Photocatalytic degradation of an azo dye in a tubular continuous-flow photoreactor with immobilized TiO2 on glass plates

The photocatalytic degradation of C.I. Acid Red 27 (AR27), an anionic monoazo dye of acid class, in aqueous solutions was investigated in a tubular continuous-flow photoreactor with immobilized TiO2 on glass plates. The removal percent is a function of photoreactor length, volumetric flow rate and light intensity. The removal efficiency increases as the light intensity increases but it decreases when the flow rate is increased. The AR27 degradation was followed through HPLC, UV-vis and chemical oxygen demand (COD) analyses. The results of these analyses showed that the final outlet stream from the photoreactor was considerably mineralized. NH4+, NO3-, NO2- and SO42- ions were analyzed as mineralization products of nitrogen and sulfur heteroatoms, respectively. Results show that the final concentration of SO42- ions and N-containing mineralization products are less than the final expected stoichiometric values. Based on the results obtained in present and previous studies, a reaction pathway for the photocatalytic degradation of AR27 is proposed. The kinetic analysis of the decolorization of AR27 in continuous-mode shows a pseudo-first-order reaction. Results show that a linear relation exists between pseudo-first-order reaction rate constant and reciprocal of volumetric flow rate. (c) 2006 Elsevier B.V. All rights reserved.