No abstract

Recebido em 13/1/04; aceito em 27/1/05; publicado na web em 30/6/05 CONSTRUCTION AND PERFORMANCE STUDIES OF A CPC TYPE PHOTOCHEMICAL REACTOR. A CPC (Compound Parabolic Concentrator) reactor was projected and constructed aiming to promote the degradation of the organic matter present in considerable volumes of aqueous effluents, under the action of solar radiation. The essays were done using a model effluent which consists of a mixture of fragments of a sodium salt of lignosulphonic acid possessing a mean molecular weigth of 52,000 Daltons, and a real effluent, from a chip board industry. The volume of effluent in each test was about 50 L. The tests involved heterogeneous (TiO 2 P25 Degussa and formulations made from the association of TiO 2 with a photosensitiser), and homogeneous (thermal and photochemical Fenton reactions) catalysis of the effluents. The results demonstrate the viability of application of this kind of reactor even when the load of organic pollutants is high.

No abstract

No abstract

In the present paper, we propose and study by numerical simulations a multiscale model for plant invasion based on allelopathic suppression in a homogeneous environment. The negative effects on seed production and germination, establishment and mortality of native plants generated by the rootsecreted alien phytotoxin constitute the basic mechanism contributing to invasiveness. We obtained the invasion patterns, their success probabilities, the time evolution of plant populations, the gyration radius and the border roughness of the invaded region. As an important result, it was observed that, in addition to the phytotoxin nature (synthesis and degradation rates, diffusivity and phytotoxic threshold), invasive patterns and invasion success depend on the kind of native plants present in the area. In fact, both success and invasion speed decrease in the presence of resistant native plants. Also, self-affine invasion fronts are smooth (Hurst exponent H = 1) in the absence of resistant plants, but are rough (H = 1) on the contrary. Furthermore, if the resistant native species are randomly distributed on the landscape, the invasion front exhibits long-range correlations (H * 0.76), while its border is anti-correlated (H * 0.20), if resistant plants are distributed in patches. Finally, the cluster size distribution functions of resistant plants are exponentials with characteristic cluster sizes increasing in time.

In this study, we investigate the generation of hydroxyl radicals mediated by a composite containing TiO 2 and 1.6% m/m of zinc phthalocyanine (TiO 2 /ZnPc) in aqueous suspensions containing methanol as oxidisable substrate. The composite features a specific surface 20% less than the value estimated for TiO 2 P25, probably due to the covering of the surface of the oxide by ZnPc and the pH of the isoelectric point of this composite equal of 5.5, about two units of pH lower than the value estimated for TiO 2 P25, are probably related to the difference in photocatalytic activity found for these materials. To assess the influence of different spectral bands of electromagnetic radiation on the production of hydroxyl radicals, we used different sources of radiation in experiments conducted to estimate the quantum efficiency of hydroxyl radical formation (HO•), via photocatalytic oxidation of methanol. The association between zinc phthalocyanine and TiO 2 has allowed the formation of a light absorber material with absorption spectral range extended to the visible region. Our results suggest that, despite the higher values of  HO• for TiO 2 P25, the combination of visible and ultraviolet radiation furnished by a high pressure mercury lamp without the protective bulb, or solar radiation, causes the composite to present good values for the same parameter.

No abstract

No abstract