51.77° for undoped SrS and doped SrS respectively, and a flawless crystalline peak with a cubic phase that is indexed at orientations (111), (112), (200), and (211). SrS/Ag of deposited different precursor temperatures (room, 35, 40, and 45)^o correspond to 2theta values of 26.69°, 33.79°, 37.60°, and 51.77° respectively. The crystal lattice is shown by the rise in peak intensity with higher 2theta degree values; the appearance of an unindexed peak is caused by the substrate utilized for the deposition. Clove-like material with precipitate is visible in the SrS material's micrograph; the big nano grain on the surface of the substrate exhibits photon absorption but lacks any signs of pinholes. At the introduction of dopant and heating the precursor at 35 °C, 40 °C, and 45 °C there is a drastic change in the micrograph of the films, for the films at 35 °C the nanoparticle clave together with a melted wax with a sharp large white precipitate which is very visible on the surface of the film and the material deposited at 40 °C and 45 °C there is no visible precipitate on the film which show that as the precursor temperature increases it eliminate lattice strain and improve the photovoltaic properties of the deposited material. The energy band gap of strontium sulphide (SrS) and strontium sulphide doped silver (SrS/Ag) at different precursor temperatures of 35 °C, 40 °C, 45 °C is 1.50–2.35 eV.     

Synthesis and characterization of spinel-type CuAl<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocrystalline by modified sol–gel method

Nanocrystalline Copper aluminate (CuAl₂O₄) was prepared by sol–gel technique using aluminum nitrate, copper nitrate, diethylene glycol monoethyl ether and citric acid were used as precursor materials. This method starts from of the precursor complex, and involves formation of homogeneous solid intermediates, reducing atomic diffusion processes during thermal treatment. The formation of pure crystallized CuAl₂O₄ nanocrystals occurred when the precursor was heat-treated at 600 °C in air for 2 h. The stages of the formation of CuAl₂O₄, as well as the characterization of the resulting compounds were done using thermo–gravimetric analysis, X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The products were analyzed by transmission electron microscopy and ultraviolet–visible (UV–Vis) spectroscopy to be round, about 17–26 nm in size and E _g = 2.10 eV.     

Synthesis of Bi<Subscript>4</Subscript>Ge<Subscript>3</Subscript>O<Subscript>12</Subscript> ceramic scintillators by the polymeric precursor method

Bismuth germanate ceramic powders were synthesized for the first time by the polymeric precursor method (Pechini’s method). Differential thermal analysis and thermogravimetric techniques were used to study the decomposition of the resin precursor, which indicated a suitable calcination temperature at 600 °C. It was observed that the mass loss occurs in two main stages that are associated with two exothermic reactions. The crystalline phases of the powders were inspected by the X-ray diffraction technique after thermal treatment between 300 and 600 °C. Single phase Bi₄Ge₃O₁₂ ceramic bodies were obtained after sintering at 840 °C for 10 h. The sintered ceramics presented a luminescence band emission centred at around 530 nm when excited with X-rays and UV radiation.     

Multidisciplinary green approaches (ultrasonic,co-precipitation,hydrothermal, and microwave) for fabrication and characterization of Erbium-promoted Ni-Al2O3 catalyst for CO2 methanation

The dispersion of nickel catalysts is crucial for the catalytic ability of CO₂ methanation, which can be influenced by the fabrication method and the operation process of the catalysts. Therefore, a series of fabrication methods, including ultrasonic, hydrothermal, microwave, and co-precipitation, have been applied to prepare 25Ni-5Er-Al₂O₃ catalysts. The fabrication method can partially influence the structural and catalytic activity of the nickel aluminate catalysts. Among the catalysts modified by Erbium prepared with various methods, the catalyst fabricated by ultrasonic pathway exhibited better catalytic performance and CH₄ selectivity especially, at a temperature (400 ℃). The impact of the temperature of the reaction (200–500 °C) was examined under a stoichiometric precursor ratio of (H₂:CO₂) = 4: 1, atmospheric pressure, and space velocity (GHSV) of 25000 mL/gcath. The results demonstrate that the ultrasonic method is strongly efficient for fabricating Ni-based catalysts with a high BET surface area of about 190.33 m²g^?1. The catalyst composed via the ultrasonic technique has 69.38 % carbon dioxide conversion and 100 % methane selectivity at 400 °C for excellent catalytic performance in CO₂ methanation reactions. The fabrication effect can be associated with its high surface area, which is achieved via the hot spot mechanism. Besides, the addition of Erbium promotes the Ni dispersion on the supports and stimulates the positive reaction because of the erbium oxygen vacancies.     

SrSnO<Subscript>3</Subscript>:Nd obtained by the polymeric precursor method

In this work, the synthesis of Nd-doped SrSnO₃ by the polymeric precursor method, with calcination between 250 and 700 °C is reported. The powder precursors were characterized by TG/DTA and high temperature X-ray diffraction (HTXRD). After heat treatment, the material was characterized by XRD and infrared spectroscopy. Ester and carbonate amounts were strictly related to Nd-doping. According to XRD patterns, the orthorhombic perovskite was obtained at 700 °C for SrSnO₃ and SrSn_0.99Nd_0.01O₃. For Sr_0.99Nd_0.01SnO₃, the kinetics displayed an important hole in the crystallization process, as no peak was observed in HTXRD up to 700 °C, while a XRD patterns showed a crystalline material after calcination at 250 °C.     

LiFePO<Subscript>4</Subscript>/CA cathode nanocomposite with 3D conductive network structure for Li-ion battery

A novel LiFePO₄/Carbon aerogel (LFP/CA) nanocomposite with 3D conductive network structure was synthesized by using carbon aerogels as both template and conductive framework, and subsequently wet impregnating LiFePO₄ precursor inside. The LFP/CA nanocomposite was characterized by X-ray diffraction (XRD), TG, SEM, TEM, nitrogen sorption, electrochemical impedance spectra and charge/discharge test. It was found that the LFP/CA featured a 3D conductive network structure with LiFePO₄ nanoparticles ca. 10–30 nm coated on the inside wall of the pore of CA. The LFP/CA electrodes delivered discharge capacity for LiFePO₄ of 157.4, 147.2, 139.7, 116.3 and 91.8 mA h g⁻¹ at 1 °C, 5 °C, 10 °C, 20 °C and 40 °C, respectively. In addition, the LFP/CA electrode exhibited good cycling performance, which lost less than 1% of discharge capacity over 100 cycles at a rate of 10 °C. The good high rate performances of LiFePO₄ were attributed to the unique 3D conductive network structure of the nanocomposite.     

Purification,Properties, and Application of a Novel Acid Urease from <Emphasis Type="Italic">Enterobacter</Emphasis> sp.

It has been demonstrated that acid urease is capable of decomposing urea in fermented beverage and foods. As urea is a precursor of ethylcarbamate, a potential carcinogenic compound, measures must be taken to control the level of urea. We herein describe the purification and characterization of a novel acid urease from Enterobacter sp. R-SYB082 and its application to the removal of urea in Chinese rice wine. The enzyme was purified to electrophoretic homogeneity using ethanol precipitation, Superdex 200 and Mono Q with a fold purification of 21.1 and a recovery of 49%. The molecular weight of the enzyme was 430,000 Da by gel filtration and 72,000 Da by sodium dodecyl sulfate polyacrylamide gel electrophoresis, suggesting that it was a hexamer. The activity of this purified enzyme was optimal at pH 4.5 and 35 °C. The temperature stability was under 55 °C, and the pH stability was 4.0~5.0. The enzyme exhibited an apparent K _m of 19.5 μmol/l and a V _max of 109 μmol urea/mg·min at 35 °C and pH 4.5. When incubating two different kinds of Chinese rice wine with the enzyme (0.08 U/ml) at 35 °C for 7 days, over 85% of urea was decomposed, and at 20 °C, above 78% was removed. The result showed that the enzyme is applicable to elimination of urea in Chinese rice wine.     

Synthesis,characterization of nanosized CoAl<Subscript>2</Subscript>O<Subscript>4</Subscript> and its electrocatalytic activity for enhanced sensing application

Nanosized cobalt aluminate (CoAl₂O₄) was prepared by thermolysis of heteronuclear coordination compound, namely [Al₂Co(C₂O₄)₄(OH₂)₆]. The synthesized precursor was characterized by chemical analysis, vibrational spectra and thermal analysis. The cobalt aluminate obtained after a heating treatment of the precursor at 700 °C was characterized by IR, XRD, TEM coupled with SAED measurements. Two types of carbon-based electrodes, glassy carbon and boron-doped diamond electrodes were decorated with the obtained cobalt aluminate in order to enhance the electroanalytical performance for the tetracycline (TC) detection in the aqueous solutions. Cyclic voltammetry technique was used to determine the effect of the nanosized CoAl₂O₄ on the electrochemical oxidation of TC and as consequence, for TC detection at both carbon-based electrodes. The obtained cobalt aluminate exhibited the electrocatalytic activity toward TC detection in direct relation with the type of the carbon substrate, which allowed enhancing the electroanalytical parameters of TC detection in the aqueous solution.     

Structure and multiferroic properties of Bi<Subscript>5</Subscript>FeTi<Subscript>3</Subscript>O<Subscript>15</Subscript> thin films prepared by the sol–gel method

The Bi₅FeTi₃O₁₅ (BFTO) films of layered structure have been fabricated on Pt/Ti/SiO₂/Si substrates by the sol–gel method. The thermal decomposition behaviors of precursor powder were examined using thermo-gravimetric and differential scanning calorimeters analysis. The optimal heat treatment process for BFTO films were determined to be low-temperature drying at 200 °C for 4 min and high-temperature drying at 350 °C for 5 min followed by annealing at 740 °C for 60 min, which led to the formation of compact films with uniform grains of ~300 nm. The structural, surface topography, ferroelectric and magnetic properties of the films were investigated. The remnant polarization (2P _r) of BFTO thin films under an applied electric field of ~550 kV/cm are determined to be 67.5 μC/cm² . Meanwhile, the weak ferromagnetic properties of the BFTO films were observed at room temperature.     

Synthesis of Cu2Mo6S8 powders and thin films from intermediate oxides prepared by polymeric precursor method

Powders and thin films of the copper molybdenum sulfide Cu₂Mo₆S₈ were synthesized from intermediate oxides prepared by polymeric precursor method based on Pechini process. In the case of the thin films, deposition was performed onto R-plane sapphire single crystal by spin coating. The influence of temperature and duration of the 3 step heat treatment cycle (calcination, sulfurization and reduction) were investigated to optimize the synthesis conditions. The first step of calcination under air atmosphere performed for 3 h at 450 °C and 400 °C is suitable to obtain the intermediate oxides powders and thin films, respectively. The sulfurization treatment at 600 °C for 2 h under H₂S/H₂ gas flow followed by reduction at 650 °C for 4 h under H₂ gas flow allowed to obtain Cu₂Mo₆S₈ in powder or thin film form. In the last case, a multilayer process led to dense and homogeneous films. Moreover, the insertion and superconducting behaviour of the final powders allowed to validate the Cu₂Mo₆S₈ synthesis by this moderate temperature process.     

A facile synthesis of NaNbO<Subscript>3</Subscript> powders by decomposition of ammonium niobium oxalate with sodium salt at low temperature

A facile synthesis of NaNbO₃ powders was performed by solid-state reaction at low temperature. Stoichiometric ammonium niobium oxalate and Na₂CO₃ were mixed in water and then calcined at different temperatures for various times after drying. A combination of X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy and thermogravimetric (TG) analysis was used to characterize the product and precursor compound. The XRD patterns show that single-phase NaNbO₃ powders with high crystallinity can be synthesized at 425 °C for 15 min. The particle size from XRD data is found to be about 40 nm for NaNbO₃ powders calcined at 500 °C for 3 h, which is in good agreement with SEM data. The SEM photograph shows that NaNbO₃ powders are cuboid-like and well crystallized when calcination at 800 °C for 3 h. The product compositions prepared using other sodium reactants, such as HCOONa and NaNO₃, are also discussed.     

Structure and dielectric properties of HfO<Subscript>2</Subscript> films prepared by a sol–gel route

Mono- and multilayer HfO₂ sol–gel thin films have been deposited on silicon wafers by dip-coating technique using a solution based on hafnium ethoxide as precursor. The densification/crystallization process was achieved by classical annealing between 400 and 600 °C for 0.5 h (after drying at 100 °C). Systematic TEM studies were performed to observe the evolution of the thin film structure depending on the annealing temperature. The overall density of the films was determined from RBS spectrometry correlated with cross section (XTEM) thickness measurements. After annealing at 450 °C the films are amorphous with a nanoporous structure showing also some incipient crystallization. After annealing at 550 °C the films are totally crystallized. The HfO₂ grains grow in colonies having the same crystalline orientation with respect to the film plane, including faceted nanopores. During annealing a nanometric SiO₂ layer is formed at the interface with the silicon substrate; the thickness of this layer increases with the annealing temperature. Capacitive measurements allowed determining the value of the dielectric constant as 25 for four layer films, i.e. very close to the value for the bulk material.     

Synthesis and characterization of SmAlO<Subscript>3</Subscript> dielectric material by citrate precursor method

SmAlO₃ nanopowder synthesized by a citrate precursor method using citric acid as a chelating agent and ethylene glycol as an esterifying agent was reported in this paper. The phase purity of the as-prepared powder was examined using thermogravimetry (TG) analysis and differential scanning calorimetry (DSC) analysis, Fourier transform infrared spectroscopy (FTIR). The X-ray diffraction (XRD) studies showed that pure SmAlO₃ phase with orthorhombic perovskite structure could be synthesized at 800 °C for 2 h without any detectable intermediate phase. The average particle size calculated from transmission electron microscopy (TEM) investigation for the powder synthesized at 900 °C was as low as 45 nm. The nanopowder was sintered to a density of 97% of the theoretical density at 1,550 °C for 2 h and the bulk ceramics exhibited excellent microwave dielectric properties as follows: a dielectric constant of 20.54, a quality factor of 75,380 GHz and a temperature coefficient of resonate frequency of −69.2 ppm/K.     

High surface area sol–gel alumina–titania nanocatalyst

Alumina–titania mixed oxide nanocatalysts with molar ratios = 1:0.5, 1:1, 1:2, 1:5 have been synthesized by adopting a hybrid sol–gel route using boehmite sol as the precursor for alumina and titanium isopropoxide as the precursor for titania. The thermal properties, XRD phase analysis, specific surface area, adsorption isotherms and pore size details along with temperature programmed desorption of ammonia are presented. A specific surface area as high as 291 m²/g is observed for 1:5 Al₂O₃/TiO₂ composition calcined at 400 °C, but the same composition when calcined at 1,000 °C, resulted in a surface area of 4 m²/g, while 1:0.5 composition shows a specific surface area of 41 m²/g at 1,000 °C. Temperature programmed desorption (of ammonia) results show more acidic nature for the titania rich mixed oxide compositions. Transmission electron microscopy of low and high titania content samples calcined at 400 °C, shows homogeneous distribution of phases in the nano range. In the mixed oxide, the particle size ranges between 10–20 nm depending on titania content. The detailed porosity data analysis contributes very much in designing alumina–titania mixed oxide nanocatalysts.     

One-step hydrothermal synthesis of LiMn2O4 cathode materials for rechargeable lithium batteries

LiMn₂O₄ cathode materials with high discharge capacity and good cyclic stability were prepared by a simple one-step hydrothermal treatment of KMnO₄, aniline and LiOH solutions at 120–180 °C for 24 h. The aniline/KMnO₄ molar ratio (R) and hydrothermal temperature exhibited an obvious influence on the component and phase structures of the resulting product. The precursor KMnO₄ was firstly reduced to birnessite when R was less than 0.2:1 at 120–150 °C. Pure-phased LiMn₂O₄ was formed when R was 0.2:1, and the LiMn₂O₄ was further reduced to Mn₃O₄ when R was kept in the range of 0.2–0.3 at 120–150 °C. Moreover, LiMn₂O₄ was fabricated when R was 0.15:1 at 180 °C. Octahedron-like LiMn₂O₄ about 300 nm was prepared at 120 °C, and particle size decreased with an increase in hydrothermal temperature. Especially, LiMn₂O₄ synthesized at 150 °C exhibited the best electrochemical performance with the highest initial discharge capacity of 127.4 mAh g⁻¹ and cycling capacity of 106.1 mAh g⁻¹ after 100 cycles. The high discharge capacity and cycling stability of the as-prepared LiMn₂O₄ cathode for rechargeable lithium batteries were ascribed to the appropriate particle size and larger cell volume.     

Sol-gel processing and characterization of potassium niobate nano-powders by an EDTA/citrate complexing method

The present research describes a modified sol-gel technique used to obtain nano-crystalline potassium niobate (KNbO₃) powders by using ethylene diamine tetraacetic acid (EDTA)/citrate as a complexing agent. The metal ions chemically interact with EDTA in the precursor sol. The aging treatments lead to the formation of a precursor-polymeric gel network. The effects of the amounts of citric acid and EDTA on the stability of the precursor sol are investigated. The influence of excess K on the formation of pure-phase KNbO₃ powders is also studied. The obtained gels and powders are characterized by thermogravimetric-differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that a stable precursor sol is formed when n(CA):n(Mⁿ⁺) = 3:1 and n(EDTA) :n(NH₄OH) = 1:3.5. The xerogel is calcined at 700–850 °C to prepare the KNbO₃ nano-powder. The smallest grain size of the sample obtained at 850 °C is about 60 nm when the K/Nb molar ratio equals 1.2.