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This glossary of terms covers phenomena considered under the very wide terms photocatalysis and radiation catalysis. A clear distinction is made between phenomena related to either photochemistry and photocatalysis or radiation chemistry and radiation catalysis. The term "radiation" is used here as embracing electromagnetic radiation of all wavelengths, but in general excluding fast-moving particles. Consistent definitions are given of terms in the areas mentioned above, as well as definitions of the most important parameters used for the quantitative description of the phenomena. Terms related to the up-scaling of photocatalytic processes for industrial applications have been included. This Glossary should be used together with the Glossary of terms used in photochemistry, 3 rd edition,

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Precise kinetic studies of photocatalytic reactions in solid catalyst water suspensions require the accurate description of the radiation fieldlight distributioninside the reactor. Solution of the radiative transport equation (RTE) inside the reaction is one of the best ways of accessing to such information. For solving this equation, a minimum of two parameters (the absorption and scattering coefficients) and one scattering spatial distribution function (the phase function) are needed. These attributes are directly associated with the optical behavior of the reacting system and are not independent of catalysts more conventional properties. A complete report on the physical and optical characteristics of titanium dioxide particulate suspensions in water is presented. Results were obtained for six different commercially available powders. The investigated parameters were (i) size of elementary particles, (ii) size of particle aggregates in water suspensions, (iii) specific surface area, (iv) spectral extinction coefficient, (v) spectral absorption coefficient, and (vi) spectral scattering coefficient. The last three were obtained as a function of wavelength in the range 275−405 nm. All measurements were made following a standardized protocol for the preparation of the solid suspensions. Scattering and absorption effects could be deconvoluted from the extinction coefficient by applying a very simple radiation transport model to the analysis of the experimental data. Experimental information was obtained by means of specially designed spectrophotometric measurements made with conventional cells, combined with results obtained with an integrating sphere accessory operated in the transmission mode. These propertiesparticularly the optical onesare required to solve the RTE and (i) to calculate precise values of photocatalytic reaction quantum yields and (ii) to fully characterize radiation energy absorption effects in the kinetics of photocatalytic reactions. Moreover, these data are indispensable for devising scaleup procedures in photocatalytic reactor design.

The evaluation of the radiation field inside a slurry reactor constitutes a central step in the study of photocatalytic reactions. This task can be achieved by solving the radiative transfer equation (RTE) for the system under study. To solve the RTE, three optical properties of the catalyst suspensions are needed:  the absorption coefficient, the scattering coefficient, and the phase function for scattering. In the present work, a novel experimental method to measure the optical properties of aqueous titanium dioxide (TiO2) suspensions is proposed. The method involved diffuse reflectance and transmittance spectrophotometric measurements of the catalyst suspensions, the evaluation of the radiation field in the sample cell, and the application of a nonlinear optimization program to adjust the model predictions to the experimental data. Three commercial brands of TiO2 were investigated:  Aldrich, Degussa P25, and Hombikat UV 100.

The radiation field for an annular-type photocatalytic reactor has been modeled, and the resulting integro-differential equation has been solved resorting to the discrete ordinate method. The spatial domain was described in terms of two cylindrical coordinates and the field of direction with two angular variables. The radiation entering through the inner reactor wall was obtained from the extended source with voluminal emission model. The system parameters for the radiative-transfer equation were taken from experimental measurements. Resorting to computational experiments, the effects produced by different concentrations of (1) transparent scattering centers and (2) radiation absorbing (catalytic) particles were investigated. In the second case, Aldrich and Degussa P 25 titanium dioxide particles were used. The following information is reported:  (1) specific intensities as a function of position inside the reactor and of the angular distribution of directions; (2) incident radiation profiles and local volumetric rate of energy absorption profiles, both as a function of the spatial position inside the reactor.