Mario Borlaf

Electrophoretic deposition of TiO2/Er3+ nanoparticulate sols

TiO(2) and TiO(2)/Er(3+) nanoparticulate sols were obtained by the colloidal sol-gel route. Thanks to the combination of three optical techniques (laser diffraction, LD, dynamic light scattering, DLS, and multiple light scattering, MLS), the peptization time was quantified, demonstrating that erbium(III) ions retard the process. The isoelectric point of TiO(2) shifts up to higher pHs when Er(3+) ions are present, which suggests that they are adsorbed onto the surface of the TiO(2) nanoparticles. Moreover, the viscosity of the sols increases when the erbium(III) amount increases. The xerogels obtained from each sol were characterized by XRD and HRTEM, obtaining in all cases anatase as the major phase, although traces of brookite were also present. In the EPD experiments, the addition of ethanol was necessary to reduce the water hydrolysis and facilitate the drying process. As a result, transparent thin films were obtained at short times and low current densities and opal films for larger current densities and deposition times; in addition, the thickness, measured by ellipsometry, increased gradually, but the refractive index did not change significantly (1.9-2). The topography profile of the films and the particle size were obtained by atomic force microscopy (AFM), giving similar values to those measured by DLS, indicating that the addition of ethanol helps to maintain stabilization without further agglomeration or sedimentation.

Synthesis and characterization of TiO2/Rh3+ nanoparticulate sols, xerogels and cryogels for photocatalytic applications

Nanoparticulate TiO2/Rh3+ sols have been synthesized by the colloidal sol–gel route. The combination of the data measured with optical techniques such as laser diffraction, dynamic light scattering and multiple light scattering with a near-infrared light allows us to follow up the evolution of the peptization process and to establish the effect of the presence of Rh3+ on it. It is observed that the presence of rhodium ions retards the peptization step (t2) and decreases both the average particle size of the nanoparticles and the viscosity of the nanoparticulate sols. In addition, when Rh3+ is present the isoelectric point shifts up to higher pH, which suggests that chemical adsorption of the rhodium (III) cations onto the surface of the TiO2 nanoparticles is produced. The xerogels and cryogels obtained from the sols are constituted by anatase as major phase and traces of brookite. The phase transition is observed at lower temperatures for the xerogels containing rhodium (III) and at higher temperatures in the case of the cryogels. Finally, photocatalytic activity is higher in the case of the TiO2/Rh3+ sols due to the rhodium (III) effect on the electronic transitions from the valence band to the conduction band.

Thin Films of Europium (III) Doped-TiO2 Prepared by Electrophoretic Deposition from Nanoparticulate Sols

Colloidal sol-gel is a common method used for the preparation of stable and homogeneous sols and thin films. The nanoparticulate sols can be easily deposited by EPD, which is a versatile technique for producing denser and thicker coatings than those produced by other techniques like dipping. A complete characterization of the sols, such as colloidal stability and electrophoretic mobility, which can be determined through zeta potential measurements, as well as the influence of deflocculants in the surface properties, is needed before using electrophoretic deposition. In this work, we have prepared sols of TiO2 with an alkoxide:water molar ratio of 50:1 and Eu (III) doped-TiO2 (2 mole % Eu (III)) using as precursors titanium (IV) isopropoxide and europium (III) acetate hydrate, respectively. The stability of the particulate sols was studied in terms of conductivity, zeta potential and viscosity evolution. Anatase stable sols, after peptization and without the use of any additive, were deposited on stainless steel substrates by electrophoretic deposition under both constant current and constant voltage conditions. Using different intensities and deposition times we have obtained thin films with different features (thicknesses and morphology) and different optical properties. The presence of europium (III) increases particle size, viscosity and peptization time and decreases the band gap of TiO2.