Synthesis and photocatalytic activity of mesoporous SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>

Mesoporous SiO₂–TiO₂ was synthesized by the sol–gel method using Si(OC₂H₅)₄, Ti(OC₂H₅)₄, and stearyltrimethylammonium chloride. By using acetylacetone as the capping agent of Ti(OC₂H₅)₄, homogeneous SiO₂–TiO₂ composite was obtained. Spherical mesoporous SiO₂–TiO₂ was also synthesized by the sol–gel method using W/O emulsion under microwave irradiation. The specific surface area of these mesoporous SiO₂–TiO₂ materials decreased when the Ti/Si molar ratio was higher than 0.1, which indicated that Ti was homogeneously distributed in mesoporous SiO₂ matrix at Ti/Si ≦ 0.1. The photocatalytic activity of mesoporous SiO₂–TiO₂ materials was investigated by the degradation of methylene-blue in water under UV light irradiation. Mesoporous SiO₂–TiO₂ was effective for the adsorption–decomposition of methylene-blue.     

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.     

Physicochemical properties of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> xerogel modified by hydrogen peroxide

How the specific surface area and the amorphous-to-crystalline titania phase ratio in TiO₂–SiO₂ (14 mol % TiO₂) xerogels change during the fivefold repeated cycles comprising the hydrogen peroxide treatment of the xerogel followed by drying and calcining of the binary material, was traced by the BET method, X-ray powder diffraction, and IR spectroscopy.     

Photocatalytic degradation of metoprolol in water suspension of TiO<Subscript>2</Subscript> nanopowders prepared using sol–gel route

Nanocrystalline titanium dioxide (TiO₂) powders have been synthesized by sol–gel method using titanium tetrachloride (TiCl₄) or tetrabutyl titanate (Ti(OC₄H₉)₄ as precursors, different alcohols and calcination temperatures in the range from 400 to 650 °C. The photocatalytic activity of as-prepared powders has been tested for the degradation of metoprolol tartrate salt, a selective β-blocker used to treat a variety of cardiovascular diseases, and compared to photocatalytic activity obtained from Degussa P25. Nanosized TiO₂ powders prepared from TiCl₄ and amyl-alcohol, calcined at 550 °C, displayed an activity comparable to Degussa P25, whereas the sample from the same series, calcined at 650 °C, showed higher photocatalytic activity in the whole range of the catalyst loading. Structural, morphological and surface properties of synthesized TiO₂ nanopowders have been investigated by XRD, SEM, EDS and BET measurements, as well as FTIR and Raman spectroscopy, in order to find out the material properties which enable rapid an efficient decomposition of metoprolol under UV radiation.     

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.     

Photoelectrochemical performance of bilayered Fe–TiO<Subscript>2</Subscript>/Zn–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films for solar generation of hydrogen

A visible-light sensitive bilayered photoanode of Fe–TiO₂/Zn–Fe₂O₃ has been developed by spray pyrolytically depositing Zn–Fe₂O₃ layers onto predeposited Fe–TiO₂ thin film on ITO substrate. Fe–TiO₂/Zn–Fe₂O₃ photoelectrodes were characterized by XRD, Raman, AFM, UV-vis absorption spectroscopy. Photoelectrochemical properties of bilayered Fe–TiO₂/Zn–Fe₂O₃ photoelectrode were studied by Mott–Schottky curves and I–V characteristics. Bilayered Fe–TiO₂/Zn–Fe₂O₃ photoelectrode was observed to possess much higher separation efficiency of photogenerated charge carriers and could generate nine times better photocurrent density than pure Fe–TiO₂. Solar to hydrogen conversion efficiency exhibited by this electrode was 0.77%.     

Preparation of diatomite–TiO<Subscript>2</Subscript> composite for photodegradation of bisphenol-A in water

To enhance the photodegradation performance of pure titanium dioxide (TiO₂), diatomite was used as a porous carrier to immobilize TiO₂ powders using calcination method. The photodegradation of bisphenol-A (BPA; 4,4′-isopropylidenediphenol), which has been listed as one of endocrine disrupting chemicals, was carried out in a batch suspension reactor using pure TiO₂ powders and diatomite–TiO₂ composites, respectively. Under the controlled conditions, the photocatalytic efficiencies of the BPA degradation by the diatomite–TiO₂ composites can be found to be higher than those by pure TiO₂ powders. This result should be attributable to the accessibility of the BPA molecules to the surface of TiO₂ particle in the modified photocatalysts, showing that the enrichment of the organic solute enhanced the rate of photodegradation on the diatomite–TiO₂ composite. However, the photodegradation efficiency was not dependent on the pore properties of these TiO₂ photocatalysts. The experimental results further indicated that the photodegradation kinetics for the destruction of BPA in water followed the first-order model well. The apparent first-order reaction constants (k _obs), thus obtained from the fittings of the model, were in line with the destruction-removal efficiencies of BPA in all the photocatalytic experiments.     

Layer-by-layer deposition of open-pore mesoporous TiO<Subscript>2</Subscript>-Nafion® film electrodes

The formation of variable thickness TiO₂ nanoparticle-Nafion® composite films with open pores is demonstrated via a layer-by-layer deposition process. Films of about 6 nm diameter TiO₂ nanoparticles grow in the presence of Nafion® by “clustering” of nanoparticles into bigger aggregates, and the resulting hierarchical structure thickens with about 25 nm per deposition cycle. Film growth is characterized by electron microscopy, atomic force microscopy, and quartz crystal microbalance techniques. Simultaneous small-angle X-ray scattering and wide-angle X-ray scattering measurements for films before and after calcination demonstrate the effect of Nafion® binder causing aggregation. Electrochemical methods are employed to characterize the electrical conductivity and diffusivity of charge through the TiO₂-Nafion® composite films. Characteristic electrochemical responses are observed for cationic redox systems (diheptylviologen^2+/+, \({\text{Ru}}{\left( {{\text{NH}}_{3} } \right)}^{{3 + /2 + }}_{6} \), and ferrocenylmethyl-trimethylammonium^2+/+) immobilized into the TiO₂-Nafion® nanocomposite material. Charge conduction is dependent on the type of redox system and is proposed to occur either via direct conduction through the TiO₂ backbone (at sufficiently negative potentials) or via redox-center-based diffusion/electron hopping (at more positive potentials).     

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.     

SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript> xerogels for tailoring the release of brilliant blue FCF

Xerogels consisting of SiO₂ and TiO₂ were explored for controlled release of brilliant blue FCF (BBF). Both SiO₂ and SiO₂–TiO₂ xerogels were prepared by way of sol–gel processing, and the BBF release behavior was compared. SiO₂–TiO₂ xerogels with varying TiO₂ content were also studied and the BBF release behavior was determined for each SiO₂–TiO₂ xerogel. It was found that the release of BBF from SiO₂ xerogels can be increased by the addition of TiO₂ content, and the amount and rate of BBF released from the SiO₂–TiO₂ xerogels can be changed by modifying the amount of TiO₂ included during the preparation of the xerogels, where the SiO₂–TiO₂ xerogels with a higher content of TiO₂ released a higher fraction of BBF in water media when compared to the release from SiO₂–TiO₂ xerogels with lower amounts of TiO₂. The experimental results have to be explained by a combination of porous structure, in situ dissolution–condensation during the BBF elution and the change of surface chemistry of the xerogel network with the addition of TiO₂.     

Photocatalytic and photoelectrocatalytic degradation of metoprolol tartrate in aqueous media by recyclable Co doping Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/TiO<Subscript>2</Subscript> magnetic core–shell nanocomposites

Magnetically recoverable cobalt doping Fe₃O₄/TiO₂ magnetic nanocomposites with an acceptable core–shell structure were prepared via a sol-gel process at low calcination temperature. The crystalline size and structure, morphology, and magnetic properties of resulting particles have been characterized by X-ray diffraction (XRD), fourier transform infrared (FT-IR), FT-Raman, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and vibrating sample magnetometry (VSM). Metoprolol tartrate (MET) as a pharmaceutical pollutant was used to observe the photocatalytic degradation ability of the magnetically recoverable particles. The process of degradation under UV irradiation at controlled temperature was studied and the remaining concentrations of MET as a contaminant were measured by UV-Vis spectrometer at λ = 229 nm. This ability remained 95.76% after three times of repetitive use at the same conditions. Various parameters such as reaction temperature, pH, and speed of stirring of the aqueous solution had an effect on the rate of degradation. The amount of cobalt dopant and nanocomposites are also effective on the rate of degradation. Coupling of electrical current with photocatalytic process has proven to be effective in the degradation of MET aqueous solution clearly.     

The effect of synthesis conditions on the structure of compounds formed in the Dy<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> system

Crystallization and phase transition processes taking place in the Dy₂O₃–TiO₂ system during the isothermal annealing of the precursors synthesized by co-precipitation were studied. The phase composition of the obtained powders is determined by not only the chemical composition of the precursor (Dy₂O₃: TiO₂ ratio) and annealing temperature but also by the procedure of precursor synthesis determining the uniformity of Dy and Ti distribution in the precursor precipitate. Higher homogeneity of precursor particles provides the formation of almost single-phase nanocrystaline dysprosium titanate (Dy₂TiO₅, Dy₂Ti₂O₇) powders at annealing temperatures of 800–1000°C.     

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.     

Functional SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>–PEG hybrid resin by direct chelation with catecholic compound

The mesoporous inorganic–organic SiO₂–TiO₂–PEG hybrid resin systems with various useful functionalities were directly synthesized by a binary sol–gel reaction of TEOS–TiCl₄ and the subsequent chelation with a chatecholic compound (dihydroxy benzene), dihydroxy-m-benzenedisulfonic acid disodium salt, on the surface Ti ion of the ordered mesoporous SBA-15 network structure, respectively. Moreover, the hybrid resins consisting of polyethylene glycol and a silane coupling agent exhibited the controlled wettability, excellent coating processibility on various substrates with strong abrasion resistance. Furthermore, the transparent and low viscous resin showed the successful performance to fabricate various nanoscale patterns with the feature size down to 170 nm by imprint lithography. Based on the excellent patternability, nanofluidics with 100 nm of the narrowest dimension channel height was fabricated to employ a capillary electrophoresis for separation DNAs without gel matrix. In addition, the presence of sulfonic acid in the resin also showed the solid acid catalytic performance. These results reveal that the developed hybrid materials are very useful as an imprint resin as well as versatile microchemical applications.     

Sol–Gel Derived Rh/TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> Nanocomposite Membranes

A porous borosilicate substrate has been coated with base catalysed SiO₂ sol–gel nanoparticles. Onto these were deposited the vapour of titanium isopropoxide, where it reacted with the surface OH groups to give a TiO₂-overcoat. This nanocomposite sol–gel derived TiO₂/SiO₂ membrane was then doped with 1%Rh giving Rh/TiO₂/SiO₂ membranes. These are shown to be coherent and crack-free, to have good permeability and activity in the isomerisation of butanes. It appears that sol–gel chemistry will allow such membranes to be totally engineered at a nm level.     

Preparation and activity evaluation of relative p–n junction photocatalyst Co-TiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript>

Co-TiO₂ photocatalyst was prepared by a sol–gel method using Co(NO₃)₂ · 6H₂O and tetrabutyl titanate [Ti(OC₄H₉)₄] as raw materials, and Co-TiO₂/TiO₂ photocatalyst was synthesized by mixing the Co-TiO₂ sol with TiO₂ sol. The Co-TiO₂/TiO₂ was characterized by X-ray powder diffraction, UV–Vis diffuse reflection spectrum, scanning electron microscopy, transmission electron microscopy, fluorescence spectra and X-ray photoelectron spectroscopy. The photocatalytic activity of the photocatalyst was evaluated by photocatalytic reduction of Cr₂O₇ ²⁻ and photocatalytic oxidation of methyl orange under UV irradiation. The results showed that, for the photocatalytic reduction of Cr₂O₇ ²⁻, the optimum percentage of Co-doped for the Co-TiO₂ was 0.5% (mole ratio of Co/Ti), and the optimum percentage of Co-TiO₂ for the Co-TiO₂/TiO₂ was 2.0% (mole ratio of Co-TiO₂/TiO₂). The photocatalytic reduction activities of the Co-TiO₂/TiO₂ and Co-TiO₂ are much higher than that of TiO₂. However, the photocatalytic oxidation activities of the Co-TiO₂/TiO₂ and Co-TiO₂ are much lower than that of TiO₂. Effects of heat treatment on the photocatalytic activities of the Co-TiO₂/TiO₂ and Co-TiO₂ were investigated. The mechanisms of influence on the photocatalytic activity were also discussed.     

Diagram of the PbF<Subscript>2</Subscript>–SnF<Subscript>2</Subscript> system

A phase diagram of the PbF₂–SnF₂ system has been studied by differential thermal analysis and X-ray powder diffraction. The system forms Pb_1–хSn_хF₂ (х ≤ 0.33) solid solution and three compounds. Pb₂SnF₆ decomposes in solid state by a peritectoid reaction at 350°С; Pb₃Sn₂F₁₀ and PbSnF₄ melt by peritectic reactions at 565 and 380°С, respectively. The eutectic coordinates are 180°С, 90 mol % SnF₂.     

Calorimetric study of the acidic character of V<Subscript>2</Subscript>O<Subscript>5</Subscript>–TiO<Subscript>2</Subscript>/SO<Subscript>4</Subscript><Superscript>2−</Superscript> catalysts used in methanol oxidation to dimethoxymethane

The surface acidic properties of sulfated vanadia–titania catalysts prepared by various methods were investigated by adsorption microcalorimetry, using ammonia as probe molecule. The acidic characteristics of the samples were shown to be strongly affected by the preparation method, calcination temperature, and sulfur content. The samples prepared by sol–gel and mechanical grinding exhibited higher acidity than co-precipitated samples. Moreover, increasing the calcination temperature of co-precipitated samples resulted in a decrease in surface area from 402 to 57 m² g⁻¹ and sulfur content from around 4 to 0.2 mass%, but up to a certain point generated a stronger acidity. The optimal calcination temperature appeared to be around 673 K.     

Coagulation and heterocoagulation interactions of components in aqueous dispersed systems microcrystalline cellulose–TiO<Subscript>2</Subscript>, microcrystalline cellulose–TiOSO<Subscript>4</Subscript>, and TiO<Subscript>2</Subscript>–TiOSO<Subscript>4</Subscript>

A procedure was developed for recovery and concentration of residual palladium(II) from a “lean” refining solution by extraction with 1Н-1,2,4-triazole derivatives. Palladium(II) is extracted quantitatively from 1 M hydrochloric acid solutions and under optimum conditions is selectively separated from platinum(IV) and rhodium(III).