Study of Water,Methanol And Isopropanol Adsorption on The Surface of Titanosilicas of Different Structure

The adsorption of water, methyl and i-propyl alcohol vapours has been studied on the surface of titanosilicas produced by various methods, as well as on the surface of pure silicon and titanium oxides. Based on findings of the studies, it was concluded that the presence on the surface of pyrogenic titanosilicas (TAS) of hydrolytically unstable Si-O-Ti bonds is responsible for their increased adsorption activity towards water molecules. A dissociative adsorption of H₂O on titanosiloxane bridges is accompanied by an appearance of additional groups ≡SiOH and ≡TiOH, which, in turn, become sites of adsorption of subsequent water molecules. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mesoporous Titanium-containing Silicas. Synthesis and geometrical characteristics

Mesoporous titanium-containing silicas with TiO₂ contents from 1 up to 70 mol% were prepared. The obtained samples have been characterized by the powder X-ray diffraction data, the diffuse reflectance infrared Fourier transform method, and nitrogen adsorption at 77 K. Specific surface area, total pore volume, distribution pore volume on pore sizes were determined from nitrogen adsorption isotherm for synthesized titanosilicas. This revised version was published online in August 2006 with corrections to the Cover Date.     

Liquid-phase Reductive Deposition as Novel Preparation Method for Highly Dispersive Nickel Catalysts

We have been developing the selective deposition method onto TiO₂ nanoparticles, named as the liquid-phase selective-deposition method, where TiO₂ plays a role of formation center of Ni nanoparticles as well as protection from the aggregative growth of the particles. The concept of this method is to well disperse and stabilize Ni nanoparticles on TiO₂ surface by specific adsorption of Ni precursory complexes and then heterogeneous nucleation on the adsorption sites. The particle size was decreased with increasing the amount of Zn added, thus the catalytically active Ni surface area was increased. The selective deposition onto TiO₂ surface and addition of Zn to the nanoparticle promoted the catalytic activity of Ni–Zn nanoparticle, e.g. the catalytic activity of Ni–Zn/TiO₂ was ca. 10 times higher than that of the unsupported Ni nanoparticles. Ni in the nanocomposite was assigned as metallic, although their surface was oxidized under the atmospheric condition, but Zn and B were deposited as their oxide.     

Investigation of Br–N Co-doped TiO<Subscript>2</Subscript> photocatalysts: preparation and photocatalytic activities under visible light

Bromine (Br) and nitrogen (N) co-doped TiO₂ ((Br–N–TiO₂) photocatalysts were prepared by a sol–gel method. The catalysts were characterized by X-ray Diffraction (XRD), N₂ adsorption and desorption isotherms, X-ray Photoelectron Spectra (XPS), UV-Vis Diffraction Spectra and Electron Spin Response (ESR) Spectra. Experiments on photodegradation of Methylene Blue (MB) and Sulfosalicylic Acid (SSA) under visible light were carried out to evaluate the photocatalytic activities of the catalysts. Chemical Oxygen Demand (COD) analysis was also conducted to evaluate the mineralization degrees of the catalysts in MB photodegradation. Enhanced photocatalytic activities were observed for the Br–N–TiO₂ catalysts in the experiments of MB and SSA photodegradation. A possible mechanism was proposed to explain the improved photocatalytic activities of the Br–N–TiO₂ catalysts.     

TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> hybrid nanomaterials: synthesis and variable UV-blocking properties

Silica and core–shell structured titania/silica (TiO₂/SiO₂) nanoparticles with particles size ranging from tens to hundreds of nanometers were prepared and deposited onto cotton fabric substrates by sol–gel process. The morphologies of the nanoparticles were characterized by field-emission scanning electron microscope (FE-SEM). The photocatalytic decomposition properties as well as UV-blocking properties of the fabrics treated with SiO₂ and TiO₂/SiO₂ nanoparticles were investigated.     

Physicochemical and catalytic characterizations of materials prepared from copper malonate by thermal decomposition or chemical reduction

Results of Carr and Galwey [1] concerning copper malonate (CM) decomposition in vacuo at 510 K prompted present studies on the utility of CM as a low-temperature precursor of oxide-supported copper catalysts. CM deposited upon metal oxides has been converted to copper particles by vacuum thermal decomposition or reduction with aqueous hydrazine. Using the dehydrogenation of isopropanol to acetone as a catalytic probe reaction, comparisons are made between levels of catalytic activity and selectivity induced in TiO₂, MgO and Ca(OH)₂ supports by copper deposited thereon. Effects of particle size, prereduction temperature, and support reducibility are described and evidence is given for a strong metal support interaction (SMSI)-like inhibition of activity of Cu/TiO₂ by prior high temperature reduction.     

The effect of nanosized titania-silica film composition on the photostability of adsorbed methylene blue dye

The effect of nanosized porous films (average density 10 g/m²) of TiO₂. TiO₂/SiO₂, and SiO₂ on the photostability of adsorbed methylene blue (MB) dye during UV irradiation in air was investigated by optical spectroscopy and laser-induced mass spectrometry. The effectiveness of the photodecomposition of MB decreases in the order TiO₂ > TiO₂/SiO₂ > SiO₂ with rate constants 1E-2, 0.6E-2, and 0.3E-2 min⁻¹ respectively. A mechanism including the participation of both excited states of the dye molecules and photoexcited titanium dioxide is proposed for the photodecolorization of MB adsorbed on the surface of the investigated films. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 4, pp. 220–225, July–August, 2007.     

Electrocatalytic evaluation of liquid phase deposited methylene blue/TiO2 hybrid films

Methylene blue (MB)/TiO₂ hybrid thin films were prepared on glassy carbon (GC) electrode surface by the liquid phase deposition (LPD) process. The electrochemical measurements indicated that MB retained its electrochemical activity in the hybrid films. The linear dependence of the reduction peak current for MB upon the scan rate and linear relationship between the middle point potential of MB and pH revealed the surface-confined two-proton two-electron electrochemical characteristics of MB entrapped in hybrid LPD films. Although the electron transfer of K₃[Fe(CN)₆] on GC surface was inhibited by TiO₂ film, the catalytic reduction of K₃[Fe(CN)₆] by MB was observed on the MB/TiO₂ hybrid films. The electrocatalytic activity of hybrid films was also demonstrated as an “artificial peroxidase” for the catalytic reduction of H₂O₂.     

Application of a dioxo-molybdenum(VI) complex anchored on TiO<Subscript>2</Subscript> for the photochemical oxidative decomposition of 1-chloro-4-ethylbenzene under O<Subscript>2</Subscript>

The catalytic activity of dioxo-molybdenum(VI)-dichloro[4,4′-dicarboxylato-2,2′-bipyridine] covalently anchored through the carboxylate function to the surface of TiO₂ has been tested for the oxidative degradation of 1-chloro-4-ethylbenzene in MeCN solution under argon and UV irradiation (λ = 254 nm). After 4–5 h of photochemical reaction, the Mo complex was reoxidized in the presence of O₂ in the dark, and then the reaction was continued under argon. The reaction proceeds by the intermediate formation of 4′-chloroacetophenone that undergoes further decomposition to chlorobenzene, plus small amounts of oxygen-containing organochlorine compounds, CO₂ and H₂O. Similar results were obtained for the decomposition of 4′-chloroacetophenone under the same conditions, which also gave chlorobenzene as one of the main products. The ratio of [final product]/[Mo complex] increases during the decomposition of 1-chloro-4-ethylbenzene (up to 350–400% for 30–35 h of reaction), which provides evidence of a catalytic process. The probable photochemical reactions are discussed.     

Sol–gel synthesis,characterization and photocatalytic activity of mesoporous TiO<Subscript>2</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3 </Subscript>granules

Mesoporous TiO₂/γ-Al₂O₃ composite granules were prepared by combining sol–gel/oil-drop method, using various titania solution. The product granules can be used as a photocatalyst or adsorbent in moving, fluidized bed reactors. The phase composition and pore structure of the granules can be controlled by calcination temperature and using different titania solution. In the photocatalysis of NH₃ decomposition, TiO₂/γ-Al₂O₃ granules using Degussa P25 powder treated thermally at 450 °C showed the highest catalytic ability. However, TiO₂/γ-Al₂O₃ granules using titania made by hydrothermal method had comparable performance in NH₃ decomposition.     

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.     

Preparation and characterization of transparent TiO2 thin films coated on fused-silica substrates

The transparent TiO₂ thin films coated on fused-SiO₂ substrates were prepared by the sol–gel method and spin-coating technique. Effects of calcination temperature on crystal structure, grain size, surface texture, and light transmittance of the films were investigated. After calcining at 600–1,200 °C, the thicknesses of the TiO₂ films were all around 80 nm and the molecular structures of the films were anatase, even at 1,200 °C. The calcined TiO₂ films had the ultraviolet light (wavelength 200–400 nm) transmittances of ≤29% and the visible light (wavelength 400–800 nm) transmittance of ≥72%. By photocatalytically decomposing the methylene blue (MB) in water, the photocatalytic activities of the TiO₂ thin films were measured and represented using the characteristic time constant (τ) for the MB degradation. While the films prepared at 1,000 and 1,200 °C photodecomposed about 54 mol% of the MB in water (the corresponding τ ≈ 14.8 h) after exposing to 365-nm UV light for 12 h, the films prepared at 600 and 800 °C had smaller τ (≈9.0 h) and photodecomposed about 74 mol% of the MB in water at the same testing conditions.     

TiO<Subscript>2</Subscript>/TiO<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>N<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> nanocomposite and its acetaldehyde photodecomposition ability

Nitrogen-doped titania was coupled with the commercial titania nanoparticles by mechanical milling in liquid medium. The as-prepared nanocomposites (TiO₂/TiO_2−x N _y ) were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) specific surface area, UV–Vis spectroscopy, chemiluminescence, and acetaldehyde decomposition activity techniques. When a small amount of nitrogen-doped titania was added into the commercial titania, higher intensity and longer lifetime of ¹O₂ was observed, and the photocatalytic activity was efficiently improved. The TiO_2−x N _y acts as the acceptor of photoinduced holes. The recombination of the electron-hole was effectively depressed by the heterogeneous electron transfer. This could be an effective way to obtain highly active photocatalysts.     

Gold particles supported on self-organized nanotubular TiO2 matrix as highly active catalysts for electrochemical oxidation of glucose

Au/TiO₂/Ti electrode was prepared by a two-step process of anodic oxidation of titanium followed by cathodic electrodeposition of gold on resulted TiO₂. The morphology and surface analysis of Au/TiO₂/Ti electrodes was investigated using scanning electron microscopy and EDAX, respectively. The results indicated that gold particles were homogeneously deposited on the surface of TiO₂ nanotubes. The nanotubular TiO₂ layers consist of individual tubes of about 60–90 nm in diameter, and the electrode surface was covered by gold particles with a diameter of about 100–200 nm which are distributed evenly on the titanium dioxide nanotubes. This nanotubular TiO₂ support provides a high surface area and therefore enhances the electrocatalytic activity of Au/TiO₂/Ti electrode. The electrocatalytic behavior of Au/TiO₂/Ti electrodes in the glucose electro-oxidation was studied by cyclic voltammetry. The results showed that Au/TiO₂/Ti electrodes exhibit a considerably higher electrocatalytic activity toward the glucose oxidation than that of gold electrode.     

Electrochemical study of methylene blue/titanate nanotubes nanocomposite and its layer-by-layer assembly multilayer films

Titanate nanotubes (TNT) were proven to be efficient support for the immobilization of methylene blue (MB). UV–vis absorption and Fourier transform infrared spectra showed that the effect of MB absorbed on TNT was better than nanocrystalline anatase TiO₂ (TNP). The quantity of MB absorbed onto TNT was found to be greater than that of TNP and the electrode modified with the MB–TNT film was more stable due to the strong interaction between TNT and MB as well. The absorption of MB on TNT was impacted by the pH value of the reaction solution for the change of surface charge. Electrochemical oxidation of dopamine (DA) at different electrodes was studied. The result showed that the MB–TNT composite film exhibited excellent catalytic activities to DA compared to those of pure TNT, which is a result of the great promotion of the electron-transfer rate between DA and the electrode surface by the MB–TNT film. Furthermore, the layer-by-layer self-assembly behavior of the electrochemically functional MB–TNT nanocomposite was also discussed after obtaining the stable colloid suspension of MB–TNT. The excellent electrochemical ability and the easy fabrication of layered nanocomposite make the MB–TNT nanocomposite very promising in electrochemistry study and new nanotube-based devices.     

Deposition of SnO2 on the Anatase TiO2 {105} Facets with High Photocatalytic Performance

Anatase TiO2 as a promising photocatalyst has been widely employed in the decontamination treatment of polluted water, air purification and water splitting. Coupling TiO2 with other semiconductor materials could further enhance the photocatalytic activity. Here, we successfully synthesized the SnOz/TiO2 catalyst by depositing SnO2 particles on the anatase TiO2 {105} facets through a gas phase oxidation process. The SnOz/TiO2 catalyst shows higher photocatalytic activity for decomposition of MB than that of the pure YiO2 catalyst. The enhanced photo- catalytic activity can be attributed to the efficient charge separation since TiO2 and SnO2 catalyst have staggered energy level.     

Marked Effect of Various Supports and Additives Upon Liquid Phase Methanol Reforming with Water over Supported Group 8–10 Metal Catalysts

The support effects (SiO₂, TiO₂, Al₂O₃, MgO, CeO₂ and ZrO₂) as well as addition effect of group 6b and 7b elements were studied over various supported group 8–10 metal catalysts. Basic oxide support improved the selectivity to CO₂ and acidic support suppressed the catalytic activity and selectivity. Among the investigated catalysts Pt–Mo/TiO₂ was the most active catalysts, whereas Ir–Re/SiO₂ was the most selective catalysts for H₂ and CO₂ formation. The mechanism of the liquid phase methanol reforming reaction over silica supported Pt–Ru catalyst was studied by kinetic investigations. The rate of H₂ formation over Pt–Ru/SiO₂ catalysts was more than 20 times faster than that over Pt/SiO₂ catalysts with high selectivity for CO₂ (72.3%), indicating a marked addition effect of Ru. In the case of HCHO–H₂O reaction over Pt–Ru/SiO₂, the H₂ formation rate was five times larger than that in the CH₃OH–H₂O reaction but selectivity to CO₂ was only 4%. On the contrary, in the HCOOCH₃–H₂O and HCOOH–H₂O reactions, both high activity and selectivity were observed over Pt–Ru/SiO₂. These results clearly indicate that the CO₂ formation does not proceed via HCHO decomposition and following water gas shift reaction.     

Preparation of nanocrystalline Fe-doped TiO<Subscript>2</Subscript> powders as a visible-light-responsive photocatalyst

Nanocrystalline Fe-doped TiO₂ powders were prepared using TiOSO₄, urea, and Fe(NO₃)₃ · 9H₂O as precursors through a hydrothermal method. The as-synthesized yellowish-colored powders are composed of anatase TiO₂, identified by X-ray diffraction (XRD). The grain size ranged from 9.7 to 12.1 nm, calculated by Scherrer’s method. The specific surface area ranged from 141 to 170 m²/g, obtained by the Brunauer–Emmett–Teller (BET) method. The transmission electron microscopy (TEM) micrograph of the sample shows that the diameter of the grains is uniformly distributed at about 10 nm, which is consistent with that calculated by Scherrer’s method. Fe³⁺ and Fe²⁺ have been detected on the surface of TiO₂ powders by X-ray photoelectron spectroscopy (XPS). The UV–Vis diffuse reflection spectra indicate that the light absorption thresholds of the Fe-doped TiO₂ powders have been red-shifted into the visible light region. The photocatalytic activity of the Fe-doped TiO₂ was evaluated through the degradation of methylene blue (MB) under visible light irradiation. The Fe-doped TiO₂ powders have shown good visible-light photocatalytic activities and the maximum degradation ratio is achieved within 4.5 h.     

Preparation of Ni/TiO2 Nanoparticles and Their Catalytic Performance on the Thermal Decomposition of Ammonium Perchlorate

Metal/oxide nanoparticles are attractive because of their special structure and better properties. The Ni/TiO₂ nanoparticles were prepared by a liquid phase chemical reduction method in this paper. The obtained‐products were characterized by inductively coupled plasma (ICP), X‐ray diffraction (XRD), high‐resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). The results show that Ni particles in Ni/TiO₂ nanoparticles exhibit better dispersion and the size of most Ni particles is 10 nm or so. The catalytic activity of Ni/TiO₂ nanoparticles on the thermal decomposition of ammonium perchlorate (AP) was investigated by simultaneous thermogravimetry and differential thermal analysis (TG‐DTA). Results show that composite process of Ni and TiO₂ can improve the catalytic activity of Ni nanoparticles on the thermal decomposition of AP, which is mainly attributed to the improvement of Ni dispersion in Ni/TiO₂ nanoparticles. The catalytic activity of Ni/TiO₂ nanoparticles increases with increasing the weight ratio of Ni to AP.     

Sol–gel doped TiO<Subscript>2</Subscript> nanomaterials: a comparative study

Among the great number of sol–gel prepared nanomaterials, TiO₂ has attracted significant interest due to its high photocatalytic activity, excellent functionality, thermal stability and non-toxicity. The photocatalytic degradation of pollutants using un-doped and doped TiO₂ nanopowders or thin films is very attractive for applications in environmental protection, as a possible solution for water purification. The present work describes a comparative structural and chemical study of un-doped TiO₂ and the corresponding S- and Ag-doped materials. The photocatalytic activity was established by testing the degradation of organic chloride compounds from aqueous solutions. Sol–gel Ag-doped TiO₂ coatings, prepared by co-gelation and sol–gel Ag-doped TiO₂ coatings obtained from nanopowders were also compared. Their structural evolution and crystallization behaviour (lattice parameters, crystallite sizes, internal strains) with thermal treatment were followed by thermal analysis, X-ray diffraction, transmission electron microscopy, atomic force microscopy and specific surface areas measurements. X-ray photoelectron spectroscopy analyses were performed to characterize the surface composition and S or Ag speciation, which was used to interpret the catalytic data.