Photocatalytic degradation of a mixture of Crystal Violet (Basic Violet 3) and Methyl Red dye in aqueous suspensions using Ag+ doped TiO2

The photocatalytic degradation of a mixture of two dyes: Crystal Violet (CV), also known as C.I. Basic Violet 3, which is a cationic triphenylmethane dye and Methyl Red (MR), which is an anionic azo dye was studied using untreated TiO2 and silver ion doped TiO2 under UV irradiation. To increase the photocatalytic efficiency of TiO2 and to make its separation from the treated effluent after degradation easier, it was doped with silver ion using liquid impregnation method. The degradation of the dyes in the mixture was measured spectrophotometrically at their respective λmax values. The degradation kinetics fitted well to the Langmuir–Hinselwood pseudo first order rate law. The effects of pH and different interfering substances like Cl−, NO3−, SO42−, HPO42−, Ca2+, Fe2+, humic acid, O2 and electron acceptors like H2O2, (NH4)2S2O8 and KBrO3 on the degradation were also investigated. Several mixtures of these dyes prepared by mixing CV (5 × 10−5 mol dm−3) and MR (7.5 × 10−5 mol dm−3) in the V/V ratios of 1:1, 1:5 and 1:10 degraded by >99% on UV irradiation for 90 min in the presence of Ag+ doped TiO2 and about 70% under similar conditions in presence of TiO2. COD removal was measured at regular intervals to quantify the mineralization of the dye. Above 86% mineralization was observed using 90 min irradiation.