Influence of platinum nano-particles on the photocatalytic activity of sol–gel derived TiO2 films

Different 1-step or 2-step photo-platinization methods have been implemented to load sol–gel TiO₂ photocatalytic thin films with platinum nano-particles. These methods enable flexible variations in the amount of loaded particles, and they strongly influence the structure and size of these particles and the morphology of derived platinized films. The photocatalytic activity of platinized films has been studied. It is shown that optimal platinization conditions allow envisaging thin film photocatalysts with enhanced properties. Best performances are reached when the films are loaded with platinum particles for 30 or 60 min using a 1-step platinization method, which yields photocatalytic activities about 4 times greater than that of non-platinized films. Photocatalytic activity differences induced by the 1-step or 2-step photo-platinization methods are discussed in relation to the amount of loaded platinum together with structural and morphological features.     

Structural characterization and frequency response of sol–gel derived Bi3/2MgNb3/2O7 thin films

The Bi_3/2MgNb_3/2O₇ (BMN) thin films were prepared via a modified sol–gel process on glass substrates at various post-annealing temperatures. The crystalline structure, morphology and frequency response have been investigated systematically. The X-ray diffraction results indicated that the BMN thin films had different orientations depending on post-annealing temperature. Thin films annealed above 650 °C presented well crystallized cubic pyrochlore structure with (222) orientation, and (400) preferentially oriented were observed when they were annealed below 600 °C. The surface morphology images of the BMN thin films revealed different grain size and grain size distribution, and the average grain size increased from 28.3 to 37.0 nm as the post-annealing temperature increasing. The low frequency dielectric properties of the BMN thin films were closely correlated with the (222) orientation, which was favorable to enhanced dielectric constant and tunability. The high-frequency optical measurements revealed an average transmittance (T _av ) varying between 76.6 and 82.2 % and band gap energy (E _g ) ranging from 3.40 to 3.44 as a function of the temperature and the crystallite size. Thin film annealed at 700 °C possessed the best crystallinity and highest (222) orientation, and showed the best electrical properties, with a dielectric constant of 105 at 1 MHz, dielectric tunability of 25.8 %, and an average optical transmittance of 82.2 % in the visible range (400–800 nm), making it promising for optical/electronic tunable devices applications.     

Morphology and crystal structure of CeO2-modified mesoporous ZrO2 powders prepared by sol–gel method

Mesoporous ZrO₂ powder modified by CeO₂ has been prepared by sol–gel method combined with novel heat-treatment without any templates. The morphology and crystal structure were characterized by Fourier transform infrared spectrophotometer (FT-IR), thermal gravimetry/differential thermal analysis (TG/DTA), X-ray diffraction (XRD), Raman spectroscope, N₂ absorption–desorption, scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM). It was demonstrated that the morphologies and crystal structures were varied with the CeO₂ content and calcination temperatures. Some circular grooves with diameter about 300–500 nm and thickness of 150–200 nm were observed for 30 mol% CeO₂ modified samples. Tetragonal ZrO₂ and cubic (Ce,Zr)O₂ solid solution were in turn observed with CeO₂ content increasing. The oxygen storage capacity (OSC) of the mesoporous powders was determined by thermalgravimetry (TG) under cyclic thermal treatments.     

Physico-chemical and electrochemical characterization of Ti/RhOx–IrO2 electrodes using sol–gel technology

Sol–gel technology has been successfully used for the incorporation of RhO_x–IrO₂ on a Ti substrate. RhO_x–IrO₂ was prepared from chloride precursors of Rh and Ir, for surface studies. These metal oxides were then immobilised on solid Ti substrates via dip withdrawal coating methods to form thin films. The Ti/RhO_x–IrO₂ thin films were extensively characterized in terms of surface characterization and chemical composition and used in the oxidation of phenol. Thermo-gravimetric analysis (TGA) determined the calcination temperature at 700 °C where no further structural changes occurred due to mass loss. The rhodium oxide showed two-phase formations, RhO₂ and Rh₂O₃, which were attributed to high calcinated temperatures compare to one phase IrO₂ which was stable at lower temperatures. The scanning electron microscopy (SEM) showed that the morphology of the film was found to be rough with a grain-like appearance in the 150-nm range. The phase composition of these metal oxides was determined by X-ray diffraction (XRD) technique and found to have crystalline structures. The results obtained from Rutherford backscattering spectrometry (RBS) revealed information regarding the chemical composition of the metal oxides and confirmed the diffusion of Rh and Ir into the Ti substrate. Electrochemical characterization of the Ti/RhO_x–IrO₂ electrode, via cyclic voltammetry (CV), showed distinctive redox peaks: anodic and cathodic peaks associated with the oxidation and reduction of the ferricyanide–ferrocyanide couple was seen at 250 and 100 mV respectively; the peak observed at 1000 mV was associated with oxygen evolution and a broad reductive wave at −600 mV can be ascribed to the Ti/RuO_x–IrO₂ reduction, which proved that the Ti/RhO_x–IrO₂ electrode were electroactive and exhibit fast electrochemistry.     

Adsorptive properties of sol–gel derived hybrid organic/inorganic coatings

Hybrid organic-inorganic sol–gel derived coatings have been prepared by dip coating on glass substrates from alcoholic solutions of tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), 3-aminopropyltriethoxysilane (APTES), 3-glycidoxypropyltrimethoxysilane (GPTMS) and phenyltriethoxysilane (PhTES). The hybrid materials have been fully characterized by means of solid state NMR spectroscopy and X-ray diffraction. The degree of cross-linking and the extent of interaction between silica and silsesquioxane phases appear dependent on the ratio between TEOS and organotrialkoxysilane and on the chemical features of the organic function linked to silicon, and influence the sorption ability towards aromatic compounds of hybrid films. The hybrid coatings have been put into an optical-grade quartz chamber placed into a UV–VIS–NIR spectrophotometer and the organic compounds have been allowed flowing through the chamber recording of molecule absorption spectra vs. time. Absorbance curves vs. time have also been collected at a fixed wavelength for different molecule-coating couples and simple kinetic models have been used for comparing the adsorption capability of the different films, which has been related to the chemical interactions between molecules and coatings.     

Phase and structural evolution of sol–gel synthesized ZrO2/Si thin films under heat treatment

ZrO₂/Si thin films were fabricated using a sol–gel technique, and the chemical state change and structural evolution from sol to gel to Zr oxide by heat treatment were investigated. The precursor sol was synthesized using a Zr-acetylacetonate (Zr-acac) precursor, spin-coated, dried on Si(100) substrates, and then annealed at 300–700 °C in air. With increased annealing temperature of the sol–gel-derived layer, Zr-acac decomposed into Zr-acetate, an amorphous ZrO₂ phase formed, and crystallization into a tetragonal phase occurred. In addition, the ZrO₂ layer became denser and the interfacial layer between ZrO₂ and Si thickened, whereas the surface morphology was nearly unaffected and remained smooth with root-mean-square values < 4.5 ?.     

Photocatalytic activity of nanostructured γ-Al2O3/TiO2 composite powder formed via a polyelectrolyte-multilayer-assisted sol–gel reaction

Nanostructured, γ-Al₂O₃/TiO₂ composite powder was fabricated via an in situ, sol–gel reaction of titanium iso-propoxide in a self-assembled, polyelectrolyte multilayer (PEM) formed on the surface of high-specific-area, polycrystalline, γ-Al₂O₃ lamellas. The infiltration of the titanium precursor into the PEM, followed by the hydrolysis and condensation reactions with the water absorbed in the PEM after annealing, resulted in the formation of a nanostructured TiO₂ layer on the surface of the γ-Al₂O₃ lamellas. Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were employed to evaluate the morphology, the chemical composition and the crystallinity of the γ-Al₂O₃/TiO₂ particles of the composite powder. The as-formed, nanostructured, γ-Al₂O₃/TiO₂ composite powder exhibited a 2.7-times-higher photo-activity in the near-UV region compared to commercially available TiO₂ (Degusa P25), as monitored by the photo-decomposition of a methylene blue (MB) dye.     

Dielectric properties of Fe-doped TiO2 nanoparticles synthesised by sol–gel route

Fe-doped nanocrystalline samples of titanium oxide have been synthesised by sol–gel route and conventional sintering process at 450°C under atmospheric conditions. These samples are characterised by X-ray diffraction (XRD), X-ray photoelectron spectroscopy, transmission electron microscopy (TEM) and dielectric property measurement. Samples with Fe content more than 4?mole% crystallises in rutile phase and those with less than 4?mole% crystallises in anatase phase. Nanocrystallite size has been controlled by Fe doping. Crystallite size was found to decrease with Fe concentration in the anatase phase samples whereas reverse happens in rutile phase samples of titanium oxide. There is a slight variation in numerical values of crystallite sizes measured by the two techniques: TEM and XRD peak broadening. The highest crystallite size was 86?nm in 10?mole% Fe-doped samples and the lowest 20?nm in 4?mole% Fe-doped sample. Large dispersions and anomalous values of the dielectric constant, εr were observed at low frequency in anatase phase samples. Rutile phase samples exhibit little dispersion over the measurement frequency range of 20?Hz to 10?MHz. The dielectric constant value of all the samples stabilises to a constant value at higher frequencies. This value is dependent on the final crystalline phase but independent of the crystallite size. The anomalous dielectric behaviour of anatase samples at low frequencies is assigned to the adsorbed –OH ions on the sample surface.     

Structural characterisation and antibacterial activity of PP/TiO2 nanocomposites prepared by an in situ sol–gel method

Polypropylene/titanium dioxide (PP/TiO₂) nanocomposites can be prepared using a novel method based on the hydrolysis–condensation reactions (sol–gel method) of titanium alkoxide inorganic precursors that have been premixed with polypropylene under molten conditions. The resultant nanocomposites were characterised by transmission electronic microscopy (TEM), X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). These techniques showed the formation of the titanium oxi-hydroxide chemical structure (Ti_xO_y(OH)_z) with a diameter of approximately 10 nm in the polymer matrix. Furthermore, a condensation degree of around 17% was determined using XPS analysis. The antibacterial activity was tested according to the JIS Z 2801:2000 standard with Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) in the absence of light. Correlations between the microstructure and the chemical composition of PP/TiO₂ nanocomposites and the antibacterial properties of these nanocomposites were discussed. The structure of titanium oxi-hydroxide derivative particles (Ti_xO_y(OH)_z) within the polypropylene matrix has been shown to impact strongly on the antibacterial properties in comparison with the results obtained with a dispersion of anatase titanium dioxide into the PP.     

An investigation of V2O5/polypyrrole composite cathode materials for lithium-ion batteries synthesized by sol–gel

A lamellar compound of V₂O₅ was prepared by a simple sol–gel method using H₂O₂ and V₂O₅ as starting materials. The composites of V₂O₅/PPy (polypyrrole) were synthesized by in situ polymerization, and characterized by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectrum, and X-ray diffraction (XRD). The electrochemical properties of the composites were investigated with galvanostatic charge–discharge test, cyclic voltammetry and A.C. impedance techniques. The results show that pyrrole was uniformly polymerized around the V₂O₅, and the V₂O₅/PPy composite possessed excellent electrochemical performance. The specific discharge capacity of the 2.5% mass percent PPy composites (271.8 mAh g⁻¹) was higher than that of pure V₂O₅ (247.6 mAh g⁻¹) at 0.1C rate and it has the voltage limits of 1.8–4.0 V. Furthermore, the specific discharge capacity remained at 225.4 mAh g⁻¹ after 50 cycles. The chemical diffusion coefficient D_Li⁺$D_{{\text{Li}}^{+}}$ values were calculated, depending on x-values in Li_x+1.1V₂O₅. The values of D_Li⁺$D_{{\text{Li}}^{+}}$ range from 2.18 × 10⁻¹² cm² s⁻¹ to 4.5 × 10⁻¹⁴ cm² s⁻¹ for V₂O₅/PPy composite, and it decreased as the amount of intercalated Li⁺ increased.     

Innovative one-step immobilization of TiO2 on polymer material by the sol–gel method under IL/MW conditions

An innovative one-step immobilization of titanium dioxide (TiO₂) nano-particles on organic polymer (PMMA) substrate at ambient condition is reported in this article. This immobilization can be achieved by the sol–gel method under ionic liquid/microwave heating conditions. In this method, a sol–gel reaction is conducted at specific sites of the polymer surface. These sites are the tiny cavities of the rough surface resulting from the softening and swelling effect of an alcohol, such as isopropyl alcohol, on the polymer surface under microwave irradiation. The roughness of the polymer surface is an important factor for the effective immobilization. In addition, ionic liquid can induce low temperature surface anatase crystallization of immobilized titanium dioxide in a short time. From the field emission scanning electron microscopy and energy dispersive spectroscopy observation, the TiO₂ particles could be effectively immobilized on the PMMA substrate. Raman spectra analysis data showed that the immobilized TiO₂ was anatase phase. The experimental data also shows that the immobilized TiO₂ prepared by this novel method has good immobilization stability and photocatalytic water treatment performance.     

Enhanced hydrophilicity of the Si substrate for deposition of VO2 film by sol–gel method

We have illustrated the role of hydrophilic nature of Si substrate played in the improvement of the contact performance between the vanadium dioxide (VO₂) film and Si substrate. The VO₂ films were fabricated by sol–gel method on single crystal Si substrate, which was pre-treated with hydrophilic solution and obtained a quite improved hydrophilicity. The bonding of Si substrate with precursor V₂O₅ gel was interpreted. The morphology and crystalline structure of the films were investigated by field-emission scanning electron microscopy, atomic force microscopy and X-ray diffraction. It is shown that the surface of the film on Si substrate with enhanced hydrophilicity is quite homogeneous and uniform. The film exhibits the formation of VO₂ phase with (011) preferred orientation. Moreover, the optical pump induced phase transition property of the film was studied by terahertz time-domain spectroscopy, which revealed around 70% reduction of transmission at 0.1–1.5?THz in the VO₂ film across the phase transition.     

Properties of sol–gel synthesized n-ZnO/n-GaN (0001) isotype heterojunction

The electronic and optical properties of sol–gel synthesized n-ZnO/n-GaN (0001) isotype heterojunction were reported. By incorporating ZnO–GaN with the same wurtzite structure and the similar lattice constant, a heterojunction was fabricated. The junction properties were evaluated by measuring the electrical characteristics. The n-ZnO/n-GaN heterostructure exhibits a non-ideal I–V behavior with the ideality factor greater than unity that could be ascribed to the interfacial layer, interface states and series resistance. The forward turn on voltage is about 0.7 V and the reverse breakdown voltage is more than 2 V. The optical band gaps of the ZnO film and GaN using optical absorption method were found to be 3.272 eV and 3.309 eV, respectively. The fundamental absorption edge in the film is formed by the direct allowed transitions.     

Characterization of TiO2 nanoparticles prepared using different surfactants by sol–gel method

Titania nanoparticles have been prepared using different surfactants such as, acetic acid (AA), oleic acid (OA), oley amine (OM), and a mixture of OA + OM at room temperature by sol–gel method. TiO₂ nanoparticles were collected by centrifugation of the precipitate obtained during gel formation. The collected samples were annealed at 550 and 950 °C to study the effect of annealing temperature on the structural and optical properties. The crystal structure and optical properties of titania nanoparticle is investigated by means of X-ray diffraction, Raman spectroscopy, UV–visible spectroscopy, and photoluminescence. After heat treatment at 950 °C, the mixed rutile and anatase phase of TiO₂ was revealed for the sample prepared with AA, whereas pure rutile phase was observed for the sample prepared in presence of OA, OM and the mixture of OA + OM. The energy band gap and transmittance of measured for titania nanoparticles was found to be systematically reduced with increase in annealing temperature for each surfactant. The ideality factor decreases with increase in annealing temperature for all surfactants could be related to the voltage dependence of the standard deviation of the distribution of barrier heights.     

Characterization and catalytic activity studies of sol–gel Co–SiO2 nanocomposites

Silica embedded with transition metals exhibits adequate properties for applications in catalysis, sensors and optics. Cobalt–silica (Co–SiO₂) nanocomposites were prepared by the sol–gel method and thermally treated at 700, 900, 1100 and 1250 °C. Characterization of the samples was performed by XRD and BET nitrogen adsorption. The performance of the nanocomposites was investigated by catalysis reactions of oxidation. These catalysts were found to be recyclable showing a catalytic activity even after a third recovering. The results indicate that thermal treatment of sol–gel nanocomposites at temperatures higher than 900 °C is essential for the preparation of active heterogeneous catalysts.     

Preparation and characterization of Ce0.95Zr0.05O2 nanopowders obtained by sol–gel and template methods

Ce_0.95Zr_0.05O₂ nanopowders have been prepared by a standard Pechini-type sol–gel process and by using polymethyl methacrylate (PMMA) colloidal crystals as template. The effects of these different synthesis routes, on the structure and microstructural features of the nanopowders, were evaluated by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and specific surface area measurements. For both preparation routes, the XRD analysis has shown that a cubic fluorite structure is formed with a crystallite size of ∼45–50 nm. The SEM images indicate that the powder obtained by the sol–gel Pechini-type process, is constituted by aggregated nanoparticles with relatively uniform shape and size, whereas the powder synthesized as inverse opal exhibits the formation of macropores with a mean size of ∼130 nm. The specific surface areas of the powder samples obtained by the Pechini-type sol–gel and inverse opal methods are ∼56 m² g⁻¹ and ∼90 m² g⁻¹ respectively. Additionally, the thermoluminescence (TL) signal of the synthetized samples has been measured in order to examine its potential application in the field of dosimetry of ionizing radiations.     

The preparation and properties of CeO2–TiO2 film by sol–gel spin-coating process

Ultraviolet absorbing CeO₂–TiO₂ coatings were prepared by the sol–gel spin-coating process heat treated at 500 °C. The films obtained were brilliant yellow, adherent and had some pattern on the soda-lime glass substrate. The optical transmittance, thickness and hardness of the films as a function of the number of coatings, aging time (0, 24, 48, 96 h) or aging temperature (28, 35, 40, 50 °C) were determined, and surface microstructure of the films was observed by SEM. We found some pattern on the surface of films. This pattern was similar to that of the stage for fixing the substrate. The pattern on the surface of films would be caused by the difference of thermal conductivity to slide glass in the part of metal of the stage and hollow part of the stage.     

Dielectric enhancement of BaTiO3/BaSrTiO3/SrTiO3 multilayer thin films deposited on Pt/Ti/SiO2/Si substrates by sol–gel method

Polycrystalline BaTiO₃/Ba_0.6Sr_0.4TiO₃/SrTiO₃ (BT/BST/ST) multilayer thin films with different periodicities have been deposited on Pt/Ti/SiO₂/Si substrates by using a sol–gel method. The multilayer thin films were crack free, compact and crystallized in a perovskite structure. The dielectric constant of the multilayer thin films was significantly increased and the dielectric loss was almost the same as those of uniform BT, ST and BST thin films. The dielectric constant increased with increasing stacking periodicity as the thickness of each individual layer decreased. The multilayer thin films showed excellent dielectric properties and can be promisingly used for the dielectric layer of silicon-based embedded capacitors in package substrate.     

Characterization of Li2MnSiO4 and Li2FeSiO4 cathode materials synthesized via a citric acid assisted sol–gel method

Two members of the family of orthosilicate, Li₂FeSiO₄ and Li₂MnSiO₄, are prepared by a citric acid assisted sol–gel method. As cathode materials for lithium-ion batteries, their structural, morphological and electrochemical characteristics are investigated and compared. Both cathode materials have nanoparticles with similar lattice parameters. Li₂FeSiO₄ has a maximum discharge capacity of 152.8 mAh g⁻¹, and 98.3% of its maximum discharge capacity is retained after fifty cycles. However, the discharge capacity of Li₂MnSiO₄ fades rapidly and stabilized at about 70 mAh g⁻¹ after twenty cycles. The electrochemical impedance and differential capacity analysis indicate that Li₂MnSiO₄ has larger charge transfer impedance and higher electrochemical irreversibility than Li₂FeSiO₄, which makes its electrochemical behaviors seriously deteriorate and leads to difference between two silicate materials.