Sol–gel synthesis and characterization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> nanocrystalline powder

Al₂O₃–TiO₂ nanocrystalline powders were synthesized by sol–gel process. Aluminum sec-butoxide and titanium isopropoxide chemicals were used as precursors and ethyl acetoacetate was used as chelating agent. Thermal and crystallization behaviors of the precursor powders were investigated by thermal gravimetric-differential thermal analysis, Fourier-transform infrared spectrum and X-ray diffraction. The average crystalline size of heat treated Al₂O₃–TiO₂ powders at 1,100 °C is ~100 nm.     

Sol–gel synthesis and transport property of nanocrystalline La<Subscript>2</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript> thin films

La₂Mo₂O₉ films were successfully synthesized on silicon (100) and poly-alumina substrates via modified sol–gel method with inorganic salts of La(NO₃)₃ and (NH₄)₆Mo₇O₂₄ as precursors. Pure La₂Mo₂O₉ phase was confirmed by XRD if the annealing temperature was higher than 500 °C. Energy dispersive spectrometry (EDS) of TEM revealed that the molar ratio of La to Mo was nearly 1:1. Field-emission SEM characterization showed that the films were dense, crack-free and uniform. The grain size of the films ranged from 30 to 400 nm depending upon the calcination temperature and duration time. The roughness calculated from AFM topography varied in the range between 10 and 35 nm. The thickness of the films was more than 200 nm for single-layered films. The electrical conductivity of the films reaches 0.06 S/cm at 600 °C that was almost more than one order of magnitude higher than that of the corresponding bulk material.     

Sol–gel immobilization of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> on hydrophobic clay and its removal of methyl orange from water

In this study, SiO₂/TiO₂–organoclay hybrids with high adsorption capability and high photocatalytic activity were synthesized by immobilizing mixed silica and titanium dioxide nanoparticles on organically modified clay via a hydrothermal sol–gel method. Addition of negatively charged silica particles enhanced the uniform dispersion of titanium dioxide nanoparticles on organoclay layers by decreasing the system tension, which resulted in high photocatalytic activity of SiO₂/TiO₂–organoclay hybrids. The high adsorption capability endowed by organically modified clay enriched the organic compounds around the photoactive sites, and thus greatly improved the photodegradation efficiency. Combining the high adsorption capability of organoclay with the high photocatalytic activity of TiO₂ nanoparticles, SiO₂/TiO₂–organoclay hybrids were promising and cost-effective photocatalysts in removal of pollutants from wastewater.     

Sol–gel synthesis,preparation and characterization of photoactive TIO<Subscript>2</Subscript> with ultrasound treatment

Titania was prepared by the sol–gel method from titanium isopropoxide with ultrasound influence (USI) by different pH (acetic acid (AA) or diethyl amine (DEA). Samples were represented in powder and films forms. The TiO₂ was characterized by X-ray diffraction (XRD), FTIR. XRD shows that TiO₂ prepared with diethyl amine has only the anatase phase, however the samples prepared with acetic acid–anatase and rutile phases both could be detected. Ultrasound influence increases the anatase content in comparison with its missing. Photo electromotive force (Photo EMF) datas of TiO₂ films were received in a three-electrode wet cell. It was found that the photo activity depended on the conditions of synthesis crystalline phases. Photo EMF for the TiO₂ films on the nickel electrode is 1.5 mV (TiO₂ with acetic acid conditions), 6.8 mV (TiO₂ with diethyl amine conditions) 8.0 mV (TiO₂ with acetic acid + USI conditions), 22.0 mV (TiO₂ with diethyl amine +USI conditions).     

Particulate sol–gel synthesis and optical and electrical properties of CeO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> nanocomposite

CeO₂/TiO₂ nanocomposite was synthesized by particulate sol–gel method. The X-ray diffractogram shows the presence of cubic CeO₂ and anatase TiO₂ in the composite. The high resolution scanning electron micrographs reveal the nanoparticulate nature of the prepared composite. The composite absorbs UV light and exhibits near-band gap emission corresponding to TiO₂ and deep level emission due to crystal defects. The Nyquist plot displays two semicircular arcs indicating the material heterogeneity. The physicochemical characteristics of the synthesized nanocomposite are in favour of its application as an ingredient of sunscreen formulations; under UV light the photocatalytic activity of CeO₂/TiO₂ composite, tested through the degradation of rhodamine B, is very much less than that by pristine anatase TiO₂. Reduced adsorption of moisture by the nanocomposite is a possible reason for the observed very low photocatalytic activity.     

Sol–gel synthesis and characterization of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> · CeO<Subscript>2</Subscript> doped with Pr ceramic pigments

Undoped x · α-Fe₂O₃ y · CeO₂ and doped with praseodymium ceramic pigments were obtained by the sol–gel method after heat treatment at 800 °C for 2 h. These pigments were characterized by XRD, nitrogen adsorption, scanning electron microscopy, ultraviolet-visible absorption spectroscopy and colorimetrical measurements. Red and brown colors with several tonalities were observed after changes with Ce and Pr concentration.     

Sol–gel derived TiO<Subscript>2</Subscript> wood composites

The sol–gel process was applied to enhance properties of pine sapwood. For this purpose wood prisms were soaked in nanoscaled precursor solutions prepared from titanium(IV) n-butoxide and titanium(IV) iso-propoxide, respectively, using vacuum impregnation technique. The wet composites were cured by special program with final heat treatment at 103 °C. Weight percent gains (WPG) of the wood specimen in the range of 19–25% were obtained due to these procedures. SEM investigations show that precursor solutions penetrate into the whole wood body and the titania formed after heat treatment in the composites is deposited in the pores (lumen) and partly in the cell walls of the wooden matrix. The moisture sorption was investigated in long term tests for a period of some months by storage at 20–23 °C in humid air (relative humidity of 99%) and ambient atmosphere (relative humidity 40–60%), respectively. For untreated reference samples the moisture sorption results in increasing of mass and volume according to saturation values of 24 and 13%, respectively, after about 15 days. The incorporation of titania reduces the saturation values of the moisture sorption by up to 12% in mass and by up to 5% in volume at a relative humidity of 99%. Thus, an enhancement of the dimensional stability of about 60% is obtained at best. The results demonstrate that modification of wood with sol–gel derived precursors can enhance its dimensional stability, which prevents the formation of cracks. Because of that reduced moisture sorption biological attacks should be delimited. Additionally, thermal analyses show a retarded combustion of the wood matrix due to titania infiltration.     

Rietveld refinement of sol–gel Na<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript> and its photocatalytic performance on the degradation of methylene blue

We have refined single crystals of Na₂Ti₆O₁₃ through the X-ray Rietveld method. The synthesis of the Na₂Ti₆O₁₃ was carried out by sol–gel method at 70 °C, and the obtained gel was heat treated at different temperatures. Through different analytical techniques such as X-ray Diffraction (XRD), Scanning Electronic Microscopy (SEM), Infrared Spectroscopy (FTIR), and Thermal Analysis (DTA/TGA), it was determined that Na₂Ti₆O₁₃ can be prepared at low temperature (750 °C) by sol–gel method. The product crystallizes in rectangular shape micro-fibers, free of impurities. Rietveld refinement was performed using X-ray diffraction technique taking as basis a monoclinic cell with space group C2/m. The following refined parameters were obtained: a = 15.095(7) Å, b = 3.745(3) Å, c = 9.174(1) Å, β = 99.01. Additionally, Na₂Ti₆O₁₃ was tested as photocatalysts on the degradation of methylene blue (MB) under UV light. The degradation reaction follows a first order reaction model with kinetic parameters k = 0.0089 min^?1, and t _1/2 = 78 min.     

Sol–gel synthesis and characterization of polycrystalline GdFeO<Subscript>3</Subscript> and Gd<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> thin films

Thin films of the perovskite and garnet structured gadolinium ferrites GdFeO₃ and Gd₃Fe₅O₁₂ have been synthesized by a sol–gel method, based on stoichiometric mixtures of acetyl acetone chelated Gd³⁺ and Fe³⁺ dissolved in 2-methoxy ethanol. After spin coating onto Si wafers, and heating in air at 700 °C for 20 h, neatly grown essentially single phase films were obtained. From X-ray photoelectron spectroscopy an iron deficiency is observed in the uppermost layer of both films, implying that the crystallites preferably end in planes rich in Gd and O but not in Fe. The films were also characterized by X-ray powder diffraction, scanning electron microscopy, infrared spectroscopy, and magnetic measurements.     

The oxidative-dissolution behaviors of fission products in a Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>–H<Subscript>2</Subscript>O<Subscript>2</Subscript> solution

This study was carried out to investigate the characteristics of an oxidative-dissolution of fission products (FP) when uranium (U) is dissolved in a Na₂CO₃–H₂O₂ carbonate solution. Simulated FP-oxides which contained 12 components were added to the solution to examine their dissolution behaviors. It was found that H₂O₂ was an effective oxidant to minimize the dissolution of FP. For the 0.5 M Na₂CO₃–0.5 M H₂O₂ solution, such elements as Re, Te, Cs, and MoO₂ were dissolved with yields of 98 ± 2%, 98 ± 2%, 93 ± 2%, and 26 ± 3%, respectively, for 2 h. Among these components, Re, Te, and Cs were completely dissolved within 10–20 min without regard to the concentrations of Na₂CO₃, and H₂O₂ due to their high solubility in the carbonate solution with and without H₂O₂. However, MoO₂ was very slowly dissolved and its yield was 29 ± 3% for 4 h. The pH of the dissolved solution revealed the greatest influence on the dissolution yields of the FP, exhibiting the most effective pH condition in the range of 10–12 in order to create a considerable suppression of the co-dissolution of FP during the oxidative-dissolution of U.     

Phase equilibria in the ternary systems NaCl–NaI–Na<Subscript>2</Subscript>CrO<Subscript>4</Subscript> and KCl–KI–K<Subscript>2</Subscript>CrO<Subscript>4</Subscript>

The ternary systems NaCl–NaI–Na₂CrO₄ and KCl–KI–K₂CrO₄ were studied by differential thermal analysis. In the systems, the melting points and compositions of alloys at ternary eutectic points were determined. The compositions of crystallizing phases in the eutectics were confirmed by X-ray powder diffraction analysis.     

Study of the NaF–NaBr–Na<Subscript>2</Subscript>SO<Subscript>4</Subscript> system

The NaBr–D (Na₃FSO₄) quasi-binary system and the NaF–NaBr–Na₂SO₄ ternary system were studied by differential thermal analysis. The melting points and compositions of eutectic mixtures were determined, and in-, mono-, and divariant equilibrium states were described.     

Preparation and characterization of SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Na<Subscript>2</Subscript>O glass coated cBN abrasive particles via sol–gel route

SiO₂–Al₂O₃–Na₂O glass coated cubic boron nitride (cBN) abrasive particles were prepared by sol–gel technique. The results indicated that SiO₂–Al₂O₃–Na₂O glass was excellent material for oxidation protection of cBN abrasive grains because coefficient of thermal expansion of this glass closely matched that of cBN materials. The single particle compressive strength and impact toughness of this glass coated cBN abrasive particles were significantly increased. For the application of glass coated cBN abrasives to vitrified grinding wheels, it was evident that the glass coating provided high bonding strength between cBN abrasive grains and vitrified bond system.     

Electrophoretic sol–gel synthesis of SrBi<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>9</Subscript> nanowires

We report the independent invention of perovskite ferroelectric nanowires strontium bismuth tantalate (SrBi₂Ta₂O₉, SBT). Electrophoretic sol–gel techniques have been used successfully. The morphology and structures are analyzed via SEM, TEM and XRD. SBT nanowires and nanoparticles filled template revealed 30 and 40 μm long, respectively. SBT are proved to be a single phase of orthorhombic perovskite structure. As it indicated, SBT nanowires has been crystallized at 700 °C. To minimize surface polarity, SBT nanowires oriented preferentially along the growing axis (c axis) by translation and rotation of atomic clusters of SBT.     

Crystal structure of Na<Subscript>4</Subscript>[Na<Subscript>2</Subscript>Cr<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>6</Subscript>] · 10H<Subscript>2</Subscript>O

Single crystals of the Na₄[Na₂Cr₂(C₂O₄)₆] · 10H₂O complex were synthesized for the first time. The structure of the complex was determined by X-ray diffraction analysis. The compound crystallizes in the monoclinic crystal system with the unit cell parameters a = 17.290(4) Å, b = 12.521(3) Å, c = 15.149(3) Å, β = 100.45(3)°, Z = 4, space group Cc. Anionic layers [NaCr(C₂O₄)₃] _2n ^4n? can be distinguished in the crystal structure of the complex. The Na⁺ cations and water molecules, involved in the formation of a hydrogen bond network, are located between the anionic layers.     

Low temperature synthesis of Co<Subscript>2</Subscript>SiO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> nanocomposite using a modified sol–gel method

The paper presents a study on the preparation of Co₂SiO₄/SiO₂ nanocomposites by a new modified sol–gel method. We have prepared gels starting from tetraethylorthosilicate (Si(OC₂H₅)₄), cobalt nitrate Co(NO₃)₂·6H₂O and some diols: ethylene glycol (C₂H₆O₂), 1,2propanediol (C₃H₈O₂) and 1,3propanediol (C₃H₈O₂), for a final composition: 30% CoO/70% SiO₂. During the heating of the gels at 140 °C, a redox reaction takes place between NO₃ ⁻ ions and diol with formation of some carboxylate anions. These carboxylate anions react with the Co(II) ions to form coordination compounds embedded in silica matrix, as evidenced by FT-IR spectrometry and thermal analysis. These Co(II) coordinative compounds thermally decompose in the range 250–300 °C to the corresponding oxides: CoO and/or Co₃O₄ inside the matrices pores. When CoO results, it reacts with SiO₂ at low temperature leading to Co₂SiO₄, which crystallizes at 700 °C. XRD patterns of the samples annealed at temperatures lower than 700 °C were characteristic to amorphous phases. The samples annealed at temperatures ≥700 °C, contain Co₂SiO₄ (olivine) as unique crystalline phase inside the amorphous silica matrix, according to XRD patterns. As evidenced by TEM images, Co₂SiO₄ nanoparticles are homogenously dispersed inside the silica matrix.     

Investigation of the structural and thermal properties of Y,Ag and Ce-assisted SiO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O–CaO–P<Subscript>2</Subscript>O<Subscript>5</Subscript>-based glasses derived by sol–gel method

A glass with the composition of the SiO₂–Na₂O–CaO–P₂O₅ was synthesized by sol–gel method at temperature of 900 °C, and then yttrium-, silver- and cerium-containing glasses were prepared at the same conditions using this base system. The structural and thermal properties of the glass samples were investigated by X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, energy-dispersive X-ray (EDX) spectroscopy and differential thermal analysis techniques. The Ca₅(PO₄)₂(SiO₄)₆ phase having the orthorhombic crystal system is detected for each sample without any secondary phase, and this phase is confirmed by the FTIR spectra. With the addition of Y, Ag and Ce to the SiO₂–Na₂O–CaO–P₂O₅ system, the variations in the average crystallite size, crystallinity percent, lattice parameters and unit cell volume are observed. A decrease in the crystallization peak temperature and the changes in the glass transition temperature are seen with the addition of Y, Ag and Ce to the base system. The addition of Y, Ag and Ce to the base glass increases significantly its density. The EDX spectra of the as-prepared samples verify the introduction of the as-mentioned elements.     

Structure and thermal properties of the fritted glazes in SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–CaO–MgO–Na<Subscript>2</Subscript>O–K<Subscript>2</Subscript>O–ZnO system

In this work, the structure and thermal properties of aluminosilicate fritted glazes in SiO₂–Al₂O₃–CaO–MgO–Na₂O–K₂O–ZnO system with (4.0 mol%) and without addition of ZnO were examined by GIXRD, FTIR, MAS-NMR and thermal methods (DTA, DIL). It has been found that the all experimental glazes are amorphous material (transparent glazes). On the base of spectroscopic investigations, it was found that zinc ions exist in the network glazes in the octahedral coordination—Zn²⁺ ions play a network modifier role in structure of glazes. An analysis of the data obtained from thermal tests showed that addition of ZnO into chemical composition results in decrease in glass transition temperature value (T _g) for all glazes (DTA, DIL). The coefficient of thermal expansion (α) is decreased as the whole measurement range for one series of fritted glazes.