Showing papers by "Ángel Justo published in 1995"

Preparation and characterization of TiO2 photocatalysts supported on various rigid supports (glass, quartz and stainless steel). Comparative studies of photocatalytic activity in water purification

Abstract: In the present study TiO 2 has been supported on several rigid substrates. Deposition on glass and quartz was carried out by a dip coating procedure and the deposition on stainless steel by an electrophoretic deposition process. The resulting materials have been characterized by XPS, SEM/EDX, XRD and UV-vis absorption spectroscopy. The materials were then tested for the photocatalytic degradation of malic acid. For this reaction, the sample supported on quartz showed the highest catalytic activity. The photocatalytic activity pattern as a function of the nature of the support (fused silica, glass, stainless steel) followed the decreasing order: TiO 2 /quartz > TiO 2 /steel ≈ TiO 2 /glassaphotolysis. This decline in activity has been correlated with the presence of cationic impurities (Si 4+ , Na + , Cr 3+ , Fe 3+ ) in the layer as a consequence of the necessary thermal treatments to improve the cohesion of the titania layer and its adhesion onto the support.

Contribution of the x‐ray absorption spectroscopy to study TiO2 thin films prepared by ion beam induced chemical vapor deposition

Abstract: TiO2 thin films have been prepared and their structure analyzed by XRD at grazing angles and x‐ray absorption spectroscopies (EXAFS/XANES). The deposition method is an ion beam induced chemical vapor deposition procedure (IBICVD) consisting of the bombardment of a substrate with accelerated O+2 ions while the vapor of a volatile metallic precursor is directed on its surface. The structure of the films was dependent on the type of substrate (glass, fused quartz, and sapphire) and on the conditions used for their preparation (temperature of substrate and beam energy of 1 or 10 keV). Thus, while on glass and silica/sapphire, an amorphous structure is formed when the substrate is at 300 K during preparation, a rutile‐rich structure is obtained if the substrate is at 573 K during deposition or, even to a larger degree, when using ions of 10 keV. The amorphous structure of the films grown on glass yield 100% anatase after calcining at 773 K. On sapphire, the crystallization was less perfect and besides anatase,...

Combined use of X-ray absorption and diffraction in the study of Pt/TiO2SiO2 catalyst

Abstract: Titania catalyses several photoassisted and oxidation processes. Additionally, it is widely used as support in metal catalysts. A serious restriction in both applications is the low surface area of this oxide when it is pure, usually not higher than 50 m 2 /g. To overcome this restriction, titania is dispersed onto another oxide of high surface area, SiO 2 . Several preparation methods have been used, being among them homogeneous deposition-precipitation from TiCl 3 and hydrolysis of the alcoxide. The main concern in the structural characterization of these systems is the dispersion of titania phases. Herewith we present the results of the structural study of samples TiO 2 SiO 2 and Pt/TiO 2 SiO 2 , using a combination of XRD and XANES. Two sets of samples, prepared by the methods above mentioned, have been studied. In metal free samples, although no hydrogen consumption was detected below 450°C, remarkable changes are induced in the XANES spectra after treatment in H 2 at this temperature. Some features typical of tetrahedral environments appear in this case. Nevertheless, the preparation method appears to be the most important factor in the structure of titania phases. Thus, Pt/TiO 2 SiO 2 samples prepared by the homogeneous deposition-precipitation method present rutile-like phases, while the hydrolysis of the alcoxide produces amorphous and anatase-like structures.