Synthesis and characterization of nanocrystalline tin oxide by sol–gel method

Nanocrystalline SnO₂ particles have been synthesized by a sol–gel method from the very simple starting material granulated tin. The synthesis leads a sol–gel process when citric acid is introduced in the solution obtained by dissolving granulated tin in HNO₃. Citric acid has a great effect on stabilizing the precursor solution, and slows down the hydrolysis and condensation processes. The obtained SnO₂ particles range from 2.8 to 5.1 nm in size and 289–143 m² g⁻¹ in specific surface area when the gel is heat treated at different temperatures. The particles show a lattice expansion with the reduction in particle size. With the absence of citric acid, the precursor hydrolyzes and condenses in an uncontrollable manner and the obtained SnO₂ nanocrystallites are comparatively larger in size and broader in size distribution. The nanocrystallites have been characterized by means of TG-DSC, FT-IR, XRD, BET and TEM.     

Characterization and preparation of nanocrystalline MgCuZn ferrite powders synthesized by sol–gel auto-combustion method

Nanocrystalline Mg–Cu–Zn ferrite powders were successfully synthesized through nitrate–citrate gel auto-combustion method. Characterization of the nitrate–citrate gel, as-burnt powder and calcined powders at different calcination conditions were investigated by using XRD, DTA/TG, IR spectra, EDX, VSM, SEM and TEM techniques. IR spectra and DTA/TGA studies revealed that the combustion process is an oxidation–reduction reaction in which the NO₃ ⁻ ion is oxidant and the carboxyl group is reductant. The results of XRD show that the decomposition of the gel indicated a gradual transition from an amorphous material to a crystalline phase. In addition, increasing the calcination temperature resulted in increasing the crystallite size of Mg–Cu–Zn ferrite powders. VSM measurement also indicated that the maximum saturation magnetization (64.1 emu/g) appears for sample calcined at 800 °C while there is not much further increase in M _s at higher calcination temperature. The value of coercivity field (H _c) presents a maximum value of 182.7 Oe at calcination temperature 700 °C. TEM micrograph of the sample calcined at 800 °C showed spherical nanocrystalline ferrite powders with mean size of 36 nm. The toroidal sample sintered at 900 °C for 4 h presents the initial permeability (μ _i) of 405 at 1 MHz and electrical resistivity (ρ) of 1.02 × 10⁸ Ω cm.     

Comparative study of the thermal behavior of Sr–Cu–O gels obtained by sol–gel and microwave-assisted sol–gel method

Journal of Thermal Analysis and Calorimetry - In the literature data, several papers reported the synthesis by various chemical or physical methods of the SrCu2O2 (SCO) having possible applications...     

Modified procedure for the sol–gel processing of indium–tin oxide (ITO) films

Dispersions of crystalline nanoscaled ITO and solutions of amorphous precursors were used for the preparation of transparent conductive films on glass both by large area dip-coating (30 × 30 cm²) and pad-printing. The advantages of both types of coating materials regarding single layer thickness and conductivity were combined by a coating-infiltration procedure. The resulting films showed a specific resistivity down to 1.77 10E−03 Ω cm after treatment in reducing atmosphere and an increased resistance to subsequent storage in air.     

Transparent conductive tungsten-doped tin oxide thin films synthesized by sol–gel technique on quartz glass substrates

Transparent conductive tungsten-doped tin oxide (SnO₂:W) thin films were synthesized on quartz glass substrates by sol–gel dip-coating method. It was found that the films were highly transparent and the average optical transmission was about 90% in the visible and near infrared region from 400 to 2,500 nm. The optical band gap is about 4.1 eV. The lowest resistivity of 5.8 × 10^?3 ohm cm was obtained, with the carrier mobility of 14.2 cm² V^?1 s^?1 and carrier concentration of 7.6 × 10¹⁹ cm^?3 in 3 at.% W-doping films annealed at 850 °C in air. The structural properties, surface morphology and chemical states for the films were investigated.     

Titanium dioxide fibers prepared by sol–gel process and centrifugal spinning

A new study of the preparation of nanocrystalline titanium dioxide (TiO₂) fibers is reported in the paper, which were prepared by sol–gel process with titanium acetate [Ti(CH₃COO)₄] as precursor. After that, centrifugal spinning and steam atmosphere heat-treatment were used to obtain final fibers. Here, the molecule structure of precursor was analyzed and the TiO₂ fibers obtained were characterized. Additionally, the effects of the silica (SiO₂) doping were discussed in this paper. By the Fourier transformation infrared spectrum analysis, the chain structure of –O–Ti–O–Ti–O– was confirmed in the Ti(CH₃COO)₄ precursor, as a result the precursor spinning solution showed a good spinning performance. And the pyrolysis process of precursor fibers was analyzed with the help of DSC–TG method. The phase of TiO₂ fibers obtained after heat-treatment with steam atmosphere was characterized mainly by the X-ray diffractometer (XRD), from the XRD curves, the result that the SiO₂ doping can efficiently inhibit the grain growth of TiO₂ fibers could also be verified. The microstructure of the TiO₂ fibers was observed by scanning electron microscope, which showed that diameter of TiO₂ fibers obtained with excellent continuity are from 5 to 10 μm. At last, the photocatalytic property of TiO₂ fibers was also tested.     

Nano-sized polycrystalline bismuth silicon oxide powder by sol–gel technique

Bismuth silicon oxide (Bi₁₂SiO₂₀, BSO) nano crystalline powder was prepared by sol–gel technique using bismuth nitrate and tetraethyl orthosilicate as starting materials. The prepared samples were sintered at various temperatures (750 °C maximum) and characteristic sillenite single cubic phase with crystallite size ~38 nm (calculated from room temperature powder XRD measurements) was realized at 750 °C sintering temperature. SEM analysis showed that the powder contains the nano-sized particles with almost spherical morphology. The observed frequencies in room temperature FTIR spectrum could be assigned to Bi–O, Si–O and Bi–O–Si bonds. The FWHM (full width at half maximum) of the diffraction peaks decreased while the intensity of FTIR absorption lines increased with the increase in the sintering temperature indicating better bond formation and crystallization. The thermograph of the samples recorded in the temperature range 50–1,000 °C showed almost no weight loss after ~575 °C further confirmed the conclusion arrived at from XRD and FTIR analysis. The samples sintered at 750 °C showed about 50% absorbance in 400–600 nm region which was consistent with the pale yellow color of the sample. Broad blue emission centered ~478 nm was observed when excited by 350 nm radiation from a Xe-lamp. The intensity of this broad emission band increased while its FWHM decreased with the increase in sintering temperature. Self-trapped excitons could be responsible for this emission.     

Novel photoconductive Ag/nanostructure ruthenium oxide/p-type silicon Schottky barrier diode by sol–gel method

A new Schottky photodiode of Ag/RuO₂/p-Si/Al was successfully fabricated using spin-coating technique. The ruthenium oxide (RuO₂) nanoparticles with an average size of 8 nm were synthesized using a sol–gel method. The crystal structure and morphology of the synthesized RuO₂ were analyzed by means of X-ray diffraction, energy dispersive X-ray spectroscopy, transmission electron microscopy and selective area electron diffraction. The rectification ratio of the diode was found to be 112 at ±2 V. The ideality factor and barrier height values of the Ag/RuO₂/p-Si/Al diode were obtained to be 1.47 and 0.55 eV, respectively. The Cheung–Cheung and Norde’s models were used to determine the diode parameters. The photoresponse behavior of the fabricated Ag/RuO₂/p-Si/Al diode was studied under various illumination intensities. The transient photocurrent results indicate that photocurrent under illumination is higher than the dark current and this indicates that the fabricated diode behaves as a photodiode. The capacitance–voltage–frequency measurements indicate that the capacitance of the diode depends on voltage and frequency. The obtained results suggest that the new Ag/RuO₂/p-Si/Al diode can be used an optical switching device for optical sensor applications and are also expected to be generated in the future study.     

Photocatalytic reduction of cadmium over CuFeO2 synthesized by sol–gel

The Cd²⁺ photo-electrodeposition was successfully carried out in air-equilibrated aqueous CuFeO₂ suspension. The delafossite CuFeO₂ is p-type semiconductor characterized by a low optical gap, properly matched to the sun spectrum, and a long term chemical stability in neutral solution. It has been elaborated by the sol–gel technique where the specific surface area is increased via the surface/bulk ratio. The TG/DSC plots and IR spectra show that the solid phases are formed only at temperatures exceeding 400 and at 700 °C, the system is mixed phases. When fired at 950 °C under nitrogen flow, the delafossite has been identified (CuO + CuFe₂O₄ → CuFeO₂ + ½O₂). All the XRD lines index in a hexagonal unit cell with the lattice constants a = 284.2 and c = 169.4 pm. The photocurrent onset potential (+0.35 V_SCE) is close to the flat band potential (+0.23 V_SCE) determined from the capacitance measurement. CuFeO₂/Cd²⁺ solution is a self photo-driven system, the absorption of light promotes electrons into CuFeO₂–CB with a potential (?0.93 V_SCE) sufficient to reduce Cd²⁺. This occurs because of the dark Cd²⁺ adsorption on the surface powder. The system was optimized with respect to the following physical parameters: pH 6.8, Cd²⁺ (100 ppm) and a mass concentration C_m (1 mg catalyst/ml solution). The hetero-system CuFeO₂/TiO₂ has been also reported for a comparative purpose. Prolonged irradiation (>50 min) was accompanied by a pronounced decrease in the rate of Cd-deposition owing to the competitive water reduction. Indeed, the generated bi-functional CuFeO₂/Cd particles account for the low over-potential of hydrogen and favour its evolution in aqueous solution.     

Synthesis and characterization of lead oxide nano-powders by sol–gel method

Our goal in this research was to obtain lead oxide nano-powders by sol–gel method. In this method, lead oxide nano-powders were synthesized through the reaction of citric acid (C₆H₇O₈·H₂O) solution and lead acetate [Pb(C₂H₃O₂)₂] solution as stabilizer and precursor, respectively. The effect of different parameters including calcination temperature, (molar ratio of citric acid to lead acetate) and drying conditions were investigated. The prepared lead oxide nano-powders were characterized by FT-IR spectroscopy, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. The prepared PbO samples consist of the particles in the range of 50–120 nm or the thick plate like structures with thickness of 53 nm depending on the drying conditions.     

Structural study of the MO–Nd2O3 system obtained by a sol–gel procedure

The aim of the present work was to prepare a binary MO–Nd₂O₃ system by the sol–gel method and to characterise a series of mixed oxides belonging to the binary MO–Nd₂O₃ system (M = alkaline earth metal = Mg, Ca, Sr) to obtain suitable materials with catalytic properties. The molar ratio between the two oxides was MO/Nd₂O₃ = 95/5. Different precursors as alkaline earth metal oxide source (MO), various starting solution compositions expressed in various molar ratios between reactants and different synthesis parameters (pH, temperature and time of reaction) have been used. The structural study by X-ray diffraction analysis was accomplished based on the X-ray 5.0 program, which has established the presence of the mixtures of crystalline polyphases. The lattice constants, the average size of the crystallites, the average lattice strains and the mass of unit cell variation have been calculated. The program also allowed the calculus of the anisotropy factor, which can give the image of the structural disorder. The surface defects are a consequence of structural changes inside of the crystalline lattice of the solid solutions and are quite important for catalytic properties. Some catalytic activity measurements have established the potential of the prepared sol–gel mixed oxides to be used in the oxidative dehydrogenation process of light alkanes (C₁C₄). Sample 3SrNd was shown to present the best catalytic activity and selectivity in olefins in propane conversion (${\text{C}}_2^{=}\&{\text{C}}_3^{=}$) compared with 4Ca-Nd and 1Mg-Nd samples, which was interpreted as due to a better solid solution formation of Nd³⁺ in SrO, favoured by the close ionic radius of Sr²⁺ and Nd³⁺, as well as by the high basicity of Sr and the presence of a greater number of point defects.     

Anticorrosive cerium-based coatings prepared by the sol–gel method

The development of efficient anti-corrosion and environmentally friendly coating systems are needed for the replacement of the highly toxic Cr-based conversion coatings for corrosion protection of aluminum alloys. In this study, we demonstrate that the direct application of ceramic cerium-based sol–gel coatings to AA7075-T6 substrates produces high-performance anti-corrosion layers. Electrochemical experiments and analyses of the microstructure demonstrate that the protective layers are very efficient for the passivation of the alloy surfaces operating as both passive and active barrier for corrosion protection.     

Comparative study of graphene aerogels synthesized using sol−gel method by reducing graphene oxide suspension

A graphene oxide aerogel synthesized from graphene oxide hydrogel and graphene aerogels have been synthesized using the sol?gel method by reducing a suspension of graphene oxide with various reducing agents: a mixture of hypophosphorous acid and iodine, L-ascorbic acid, sodium metabisulfite, and by hydrothermal treatment. The obtained aerogels have been studied by scanning electron microscopy, IR spectroscopy, Raman spectroscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy. Comparative studies of graphene aerogels have shown that their properties, namely density, specific surface area, reduction degree, surface morphology, defectiveness of graphene sheets, interlayer spacing, average sizes of coherent scattering regions, number of layers, and crystallite size in the basal plane in graphene crystallites depend on the method of synthesis.     

Studies on photocatalytic performance and photodegradation kinetics of zinc oxide nanoparticles prepared by microwave-assisted sol–gel technique using ethylene glycol

ZnO nanoparticles with an average particle size of 27 nm were fabricated using a microwave-assisted sol–gel method in the presence of ethylene glycol. The nanoparticles were characterized by X-ray diffraction, Monshi’s equation, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. The band gap energy of the nanoparticles was measured to be 3.27 eV by UV–Vis absorption and reflection spectroscopy. Photocatalytic activity of the synthesized nanoparticles was assessed by degrading nitrophenol in aqueous solution under UV-C irradiation. The effects of initial nitrophenol concentration, amount of photocatalyst, and of pH on the photodegradation process were investigated. Degradation samples were analyzed by UV–Vis spectroscopy. Nitrophenol was removed by 98 % within 240 min. The degradation kinetics were studied and fitted well to pseudo-first-order and Langmuir–Hinshelwood models.     

Crystallization process of lanthanum-substituted bismuth titanate synthesized by a facile sol–gel method

We present a facile sol–gel route to synthesize lanthanum-substituted bismuth titanate (BLT). The chemical reactions and crystallization process of this method using the initial materials of bismuth subnitrate [4BiNO₃(OH)₂·BiO(OH)], lanthanum nitrate [La(NO₃)₃·6H₂O] and tetrabutyl titanate [Ti(C₄H₉O)₄] were investigated by thermogravimetric and differential thermal analysis, IR spectroscopy, gas chromatography/mass spectrometry, Raman spectroscopy and XRD. The evaporation of the dissolved CO₂ in the amorphous BLT matrix is associated with the crystallization of BLT. The BLT gel is pure BLT perovskite when calcination temperature is higher than 500 °C. The grain size of the obtained nanoparticles ranges from 15 to 82 nm. The Arrhenius curve is obtained from the representation of the reduced sizes with respect to the calcination temperature. The activation energy of grain growth in BLT nanoparticles is 0.36 eV, which shows a rapidly growth process in the temperature range of 500–850 °C.     

Nano silver coated patterned silica thin film by sol–gel based soft lithography technique

We report the fabrication of nano silver coated patterned silica thin film by sol–gel based soft lithography technique. Initially, silica gel film on soda lime silica glass was prepared by dipping technique from a silica sol of moderate silica concentration. A PolydimethylSiloxane elastomeric stamp containing the negative replica of the patterns of commercially available compact disc was used for embossing the film and the embossed film was cured up to 450 °C in pure oxygen atmosphere for oxide film. Finally, a precursor solution of AgNO₃ in water containing polyvinyl alcohol as an organic binder was made and used for coating on the patterned silica film by dipping technique and cured the sample up to 450 °C in reducing gas atmosphere to obtain nano silver layer. The formation of only cubic silver (~4.0 nm) and both cubic silver (~5.2 nm) and silver oxide (~3.6 nm) crystallites at 350 and 450 °C film curing temperatures respectively were confirmed by XRD measurements. The % of nano silver metal and silver oxide were 75.4 and 24.6 respectively. The nano-structured surface feature was visualized by FESEM whereas AFM revealed the high fidelity grating structure of the films. Presence of both spherical and rectangular structure (aspect ratio, 2.37) of nano silver/silver oxide was confirmed by TEM. The films were also characterized by UV–Vis spectral study. The patterned film may find application in chemical sensor devices.     

Surface characterization and dissolution study of biodegradable calcium metaphosphate coated by sol–gel method

Coatings of biomedical implant surfaces by a bioactive calcium phosphate film render bioactivity to the implant surface and shorten the healing time. In this present study, calcium metaphosphate (CMP) sol was synthesized by sol–gel method and coated onto the titanium alloys (Ti-6Al-4V). CMP sol was first synthesized by reacting Ca(NO₃)₂4H₂O (Sigma–Aldrich 99%, USA) with (OC₂H₅)₃P (Fluka 97%, Japan) in methyl alcohol. A stoichiometric Ca/P ratio of 0.5 was obtained by varying the amounts of the reactants. Sol was then coated on Ti-6Al-4V substrates by spin coating. The coated-specimens were then dried at 70 °C for 24 h, followed by a heat treatment at 650 °C for 1 h. Structural and chemical properties of the coatings were evaluated using XRD, SEM, and EPMA. The dissolution property of the coated-CMP layer was investigated by immersing the samples in the simulated body fluid (SBF) for 1, 3, 7 and 21 days. The concentration of Ca²⁺ released was measured using ICP. After heat treatment, SEM indicated a smooth and uniform CMP layer, with CMP grains of approximately 100 nm. The CMP phase was identified with δ-CMP (JCPDS #9-363). After immersion in SBF, coatings were observed to be roughened and porous. The concentration of Ca²⁺ in SBF was observed to increase over time, indicating continuous dissolution. The presence of titanium oxide phosphate compounds were also observed on CMP surfaces after immersion. It was thus concluded that the ability to control coating properties as well as the need for low heat treatment temperature offers advance for the use of CMP coating by sol–gel process on Ti-6Al-4V implant surfaces.     

Production of monodisperse cerium oxide microspheres with diameters near 100 µm by internal-gelation sol–gel methods

Internal-gelation sol–gel methods have used a variety of sphere-forming methods in the past to produce metal oxide microspheres, but typically with poor control over the size uniformity at diameters near 100?µm. This work describes efforts to make and measure internal-gelation, sol–gel microspheres with very uniform diameters in the 100–200-µm size range using a two-fluid nozzle. A custom apparatus was used to form aqueous droplets of sol–gel feed solutions in silicone oil and heat them to cause gelation of the spheres. Gelled spheres were washed, dried, and sintered prior to mounting them on glass slides for optical imaging and analysis. Microsphere diameters and shape factors were determined as a function of silicone oil flow rate in a two-fluid nozzle and the size of a needle dispensing the aqueous sol–gel solution. Nine batches of microspheres were analyzed and had diameters ranging from 65.5?±?2.4?µm for the smallest needle and the fastest silicone oil flow rate to 211?±?4.7?µm for the largest needle and the slowest silicone oil flow rate. Standard deviations for measured diameters were less than 8% for all samples and most of them were less than 4%. Microspheres had excellent circularity with measured shape factors of 0.9–1. However, processing of optical images was complicated by shadow effects in the photoresist layer on glass slides and by overlapping microspheres. Based on the calculated flow parameters, microspheres were produced in a simple dripping mode in the two-fluid nozzle. Using flow rates consistent with a simple dripping mode in a two-fluid nozzle configuration allows for very uniform oxide microspheres to be produced using the internal-gelation sol–gel method.

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Multifunctional hybrid nanopapers based on bacterial cellulose and sol–gel synthesized titanium/vanadium oxide nanoparticles

The hybrid inorganic/organic nanopapers based on bacterial cellulose and different type of sol–gel synthesized nanoparticles are fabricated. A simple, rapid, low-cost pathway based on a diffusion step of sol–gel nanoparticles into swollen bacterial cellulose membrane via orbital incubator is developed. This alternative pathway allows to keeping intact the 3D network of the bacterial cellulose membrane while sol–gel nanoparticles are formed in situ and anchored on the nanofibers surface. Titanium, vanadium oxide nanoparticles and a mixture of both are used to functionalize bacterial cellulose membrane. Fabricated hybrid inorganic/organic nanopapers are characterized by thermogravimetric analysis, X-ray diffraction spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, MTS mechanical testing, UV–vis spectroscopy, colorimeter and semiconductor analyzer. Synthesized photochromic hybrid nanopapers modified with vanadium and titanium oxide nanoparticles can find potential application as sensitive displays, biosensors and other optical devices.     

Thermal,chemical and antimicrobial characterization of bioactive titania synthesized by sol–gel method

Journal of Thermal Analysis and Calorimetry - Chemical stability, anticorrosive properties and photocatalytic activity of titanium dioxide (TiO2) are among the most important characteristics for...