Synergy effect in the photocatalytic degradation of phenol on a suspended mixture of titania and activated carbon

TLDR: In this article, the photocatalytic degradation of phenol, chosen as an aromatic model molecule, has been performed at room temperature (20°C) in contact with a suspended mixture of titania and activated carbon (AC).

Abstract: The photocatalytic degradation of phenol, chosen as an aromatic model molecule, has been performed at room temperature (20°C) in contact with a suspended mixture of titania and of activated carbon (AC). Non-additive adsorption capacities were observed when the solids were mixed, and this was ascribed to a strong interaction, involving half of the surface of titania and ca. 14% of that of AC. A synergy effect was observed with an increase of the first order rate constant by a factor of 2.5. 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, suggesting that the same reaction mechanism occurred in the presence of photoinactive AC. The synergy effect was ascribed to an extended adsorption of phenol on AC followed by a transfer to titania where it is photocatalytically degraded. The synergy effect could not be improved by previous physical treatments of the solid mixture such as grinding and sonication. Some phenol remained adsorbed on AC when no traces of organic compounds were detected in the purified water. This adsorbed phenol could be destroyed by illuminated titania while maintaining UV-irradiation. This combined photocatalytic system may appear as a new performing one, more efficient with a shorter time necessary for decontaminating diluted used waters.