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The photocatalytic activity under UV and visible irradiation of a series of CeO2-TiO2 composite materials prepared by microemulsion and subsequently calcined at 500 °C was evaluated using acetaldehyde as a model pollutant. The activities of three composite catalysts containing 2.5, 5 and 25 M% of ceria, as well as a nano-titania reference are compared by means of efficiency parameters; the quantum (or true) efficiency, as well as the photonic (or apparent) efficiency were evaluated. To this end, the lamp emission properties, as well as the radiation field interaction with the catalyst inside the reactor were modeled and numerically calculated. For the evaluation of the radiation absorbed by the catalysts, the optical properties of the materials were measured and a radiative transfer model that considers all potential optical events was built up. The stability of the systems under reaction conditions was also studied. Overall, the results evidence that the composite containing 2.5 Ce mol% outperforms titania by a factor of at least 2, irrespective of the illumination source used in the experiment. This shows the potential of the CeO2-TiO2 composites, a highly active and stable system, for sunlight optimum profiting. [ABSTRACT FROM AUTHOR]

Abstract: Microbiologically contaminated water, in this case artificially infected with Escherichia coli was treated with low wavelength (253.7nm) radiation in a laboratory reactor where all the significant operating variables were carefully measured and controlled. A modification of the series-event model was used to interpret the experimental data which were collected employing four different levels of the incident radiation arriving at the reactor. The developed model is based on a rather complex dependence with respect to the E. coli concentration and to the radiation that is effectively absorbed by the bacteria which was precisely quantified. The mathematical description of the kinetics has three parameters: (i) the threshold limit of bacteria damage (n =2), (ii) the kinetic constant [k =9.03±0.36s−1(cm3 W−1) m ] and (iii) the reaction order with respect to the bacteria photonic absorption rate (m =0.205±0.015). About 99.99% plus inactivation was reached in all cases for rather short effective contact times and predictions from the model agree very well with experimental data in the whole range of investigated variables. [Copyright &y& Elsevier]

The kinetics of the photocatalytic decomposition of low concentrations of trichloroethylene (TCE) in water was modeled and the reaction parameters have been evaluated for different catalyst loadings. The employed reactor is a flat plate configuration irradiated by tubular lamps that have emission in the 300–400 nm wavelength range.The mass conservation model is two-dimensional while the developed radiation model is two-dimensional in space and two directional in radiation propagation. The performance of the photoreactor with this reaction can be properly represented employing only two lumped kinetic constants that can be derived from a 12 steps, complete reaction sequence. The deduced kinetic model has explicit functional dependencies for the local volumetric rate of photon absorption (LVRPA) and the effect of the catalyst concentration: rTCE,het(x¯,t)av=−SgCm,catα∫lower limit λ eλa(x¯,t,Cm,cat) dλ[α3CTCE/(1+α3CTCE)]. Values of the kinetic constants are: α=1.94×10−9 mol g1/2 cm−2 s−1/2 einstein−1/2 and α3=5.52×106 cm3 mol−1. As derived from the reaction sequence and validated with experiments, it was observed that the reaction rate is proportional to the square root of the LVRPA. The dependence on the catalyst loading, well described by the model, is more complex due to its characteristic effect on the light distribution inside the reaction space. [Copyright &y& Elsevier]

Water contaminants can be completely mineralized by UV activated powdered TiO2. By recirculating slurried titania through a fluidized bed (FB) of quartz sand, the apparent quantum efficiency of the photocatalyst can be made several fold higher than by just using the suspended powder. Although, in principle, this could be attributed to the re-distribution of the incoming radiation inside the reacting space by the extra scattering centers (the sand grains), and/or the increment of the active catalytic surface through fragmentation of the coalesced TiO2 powder by the collisions among the sand grains and the titania particles, we have found that the latter effect predominates. However, the ionic composition of the aqueous media also plays a key role (via electrostatic interactions between both particulate solids), causing a higher effective concentration of TiO2 inside the reactor. [Copyright &y& Elsevier]

Iron pillared clay (Fe-PILC) was prepared from a montmorillonite and was characterized by scanning electron microscopy and X-ray fluorescence. Fe-PILC catalytic activity was evaluated in photo-Fenton processes applied to the degradation of 2-clorophenol. Different catalyst loads were assayed. The Fe-PILC allowed almost complete degradation of the contaminant. An increase in the contaminant degradation rate was observed, following leaching of iron during catalytic assays, which suggest the existence of a homogeneous photo-Fenton mechanism. The catalytic performance of the Fe-PILC was compared with that for goethite and zero valent iron nanoparticles. Differences were found regarding the achieved degradation levels, the efficiency in oxidant consumption, and the extension of iron leaching.

The aim of this work is to study the degradation kinetics of the endocrine disruptor benzyl butyl phthalate using ozone and UV radiation. The model comprises four parallel subsystems that are identified and isolated: (1) direct photolysis, (2) direct ozonation in the absence of hydroxyl radicals, (3) complete ozonation (direct + indirect oxidation), and (4) ozone + UV. To determine the nature of ozone attacks and the influence of ·OH radicals on O3 activity, two sets of experiments were performed: (i) conventional ozonation and (ii) the same ozonation experiments in the presence of tert-butanol as radical scavenger, where only the reactions involving molecular ozone are present. The explored variables were (i) ozone concentration, (ii) incident radiation rate at the reactor windows, (iii) reaction pH, and (iv) the presence of radical scavengers. Major intermediates of BBP degradation were identified. Degradation kinetics was correctly modeled by a pseudo-second-order kinetic model based on the sum of all the effects occurring during the treatment. The corresponding kinetic constants were obtained, and the relative contributions of each of the considered subsystems were evaluated.