Solar photocatalytic degradation of 4-chlorophenol using the synergistic effect between titania and activated carbon in aqueous suspension

The photocatalytic degradation of 4-chlorophenol, chosen as an aromatic model pollutant, has been performed in contact with a suspended mixture of titania and of activated carbon (AC). Non-additive adsorption capacities were observed when the two solids were mixed. This was ascribed to a strong interaction between both solids. A synergy effect was observed with an increase of the first order rate constant by a factor of 2.4. As for neat titania, the same main intermediate products (hydroquinone and benzoquinone) were found but in much smaller quantities and during a much smaller lifetime. The synergy effect was ascribed to an extended adsorption of 4-chlorophenol on AC followed by a transfer to titania where it is photocatalytically degraded. When extrapolating these experiments by a volume factor of 12 500 to the solar pilot plant at PSA, an identical synergy factor of 2.4 was found, thus confirming the transpositivity of laboratory experiments to large solar set-ups. The synergy effect was not destroyed when re-using the double phase photocatalyst. This combined photocatalytic system may appear as a new performing one, more efficient with a shorter time necessary for decontaminating diluted used waters, which could be of interest in producing drinking water in dry sunny areas. (C) 1999 Elsevier Science B.V. All rights reserved.