ABSORPTION AND SCATTERING COEFFICIENTS OF TITANIUM-DIOXIDE PARTICULATE SUSPENSIONS IN WATER

Precise kinetic studies of photocatalytic reactions in solid catalyst water suspensions require the accurate description of the radiation fi eld-light distribution-inside the reactor. Solution of the radiative t ransport equation (RTE) inside the reaction is one of the best ways of accessing to such information. For solving this equation, a minimum o f two parameters (the absorption and scattering coefficients) and one scattering spatial distribution function (the phase function) are need ed. These attributes are directly associated with the optical behavior of the reacting system and are not independent of catalysts more conv entional properties. A complete report on the physical and optical cha racteristics of titanium dioxide particulate suspensions in water is p resented. Results were obtained for six different commercially availab le powders. The investigated parameters were (i) size of elementary pa rticles, (ii) size of particle aggregates in water suspensions, (iii) specific surface area, (iv) spectral extinction coefficient, (v) spect ral 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 protoc ol for the preparation of the solid suspensions. Scattering and absorp tion effects could be deconvoluted from the extinction coefficient by applying a very simple radiation transport model to the analysis of th e experimental data. Experimental information was obtained by means of specially designed spectrophotometric measurements made with conventi onal cells, combined with results obtained with an integrating sphere accessory operated in the transmission mode. These properties-particul arly the optical ones-are required to solve the RTE and (i) to calcula te precise values of photocatalytic reaction quantum yields and (ii) t o fully characterize radiation energy absorption effects in the kineti cs of photocatalytic reactions. Moreover, these data are indispensable for devising scaleup procedures in photocatalytic reactor design.