Photocatalytic degradation of photosensitizing and non-photosensitizing dyes over chromium doped titania photocatalysts under visible light

Abstract

A series of 0.5–4 mol% Cr-doped TiO2 photocatalysts were tested over photocatalytic degradation of photosensitizing (Methylene Blue) and non-photosensitizing (Congo Red) dyes under visible light irradiation. Presence of Cr dopant has induced anatase-rutile phase transition, leading to high rutile percentage of 45% in the material. Besides, the addition of Cr dopant has extended the absorption wavelength of TiO2 to visible light region. As evidenced from the fluorescence analysis, electron-hole recombination rate of Cr-doped TiO2 decreased with increasing of Cr dopant content up to 3 mol% in the materials. Despite using the same series of photocatalysts, the optimum amount of Cr dopant which gave the best photocatalytic activity was different: 1 mol% Cr-doped TiO2 and 3 mol% Cr-doped TiO2 were the best photocatalysts for photodegrading Methylene Blue and Congo Red, respectively. The results strongly suggested that the nature of targeted subtract in photocatalysis reaction affected the photocatalytic performance of the Cr-doped TiO2. Possible mechanisms for photocatalytic degradation of the two different dyes over the photocatalyst were presented.