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 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.     

Modeling and optimization of densification of nanocrystalline Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powder prepared by a sol–gel method using response surface methodology

Response surface methodology (RSM) based on central composite design (CCD) was successfully applied to the optimization and modeling of densification of nanocrystalline Al₂O₃ powder prepared by sol–gel method. The effects of three operating variables, sintering temperature, calcination temperature and milling time on the densification of nanocrystalline Al₂O₃ were systematically evaluated. A quadratic model for densification was proposed. Analysis of variance (ANOVA) indicated that the proposed quadratic model could be used to navigate the design space. The simulated values obtained from the statistical model were in conformity with the experimental results within an average error of ±1.5%. The optimum operating conditions for densification were found to be 1,579 °C of sintering temperature, 909 °C of calcination temperature and 117 min of milling time. The obtained density under the optimum conditions determined by RSM was 98.5%. The results confirmed that RSM based on central composite design was an accurate and reliable method to optimize the densification conditions of nanocrystalline Al₂O₃ powder.     

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.     

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.     

Sol–gel synthesis of Eu<Superscript>3+</Superscript>: Tb<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> nanophosphor

Eu (0.1, 0.5 and 1.0 mol%) doped Tb₃Al₅O₁₂ (TAG) was prepared by sol–gel technique through nitrate-citrate route followed by sintering in air (1,100 °C maximum temperature). XRD analysis showed that Eu³⁺ enters the TAG lattice substitutionally replacing the Tb³⁺ ion. Both XRD as well as FTIR investigation showed improvement in crystalline phase with the increase in the sintering temperature. SEM and TEM analysis showed that the powder contains the particles in 5–20 nm size with almost spherical morphology. The excitation spectrum recorded in 300–500 nm showed dominant absorption due to Tb³⁺ while the emission spectra recorded with 380 nm excitation had strong red emission characteristic of Eu³⁺. The intensity of this emission increases with the increase of the Eu concentration from 0.1 to 0.5 mol%. However, the emission intensity decreased on further increase in Eu concentration to 1.0 mol%. This intensity variation with dopant concentration is attributed to well-known “concentration quenching” observed in rare-earth doped materials. Reasonably strong red emission due to Eu was observed when excited with the blue (480 nm) radiation of a Xe lamp indicating the usefulness of the material for the realization of white light LED.     

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.     

Preparation and characterization of TiO<Subscript>2</Subscript> sol–gel modified nanocomposite films

In this study, the role of TiO₂ MT-150A loading in the polymeric sol was investigated for the synthesis of immobilized TiO₂ nanocomposite films on glass substrate using the MT-150A nanoparticles-modified sol–gel method. The nanocomposite film properties were examined using different material characterization techniques including X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, UV–Vis spectrophotometer, Scotch tape test and pencil hardness test. The hydrophilicity of films during UV/Vis irradiation and storage in a dark place were evaluated by a contact angle analyzer. The MT-150A loading had a significant effect on the amount of crystallite phases in the films. However, increasing the MT-150A loading in the sol resulted in an increase in rutile phase content. In addition, increasing MT-150A loading in the sol yielded films with higher hydrophilicity but a concentration of 10–30 g/L MT-150A in the sol was found as the maximum for obtaining films with good adherence on the glass substrate.     

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.     

Effect of mechanical activation of reagents’ mixture on the high-temperature synthesis of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiB<Subscript>2</Subscript> composite powder

A powder mixture of Al/TiO₂/H₃BO₃ = 10/3/6 in molar ratio was used in this study to form the Al₂O₃–TiB₂ ceramic composite via thermite reactions (combustion synthesis). As no combustion synthesis occurred for an unmilled sample in a furnace, the mixture was milled in a planetary ball-mill for various milling times, and the as-milled samples were in situ synthesized in the furnace at a heating rate of 10 °C/min. The differential scanning calorimetry (DSC) measurements were performed with the same heating rate on the unmilled and the as-milled samples to evaluate the influences of the milling on the mechanisms and efficiencies of reactions. Although no combustion synthesis occurred for the unmilled sample in the furnace, two exothermic peaks were detected in its DSC curve after the melting of the Al. For the as-milled samples, significant changes revealed in the DSC curves, suggest that the milling process before the combustion synthesis changed the mechanisms and efficiencies of reactions. In addition, the intensity and the temperature of the exothermic peaks in the DSC curves changed by increasing the milling time. According to the XRD analyses, by enhancing the milling time, the purity of the final products would increase, confirming that the efficiency of the reactions increased. Finally, the microstructures of the as-milled and as-synthesized samples were examined by a SEM, and it was shown that the morphology of the reactant powders was altered by increasing the milling time.     

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.     

Atmospheric control of gel-oxide transformation in sol–gel derived Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Y<Subscript>2</Subscript>O<Subscript>3</Subscript> fibers

Via sol–gel processing metal–organic fibers were produced and dried up to 140 °C. For these gel fibers the influence of a treatment in different atmospheres was investigated for the temperature range of 200–850 °C. The atmospheres were nitrogen, water vapor, evaporated nitric and hydrochloric acid and evaporated hydrogen peroxide. In the presence of moisture and especially with acidic moisture fibers were transformed almost completely to their oxide composition (82 mol% Al₂O₃·18 mol% Y₂O₃). In these inorganic amorphous structures considerable differences were observed on several structural levels. On the atomic scale, the coordination of Al ions was investigated by ²⁷Al MAS NMR and skeletal density by He-pycnometry. Porosity in the nm scale was characterized by N₂-sorption. As a macroscopic effect of different treatment atmospheres, the longitudinal shrinkage was observed. For fibers treated at 500 °C the relative shrinkage varied by 100% (comparing water vapor and nitrogen atmosphere). No simple correlation between the release of organic constituents, the formation of porosity and the shrinkage could be found. These aspects were controlled by the rigidity of the inorganic network against atomic reconstitution. The kind of atmosphere was found to be an effective parameter to control various aspects of the xerogel structure.     

Synthesis and properties of γ-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> solid solutions

The textural and structural properties of mixed oxides Ga₂O₃–Al₂O₃, obtained via impregnating γ-Al₂O₃ with a solution of Ga(NO₃)₃ and subsequent heat treatment, are studied. According to the results from X-ray powder diffraction, gallium ions are incorporated into the structure of aluminum oxide to form a solid solution of spinel-type γ-Ga₂O₃–Al₂O₃ up to a Ga₂O₃ content of 50 wt % of the total weight of the sample, accompanied by a reduction in the specific surface area, volume, and average pore diameter. It is concluded that when the Ga₂O₃ content exceeds 50 wt %, the β-Ga₂O₃ phase is observed along with γ-Ga₂O₃–Al₂O₃ solid solution. ⁷¹Ga and ²⁷Al NMR spectroscopy shows that gallium replaces aluminum atoms from the tetrahedral position to the octahedral coordination in the structure of γ-Ga₂O₃–Al₂O₃.     

Facile synthesis of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> core–shell nanobelts

We report a facile chemical approach for the synthesis of one-dimensional V₂O₅/TiO₂ core–shell nanobelts. The coated V₂O₅ nanobelts are synthesized by a hydrothermal method which is feasible for large-scale production. V₂O₅ nanobelts coated with a thin layer of TiO₂ sol are formed before sintering, and after sintering one-dimensional V₂O₅/TiO₂ core–shell nanobelts, composed of single-crystalline V₂O₅ nanobelts cores uniformly coated with anatase TiO₂ nanoparticle shells are obtained. The influences of the synthetic parameters, such as sintering temperature and titanium/vanadium mole ratios, on the morphology of the resulting products are investigated. Interestingly, the shape of single-crystalline of V₂O₅ nanobelts is totally preserved after sintering; the morphology can be readily controlled to be smooth or rough by altering the sintering temperature of the shells and titanium/vanadium mole ratio.     

Simple sol–gel route to synthesis of mesoporous TiO<Subscript>2</Subscript>

Mesoporous TiO₂ with a high specific surface area was prepared from titanium sulfate solution in a simple sol–gel route, where formamide was used as pH adjusting agent. TiO₂ had a high resistance to phase transformation, and maintained monophasic anatase after calcinating at 600 °C. The highest specific surface area achieved on the prepared samples is 231.90 m² g⁻¹ after calcinating at 450 °C.     

Synthesis and characterization of Fe doped mesoporous Al<Subscript>2</Subscript>O<Subscript>3</Subscript> by sol–gel method and its use in trichloroethylene combustion

Two mesoporous alumina samples were synthesized using the sol–gel method, and these samples were tested as catalysts in trichloroethylene combustion reaction. One alumina sample was doped with Fe to study the influence of a small amount of this agent on the characteristics and properties of alumina as a catalyst. Both catalysts (pure alumina and alumina doped with Fe) were thoroughly characterized by different techniques, such as DTA/TGA, FT-IR, XRD, SEM and TEM, and the porous characterization was conducted using a N₂ physisorption technique. The doping agent presented a particular influence on the morphology and textural porosity in the alumina catalyst and therefore, it exhibited different catalytic behavior than the pure alumina catalyst. For both catalysts, the crystalline phase of γ-alumina was reported using XRD technique, and the crystallite size ranged from 7.8 to 12.8 nm. Using TEM images, the alumina catalyst doped with Fe revealed to contain a mixture of three types of iron oxide (maghemite, magnetite and hematite), mainly as roughly spherical nanoparticles. For both alumina catalysts, trichloroethylene catalytic combustion was conducted on a packed bed reactor in air at a temperature range of 50 to 600 °C. The alumina catalyst doped with Fe showed a higher catalytic activity than pure alumina, mainly due to the presence of micropores and grain morphology of flat faces.     

Preparation and characterization of nanocrystalline CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> deposited on SiO<Subscript>2</Subscript>: in situ sol–gel process

In situ base catalyst assisted sol–gel process is used for the synthesis of nanocrystalline CoFe₂O₄ deposition on SiO₂ particles. The SiO₂ particles were prepared using base catalyst assisted sol–gel process and the consecutive formation and deposition of nanocrystalline CoFe₂O₄ on SiO₂ particles was monitored using Powder X ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Thermo Gravimetric And Differential Thermal Analysis (TG/DTA), Scanning Electron Microscopy and Energy Dispersive X ray Spectroscopy (SEM–EDS) and High Resolution Transmission Electron Microscopy (HRTEM). The crystallite size of CoFe₂O₄ is calculated using Scherrer’s formula and it is found to be 8 nm. The HRTEM images and selective area electron diffraction (SAED) results confirmed the formation of nanocrystalline CoFe₂O₄ particles deposited over SiO₂ spheres.     

Structure,Magnetic and Photochemical Properties of Fe–TiO<Subscript>2</Subscript> Nanoparticles Stabilized in Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Matrix

Fe–TiO₂ nanoparticles with Fe concentration from 0.24 to 5 wt % were synthesized in a Al₂O₃ matrix through multiple impregnations from organic solutions of Ti n-butoxide and Fe acetylacetonate. Microstructure, morphology and magnetic properties of the composites were studied using X-ray analysis, transmission electron microscopy, energy-dispersive analysis, Mössbauer spectroscopy and magnetic susceptibility. It was shown that the deposition of the solution with low concentration of Ti n-butoxide leads to the formation of mostly extensive Fe–TiO₂ films with a small fraction of individual Fe–TiO₂ nanoparticles. On the contrary, the increase of Ti n-butoxide concentration results in the formation of a great number of individual Fe–TiO₂ nanoparticles on Al₂O₃. The size of these particles increases from 2–3 nm to 5–8 nm with the increase of Fe content in the samples from 0.24 to 1.0 (wt %). Mössbauer spectroscopy revealed two types of magnetic ions. The first type of paramagnetic Fe³⁺ demonstrate spin–lattice relaxation properties while another one substitutes Ti⁴⁺ in the TiO₂ structure thus forming Fe–TiO₂ stabilized particles in the matrix. According to the magnetic data antiferromagnetic and ferromagnetic types of exchange spin coupling occur in Fe–TiO₂/Al₂O₃ composites. The increase of Fe concentration in the composites from 1 to 5 wt % results in the narrowing of the TiO₂ band gap from 3.2 to 2.7 eV and shifting the absorption edge in visual spectrum from 350–400 to 450–500 nm.