Photocatalytic degradation of methylene blue dye from aqueous solution using silver ion-doped TiO₂ and its application to the degradation of real textile wastewater.

Methylene blue dye (MB) was degraded photocatalytically in aqueous solution using Ag(+) doped TiO(2) under UV irradiation. The degradations of the dye using untreated TiO(2) and Ag(+) doped TiO(2) were compared. Ag(+) doped TiO(2) was found to be more efficient. Using Ag(+) doped TiO(2) the filtration process was eliminated, as the particles became more settleable. The effect of various parameters such as catalyst loading, initial dye concentration, depth of solution, degree of adsorption, pH and O(2) on dye degradation was studied. The extent of mineralization was studied by observing the COD removal at different time intervals. The effects of various interfering ions such as Cl(-), NO(3) (-), CO(3) (2-), SO(4) (2-), Ca(2+) and Fe(3+) and electron acceptors such as H(2)O(2), KBrO(3) and (NH(4))(2)S(2)O(8) on the dye degradation was also studied. The degradation kinetics fitted well to Langmuir-Hinshelwood pseudo first order rate law. An aqueous solution of MB (20ppm) degraded by more than 99% after UV irradiation for 180 min with Ag(+) doped TiO(2) (2 g/L) and by more than 95% with untreated TiO(2) (2 g/L)(.) The COD removal was more than 91% with Ag(+)doped TiO(2) and more than 86% with untreated TiO(2) after 240 min. The degradation and COD removal of 5 times diluted textile wastewater was more than 98% and 79% respectively with 1 g/L Ag(+) doped TiO(2) after UV irradiation for 420 min.