Synthesis and luminescence properties of ternary europium complexes in titania matrix in the presence of dimethylformamide by a sol-gel process

In-situ synthesis of ternary europium complex with thenoyltrifluoacetone (TTA) and 1,10-phenanthroline (phen) in titania matrix in the presence of dimethylformamide (DMF) by a sol-gel process was described, which was confirmed by the luminescence excitation spectra and infrared spectra. The titania gel that contains europium complex exhibits Eu3+ characteristic emission bands and presents a longer fluorescence lifetime than the pure complexes dissolved in ethanol solution. The concentration effect on the luminescence intensity was also investigated.

Study on the energy transfer between UO22+ and Eu3+ in sol-gel derived titania matrix by luminescence spectroscopy

The TiO2 gel doped with UO22+ and Eu3+ has been prepared by a sol-gel method. The quenching of the UO22+ emission by Eu3+ and the energy transfer from the excited state of UO22+ to the ground state oh Eu3+ have been investigated. The energy transfer has been studied by the measurement of luminescence lifetime tau, calculations of energy transfer efficiency eta(ET) and energy transfer rate W-ET The experimental results indicated that the quenching is combined static and dynamic mechanism, but the static mechanism is dominant.

Preparation of titania-based catalysts for formaldehyde photocatalytic oxidation from TiCl4 by the sol-gel method

Titania sols were prepared by acid hydrolysis of a TiCl4 precursor instead of titanium alkoxides. The effect of acid concentration on the particle size and stability of sol was investigated. Stable titania sols with mean particle size of 14 nm could be obtained when the H+/Ti molar ratio was 0.5. The titania sols were modified with Pt, SiO2, ZrO2, WO3 and MoO3 to prepare a series of modified catalysts, which were used for the photocatalytic oxidation of formaldehyde at 37 degreesC. They showed different photocatalytic activities due to the influence of the additives. Comparing with pure TiO2, the addition of silica or zirconia increased the photocatalytic activity, while the addition of Pt and MoO3 decreased the activity, and the addition Of WO3 had little effect on the activity. It is of great significance that the conversion of formaldehyde was increased up to 94% over the SiO2-TiO2 catalyst. The increased activity was partly due to higher surface area and porosity or smaller crystallite size. A comparison of our catalyst compositions with the literature in this field suggested that the difference in activity due to the addition of a second metal oxide maybe caused by the surface chemistry of the catalysts, particularly the acidity. (C) 2001 Elsevier Science B.V. All rights reserved.

Highly selective and efficient hydrogenation of carboxylic acids to alcohols using titania supported Pt catalysts

Selective hydrogenation of carboxylic acids to alcohols and alkanes has been achieved under remarkably mild reaction temperatures and H-2 pressures (333 K, 0.5 MPa) using Pt/TiO2 catalyst.

Capillary microreactors wall-coated with mesoporous titania thin film catalyst supports

A new method for catalyst deposition on the inner walls of capillary microreactors is proposed which allows exact control of the coating thickness, pore size of the support, metal particle size, and metal loading. The wall-coated microreactors have been tested in a selective hydrogenation reaction. Activity and selectivity reach values close to those obtained with a homogeneous Pd catalyst. The catalyst activity was stable for a period of 1000 h time-on-stream.

Control of the thickness of mesoporous titania films for application in multiphase catalytic microreactors

A new method of sol-gel polymer template synthesis of mesoporous catalytic thin films has been proposed which allows controlling the chemical nature of the film, the porosity, thickness and loading with an active species. The mesoporous films with a long-order structure can be obtained in a narrow range of surfactant-to-metal precursor molar ratios from 0.006 to 0.009. The catalytic film thickness was varied from 300 to 1000 nm while providing a uniform catalyst distribution with a desired catalyst loading (1 wt. % Au nanoparticles) throughout the film. The films were characterized by TEM, SEM, ethanol adsorption and contact angle measurements. The calcination of the as-synthesized films at 573 K reduced Ti4+ sites to Ti3+. A 300 nm thick Au-containing film showed an initial TOF of 1.4 s(-1) and a selectivity towards unsaturated alcohols as high as 90% in the hydrogenation of citral. Thicker films demonstrated a high selectivity towards the saturated aldehyde (above 55%) and a lower intrinsic catalytic activity (initial TOF of 0.7-0.9 s(-1)) in the absence of internal diffusion limitations.

Adsorption and photocatalysed destruction of cationic and anionic dyes on mesoporous titania films: Reactions at the air-solid interface

Cationic dyes, such as methylene blue (MB), Thionine (TH) and Basic Fuschin (BF), but not anionic dyes, such as Acid Orange 7 (AO7), Acid Blue 9 (AB9) and Acid Fuschin (AF), are readily adsorbed onto mesoporous titania films at high pH (pH 11), i.e. well above the pzc of titania (pH 6.5), due to electrostatic forces of attraction and repulsion, respectively. The same anionic dyes, but not the cationic dyes, are readily adsorbed on the same titania films at low pH (pH 3), i.e. well below titania's pzc. MB appears to adsorb on mesoporous titania films at pH 11 as the trimer (lambda(max) = 570 nm) but, upon drying, although the trimer still dominates, there is an absorption peak at 665 nm, especially notable at low [MB], which may be due to the monomer, but more likely MB J-aggregates. In contrast, the absorption spectrum of AO7 adsorbed onto the mesoporous titania film at low pH is very similar to the dye monomer. For both MB and AO7 the kinetics of adsorption are first order and yield high rate constants (3.71 and 1.481 g(-1) min(-1)), indicative of a strong adsorption process. Indeed, both MB and AO7 stained films retained much of their colour when left overnight in dye-free pH 11 and 3 solutions, respectively, indicating the strong nature of the adsorption. The kinetics of the photocatalytic bleaching of the MB-titania films at high pH are complex and not well-described by the Julson-Ollis kinetic model [A.J. Julson, D.F. Ollis, Appl. Catal. B. 65 (2006) 315]. Instead, there appears to be an initial fast but not simple demethylation step, followed by a zero-order bleaching and further demethylation steps. In contrast, the kinetics of photocatalytic bleaching of the AO7-titania film give a good fit to the Julson-Ollis kinetic model, yielding values for the various fitting parameters not too dissimilar to those reported for AO7 adsorbed on P25 titania powder. (C) 2008 Elsevier B.V. All rights reserved.

Limiting withdrawal rate and maximum film thickness during dip-coating of titania sols onto a Si substrate

The article highlights new insights into production of thin titania films widely used as catalyst support in many modern reactors including capillary microreactors, microstructured fixed-bed reactors and falling film microreactors. Dip-coating of a Mania sol onto a Si substrate has been studied in the range of the sol viscosities of 1.5-2.5 mPa s and the sol withdrawal rates of 0.2-18 mm/s. Different viscosities of sols were created by addition of desired amounts of nitric acid to the synthesis mixture of titanium isopropoxide and Plutonic F127 in ethanol which allowed to control the rate of the condensation reactions. Uniform inesoporous titania coatings were obtained at the solvent withdrawal rates below 10 mm/s at sol viscosities in the range from 1.6 mPa s to 2.5 mPa s. There exists a limiting withdrawal rate corresponding to a capillary number of ca. 0.01 beyond which uniform titania films cannot be obtained. Below the limiting withdrawal rate, the coating thickness is a power function of the sol viscosity and withdrawal rate, both with an exponent of 2/3. The limiting withdrawal rate increases as the solvent evaporation rate increases and it decreases as the sol viscosity increases. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Adsorption and photocatalytic bleaching of acid orange 7 on P25 titania

The observed adsorption of acid orange 7, AO7(-), on P25 titania over a range of pH values (pH 2-8) gives a good fit to data generated using a charge distribution, multisite complexation, i.e. CD-MUSIC, model, modified for aggregated dye adsorption. For this system the model predicts that both the apparent dark Langmuir adsorption constant. K-L, and the number of adsorption sites, n(o), increase with decreasing pH, and are negligible above pH 6. At pH 2 the CD-MUSIC model predicts the fraction of singly co-ordinated sites occupied by the dye,f(AO7), is ca. 32% under the in situ monitoring experimental conditions used in this work to study the photocatalytic bleaching of AO7(-) under UV light illumination ([TiO2] = 20 mgdm(-3); [AO7(-)](total) = 4.86 x 10(-5) M). Although AO7(-) adsorption on P25 titania is insignificant above pH 6 and increases almost linearly and markedly below this pH, the measured initial rate of bleaching of AO7(-), photocatalysed by titania using UV appears to only increase modestly (

A study of factors that change the wettability of titania films

The effect of several pretreatment methods on the wettability of polycrystalline titania-coated glass (Pilkington Activ) and plain glass are investigated. UV/ozone, immersion in aqua regia, and heating (T > 500 degrees C) render both substrates superhydrophilic (i.e., water contact angle (CA)

Novel low-temperature photocatalytic titania films produced by plasma-assisted reactive dc magnetron sputtering

Robust, active, anatase titania films, 250 nm thick, are deposited onto glass at low temperatures, i.e., 2.0 for the photocatalytic mineralization of stearic acid. These films are typically 6.9 times more active than a sample of commercial self-cleaning glass, comprising a 15 nm layer of fitania deposited by CVD, mainly because they are much thicker and, therefore, absorb more of the incident UV light. The most active of the films tested comprised particles of P25, but lacked any significant physical robustness. Similar results, but much more quickly obtained, were generated using a photocatalyst- sensitive ink, based on the redox dye, resazurin, Rz. All fitania films tested, including those produced by magnetrom sputtering exhibited photo-induced superhydrophilicity. The possible future application of PAR-DG-MS for producing very active photocatalytic films on substrates not renowned for their high temperature stabilities, such as plastics, is noted. (c) 2006 Elsevier B.V All rights reserved.