In situ formation of bis(8-hydroxyquinoline) zinc(II) complex in the interlayer spaces of smectites by solid–solid reactions

Bis(8-hydroxyquinoline) zinc(II) complex (Znq₂), an electroluminescent material used for organic light emitting devices (OLEDS), formed in the interlayer spaces of smectites by solid–solid reactions between Zn(II)-smectites (Zn(II)-synthetic saponite and Zn(II)-montmorillonite) and 8-hydroxyquinoline at ambient condition. The intercalation of 8-hydroxyquinoline molecules into Zn(II)-smectites and the in situ complex formation of Znq₂ chelate in smectites were confirmed by powder XRD, FT-IR, TG–DTA, UV–vis absorption and photoluminescence spectroscopies, and elemental (CHN) analysis. The photoluminescence intensity of the Znq₂ complex in synthetic saponite was higher than that of the complex in montmorillonite, suggesting the very low content of quenching impurities in synthetic saponite. The difference in the luminescence bands were thought to be caused by the different molecular structure and molecular packing of the complex formed in the interlayer spaces.     

A study of water releases in ground (GCC) and precipitated (PCC) calcium carbonates

Precipitate calcium carbonates (PCCs) are important industrial products mainly used as fillers. Because of their regular, synthesized characteristics (e.g. grain shape or grain size distribution) PCCs are distinct from natural ground calcium carbonates (GCCs). A thermal study on GCC samples showed only the presence of surface physisorbed water with a monotonic weight loss up to the carbonate decomposition. In the case of PCC samples, two supplementary water releases were observed. The first one appeared at around 525 K and the second one at around 725 K. The nature of the water present in two different PCC samples was investigated by thermal analyses (thermogravimetric and Karl Fischer analyses), Rietveld analyses on X-rays powder diffraction, infrared and Raman spectroscopies and solid state ¹H MAS NMR. The second water release at about 725 K was clearly identified as being portlandite dehydration. Ca(OH)₂ was present in the PCC in an amorphous state. Its crystallization occurred simultaneously to the first water release at about 525 K. Structural effects observed on calcite during the first water release led to the assignment to structural water molecules inserted in the structure of calcite.     

Synthesis and characterization of a new monophosphate [2,5-(CH3)2C6H3NH3]H2PO4

Chemical preparation, calorimetric studies, crystal structure and spectroscopic investigations are given for a new noncentrosymmetric organic cation monophosphate [2,5-(CH₃)₂C₆H₃NH₃]H₂PO₄. This compound is orthorhombic P2₁2₁2₁ with the following unit-cell parameters: a=5.872(4), b=20.984(3), c=8.465(1) Å, Z=4, V=1043.0(5) Å³ and D_x=1.396 g cm⁻³. Crystal structure has been solved and refined to R=0.048 using 2526 independent reflections. Structure can be described as an inorganic layer parallel to (a,b) planes between which organic groups [2,5-(CH₃)₂C₆H₃NH₃]⁺ are located. Multiple hydrogen bonds connecting the different entities of compound thrust upon three-dimensional network a noncentrosymmetric configuration.     

Synthesis of Cu2ZnSnSe4 compound powders by solid state reaction using elemental powders

The solid state reaction method was used to synthesize single phase and near stoichiometric Cu₂ZnSnSe₄ compound from elemental Cu, Zn, Sn and Se powders in a quartz tube furnace under an Ar flow at atmospheric pressure. These elemental powders were initially milled using zirconia balls. The α-CuSe phase was present in all of the milled powders because of the mechanical alloying effect between the Cu and Se powders. The solid state reaction mechanism was examined for the synthesis process. The phase analysis suggested that the Cu₂ZnSnSe₄ powder crystallized into the stannite phase with a high degree of crystallinity after near stoichiometric molar ratios of the powders was reacted at 500 °C for 6 h. This study showed that the solid state reaction method was a straightforward technique for the synthesis of the Cu₂ZnSnSe₄ compound powders from the elemental powders.     

Mesoporous (ZrO2-TiO2)/Al2O3 ternary carriers as hydrodesulfurization catalysts support

Ternary systems at various compositions were synthesized by coprecipitating Zr and Ti (to get a ZrO₂-TiO₂ 40-60 mol%) chlorides in aqueous basic media (provided by urea thermal decomposition) over an alumina substrate. Materials characterization included N₂ physisorption, X-ray diffraction, thermal analysis, high-resolution electron microscopy and Raman and UV-vis spectroscopies. High interaction among components was clearly evidenced by various techniques. Textural properties of ternary oxides could be tuned depending on composition of formulations. Mixed oxides with 10 or 20 mol% of ZrO₂-TiO₂ (at 40-60% mol, in turn) had the most suitable combination of textural properties (surface area, average pore diameter and pore volume) for the intended application (support of catalyst for hydrodesulfurization de oil-derived middle distillates). The suitability of those ternary supports was demonstrated in the dibenzothiophene hydrodesulfurization where the corresponding supported MoS₂ catalysts (at 2.8 atom Mo nm⁻²) were much more active (on a per mass of catalyst basis) than when impregnated over either alumina or zirconia-titania oxides.     

Preparation, characterization and ionic conductivity studies of ZrO2 dispersed mixed halide matrix (KCl)0.9-(NaCl)0.1

Composite electrolytes in the system [(KCl)_0.9:(NaCl)_0.1]_1−y:(ZrO₂)_y were prepared and their ionic conductivities were studied. In our previous study on the mixed halide system (KCl)_1−x:(NaCl)_x, maximum conductivity (∼50 times that of the base KCl matrix) was found when x=0.1. The matrix (KCl)_0.9:(NaCl)_0.1 was dispersed with different concentration of ZrO₂ (powder) for the preparation of composites and their conductivities were determined. The maximum conductivity was developed for the composite having composition y=0.5. The matrices were prepared by melt-quench technique and the dispersion of ZrO₂ was carried out in liquid medium. The conductivity measurements of the composites were carried out by impedance spectroscopy technique. The composite [(KCl)_0.9:(NaCl)_0.1]_0.5:(ZrO₂)_0.5 was characterized by X-ray diffraction (XRD) analysis, differential thermal analysis (DTA), thermogravimetric analysis (TG) and scanning electron microscopy (SEM). The conductivity of the composite [(KCl)_0.9:(NaCl)_0.1]_0.5:(ZrO₂)_0.5 as a function of temperature was also studied. The conductivity increase in the composite could be attributed to enhancement of defect concentration in the space charge region created at the interface between the host halide and the dispersoid.     

Phase evolution in gel-precipitated LaAlO3 ceramics

Lanthanum aluminate ceramic powders could be prepared by a combined gel precipitation process from metal chlorides using ammonia. A slight modification in the conventional gel precipitation technique was carried out by introducing a step of ultrasonication followed by centrifugal washing of the gel. The dried gels produced pure phase lanthanum aluminate powders on calcination at 1100 °C for the combined gel-precipitated powders, and at 600 °C for the washed gel. The phase evolution was studied and it was found that the delay in obtaining monophasic LaAlO₃ in the combined gel-precipitated powder owed to the crystallization of an impure phase LaOCl. This phase was not detected in the washed gel (WG) powders. TEM micrographs showed a uniform morphology for the calcined WG powders, which were in contrast to the irregular particles in the gel-precipitated (GP) powders. The uniform morphology was assigned to the ultrasonic effects during washing of the gel.     

New soft porous frameworks based on lambda-zirconium phosphate and aliphatic dicarboxylates: Synthesis and structural characterization

New dicarboxylate-functionalized pillared materials with a general formula of λ-ZrPO₄(OH)_1-x(OOC(CH₂)_nCOO)_x/2(dmso) (n=6, 8 and 10) have been prepared by post-synthesis modification of the inorganic layers of λ-zirconium phosphate (λ-ZrP), where the superficial Chloride monovalent anionic ligands of λ-layer are partially exchanged with the divalent anionic ligands of a series of long-chain aliphatic dicarboxylic acids, namely octanedioic acid, decanedioic acid and dodecanedioic acid. The synthesized materials are characterized by X-ray diffractometry, FT-IR spectrophotometry, elemental and thermogravimetric analyses. The X-ray diffraction patterns show that the obtained solid phases are pure. Furthermore, the interlayer distance of λ-ZrP systematically increases from 1.02 to 1.59 nm as a result of the incorporation of the mentioned acids inside the interlayer gallery.     

Synthesis and characterization of micrometric ceramic powders for electro-rheological fluids

Micrometric lamellar ceramic powders of the displacive ferroelectric oxide Bi₄Ti₃O₁₂ were synthesized by co-precipitation of bismuth nitrate and ammonia titanyl solutions followed by a heat treatment. It was found that a complete thermal decomposition is reached at 1000 °C. Structural and thermal evolution of these ceramic powders were studied by X-ray diffraction, thermogravimetry and differential thermal analysis. The homogeneity in size and morphology of these ferroelectric particles are appropriate to prepare electro-rheological fluids. One of these fluids was prepared by dispersing the powders in silicone oil; the complex cluster structure formed by the particles, under an applied AC electric field, was observed.     

Self-assembly and characterization of Ca-Al-LDH nanohybrids containing casein proteins as guest anions

Casein, a natural biopolymer contained in milk, has been successfully intercalated into a Ca-Al-LDH host structure. Synthesis was performed by rehydration of tricalcium aluminate in the presence of casein. The resulting nanohybrids were characterized by powder X-ray diffraction (XRD), elemental analysis, infrared spectroscopy (IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Further experiments revealed that the single protein strains intercalate instead of the entire casein sub micelles, which are present in milk. Additionally, the pure phospho protein fractions α- and β-casein, which make up ∼80 wt% of total casein were isolated and intercalated into the Ca-Al-LDH host structure, yielding a biopolymer-inorganic hybrid material.     

Effects of preheating on diaspore: Modifications in colour centres, structure and light emission

The thermal properties and thermal stability of diaspore-corundum (AlOOH-Al₂O₃), from Goian (Pontevedra, Spain) were studied by means of differential thermal analysis (DTA), thermogravimetry (TG), high temperature X-ray diffraction (HTXRD) and thermally stimulated luminescence (TL) techniques. The samples were annealed to link the combined effect of (i) dehydroxylation, (ii) oxidation-reduction of chromophores (Mn 0.5%, Fe₂O₃ 0.12%, TiO₂ 0.021% and Cr 80 ppm) determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and (iii) phase transitions whilst sample heating (i.e. α-AlOOH→α′-Al₂P₃→α-Al₂O₃). The blue colour of diaspore, attributed to the Ti⁴⁺-Fe²⁺ intervalence-charge-transfer mechanism, turns to white (circa 500 °C) in good agreement with the DTA endothermic peak (dehydroxylation). The coexistence of α-AlOOH and α′-Al₂P₃ phases has been detected by in situ HTXRD and could be correlated to the thermoluminescence tests performed on preheated aliquots (up to 500 °C).     

Synthesis, growth and characterization of a new derivative 4-ethoxy-N-methyl-4-stilbazolium besylate monohydrate single crystal

A new organic material 4-ethoxy-N-methyl-4-stilbazolium besylate monohydrate, a derivative in the stilbazolium family, known for efficient nonlinear optical materials, has been synthesized for the first time. Employing the slow evaporation technique, optically transparent good quality single crystals of size 15 mm×10 mm×5 mm were grown from methanol. The cell dimensions obtained by single crystal X-ray diffraction studies reveal that the crystal belongs to the monoclinic system. Functional groups of the grown crystal were identified from FTIR and NMR spectral analysis. UV−vis−NIR studies show that the crystal is transparent in the wavelength range 460-1100 nm. The thermal stability of the compound was determined by thermal analyses of the specimen.     

Hydrogen desorption processes in Li-Mg-N-H systems

Li-Mg-N-H systems composed of Mg(NH₂)₂ and LiH with various ratios can reversibly store a large amount of hydrogen under the temperature condition above 150 °C. These composites with 3:6, 3:8 and 3:12 ratio of Mg(NH₂)₂ and LiH have been independently reported by four groups as promising candidates of high performance hydrogen storage materials possessing the reversibility and the high capacity. In any cases, an interaction between NH₃ and LiH plays an important role for the progress of hydrogen desorbing and absorbing reactions. For the hydrogen desorption process, the NH₃ molecule generated from Mg(NH₂)₂ reacts with LiH, forming LiNH₂ and H₂. Especially, under an equilibrium condition, in situ diffraction results indicated that the single phase of LiNH₂·MgNH (LiMgN₂H₃) could be generated other than the separated two phases. As a next step, the NH₃ molecule generated from LiNH₂ reacts with LiH, desorbing H₂. As a result, the dehydrogenated phase was evaluated to be Li₂NH·MgNH (Li₂MgN₂H₂) or separated two phases, in which the final phase should depend on the experimental conditions. Thus, if the amount of LiH is enough to react with NH₃, the hydrogen desorption processes are described by the NH₃ generation from the corresponding amides and the imide.     

Effect of pH of colloidal suspension on crystallization and activation energy of deep levels in SnO2 thin films obtained via sol-gel

Colloidal suspensions of tin dioxide (SnO₂) are prepared by the sol-gel method from suspensions with distinct pHs. The particles in solution are embedded by an electrical layer. Decreasing the pH contributes to the destruction of this layer, leading to a high degree of aggregation among particles (clusters) due to the generation of cross-linked bonds (Sn-O-Sn) between them. The aggregation affects the electrical properties of films deposited by dip-coating from these solutions, due to the higher packing produced by acid pH. The X-ray diffractograms of films indicate higher crystallinity for lower pH. The Arrhenius plot leads to activation energies of the deepest level, which was between 67 and 140 meV, for the films prepared from suspensions with pH 6-11. Lower pH films also presented higher electrical conductivity. Obtained activation energies may be related to different types of defects, which could be associated with oxygen vacancies with distinct neighborhoods, influenced by the pH and potential barriers between grains, due to distinct packing caused by cross-linked bonds. TGA/DTA results indicate an easier crystallization process for lower pH, which ends at lower temperature, in good agreement with X-ray diffraction data.     

Morphology and properties of poly(methyl methacrylate)/clay nanocomposites by in-situ solution polymerization

Poly(methyl metacrylate)/montmorillonite (PMMA)/(MMT) nanocomposites were prepared by in-situ solution polymerization of methyl methacrylate monomer in the presence of the organic modified MMT-clay. After the organic modification by ionic exchanging with amine salts, the organoclay becomes more hydrophobic and compatible then pristine clay with methyl methacrylate monomer. The modified clays are characterized by wide angle X-ray diffraction (WAXRD). The powdered X-ray diffraction and transmission electron microscopy (TEM) techniques were employed to study the morphology of the PMMA/clay nanocomposites which indicate that the modified clays are dispersed in PMMA matrix to form both exfoliated and intercalated PMMA/modified clay nanocomposites. The thermo-mechanical properties were measured by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC). Gas permeability analyzer (GPA) shows the excellent gas barrier property of the PMMA nanocomposites which is in good agreement with the morphology. The optical property was measured by UV-vis spectroscopy which shows that these materials have good optical clarity, and UV resistance.     

Effects of vitrification suppression on structure morphology, conductivity and dielectric properties of vanadium phosphate glasses

Vitrification suppression in the (V₂O₅)_1−x (P₂O₅)_x glasses where x=0.10, 0.15, 0.20, and 0.25 was controlled by changing the rate of quenching glasses. The structure variations occurring in the glasses were detected by differential thermal analysis and optical microscope. The results implied the separation and growth of V₂O₅ orthorhombic microcrystal in the samples with x=0.10 and 0.15 whereas other samples did not illustrate remarkable changes in their microstructure. However, in temperature range between 300 and 473 K a semiconducting behavior for all samples appears during the study of electrical conductivity-temperature dependence. A decrease in conductivity values accompanied with some variations in activation energies by reducing quenching rate was observed. The conductivity results suggested that the conduction occurs by the phonon assisted hopping of a small polaron between V⁴⁺ and V⁵⁺ states at relatively higher temperature range above θ_D/2. Whereas at relatively low temperatures the conduction may occur by electron jumping between filled and empty states at Fermi level in the disordered matrix besides polaronic conduction. Reasonable values for the density of localized states, carrier concentration and carrier mobility were estimated and discussed. Also, dielectric constant and dielectric loss were studied as a function of frequency at different temperatures confirming the structure variations in the glass system.     

Effect of urea and thiourea on nonlinear optical hippuric acid crystals

Pure, urea and thiourea doped hippuric acid (HA) single crystals have been grown in acetone using slow evaporation technique at a constant temperature, with the vision to improve the properties of the crystals. The crystal systems and the unit cell parameters of the grown crystals were identified from single crystal X-ray diffraction. The crystalline nature of the grown crystals was confirmed by powder X-ray diffraction and the diffraction peaks were indexed. The variations in composition due to the addition of dopants were identified by CHNS analysis. FT-IR studies reveal the presence of different vibrational bands. The optical characteristics were assessed by UV–vis analysis and it indicates the transmission in the visible region. TGA and DSC studies indicate the thermal behavior of pure and doped crystals. The Second Harmonic Generation (SHG) has been tested using Kurtz Powder Technique for the pure and doped crystals. It is found that the thiourea doped hippuric acid crystals have SHG efficiency of 2.08 times higher than that of potassium dihydrogen phosphate (KDP) single crystal. The dielectric studies were carried out, and the variations of dielectric constant and dielectric loss with temperature have been studied.     

Synthesis of nanocrystalline and mesoporous zinc sulphide from a single precursor Zn(SOCCH3)2Lut2 complex

We report the formation of mesoporous zinc sulphide, composed by the fine network of nanoparticles, which was formed via a single precursor Zn(SOCCH₃)₂Lut₂ complex. The complex was chemically synthesized using zinc carbonate basic, 3,5-lutidine and thioacetic acid, in air. The metal precursor complex was characterized using different conventional techniques. Thermogravimetric analysis (TGA) result indicates that the decomposition of the complex starts at 100 °C and continues up to 450 °C, finally yielding ZnS. ZnS nanocrystals were characterized by powder X-ray diffraction (XRD) technique, field emission scanning electron microscopy (FESEM), N₂-sorption isotherm, UV-vis spectroscopy and photoluminescence (PL) spectroscopy. The grain diameter of nanocrystals was found to be 4-5 nm. The material followed Type-IV N₂-sorption isotherm, which is the characteristic of mesoporous materials. The band gap energy, as obtained from optical measurements was around 3.8 eV.     

Synthesis, crystal structure, Cu doped EPR, thermal and voltammetric studies of [Ni(isonicotinamide)2(H2O)4]·(sac)2 single crystal

The single crystal of [Ni(ina)₂(H₂O)₄]·(sac)₂, (NINS), (ina is isonicotinamide and sac is saccharinate) complex has been prepared and its structural, spectroscopic and thermal properties have been determined. The title complex crystallizes in monoclinic system with space group P2₁/c, Z=2. The octahedral Ni(II) ion, which rides on a crystallographic centre of symmetry, is coordinated by two monodentate ina ligands through the ring nitrogen and four aqua ligands to form discrete [Ni(ina)₂(H₂O)₄] unit, which captures two saccharinate ions in up and down positions, each through intermolecular hydrogen bands. The magnetic environment of copper(II) doped NINS crystal has also been identified by electron paramagnetic resonance (EPR) technique. The g and A values of Cu²⁺ doped NINS single crystal were calculated from the EPR spectra recorded in three mutually perpendicular planes. These values indicated that the paramagnetic centre has a rhombic symmetry with the Cu²⁺ ion having distorted octahedral environment. The complex exhibits only metal centred electroactivity in the potential range of −2.00, 1.25 V versus Ag/AgCl reference electrode.