Photocatalytic degradation of a mixture of Crystal Violet (Basic Violet 3) and Methyl Red dye in aqueous suspensions using Ag + doped TiO 2

Abstract

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 TiO 2 and silver ion doped TiO 2 under UV irradiation. To increase the photocatalytic efficiency of TiO 2 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 λ max 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 −, NO 3 −, SO 4 2−, HPO 4 2−, Ca 2+, Fe 2+, humic acid, O 2 and electron acceptors like H 2O 2, (NH 4) 2S 2O 8 and KBrO 3 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 TiO 2 and about 70% under similar conditions in presence of TiO 2. COD removal was measured at regular intervals to quantify the mineralization of the dye. Above 86% mineralization was observed using 90 min irradiation.