PHOTOSYNTHETIC MEMBRANES .23. DEGRADATION OF SOME CHLOROALIPHATIC WATER CONTAMINANTS BY PHOTOCATALYTIC MEMBRANES IMMOBILIZING TITANIUM-DIOXIDE

The TiO2-mediated photodegradation of chloroethanoic acid, trichloroethene and tetrachloroethene, chosen as model molecules of aliphatic chloro-organics was studied at 303 +/- 2 K by employing polymeric membranes photografted on cellulose to immobilize the TiO2 (3.0-5.6 mg cm-2). The radiant flux in the absorption range and the volume-surface ratio in the photoreactor cell were kept constant at 2.5 +/- 0.2 mW cm-2 and 1.1 +/- 0.1 mL cm-2 respectively. The initial rate of photodegradation was studied as a function of the initial concentration of reactants by the linearized form of the Langmuir-Hinshelwood equation, by which rate constants k and equilibrium adsorption constants K were evaluated. Values of k (5.7 +/- 0.5-mu-mol h-1) are independent of the chemical nature of the three reactants investigated, in agreement with other literature findings. Values of K are compared with those measured in aqueous suspensions of TiO2 with the same chloro-organics and with the values predicted by a mechanism involving hydroxyl radicals as the primary oxidant adsorbed on the photocatalyst surface. Satisfactory performance and potential technological advantages of photocatalytic membranes are discussed.