Adsorption and photocatalytic degradation of phthalic acid on TiO2 and ZnO

The photocatalytic degradation of phthalic acid (H2Ph) with TiO2 (Degussa P-25) and ZnO (Aldrich) at different pHs and substrate concentrations (10-150 ppm) has been studied. The concentration and mineralization of H2Ph has been monitored. Results in optimal conditions are: k degrees = 6.63.10(-4) s(-1), %TOC = 86.02 for TiO2 and k degrees = 12.7.10(-4) s(-1), %TOC=81.90 for ZnO. Dissolved zinc was monitored during reaction. Zinc concentration in solution showed a maximum when that of the organic compound was at its minimum. At this step zinc in solution decreases. Catalyst solubility, catalyst photocorrosion and extraction by the substrate, could be main processes explaining dissolved zinc concentration along the reaction. Adsorption and rate constants have been obtained by using the Langmuir-Hinselwood model. Adsorption constants in the dark and adsorption constants obtained from Langmuir-Hinselwood kinetic model have been compared. The adsorption constant values in TiO2 studies are greater than in ZnO ones. Considering the relationship between degradation rate and surface bonding FTIR studies have been performed. FTIR results show that H2Ph molecule interacts with ZnO and TiO2 surfaces. In both cases, H2Ph interaction occurred by means of the formation of a phthalate.