PHOTOCATALYTIC REACTORS .1. OPTICAL BEHAVIOR OF TITANIUM-OXIDE PARTICULATE SUSPENSIONS

Photocatalytic reactions employing finely divided titanium dioxide have become increasingly attractive, particularly for their potential applications to pollution abatement in water streams. Kinetic and reactor design studies require the knowledge of the existing radiation field in order to evaluate the volumetric rate of energy absorption inside the reaction vessel. To describe this photon distribution, the radiation absorption and transport properties of the solid suspensions must be known inside the reaction space. From the fundamental principles of radiative transport, an apparent property has been defined, the apparent Napierian extinctance, which was used to investigate the optical properties of photocatalytic suspensions employing simple spectrophotometric measurements. The effects of particle size, particle concentration, stirring, recycling, environmental pH, oxygen bubbling and strong irradiation on the apparent Napierian extinctance of titanium oxide suspensions as a function of wavelength are reported. Data from different titanium oxides or titanium oxides having different nominal particle sizes, as well as from agglomerates formed after the stirring or recycling of neutral reacting solutions, cannot be interpreted in terms of a Lambert-type equation. These findings constitute a confirmation of predictions from radiation theory which indicate that at least two parameters, or more precisely, two parameters and one distribution function are required to describe fully the radiation transport even in non-reactive solid suspensions.