Micro- and nanocomposite particles of the Cu–TiO<Subscript>2</Subscript> system

The micro- and nanocomposite particles of the Cu–TiO₂ system are synthesized using the laser scanning of a heliumlike film. A model of nanostructure formation on a dielectric surface is proposed.     

Self-cleaning performance of sol–gel-derived TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> double-layer thin films

The self-cleaning properties of the TiO₂/SiO₂ double-layer films prepared by sol–gel method were investigated. Thin films were prepared by spin coating onto glass and then thermally treated at different temperatures, and characterized using X-ray diffraction, atomic force microscopy, field emission scanning electron microscopy, and UV–visible spectroscopy. The cross-sectional structure of the films was observed by FESEM. The surface roughness of the films was characterized by AFM. The root mean square surface roughness of the thin films was below 2 nm, which should enhance their optical transparency. The photo-induced hydrophilicity of the films was evaluated by water contact angle measurement in air. The photocatalytic activity of the films was studied by the photocatalytic degradation of methylene blue under UV light irradiations. The TiO₂/SiO₂ double-layer thin films are plausibly applicable to developing self-cleaning materials in various applications such as windows, solar panels, cement, and paints.     

Electrodeposited Zn–TiO<Subscript>2</Subscript> nanocomposite coatings and their corrosion behavior

The present paper aims to investigate the electrodeposition on steel substrate and the corrosion behavior of Zn–TiO₂ nanocomposite coatings. Zn–TiO₂ composite coatings were electrodeposited on OL 37 steel from an electrolyte containing ZnCl₂, KCl, HBO₃ (pH 5.7) brightening agents and dispersed nanosized TiO₂. Corrosion measurements were performed in 0.2 g L⁻¹ (NH₄)₂SO₄ solution (pH 3) by using electrochemical methods (open-circuit potential measurements, polarization curves, electrochemical impedance spectroscopy). The results of electrochemical measurements were corroborated with those obtained by using non-electrochemical methods (X-ray diffraction, atomic force microscopy and scanning electron microscopy). The results indicate that the composite coatings exhibit higher corrosion resistance as compared to pure Zn coatings and a non-linear dependence of their polarization resistance on TiO₂ concentration in the plating bath was found. The importance of TiO₂ nature and concentration regarding the properties of the composite coatings was demonstrated.     

Structural analyses of RuO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>/Ti and IrO<Subscript>2</Subscript>–RuO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>/Ti anodes used in industrial chlor-alkali membrane processes

The morphology and composition of RuO₂–TiO₂/Ti and IrO₂–RuO₂–TiO₂/Ti anodes, which have been used for the production of chlorine for more than 10 years, were analyzed by various methods; such as high-resolution scanning electron microscopy, high-resolution Auger electron spectroscopy, electron probe X-ray emission microanalysis and X-ray diffraction analysis. Drastic changes in the surface morphology, including partial exfoliation of a small amount of the oxide layer and a reduction in the content of ruthenium species through dissolution, were observed for the RuO₂–TiO₂/Ti anode. For the IrO₂–RuO₂–TiO₂/Ti anode, on the other hand, there were moderate changes in the surface morphology and moderate dissolution of iridium and ruthenium species.     

Fabrication of mesoporous TiO<Subscript>2</Subscript> with high crystallinity by a fast sol–gel method

Mesoporous TiO₂ samples with high crystallinity were successfully synthesized by a fast sol–gel method using polyethylene glycol (PEG) and polyacrylamide (PAM) as dual templates using two-step calcining process. As a comparison, the sample was synthesized by traditional sol–gel method using hexadecyl trimethyl ammonium bromide as the template. The samples were characterized by X-ray diffraction, transmission electron microscopy, N₂ adsorption–desorption, and diffuse reflectance UV–visible absorption spectra. The results showed that when samples were prepared at 500–700 °C in nitrogen atmosphere and 500 °C in air atmosphere, they exhibited typical mesoporous structure, large specific surface area and high crystallinity. The effects of PEG on properties of the samples and the effect of PAM on sol–gel reaction rate were studied. The results show that PAM accelerates gel rate and PEG increases specific surface area of samples. The crystallinity of the samples was increased by using two-step calcining process. Compared with sample synthesized by traditional sol–gel method, visible light response and photocatalytic activity of sample synthesized by the fast sol–gel method were improved.     

Preparation and electrochemical characterization of LiNi<Subscript>0.8</Subscript>Co<Subscript>0.2</Subscript>O<Subscript>2</Subscript> cathode material by a modified sol–gel method

LiNi_0.8Co_0.2O₂ cathode powders for lithium-ion batteries were prepared by a modified sol–gel method with citric acid as chelating agent and a small amount of hydroxypropyl cellulose as dispersant agent. The structure and morphology of LiNi_0.8Co_0.2O₂ powders calcined at various temperatures for 4 h in air were characterized by means of powder X-ray diffraction analyzer, scanning electron microscope, thermogravimetric analyzer and differential thermal analyzer, and Brunauer–Emmett–Teller specific surface area analyzer. The results show that LiNi_0.8Co_0.2O₂ powders calcined at 800 °C exhibit the best layered structure ordering and appear to have monodispersed particulates surface. In addition, the electrochemical properties of LiNi_0.8Co_0.2O₂ powders as cathode material were investigated by the charge–discharge and cyclic voltammetry studies in a three-electrode test cell. The initial charge–discharge studies indicate that LiNi_0.8Co_0.2O₂ cathode material obtained from the powders calcined at 800 °C shows the largest charge capacity of 231 mAh g⁻¹ and the largest discharge capacity of 191 mAh g⁻¹. And, the cyclic voltammetry studies indicate that Li⁺ insertion and extraction in LiNi_0.8Co_0.2O₂ powders is reversible except for the first cycle.     

Synthesis and characterization of CuInSe<Subscript>2</Subscript> core–shell quantum dots

A synthesis of 1-dodecanetiol stabilized colloidal quantum dots of CuInSe₂ exhibiting photoluminescence in the range of 700–900 nm has been described. The effect of the shell on the energy levels of electrons in CuInSe₂–ZnS and CuInSe₂–ZnSe core–shell quantum dots has been investigated by quantum mechanical calculations.     

Synthesis and physicochemical properties of a solid oxide nanocomposite based on a ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>–MgO system

A highly dispersive powder with a (ZrO₂)_0.92(Y₂O₃)_0.03(Gd₂O₃)_0.03(MgO)_0.02 composition and specific surface area of 150 m²/g has been synthesized via a method of coprecipitation of hydroxides with the subsequent cryochemical treatment of the gel. Nanoceramics based on the cubic modification of zirconium dioxide with the grain size of ~40–45 nm have been obtained. The temperature dependence of the specific electrical conductance of the nanoceramics within a temperature range of 350–870°C in air has been studied, and the ratio of the ionic and electronic parts of the conductance has been determined. Recommendations for the use of the obtained oxide nanocomposite as an electrolyte for a high-temperature fuel cell have been given.     

Synthesis and characterization of nanocomposites Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>–SiO<Subscript>2</Subscript>–chitosan based on lbl technology

In this paper, the apparent chain-like core-shell structure Fe₃O₄–SiO₂–chitosan nanoparticles was synthesized by two-step method with cross-linking action of glutaraldehyde based on layer-by-layer technology, the composite particles were characterized by IR, XRD, TEM, SEM, EDS and VSM analytical methods, and the synthesis conditions of the product were studied. The results indicated that the diameter of the composite particles is about 106.5 nm, the parietal layer of chitosan is 20 nm, and after crosslinking action of glutaraldehyde, chitosan uniformaly coated the outer surface of Fe₃O₄–SiO₂.     

One-Dimensional Photonic SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript> Crystals: Simulation and Synthesis by Sol–Gel Technology Methods

The approach to synthesize one-dimensional photonic SiO₂–TiO₂ crystals by sol–gel methods is developed. Using the method of transfer matrices, structures consisting of 13 layers of alternating materials having the properties of one-dimensional photonic crystals with the minimal transmission coefficient of 7% in the photonic band gap range and that of 97.5% in the remaining spectrum parts are calculated and experimentally created. The positions of the photonic band gaps change along with the thicknesses of the layers of the materials composing the photonic crystal. The possibility of creating an optical filter as a result of introducing a structural defect in the form of a layer of doubled thickness is demonstrated.     

Synthesis and characterization of Ni–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite coatings containing different forms of alumina

Electrodeposited Ni–Al₂O₃ composite coatings were prepared using alumina powders synthesized from solution combustion method, precipitation method and a commercial source. Solution combustion synthesized alumina powder yielded α-phase; precipitation method yielded purely γ-phase; commercial alumina powder was a mixture of α-, δ- and γ-phases. A nickel sulfamate bath was used for electro-codeposition. The current densities (0.23 A dm⁻² for 20 h, 0.77 A dm⁻² for 6 h, 1.55 A dm⁻² for 3 h and 3.1 A dm⁻² for 1.5 h) and bath agitation speeds (100, 200, 600 and 1000 rpm) were varied. The pH variations of the bath were higher during the electrodeposition of combustion synthesized alumina. The effect of different forms of alumina particles on the microhardness and microstructure of the nickel composite coating was studied. Composite coating containing combustion synthesized alumina particles was found to have higher microhardness (550 HK). It was found that at lower agitation speed (100 rpm), bigger particles were incorporated and at higher agitation speed (1000 rpm), smaller particles were incorporated. The area fraction of alumina particles incorporated in nickel matrix was highest for commercial alumina (24%). This study shows that it is not suffice to take just the current density and stirring speeds into account to explain the properties of the coatings but also to take into account the source of particles and their properties.     

Synthesis of the study of solid solutions based on the ZrO<Subscript>2</Subscript>–HfO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>(CeO<Subscript>2</Subscript>) system

The results of the studies of the conditions of the liquid-phase synthesis of highly dispersed xerogels with a low degree of agglomeration and precursor nanopowders (~10–12 nm) based on zirconium dioxide in the ZrO₂–HfO₂–Y₂O₃(CeO₂) system are presented. The thermal decomposition of xerogels and formation of crystalline solid solutions with the structure of fluorite are investigated. The optimal conditions for the solidification of nanodispersed powders for fabricating compact ceramics based on solid solutions of ZrO₂ and the physical–chemical properties of these ceramics are studied.     

Timing of polyethylene glycol addition for the control of SiO<Subscript>2</Subscript> sol structure and sol–gel coating properties

Polyethylene glycol (PEG) was added during the sol process of sol–gel SiO₂ coating preparation to investigate the effect of PEG addition timing on particle growth, sol structure, and coating properties. When PEG was added before the addition of the catalyst, the particle size increased from 10 nm (in sol without PEG) to 20 nm, and the necessary aging time for dip coating was shortened from 5 days (in sol without PEG) to ~30 h. When PEG was added 24 h later than the catalyst, the uniform sol structure and small particle unit were obtained. With the delay of the PEG addition timing to 120 h, the improvement in the homogeneity of the sol was continued, whereas the porosity of the resulting coatings decreased. The refractive index of PEG-modified SiO₂ coatings can be adjusted in a continuous range between 1.14 and 1.20, using the timing when the PEG was added. The highest peak transmittance of glass that was coated with PEG-modified silica coatings reached 99.90%. All the coatings can be changed from hydrophilic to hydrophobic after hexamethyldisilazane vapor modification.     

Formation and stability of glasses with ultra-optical properties in TiO<Subscript>2</Subscript>–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–PbO system

To obtain ultra-optical property in glasses, as the basis for photonic applications, the glass forming region of TiO₂–Bi₂O₃–PbO system was investigated and determined by melting series of compositions in the system. The glass-forming boundary region was defined. The best compositions for glass formation were found to be around the eutectic and peritectic regions in the corresponding phase diagram. Generally, stability increased with the addition of TiO₂, acting as a conditional glass former, to a maximum of 15TiO₂ mol %. Replacing PbO with Bi₂O₃ in the glass worsened the stability, due to the increase of heavy cation Bi^3– in the glass structure. Finally, the refractive index and dispersion of some stable glasses were measured, which were as high as 2.435 and 10.2, respectively.     

Preparation and characterization of spindle-shaped nanoporous anatase TiO<Subscript>2</Subscript>–Ag<Subscript>3</Subscript>PO<Subscript>4</Subscript> heterostructure with enhanced visible light driven photocatalytic performance

A novel spindle-shaped nanoporous anatase TiO₂–Ag₃PO₄ heterostructure with high photocatalytic activity was successfully prepared by a simple method. The Ag₃PO₄ nanoparticles with a diameter of 20–50 nm were deposited on the surface of the spindle-shaped TiO₂. The effect of Ag₃PO₄ nanoparticles amounts on the photocatalytic activity was investigated. The results showed that the TiO₂–Ag₃PO₄ composite with the mass ratio of TiO₂:Ag₃PO₄ = 1:2 displayed the highest photodegradation efficiency of methylene blue (MB) and Bisphenol A (BPA), which was more highly than that of Ag₃PO₄ nanoparticles and also indicated a high stability of photocatalytic degradation. The improved activity of the TiO₂–Ag₃PO₄ composite could be attributed to the efficient separation of the photogenerated electron–hole pairs.     

Physico-Chemical Properties of Cobalt–Ruthenium (10% Co–0.5% Ru) Catalysts Supported on Binary Oxides 8.5%ZrO<Subscript>2</Subscript>/Support (SiO<Subscript>2</Subscript>, Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, TiO<Subscript>2</Subscript>) for Fischer-Tropsch Synthesis

The promotion of Fischer-Tropsch catalysts 10%Co/Al₂O₃, 10%Co/SiO₂, 10%Co/TiO₂ by 0.5% Ru and the modification of supports by 8.5 wt% ZrO₂ have been studied. The following properties: catalyst specific surface area as well as reducibility and dispersion of metallic phase were studied by different techniques: BET, TPR, and H₂ chemisorption. The modification of supports by non-reducible ZrO₂, results in a decrease of cobalt oxide reduction on Al₂O₃ and TiO₂ but not on SiO₂ supports. Additionally the enhancement of cobalt dispersion was found for all catalysts with ZrO₂ modified supports. The impact of Ru promotion is likely due to the stabilization of applied supports, prevention or blockage of interaction between surface Co species and support and an increase in cobalt oxide reducibility to the catalytically active metallic cobalt phase.     

Chemical Synthesis and Characterization of ZnO–TiO<Subscript>2</Subscript> Semiconductor Nanocomposites: Tentative Mechanism of Particle Formation

The compounds of ZnO–TiO₂ can combine the characteristics of the individual oxides which has allowed them to be used as photocatalysts in general, photodegradants in the degradation of dyes, photocatalytic oxidation of NO_x, antimicrobial, among other applications. In this study, ZnO–TiO₂ semiconductor nanocomposites were synthesized in a controlled way at low temperature. These samples of ZnO–TiO₂ were characterized using thermal analysis (TDA/TGA), IR and UV–Vis absorption spectroscopies, X-ray diffraction, and scanning electron microscopy. The primary particles showed a nanometric size (<?100 nm) and spheroidal morphology. All samples presented zincite as the main crystalline phase. When Ti⁴⁺ was added, the peaks of the diffractograms shifted slightly with respect to pure ZnO. This indicates the formation of a solid solution. Zn₂TiO₄ was observed in doped ZnO samples treated at 700 °C. The UV–Vis absorption spectra showed a band in the range between 350 and 425 nm, with a maximum around 375 nm (3.31 eV). With the addition of Ti⁴⁺, the nanocomposites showed a better absorbance in the visible range. Considering the nature of the synthesis process used, a mechanism was proposed to explanation of the formation of Nanocomposites.