Benigno Sánchez

SOLAR PHOTOCATALYTIC DEGRADATION OF WATER AND AIR POLLUTANTS: CHALLENGES AND PERSPECTIVES

Solar photocatalytic oxidation processes (PCO) for degradation of water and air pollutants have recently received increasing attention. Some field-scale experiments have demonstrated the feasibility of using a semiconductor (TiO2) in solar collectors and concentrators to completely mineralize organic contaminants in water and air. Although successful pre-industrial solar tests have been carried out, there are still discrepancies and doubt concerning process fundamentals such as the roles of active components, appropriate modelling of reaction kinetics or quantification of photoefficiency. Challenges to development are catalyst deactivation, slow kinetics, low photoefficiency and unpredictable mechanisms. The development of specific non-concentrating collectors for detoxification and the use of additives such as peroxydisulfate have made competitive use of solar PCO possible. The challenges and perspectives of solar driven PCO as illustrated in the literature and our own results in large solar field loops at the Plataforma Solar de Almeria and CIEMAT laboratories are described.

Photocatalytic destruction of toluene and xylene at gas phase on a titania based monolithic catalyst

Abstract Toluene and xylene were subjected to gas-solid heterogeneous photocatalytic oxidation on a titania based monolithic catalyst, in order to investigate the potential of solar-driven detoxification as a clean and safe method for air purification and gas phase waste destruction. Thus, gaseous streams with toluene or xylene were conducted through a monolithic catalysts based on titania dispersed on a fibrous silicate and irradiated with a Xenon lamp in the presence of air, at process temperatures from 150 to 450°C. Destructions levels higher than 96% were achieved for toluene and 99% for xylene at Area Velocity values in the range of 5–8 m h-1. A non-negligible number of undesirable sub-products (furans and benzofurans) were identified in partial oxidation conditions. The concentration of these sub-products was higher in the thermal process than with the photocatalytic system. Textural properties of the catalyst, the nature of phases and their distribution on the surface and light absorption properties were studied using techniques such as mercury intrusion porosimetry, scanning electron microscopy (SEM-EDX), X-ray diffraction and diffuse reflectance UV-Vis. spectroscopy.

Photocatalytic elimination of indoor air biological and chemical pollution in realistic conditions

The photocatalytic elimination of microorganisms from indoor air in realistic conditions and the feasibility of simultaneous elimination of chemical contaminants have been studied at laboratory scale. Transparent polymeric monoliths have been coated with sol-gel TiO(2) films and used as photocatalyst to treat real indoor air in a laboratory-scale single-step annular photocatalytic reactor. The analytical techniques used to characterize the air quality and analyze the results of the photocatalytic tests were: colony counting, microscopy and PCR with subsequent sequencing for microbial quantification and identification; automated thermal desorption coupled to gas chromatography with mass spectrometry detection for chemical analysis. The first experiments performed proved that photocatalysis based on UVA-irradiated TiO(2) for the reduction of the concentration of bacteria in the air could compete with the conventional photolytic treatment with UVC radiation, more expensive and hazardous. Simultaneously to the disinfection, the concentration of volatile organic compounds was greatly reduced, which adds value to this technology for real applications. The fungal colony number was not apparently modified.

Heterogeneous photocatalysis: degradation of ethylbenzene in TiO2 aqueous suspensions

Abstract Heterogeneous photocatalysis in TiO 2 aqueous suspensions has been used as a technique for the total destruction of organic compounds, such as ethylbenzene, in water. The photocatalytic degradation of ethylbenzene follows pseudo-first-order kinetics in a concentration range between 3 and 50 μM. Studies have shown that a Langmuir-Hinshelwood equation form can describe the initial rate of ethylbenzene disappearance. The objective of our research was to examine the degradation of intermediates species produced by the oxidation of ethylbenzene. The temporal course of the degradation was followed by high performance liquid chromatography. Gas chromatography—mass spectrometry analysis of the reactor solution from a ethylbenzene experiment revealed the presence of several intermediate species, namely 4-ethylphenol, acetophenone, 2-methylbenzyl alcohol, 2-ethylphenol and 3-ethylphenol. The influence of pH on the photocatalytic degradation of ethylbenzene was examined initial 50 /gmM solutions at two different pH values. This study shows that the degradation of ethylbenzene at higher pHs requires a much illumination time to attain quality standards of drinking water.

Photocatalysis for Continuous Air Purification in Wastewater Treatment Plants: From Lab to Reality

The photocatalytic efficiency of TiO(2)-SiMgO(x) plates to oxidize H(2)S was first evaluated in a flat laboratory reactor with 50 mL min(-1) synthetic air containing 100 ppm H(2)S in the presence of humidity. The use of the photocatalyst-adsorbent hybrid material enhanced the photocatalytic activity in terms of pollutant conversion, selectivity, and catalyst lifetime compared to previous H(2)S tests with pure TiO(2) because total H(2)S elimination was maintained for more than 30 operating hours with SO(2) appearing in the outlet as reaction product only after 18 h. Subsequently, the hybrid material was successfully tested in a photoreactor prototype to treat real polluted air in a wastewater treatment plant. For this purpose, a new tubular photocatalytic reactor that may use solar radiation in combination with artificial radiation was designed; the lamp was turned on when solar UV-A irradiance was below 20 W m(-2), which was observed to be the minimum value to ensure 100% conversion. The efficient distribution of the opaque photocatalyst inside the tubular reactor was achieved by using especially designed star-shaped structures. These structures were employed for the arrangement of groups of eight TiO(2)-SiMgO(x) plates in easy-to-handle channelled units obtaining an adequate flow regime without shading. The prototype continuously removed during one month and under real conditions the H(2)S contained in a 1 L min(-1) air current with a variable inlet concentration in the range of tens of ppmv without release of SO(2).

Influence of the methods of TiO2 incorporation in monolithic catalysts for the photocatalytic destruction of chlorinated hydrocarbons in gas phase

Abstract Three different methods of fixing titanium dioxide on a monolithic, natural magnesium silicate matrix, onto-the-wall extrusion, wash-coating and sol–gel, are compared. Photo-assisted oxidation tests with chlorinated hydrocarbons, trichloroethylene (TCE) alone and in mixtures with perchloroethylene (PCE) were carried out with the monolithic photocatalysts. Results show that the use of extruded titania monoliths provides significant advantages for best stability of anatase, porosity and resistance to loss of active phase due to erosion. Catalysts obtained by the sol–gel method maybe a good option for this application, but the coating method must still be improved.

TiO2 on magnesium silicate monolith: effects of different preparation techniques on the photocatalytic oxidation of chlorinated hydrocarbons

In this article, the comparative results of the photocatalytic oxidation of trichloroethylene (TCE) alone and a mixture of chlorinated hydrocarbons (trichloroethylene, perchloroethylene and chloroform) in gas phase, obtained with three different monolithic catalysts in a flat reactor frontally illuminated with a Xenon lamp are presented. The three catalysts incorporate titanium dioxide (TiO2) as active phase on a magnesium silicate support, by means of different procedures: (i) incorporation of commercial TiO2 powder into the silicate matrix (“massic monolith”); (ii) sol–gel coating of the silicate support; (iii) impregnation with a commercial TiO2 aqueous suspension of the same silicate support. In the first case, the massic monolith was made from a 50:50 w/w mixture of magnesium silicate and “Titafrance G5” TiO2 powder. In the second case, a magnesium silicate monolith was coated with several layers of an aqueous TiO2 sol prepared from hydrolysis and condensation of titanium tetra-isopropoxide (Ti(OC3H7)4) in excess of acidified water (acid catalysis). The third catalyst was prepared by impregnating the same silicate support with several layers of “Titafrance G5” TiO2 powder water suspension. All the catalysts were thermal treated under comparable conditions in order to fix the TiO2 active phase to the silicate support. Although the performance of the massic monolith was better than the sol–gel monolith, the latter is of great interest because this technique allows the chemical composition of the active films to be easily modified.

DETECTION OF ESTROGEN ALPHA AND PROGESTERONE RECEPTORS AND CELL PROLIFERATION IN THE UTERUS DURING EARLY PREGNANCY IN THE GOAT

The objectives of this study were to investigate in the goat uterus the expression of estrogen-alpha (ER alpha) and progesterone receptors (PR) and their relationship to proliferation indices (Ki-67) during peri-implantation on Days 22 to 30 post coitum (pc). Immunohistochemical methods were used to quantify ER alpha and PR for luminal and deep regions of the endometrium and of the myometrium. On Day 22 pc cell proliferation was only observed in the luminal epithelium. On Day 24 pc, high cell proliferation indices were seen in luminal epithelium and proliferation began in the luminal stroma and glands. There was a positive correlation between Ki-67 and total ER alpha score in the luminal epithelium (r = 0.53, P < 0.01). Levels of PR scores were highly correlated with Ki-67 indices in luminal epithelium (r = 0.74, P < 0.01) and stroma (r = 0.70, P < 0.01). No Ki-67 expression was observed in deep glands, stroma or myometrium on any of the days studied. Results indicate that patterns of ER alpha and PR expression differ markedly, and that there was a high correlation between PR expression and cell proliferation in the caprine uterus during the peri-implantation period.

Immunohistochemical localization of epidermal growth factor, transforming growth factor-α and growth factor-βs in the caprine peri-implantation period

Abstract Control over the action of steroid hormones in the uterus and conceptus during the initial period of gestation appears to be regulated locally by growth factors. This study involved immunohistochemical detection of epidermal growth factor (EGF), transforming growth factor-α (TGF-α) and transforming growth factor-βs (TGF-βs), to determine their role in the caprine peri-implantation period. Epidermal growth factor was expressed in the luminal and glandular endometrial epithelium of goats on all days studied (Days 22 to 30 post coitum), but it was not detected in trophoblastic cells or in other embryonic structures. Between Days 22 and 30 post coitum, TGF-α was detected in the epithelial cells and superficial stroma of the uterus and in the trophoendodermic cells of the embryo. Transforming growth factor-βs expression, observed in the endometrium, embryo and extraembryonic membranes on Day 22 post coitum, decreased by Day 24 post coitum and disappeared in the embryo by Day 30 post coitum, while remaining in the other structures. The presence of these growth factors during the periimplantation period in the goat suggests their participation in proliferation and differentiation phenomena which occur during implantation and embryonic development.

Fibroblastic growth factor receptor (FGF-R) expression during uterine involution in goat

To investigate the possible participation of fibroblastic growth factors (FGFs) in endometrial involution, 20 multiparous goats, slaughtered on days 0, 1, 4, 10, 16 and 22 postpartum (pp), were used. Samples of different parts of the previous pregnant horns were taken and processed using streptoavidin-biotin-peroxidase complex method to analyse FGF receptor (FGF-R) expression. The percentage of positive cells in luminal epithelium, superficial and deep glands and stroma was evaluated. Epithelial, glandular and stromal cells exhibited FGF-R immunoreactivity. No differences between caruncular and inter-caruncular epithelium were observed and staining was most evident in the superficial glands. The greatest degree of FGF-R expression was seen on days 10 and 16 pp, coinciding with epithelial and stromal cellular regeneration. These results suggest that caprine uterine involution is associated with variations in the expression of FGF-R.