Photocatalytic oxidation of sulfamethazine

The photocatalytic degradation of sulfamethazine (SMT), a sulfonamide drug, has been investigated in aqueous heterogeneous solutions containing n-type oxide semiconductors as photocatalysts. The disappearance of the organic molecule follows approximately a pseudo-first-order kinetics according to the Langmuir-Hinshelwood model. It was observed that, with TiO2 P-25 and ZnO as photocatalysts, quantitative degradation of the organic molecule occurs after 4 It. During this time the desulfurization of the substrate is complete, while only 30% of the nitrogen in the organic compound was recovered in the form of nitrate and ammonium ions, indicating that various other nitrogen-containing organic compounds remain in the solution. The addition of H2O2 leads, in the case of TiO2 P-25, to a twofold increase on the reaction rate, while a negative effect has been observed in the presence of ZnO. The initial apparent photonic efficiency (xi(0)) of the photooxidation and the mineralization under various experimental conditions have been calculated. (c) 2004 Elsevier Ltd. All rights reserved.