Visible light assisted photocatalytic degradation of azo dyes

Irradiation of aqueous solutions of azo dyes by visible light in the presence of titanium dioxide thin films resulted in the degradation of the organic dye pollutants to harmless intermediates and colorless products. The dyes that were studied are: Chicago Sky Blue 6B and Benzopurpurin 4B. Results obtained indicated that complete mineralization of the dyes took place under the experimental conditions. There was an increase in conductivity after the complete mineralization experiments possibly indicating the formation of ions such as NO3- and SO42-. Changing some experimental conditions like pH, temperature and starting concentrations of dyes affected the rate of dye degradation. There was an increase in the rate of disappearance of the dye color at lower pH. Very high concentrations of dye solutions required long degradation times.