Photocatalytic degradation of methyl blue by silver ion-doped titania: Identification of degradation products by GC-MS and IC analysis

An anionic triphenyl methane dye, methyl blue ((disodium;4-[4-[[4-(4-sulfonatoanilino)phenyl]-[4-(4-sulfonatophenyl)azaniumylidenecyclohexa-2,5-dien-1-ylidene]methyl]anilino]benzene sulfonate) was degraded photocatalytically with undoped micro-TiO2- and Ag+-doped micro TiO2 in a slurry-type batch reactor under UV irradiation and the efficiency was compared with that obtained using nano-TiO2- and Ag+-doped nano-TiO2. The influence of different parameters, i.e., photocatalyst loading, dye concentration, initial pH, temperature, depth of solution, interfering ions and electron acceptors on the dye degradation was investigated. The decolorization and mineralization efficiency was better for Ag+-doped micro-TiO2 than undoped micro-TiO2. Nano-TiO2 was more efficient than micro-TiO2, while Ag+-doped nano-TiO2 was the most efficient of all. Cost analysis showed degradation using micro-TiO2- and Ag+-doped micro-TiO2 are much cheaper than that using nano-TiO2 and Ag+-doped nano-TiO2. Therefore Ag+-doped micro-TiO2 was used for the detailed study. The degradation products formed were identified using GC-MS analysis after photocatalytic degradation for 180min with Ag+ -doped micro TiO2. Ion chromatography analysis was carried out for anions to identify the end products of degradation.