HETEROGENEOUS PHOTOCATALYTIC OXIDATION OF PHENOL WITH TITANIUM-DIOXIDE POWDERS

The photocatalytic oxidation of phenol in oxygenated solution with suspensions of titanium dioxide powders has been investigated. The experimental results indicate that there is an optimum value for the TiO2 content. Sufficient O2 supply is needed, but a too high gas flow rate induces large bubbles that eliminate the gas residence time and the gas/liquid contact interface. The initial concentration of phenol demonstrates a negative effect on the pseudo-first-order reaction rate constant. A mechanism of the phenoxide ions being adsorbed on the TiO2 surface has been proposed to account for this inverse effect. Moreover, the different pH regions affect the competitive adsorption between the phenoxide ions and OH- ions on the TiO2 surface, which in turn influences the generation of the hydroxyl radicals on the TiO2 surface.