Decolouration of Orange II solutions by TiO2 and ZnO active layers screen-printed on ceramic tiles under sunlight irradiation

in this work TiO2 and ZnO layers have been deposited by screen-printing in common ceramic tiles. These layers were characterized and tested for the photocatalytic degradation of organic dye Orange 11 in aqueous solutions, under direct exposure to the sunlight. Optimal processed layers showed an interesting decolourisation performance, as denoted by an attenuation degree of 90% and decolouration rate, assuming an apparent first order reaction, reaching 2.9 x 10(-3) min(-1). In the actual conditions, TiO2, layers show superior performance than ZnO. The previous alkalinisation of the dye solution is not recommended, since better performance is achieved under the naturally resulting pH (6.7) of the solution (20 g/L). Thus these layered ceramic tiles can be regarded as an alternative to photocatalytic suspensions of the same material with the advantage of avoiding the removal of the photocatalyst at the end of the process. (C) 2008 Elsevier B.V. All rights reserved.