N-F codoped TiO2 films were immobilized on stainless steel sheets through a combined approach involving a dip-coating technique and a hydrothermal treatment, followed by calcination at 400°C in the presence of air. Photocatalyst characterization was conducted using XRD, Raman and UV-VIS spectroscopy as well as SEM. The films were tested in a three-electrode cell for the photoelectrocatalytic degradation of CN-containing compounds. The results showed that the increase in the degradation rate of CN-containing compounds is both influenced by a synergistic effect of the doping agents and strongly dependent on the concentration of CN-containing compounds in the solution. Nitrogen contributed to the enhanced photoactivity under visible light due to the generation of localized states within the band gap of TiO2, whereas the presence of fluoride improved the superficial properties of the film, which resulted in higher amounts of CN-containing compounds that were degraded by direct charge transfer through the photogenerated holes.

Mediante el proceso sol-gel se sintetizaron polvos y recubrimientos de biovidrio/Al2O3 en diferentes proporciones con el fin de evaluar el efecto de la alúmina en las características bioactivas y electroquímicas de las películas de biovidrio. Los polvos cerámicos fueron caracterizados estructuralmente con ayuda de las técnicas de difracción de rayos X y espectroscopia de infrarrojo, obteniéndose evidencia de que los iones aluminio reemplazan a los de calcio en el biovidrio, formándose el enlace Si-O-Al en los materiales compuestos. De los resultados de los ensayos de bioactividad in vitro en fluido fisiológico simulado se pudo inferir que el nuevo enlace disminuye las características bioactivas del biovidrio dado que el aluminio actúa como una barrera para la generación de los enlaces Si-OH, necesarios para la nucleación de las apatitas desde el fluido fisiológico simulado. La caracterización electroquímica mediante resistencia a la polarización lineal, polarización potenciodinámica y espectroscopia de impedancia electroquímica, evidenció que el aumento del contenido de alúmina en el material compuesto biovidrio/Al2O3 incrementa la resistencia a la polarización del sustrato de acero AISI 316L. No obstante que el recubrimiento de biovidrio es el que confiere menor carácter protector al sustrato contra la corrosión, por su alta reactividad en el fluido fisiológico simulado, tal comportamiento se invierte una vez se ha formado la capa de apatitas, que actúa como una barrera difusional a las especies electroactivas del medio.

Bioglass/ Al2O3 powders and coatings at different ratios were synthesized by sol-gel process in order to evaluate the effect of alumina in the bioactive and electrochemical properties of the bioglass coatings. The ceramic powders were structurally characterized using the xray diffraction and Infrared spectroscopy techniques, which evidenced that aluminum ions replace calcium ions in the bioglass and that Si-O-Al bond is formed in the composites. From in vitro bioactivity tests in simulated body fluid could be inferred that the new bonds decrease the bioglass bioactivity because aluminum acts as a barrier to the generation of Si-OH bonds, which are necessary for nucleation of apatites from the simulated body fluid. The electrochemical characterization performed through linear polarization resistance, potentiodynamic polarization and electrochemical impedance spectroscopy testing showed that the increasing of the alumina content of the bioglass/Al2O3 composite promotes the AISI 316L steel substrate polarization resistance. Although bioglass coating provides a lower protection to the substrate against corrosion, because of its high reactivity in the simulated body fluid, such behavior is reversed once the apatite layer has been formed, since it acts as a diffusional barrier to medium electroactive species.

TiO2 porous films were prepared on ITO coated glass slides by the sol-gel dip-coating method assisted with Polyethylene glycol (PEG). The films were used as photo-anodes in the photo-assisted electrolytic removal of cuprous ions in cyanide media. These were characterized by SEM, UV-Visible spectroscopy and XRD. The PEG modified films were free of cracks and developed a porous structure after heat treatment at 500 ºC, due to the thermal decomposition of the structure associated PEG. It was demonstrated that the photo-assisted electrochemical reduction of copper is promoted by the use of modified TiO2 films as photo-anodes, thanks to the greater surface area given by the PEG decomposition. However, the film thickness was found to be a critical factor in the process, to such an extent that films composed of 5 layers were completely inefficient, meaning that despite the open porosity, multilayered films acted as a barrier within the photo-electrolytic process.

Se prepararon recubrimientos de hidroxiapatita (HA) reforzados con TiO2 sobre acero AISI 316L mediante el proceso sol gel/dip coating. El espesor de los recubrimientos se determinó por microscopia óptica confocal, mientras que la fuerza de adherencia se evaluó con un medidor de adhesión pull-off. Después de seleccionar las mejores condiciones, para la formación de una película con propiedades mecánicas adecuadas, se evaluó la bioactividad in vitro del recubrimiento durante dos semanas, y se comparó con la de los recubrimientos de HA y TiO2. La formación de apatitas se corroboró con ayuda de la técnica de SEM EDX. Finalmente, se evaluó la velocidad de corrosión del acero, para estudiar la estabilidad de los recubrimientos. Los resultados mostraron que la formación de películas de HA/TiO2 llevó a la obtención de un material bioactivo, con mayor adherencia que la obtenida para las películas de HA y el TiO2. Sin embargo, la presencia de HA afectó la protección contra corrosión promovida por la presencia de TiO2

Hydroxyapatite (HA) reinforced with TiO2 coatings were prepared by sol/gel dip coating on AISI 316L stainless steel. The thickness of the coatings was determined by confocal optical microscopy and the adhesion strength was evaluated by means of a pull-off tester. After selecting the optimal conditions for the formation of a film with good mechanical properties; the in vitro bioactivity of the coating was evaluated for two weeks, and then compared with those of HA and TiO2 coatings. The growth of apatite was confirmed by SEM EDX characterization. Finally, the corrosion rate of the steel substrate was also evaluated, in order to analyze the stability of the coatings. The results showed that the formation of HA/TiO2 films produced a bio-active material with a higher adherence, when compared to that obtained for films of HA and TiO2. Nevertheless, the presence of HA affected the corrosion resistance of the film, as promoted by the presence of TiO2

Titanium dioxide porous thin films on the Anatase phase were deposited onto glass slides by the sol-gel method assisted with polyethylene glycol (PEG). The dip-coated films were characterized using scanning electron microscopy (SEM), thermogravimetric analysis (TGA and DTG), UV-visible spectroscopy and X-ray diffraction (XRD). The photocatalytic activity of the films was determined by means of methyl-orange oxidation tests. The resultant PEG-modified films were crack-free and developed a porous structure after calcination at 500 °C. Photo-oxidation tests showed the dependency of catalytic activity of the films on the number of layers (thickness) and porosity, i.e. of the interfacial area.

The influence of Anatasa/Rutile ratio on TiO2 films, grown by electrophoretic deposition was studied in the photoassisted electrolytic copper ions removal from cyanide solutions. The proper dispersant dosage allowing the simultaneous electrophoretic deposition of Anatase and Rutile was chosen based on electrokinetic measurements; evidenced by the XRD spectra of the formed films. The evaluation of films photoassisted electrolytic copper ion removal showeds that it is possible to enhance the activity of Anatase films by adding some Rutile exploiting the synergetic interaction between these two materials, achieve by its proper deposition.

In the present work TiO2 films were formed over Indium Tin Oxide (ITO) employing cathodic electrophoretic deposition (Cathodic-EPD) and Dr. Blade Technique. The films were characterized by electrochemical techniques in order to compare their electronic properties; as well as, their photoelectrochemical behavior. The electrochemical performance showed by the films, allowed to relate the modification occurring during the Cathodic-EPD, with the partial reduction of TiO2 nanoparticles, generating Ti3+ defects. These trapping states are modifying the electronic properties of the film, and diminishing the transport of the photoelectrogenerated electrons toward ITO.

El crecimiento de películas anódicas en la interfase Ti/0.1 M NaOH y su caracterización electroquímica, muestran la existencia de cambios estructurales del óxido formado desde TiO hasta el TiO2. La ocurrencia de estas transformaciones con el potencial de formación de la película (Ef ), no afectó la cinética de crecimiento de la película pasiva, pero sí el óxido formado en la interfase Ti/0.1 M NaOH. La variación de la densidad de donadores (Nd) y el potencial de banda plana (Efb) con el Ef , se atribuyó a las transformaciones estructurales.

The electrochemical characterization of the anodic film growth on Ti / 0.1 M NaOH shows structural changes from TiO to TiO2. The occurrence of these transformations as a function of the formation potential (Ef ) does not affect the growth kinetics of the passive film, but the oxide formed at the Ti/0.1 M NaOH interface. The variation of the density of donors (Nd) and the flat band potential (Efb) with Ef was attributed to structural transformations.