AN EXPERIMENTAL-METHOD FOR THE DETERMINATION OF THE PHOTON FLOW REFLECTED AND ABSORBED BY AQUEOUS DISPERSIONS CONTAINING POLYCRYSTALLINE SOLIDS IN HETEROGENEOUS PHOTOCATALYSIS

An experimental method for the evaluation of the photon flow reflected and absorbed by aqueous dispersions containing polycrystalline solids is proposed. The method is based on actinometric measurements. It is shown that the values obtained are independent of the particle sizes and of the concentration of the solids at least in the experimental conditions and in the range used in the present study (particle size range: 40-500 μm; solids concentration: 0.1-2 g liter-1). The results suggest that the values obtained should be attributed to the interfaces formed between the surface of the solids and the medium. The method is applied to a photocatalytic reaction, namely to the photodegradation of phenol carried out in a batch system using aqueous dispersions containing TiO2 or other semiconductors and insulators for comparison. It is also proposed to use separately two parameters for evaluating the photocatalytic efficiency: the "apparent quantum yield" and the "turnover number.". © 1991.