Pressure-induced electrical and structural anomalies in Pb(1-x)Ca(x)TiO(3) thin films grown at various oxygen pressures by chemical solution route

Lead calcium titanate (Pb(1-x)Ca(x)TiO(3) or PCT) thin films have been thermally treated under different oxygen pressures, 10, 40 and 80 bar, by using the so-called chemical solution deposition method. The structural, morphological, dielectric and ferroelectric properties were characterized by x-ray diffraction, FT-infrared and Raman spectroscopy, atomic force microscopy and polarization-electric-field hysteresis loop measurements. By annealing at a controlled pressure of around 10 and 40 bar, well-crystallized PCT thin films were successfully prepared. For the sample submitted to 80 bar, the x-ray diffraction, Fourier transformed-infrared and Raman data indicated deviation from the tetragonal symmetry. The most interesting feature in the Raman spectra is the occurrence of intense vibrational modes at frequencies of around 747 and 820 cm(-1), whose presence depends strongly on the amount of the pyrochlore phase. In addition, the Raman spectrum indicates the presence of symmetry-breaking disorder, which would be expected for an amorphous (disorder) and mixed pyrochlore-perovskite phase. During the high-pressure annealing process, the crystallinity and the grain size of the annealed film decreased. This process effectively suppressed both the dielectric and ferroelectric behaviour. Ferroelectric hysteresis loop measurements performed on these PCT films exhibited a clear decrease in the remanent polarization with increasing oxygen pressure.

Classical simulation of deposition of thiophene oligomers on TiO(2)-anatase: Relevance of long-range electrostatic interactions

We performed classical molecular dynamics simulations of the vapor-deposition of alpha-T4 oligomers on the TiO(2)-anatase (101) surface, comparing different sets of charges associated with the atoms of the model. The potential energy surfaces for alpha-T4 and TiO(2) were described by re-parametrizations of the Universal force field with charges given by the charge equilibration (QEq) scheme, or with fixed charges obtained by an ab initio method using the Hirshfeld partition. The two sets of charges lead to completely different results for the interface formation, and for the characteristics of the organic film, with a clearly defined alpha-T4 contact layer in the QEq case, and a more homogeneous molecular distribution when using Hirshfeld charges. The main reason for the discrepancy was found to be the incorrect charge assignment given by QEq to the sulfur and alpha-carbon atoms in thiophenes, and highlight the relevance of long-range interactions in the organization of molecular films. (C) 2009 Elsevier B.V. All rights reserved.

Thermoluminescence, structural and magnetic properties of a Li(2)O-B(2)O(3)-Al(2)O(3) glass system doped with LiF and TiO(2)

A Li(2)O-B(2)O(3)-Al(2)O(3) glass system, un-doped and doped with LiF, and/or TiO(2) was synthesized by the fusion method and its physical properties were investigated by thermoluminescence (TL), X-ray diffraction (XRD), electron paramagnetic resonance (EPR), atomic force microscopy (AFM) and differential thermal analysis (DTA). The samples were subjected to gamma-rays from a colbalt-60 ((60)Co) source. These techniques provided evidence of LiF and LiF doped with Ti crystal formation in the glass system. A TL glow peak at about 433 K was sensitive to (60)Co gamma-rays and showed good linearity with doses and consequently could be used to quantify radiation doses. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Role of Polyelectrolyte for Layer-by-Layer Compact TiO(2) Films in Efficiency Enhanced Dye-Sensitized Solar Cells

Efficient compact TiO(2) films using different polyeleetrolytes are prepared by the layer-by-layer technique (LbL) and applied as an effective contact and blocking film in dye-sensitized solar cells (DSCs). The polyanion thermal stability plays a major role on the compact layers, which decreases back electron transfer processes and current losses at the FTO/TiO(2) interface. FESEM images show that polyelectrolytes such is sodium sullonated polystyrene (PSS) and sulfonated lignin (SE), in comparison to poly(acrylic acid) (FAA), ensure an adequate morphology for the LbL TiO(2) layer deposited before the mesoporous film, even triter the sintering step at 450 degrees C. The so treated photoanode in DSCs leads to a 30% improvement On the overall conversion efficiency. Electrochemical impedance spectroscopy (EIS) is employed to ascertain the role of die compact films with such polyelectrolytes. The significant increase in V(oc) of the solar cells with adequate polyelectrolytes in the LbL TiO(2) films shows their pivotal role in decreasing the electron recombination at the FTO surface and enhancing the electrical contact of FTO with the mesoporous TiO(2) layer.

Structure effects of self-assembled Prussian blue confined in highly organized mesoporous TiO(2) on the electrocatalytic properties towards H(2)O(2) detection

Here we report the derivatization of mesoporous TiO(2) thin films for the preparation of H(2)O(2) amperometric sensors. The coordination of the bifunctional ligand 1,10 phenantroline, 5,6 dione on the surface Ti(IV) ions provides open coordination sites for Fe(II) cations which are the starting point for the growth of a layer of Prussian blue polymer. The porous structure of the mesoporous TiO(2) allows the growth, ion by ion of the coordination polymer. Up to four layer of Prussian blue can be deposit without losing the porous structure of the film, which results in an enhanced response of these materials as H(2)O(2) sensors. These porous confined PB modified electrodes are robust sensors that exhibit good reproducibility, environmental stability and high sensitivity towards H(2)O(2) detection. (C) 2010 Elsevier B.V. All rights reserved.

Reliable and fast sensor for in vitro evaluation of solar protection factor based on the photobleaching kinetics of a nanocrystalline TiO(2)/dye UV-dosimeter

A reliable and fast sensor for in vitro evaluation of solar protection factors (SPFs) of cosmetic products, based on the photobleaching kinetics of a nanocrystalline TiO(2)/dye UV-dosimeter, has been devised. The accuracy, robustness and suitability of the new device was demonstrated by the excellent matching of the predicted and the in vivo results up to SPF 70, for four standard samples analyzed in blind. These results strongly suggest that our device can be useful for routine SPF evaluation in laboratories devoted to the development or production of cosmetic formulations, since the conventional in vitro methods tend to exhibit unacceptably high errors above SPF similar to 30 and the conventional in vivo methods tend to be expensive and exceedingly time consuming. (C) 2011 Elsevier B.V. All rights reserved.

Chemical modification of a nanocrystalline TiO(2) film for efficient electric connection of glucose oxidase

A novel biosensor for glucose was prepared by adsorption of 1,1`-bis(4-carboxybenzyl)-4,4`-bipyridinium di-bromide compound (H(2)BpybcBr(2)) onto the surface of a nanocrystalline TiO(2) film deposited onto FTO glasses, which was used as a platform to assemble the enzyme glucose oxidase to the electrode surface. The H(2)BpybcBr(2)/TiO(2)/FTO modified electrode was characterized by scanning electron microscopy, X-ray fluorescence image, cyclic voltammograms and spectroelectrochemical measurements. The immobilization of GOD on functionalized TiO(2) film led to stable amperometric biosensing for glucose with a linear range from 153 mu mol L(-1) to 1.30 mmol L(-1) and a detection limit of 51 mu mol L(-1). The apparent Michaelis-Menten constant (K(m)) was estimated to be 3.76 mmol L(-1), which suggested a high enzyme-substrate affinity. The maximum electrode sensitivity was 1.25 mu A mmol L(-1). The study proved that the combination of viologen mediators with TiO(2) film retains the electrocatalytic activity of the enzyme, and also enhances the electron transfer process, and hence regenerating the enzyme in the reaction with glucose. (C) 2010 Elsevier Inc. All rights reserved.

N3-Dye-Induced Visible Laser Anatase-to-Rutile Phase Transition on Mesoporous TiO(2) Films

Titanium dioxide has been extensively used in photocatalysis and dye-sensitized solar cells, where control of the anatase-to-rutile phase transformation may allow the realization of more efficient devices exploiting the synergic effects at anatase/rutile interfaces. Thus, a systematic study showing the proof of concept of a dye-induced morphological transition and an anatase-to-rutile transition based on visible laser (532 nm) and nano/micro patterning of mesoporous anatase (Degussa P25 TiO(2)) films is described for the first time using a confocal Raman microscope. At low laser intensities, only the bleaching of the adsorbed N3 dye was observed. However, high enough temperatures to promote melting/densification processes and create a deep hole at the focus and an extensive phase transformation in the surrounding material were achieved using Is laser pulses of 25-41 mW/cm(2), in resonance with the MLCT band. The dye was shown to play a key role, being responsible for the absorption and efficient conversion of the laser light into heat. As a matter of fact, the dye is photothermally decomposed to amorphous carbon or to gaseous species (CO(x), NO(x), and H(2)O) under a N(2) or O(2) atmosphere, respectively.

Layer-by-layer TiO(2) films as efficient blocking layers in dye-sensitized solar cells

Charge recombination at the conductor substrate/electrolyte interface has been prevented by using efficient blocking layers of TiO(2) compact films in dye-sensitized solar cell photoanodes. Compact blocking layers have been deposited before the mesoporous TiO(2) film by the layer-by-layer technique using titania nanoparticles as cations and sodium sulfonated polystyrene, PSS, as a polyanion. The TiO(2)/PSS blocking layer in a DSC prevents the physical contact of FTO and the electrolyte and leads to a 28% increase in the cell`s overall conversion efficiency, from 5.7% to 7.3%. (C) 2009 Elsevier B.V. All rights reserved.

Raman evidence of the interaction between multiwalled carbon nanotubes and nanostructured TiO(2)

Nanocomposites of carbon nanotubes and titanium dioxide (TiO(2)) have attracted much attention due to their photocatalytic properties. Although many examples in the literature have visualized these nanocomposites by electron microscopic images, spectroscopic characterization is still lacking with regard to the interaction between the carbon nanotube and TiO(2). In this work, we show evidence of the attachment of nanostructured TiO(2) to multiwalled carbon nanotubes(MWNTs) by Raman spectroscopy. The nanostructured TiO(2) was characterized by both full-width at half-maximum (FWHM) and the Raman shift of the TiO(2) band at ca 144 cm(-1), whereas the average diameter of the crystallite was estimated as approximately 7 nm. Comparison of the Raman spectra of the MWNTs and MWNTs/TiO(2) shows a clear inversion of the relative intensities of the G and D bands, suggesting a substantial chemical modification of the outermost tubes due to the attachment of nanostructured TiO(2). To complement the nanocomposite characterization, scanning electronic microscopy and X-ray diffraction were performed. Copyright (C) 2011 John Wiley & Sons, Ltd.

Influence of neodymium ions on photocatalytic activity of TiO(2) synthesized by sol-gel and precipitation methods

Titanium dioxide with and without the addition of neodymium ions was prepared using sol-gel and precipitation methods. The resulting catalysts were characterized by thermal analysis, X-ray diffraction and BET specific surface area. Neodymium addition exerted a remarkable influence on the phase transition temperature and the surface properties of the TiO(2) matrix. TiO(2) samples synthesized by precipitation exhibit an exothermic event related from the amorphous to anatase phase transition at 510 degrees C, whereas in Nd-doped TiO(2) this transition occurred at 527 degrees C. A similar effect was observed in samples obtained using sol-gel method. The photocatalytic reactivity of the catalysts was evaluated by photodegradation of Remazol Black B (RB) under ultraviolet irradiation. Nd-doped TiO(2) showed enhanced photodegradation ability compared to undoped TiO(2) samples, independent of the method of synthesis. In samples obtained by sol-gel, RB decoloration was enhanced by 16% for TiO(2) doped with 0.5% neodymium ions. (C) 2010 Elsevier B.V. All rights reserved.

Behaviour of TiO(2)-SiMgO(x) hybrid composites on the solar photocatalytic degradation of polluted air

The photocatalytic performance of TiO(2)-SiMgO(x) ceramic plates for trichloroethylene abatement in gas phase has been evaluated under sun irradiance conditions. A continuous flow Pyrex glass reactor fixed on the focus of a compound parabolic collector has been used. The performance of the hybrid photocatalyst has been evaluated as the variation of TCE conversion and reaction products formation with the solar irradiance at different total gas flow, TCE concentration, and water vapour content. SiMgO(x) not only provides adsorbent properties to the photocatalyst, but it also allows the effective use of the material during low solar irradiance conditions. The adsorption-desorption phenomena play a pivotal role in the behaviour of the system. Thus, TCE conversion curves present two different branches when the sun irradiance increases (sunrise) or decreases (sunset). CO(2), COCl(2) and DCAC were the most relevant products detected. Meanwhile CO(2) concentration was insensitive to the branch analysed, COCl(2) or DCAC were not indicating the ability of these compounds to be adsorbed on the composite. An increase of the UV irradiation at total TCE conversion promotes the CO(2) selectivity. The excess of energy arriving to the reactor favours the direct reaction pathway to produce CO(2). The photonic efficiency, calculated as a function of the rate of CO(2) formation, decreases linearly with the solar irradiance up to around 2 mW cm(-2), where it becomes constant. For decontamination systems high TCE conversion is pursuit and then high solar irradiance values are required, in spite of lower photonic efficiency values. The present photocatalyst configuration, with only 17% of the reactor volume filled with the photoactive material, allows total TCE conversion for 150 ppm and 1 L min(-1) in a wide sun irradiance window from 2 to 4 mW cm(-2). The incorporation of water vapour leads to an increase of the CO(2) selectivity keeping the TCE conversion around 90%, although significant amounts of COCl(2) were observed. (c) 2010 Elsevier B.V. All rights reserved.

Interfacial Electron Transfer Dynamics Following Laser Flash Photolysis of [Ru(bpy)(2)((4,4 `-PO(3)H(2))(2)bpy)](2+) in TiO(2) Nanoparticle Films in Aqueous Environments

Nanosecond laser flash photolysis has been used to investigate injection and back electron transfer from the complex [(Ru-(bpy)(2)(4,4`-(PO(3)H(2))(2)bpy)](2+) surface-bound to TiO(2) (TiO(2)-Ru(II)). The measurements were conducted under conditions appropriate for water oxidation catalysis by known single-site water oxidation catalysts. Systematic variations in average lifetimes for back electron transfer, - were observed with changes in pH, surface coverage, incident excitation intensity, and applied bias. The results were qualitatively consistent with a model involving rate-limiting thermal activation of injected electrons from trap sites to the conduction band or shallow trap sites followed by site-to-site hopping and interfacial electron transfer, TiO(2)(e(-))-Ru(3+) -> TiO(2)-Ru(2+). The appearance of pH-dependent decreases in the efficiency of formation of TiO(2)-Ru(3+) and in incident-photon-to-current efficiencies with the added reductive scavenger hydroquinone point to pH-dependent back electron transfer processes on both the sub-nanosecond and millisecond-microsecond time scales, which could be significant in limiting long-term storage of multiple redox equivalents.

Photocatalytic degradation of methylene blue by TiO(2)-Cu thin films: Theoretical and experimental study

In this work the effect of doping concentration and depth profile of Cu atoms on the photocatalytic and surface properties of TiO(2) films were studied. TiO(2) films of about 200 nn thickness were deposited on glass substrates on which a thin Cu layer (5 nm) was deposited. The films were annealed during 1 s to 100 degrees C and 400 degrees C, followed by chemical etching of the Cu film. The grazing incidence X-ray fluorescence measurements showed a thermal induced migration of Cu atoms to depths between 7 and 31 nm. The X-ray photoelectron spectroscopy analysis detected the presence of TiO(2), Cu(2)O and Cu(0) phases and an increasing Cu content with the annealing temperature. The change of the surface properties was monitored by the increasing red-shift and absorption of the ultraviolet-visible spectra. Contact angle measurements revealed the formation of a highly hydrophilic surface for the film having a medium Cu concentration. For this sample photocatalytic assays, performed by methylene blue discoloration, show the highest activity. The proposed mechanism of the catalytic effect, taking place on Ti/Cu sites, is supported by results obtained by theoretical calculations. (C) 2010 Elsevier B.V. All rights reserved.

Photocatalyst TiO(2)-Co: the effect of doping depth profile on methylene blue degradation

In this work, we study the effect of doping depth profile on the photocatalytic and surface properties of TiO(2) films. Two thin film layers of TiO(2) (200 nm) and Co (5 nm), respectively, were deposited by physical evaporation on glass substrate. These films were annealed for 1 s at 100 and 400 A degrees C and the Co layer was removed by chemical etching. Atomic force microscopy (AFM) phase images showed changes in the surface in function of thermal treatment. The grazing-incidence X-ray fluorescence (GIXRF) measurements indicated that the thermal treatment caused migration of Co atoms to below the surface, the depths found were between 19 and 29 nm. The contact angle showed distinct values in function of the doped profile or Co surface concentration. The UV-vis spectra presented a red shift with the increasing of thermal treatment. Photocatalytical assays were performed by methylene blue discoloration and the higher activity was found for TiO(2)-Co treated at 400 A degrees C, the ESI-MS showed the fragments formed during the methylene blue decomposition.