Photocatalytic degradation of Methyl Red dye in aqueous solutions under UV irradiation using Ag+ doped TiO2

Methyl Red (CI Acid Red 2), an anionic azo dye, was degraded photocatalytically under UV irradiation using both untreated TiO2 and Ag+ doped TiO2. The dye degradation was more efficient in case of Ag+ doped TiO2. COD was measured at regular intervals to examine the extent of mineralization of the dye. The dye degradation was investigated at different pH, catalyst loading, substrate concentration as well as different concentration of interfering substances such as Cl−, NO−3, SO2−4, HPO2−4, Ca2+, Fe2+ and humic acid. The degradation of the dye was also compared in the presence and absence of O2. The aqueous solution of the dye (20 ppm) on UV irradiation for 45 min with TiO2 degraded by >85% where as it degraded by >99% with Ag+ doped TiO2. The aqueous solution of the dye (20 ppm) degraded by >90% on illumination by a simulated solar light source for 10 hours with Ag+ doped TiO2. The dye (20 ppm) was found to mineralise by >83% on photodegradation with Ag+ doped TiO2 for 1 h. The degradation kinetics fit well to the Langmuir-Hinselwood rate law.