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

Photocatalytic reactions employing finely divided titanium dioxide hav e become increasingly attractive, particularly for their potential app lications 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 t he reaction vessel. To describe this photon distribution, the radiatio n absorption and transport properties of the solid suspensions must be known inside the reaction space. From the fundamental principles of r adiative transport, an apparent property has been defined, the apparen t Napierian extinctance, which was used to investigate the optical pro perties of photocatalytic suspensions employing simple spectrophotomet ric measurements. The effects of particle size, particle concentration , stirring, recycling, environmental pH, oxygen bubbling and strong ir radiation on the apparent Napierian extinctance of titanium oxide susp ensions as a function of wavelength are reported. Data from different titanium oxides or titanium oxides having different nominal particle s izes, as well as from agglomerates formed after the stirring or recycl ing of neutral reacting solutions, cannot be interpreted in terms of a Lambert-type equation. These findings constitute a confirmation of pr edictions from radiation theory which indicate that at least two param eters, or more precisely, two parameters and one distribution function are required to describe fully the radiation transport even in non-re active solid suspensions.