PHOTOTRANSFORMATION OF HYDROPHOBIC POLLUTANTS IN AQUEOUS-MEDIUM .1. PAHS ADSORBED ON SILICA

A methodology is proposed to study the photochemical transformation of water insoluble organic pollutants dispersed in aqueous medium in the adsorbed state on chemically stable supports. The photochemical behaviours of three PAHs : anthracene, phenanthrene and benz[a]anthracene, adsorbed on two kinds of silica are studied as examples. The major products obtained in steady irradiation in the range 300-350 nm were quinones and hydrogen peroxide ; a minor formation of hydroxylated photoproducts was also observed. Silica plays an active role in the reaction since the rate of photooxidation is higher with silica than with ferric oxide, montmorillonite or cellulose. A mechanism involving a charge transfer is suggested. The kinetics is rather complex : it depends on silica, on the mass ratio PAH/silica and on the extent of the reaction.