magnesium-trisilicate and titanium-dioxide

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).

Topics: Adsorption; Air Pollution; Hydrogen Sulfide; Magnesium Silicates; Photolysis; Titanium; Ultraviolet Rays; Volatile Organic Compounds; Water Purification

Hybrid structured photocatalysts based on sepiolite, an adsorbent, and TiO2 were prepared by extrusion of ceramic dough and conformed as plates. The influence of the photocatalyst configuration was studied either by including TiO2 in the extrusion process (incorporated materials) or by coating the sepiolite plates with a TiO2 film (coated materials). The influence of the OH- surface concentration in the photocatalytic performance was studied by treating the ceramic plates at different temperatures. The samples were characterized by N2 adsorption-desorption, MIP, SEM, XRD, and UV-vis-NIR spectroscopy and tested in the photocatalytic degradation of trichloroethylene (TCE) as a target VOC molecule. Most of the catalysts presented high photoactivity, but considerable differences were observed when the CO2 selectivity was analyzed. The results demonstrate that there is a significant effect of the catalyst configuration on the selectivity of the process. An intimate contact between the sepiolite fibers and TiO2 particles for incorporated materials with a corncob-like structure favored the migration of nondesirable reaction products such as COCl2 and dichloroacetyl chloride (DCAC) to the adsorbent, reacting with OH- groups of the adsorbent and favoring the TCE mimeralization.

Topics: Catalysis; Environmental Pollutants; Magnesium Silicates; Materials Testing; Photolysis; Porosity; Titanium; Trichloroethylene

1. Two experiments were conducted to study the effects of crude enzyme preparations (beta-glucanase and arabinoxylanase) and/or 20 g/kg Sepiolite (Exal) on the performance and nutrient digestion of broiler chickens fed on maize-barley-wheat based diets. 2. In experiment 1, enzymes improved daily bodyweight gain (by 14%; P<0.001) and food:gain ratios (8%; P<0.001). Sepiolite improved bodyweight gain on the diets not supplemented simultaneously with enzymes (by 6% in 21-d-old chickens, P<0.05) but reduced it for enzymes-supplemeented diets. Changes in productive perfiormance with both additives were associated with changes in diet digestibility and nitrogen balance. 3. In experiment 2, enzyme supplementation reduced viscosity in jejunum and ileum and the mean retention time of digesta in the gut. Sepiolite inclusion significantly reduced the viscosity of jejunum digesta and modified the retention times of digesta in the gut, depending upon whether enzymes had been added. There was a decreased retention time without enzymes but an increase with enzyme supplementation. 4. Although different mechanisms are presumed for enzymes and sepiolite, both seem to counteract the negative effects of soluble, non-starch polysaccharides (NSP) in the diet by modifying jejunal viscosity and improving organic matter digestibility.

Topics: Animal Feed; Animals; Antacids; Body Weight; Cellulase; Chickens; Dietary Supplements; Eating; Edible Grain; Feces; Kinetics; Magnesium Silicates; Male; Nutritive Value; Random Allocation; Titanium; Xylosidases