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In this work, fluorine-doped SnO2-based dimensionally stable anode (DSA) types were fabricated as electrocatalytic materials to degrade methylene blue (MB) in water. The materials were obtained by using a modified Pechini method. The F-doping in anodes improved the electrocatalytic properties, which were reflected by the decrease in the Tafel slope (from 820 to 338 mVdec−1) and during the MB degradation process. A ~ 98% degradation was achieved on the F-doped anode with Cl− ions in the reaction media. The Cl− addition improved the degradation kinetics (kPSO = 0.025 min−1), and the MB degradation pathway was corroborated through liquid chromatography coupled with mass detection. The doped anode showed more than 98% of MB mineralization for 5 cycles. The obtained anodes are low cost and effective electrocatalytic materials for wastewater treatment applications. [ABSTRACT FROM AUTHOR]

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Solar radiation is the main source of renewable energy capable of satisfying the increasing energy demand without contributing to climate changes using fossil fuels. Energy harvesting from solar radiation requires innovation in materials with appropriate functional properties to produce chemical energy. This study aims to contribute in that sense. It reports the synthesis and characterization of photocathodes for hydrogen evolution based on TiO2/CuxS films formed on FTO glass. CuxS is prepared by electrodeposition of copper, followed by chalcogenide formation through immersion in a sulfide source solution and then modified by heat treatment. A TiO2 layer is deposited on CuxS film to favor its stability and charge carrier separation process. The calcination of bare CuxS film causes the formation of a mixture of copper oxides. TiO2 film acts as an effective protector, preserving a larger proportion of Cu chalcogenide species by preventing the complete oxidation, without considerably varying the reducing power of photogenerated electrons in the films. TiO2 layer favors the absorption of low energy photons and increases the photocurrent, diminishing electron-hole recombination probability. [ABSTRACT FROM AUTHOR]

Abstract: Photocatalytic activity of TiO2 under visible light irradiation can be improved by doping with nonmetal atoms. However, inter-band energy states formed upon substitutional or interstitial doping can act as recombination centers, hindering the separation of the charge carriers. In this work, sol-gel synthesized TiO2 was doped with different loadings of boron, namely 0.25, 0.5, 1, 2, and 4 wt. %, and superficially modified by the deposition of Au nanoparticles (0.5, 1.0, and 1.5 wt. %). Particle size of doped TiO2 decreased with the increase of boron loading, while surface area increased accordingly. B2O3 was segregated from TiO2 when boron loading surpassed 1 wt. %. Light absorption of the doped materials was slightly blue shifted as the boron loading increased, more likely because of the quantization effect. Tiny and well dispersed Au nanoparticles were efficiently deposited on the B-TiO2 materials. Au nanoparticle size (3-5 nm) showed no modification as Au loading increased, although deposition rate slightly decreased with the boron loading. The complete mineralization of sulfamethoxazole under UV-A/visible light irradiation was obtained using the (0.5 wt. %) Au/(0.25 wt. %) B-TiO2 material. Electrochemical characterization showed how inter band energetic states increased the separation of the photo-produced charge carriers, while Au nanoparticles hampered the recombination rate via the electron trap effect. Photocatalytic materials displayed high stability. Photoactivity dropped when tap water was tested, because of the dissolved components in the liquid matrix. Some intermediates were identified via LC-MS/MS analysis, which displayed lower antibiotic activity than the parent compound.Sol-gel synthesized TiO2 was doped with boron, and superficially modified by deposition of Au nanoparticles. The complete mineralization of sulfamethoxazole under UV-A/visible light irradiation was obtained using the (0.5 wt. %) Au/(0.25 wt. %) B-TiO2 material. Inter band energetic states speed up the separation of the photo-produced charge carriers, while Au nanoparticles hamper the recombination rate via the electron trap effect Boron doped TiO2 is efficiently synthesized by the sol-gel reaction in a wide range of B loadings.Boron doping impacted on the physical, chemical and optical properties of TiO2.Doping increased separation of charge carriers while Au NPs acted as electron traps.Outstanding visible light driven photocatalytic performance of the Au/B-TiO2 materials.High stability of the Au/B-TiO2 materials and low activity in tap water. [ABSTRACT FROM AUTHOR]

Tuning the degree of anatase crystal orientation in TiO2 nanotube arrays has emerged as a new strategy to control their photoelectrochemical performance, since electron transport through the nanotubular film is favored. However, the existing literature fails to provide an accurate approach to evaluate the impact of anatase crystal orientation, since it is normally studied using TiO2 nanotube films synthesized in different anodizing baths, which in turn affects the properties of the films. In this work, anatase crystal orientation was controlled by changing the heating rate during sample heat-treatment (450°C for 30 min), which resulted in randomly oriented anatase crystals when the film was taken from room temperature to 450°C, to highly crystalline films with preferential anatase crystal orientation when the heating rate was decreased to 5 °C min-1 and 1 °C min-1. Even though the physicochemical properties of the films were almost unaltered, increasing anatase crystal orientation resulted in higher photocurrents and photoelectrocatalytic methyl orange discoloration, showing a maximum for the film treated at a heating rate of 5°C min-1. [ABSTRACT FROM AUTHOR]

Copyright of Revista CONAMED is the property of Comision Nacional de Arbitraje Medico and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Cadernos de Saude Publica is the property of Escola Nacional de Saude Publica Sergio Arouca and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The TiO 2 nanotube films were prepared by anodizing Ti plates in 0.2 M NH 4 F ethylene glycol/10% H 2 O under different formation voltages keeping fixed the time length, or by keeping fixed the formation voltage and varying the time length. The morphology of the TiO 2 film obtained was observed by SEM images and different morphological parameters were derived from them. Furthermore, the optical and semiconducting properties of TiO 2 films were also measured. The photoelectrochemical performance toward water oxidation of the TiO 2 only showed to be dependent with the inner diameter of the nanotubes, that could be related to the interaction of the film with the light and the transport of species in the electrolyte inward or outward the film. [ABSTRACT FROM AUTHOR]

This paper studies the effect of voltage and electrolyte composition on the morphology of TiO2 nanotube films, their semiconductor properties and photoelectrochemical performance for water oxidation. TiO2 nanotube films were formed by potentiostatic anodization in fluoride containing electrolytes (using either HF or NH4F) during 1 h at four different voltages and were heat treated at 450°C to obtain anatase polymorph. SEM images showed a more significant chemical attack when NH4F was employed, which was evidenced by larger tube diameters and thinner films. UV-vis reflectance spectra showed that the TiO2 films formed in aqueous electrolyte were highly defective, presenting various broad absorption peaks in the visible region attributed to the sub-bandgap energy states. The semiconducting properties were modified by the nature of the counter-ion utilized during film growth, resulting in films with a higher donor density and a lower flatband potential in NH4F electrolytes. The films formed in NH4F showed higher photopotentials and photocurrents related to the modification of their morphology and semiconducting properties, attaining a maximum at a formation voltage of 15 V. [ABSTRACT FROM AUTHOR]

Nanoporous TiO2 films were formed by anodization in three different electrolytes fluoride-containing, at different formation potentials for 2.5 hours. Film topography and morphology were characterized by AFM and SEM images, respectively. Aditionally, an in-situ study of the anodic film growth was carried out by electrochemical impedance spectroscopy. The growth ratio for the pore size obtained from SEM images was not directly proportional to the barrier layer growth ratio derived from EIS. The main role of the counter-ion seems to be insertion of fluoride ions altering the properties of the formed oxide, decreasing the film resistance and causing a more aggressive chemical attack, observed in the increase in pore size and film roughness. The solvent tunes the chemical attack of the anodic layer, and could also be establishing the titanium oxide stoichiometry, thus altering oxygen vacancies in the film and the migration of fluoride ions through the oxide lattice. [ABSTRACT FROM AUTHOR]

The effect of pH on the potentiostatic anodization growth of TiO2 film in 0.1 M HClO4/0.05 M NH4F solution was electrochemically characterized by EIS measurements. The increase in electrolyte pH modified considerably the voltammetric behavior of Ti electrode by diminishing the active dissolution region of the material and giving rise to two current plateaus that indicate modification of properties of the formed oxide. Five different formation potentials (EF) were selected from this study to potentiostatically grow oxide films, and to evaluate their morphology, the modification of their properties, and their interaction with the electrolyte. SEM images of the formed films showed that the EF increase resulted in a larger diameter of the pores formed, but an increase in pH led to a decrease in this parameter. In-situ characterization by EIS indicated that pH increase in the electrolyte used in anodization causes lower interaction between the formed oxide and F- ions in the solution due to the change in the surface charge excess of Ti oxide, resulting in an increase in the compact layer resistance and a decrease in both the time constant associated with F- ion adsorption and F- ion diffusion coefficient within the compact oxide layer. [ABSTRACT FROM AUTHOR]

The hydration state and structural transformations of Ti films potentiostatically grown in 0.1 M NaOH are characterized utilizing EIS, Mott-Schottky and XPS techniques. Variations presented in the density of donors, the flatband potential and the fraction of species measured by XPS, in the region of characterization of these films are associated with changes in the ratio of different Ti sub-oxides within the passive film. Oxygen and hydroxyl vacancies and their respective formation rate constants are estimated from EIS spectra fits with a modified Point Defect Model. A consistent behavior is observed for the hydration state and structural transformations of the films as a function of potential. Films anodized at less positive potentials than 1.17 V vs SCE present higher hydroxyl vacancy diffusivities (e.g higher film hydration) and a heterogeneous mixture of titanium sub-oxides, whereas the opposite behavior is observed for films formed at more positive potentials than 1.17 V vs SCE, where the hydroxyl vacancy diffusivities decrease by one order of magnitude and the oxygen vacancy diffusivities increase three times. Thus, films anodized at more positive potentials present a higher dehydration, are more homogeneous and mainly composed of TiO2. [ABSTRACT FROM AUTHOR]

The present work studies the influence of applied electric field on the cathodic electrophoretic formation of TiO2 films in an aqueous medium. The growth of the film was followed by measuring current density, deposited mass, and thickness under imposed electric field (φ). In scanning electronic microscopy images of the TiO2 films formed under different electric fields, three regions can be seen: (i) formation of nuclei that are converted into agglomerates, (ii) uniform and one-sided growth, and (iii) growth by the formation of agglomerates on the TiO2 surface. The characterization of semiconductor properties showed that increased φ for film growth leads to an increase in the density of donors and to a displacement of the flatband potential toward less negative values. The photoelectrochemical characterization of the oxide films revealed that the photoelectrochemical performance of the TiO2 films decreases as a function of the electric field used to carry Out the electrophoretic deposition (EPD) process. The electrochemical behavior observed for these films seems closely related to the content of Ti3+ doping sites electrogenerated in situ during the EPD, which act as electron traps negatively affecting the electron transport toward the indium tin oxide collector, also making their photoelectrochemical activity inefficient. [ABSTRACT FROM AUTHOR]