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Obtención, caracterización y estudio de la actividad fotocatalítica de película de TiO2-CdS

出版	El autor, 2008
URL	http://books.google.com.hk/books?id=B277xAEACAAJ&hl=&source=gbs_api

註釋Actually, the great industrial development and the population explosion generate big problems, and the scientific community is treating to resolve some of them. One of the most serious problems is the efficient treatment of residual water, because it is present everywhere in the word parlicularly in the big cities, and it is in this area where materials with photocatalytic properties to degrade organic pollution are more and more necessary. This work deals with the growth and characterization of a material in form of thin film compound by TiO[subíndice]2 and CdS, with photocatalytic properties. This type of material could be an alternative in the environmental decontamination processes by means of solar radiation. TiO[subíndice]2, CdS, TiO[subíndice]2CdS, CdS/TiO[subíndice]2 and CdS-TiO[subíndice]2 thin films were grown on glass substrates by the Sol-Gel/dip coating method. After the growth the films were thermal treated at 100, 200, 300 and 400 [grados centigrados] during 0.5 h. To obtain a more detailed study was applied a thermal annealing for 12 hrs at 300 [grados centigrados] to TiO[subíndice]2, CdS and TiO[subíndice]2-CdS films. The films were characterized by the scanning electron microscopy (SEM), x-ray energy dispersive spectroscopy (EDS), Fourier transformed infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-Vis), micro-Raman and photoluminescence (PL) techniques. The TiO[subíndice]2-CdS films exhibit a morphology type "net" which is characteristic of a material formed by macromolecules. The net is 3-dimensional with rings whose diameters vary; inside these rings, granular material can be observed. The FTIR spectra of the as grown and thermal treated films present in general the vibrations associated to the OH group, except in the sample of CdS with twelve hours of thermal annealing which affects the photocatalitic activity. The TiO[subíndice]2 films exhibit the vibrations corresponding to the O-Ti-O and Ti-O groups, and CdS films the corresponding to the Cd-S, Cd-S-C and Cd-S-H groups, For the TiO[subíndice]2-CdS film, an increment in the absorption edge corresponding to CdS is observed, which extends until the TiO[subíndice]2 region. The absorption edges of both materials are in accord with the dates reported in the literature, and they shift to low energy values as the temperature of thermal annealing increases. The Raman spectra show only the phononic lines corresponding to CdS, which indicates that the applied thermal annealing was not enough to form the crystalline phase of TiO[subíndice]2; it is presents in the amorphous phase. A combination of radiative processes of TiO[subíndice]2 and CdS are clearly observed in the PL spectra, which are associated to defects or impurities, such as vacancies complexes and self trapped excitons, among others. It is observed that the defects and impurities favor the photocatalytic activity. The photocatalytic activity studies of the TiO[subíndice]2, CdS and TiO[subíndice]2-CdS f, films with one and ten coatings were carried out at room temperature with an aqueous solution of methylene blue (MB) ór isopropyl alcohol, respectively. The MB solution was inadiated in a closed box with an UV lamp and the isopropyl alcohol with UV and visible light. The MB photodegradation by the TiO[subíndice]2-CdS films (23.80 %) is greater than that performed by the CdS (10.06 %) and TiO[subíndice]2 (11.26 %). This indicates that even though the irradiation was carried out with an UV lamp, the incorporation of CdS into the TiO[subíndice]2 films improves the absorption of TiO[subíndice]2, and consequently a great percentage of generated carriers can participate in the photocatalytic process. Finally, the isopropyl alcohol photodegradation with UV light by the TiO[subíndice]2 reaches the 23 % value, while the corresponding to TiOz-CdS and CdS was 12 % and 0 %, respectively using visible light.