Photodegradation of Orange II solutions by TiO 2 active layers jet sprayed on aluminium sheets

Abstract

In this work, active TiO 2 layers have been immobilized, on aluminium sheets, by a common and cheap deposition technique: jet spray. The layers’ adhesion to the substrate was achieved by mixing the titania with a commercial thermally adherent polyester ink, which is industrially used for aluminium surface treatment (lacquering). The layers’ photocatalytic performance was tested in the degradation of the organic dye Orange II in aqueous solutions, in a batch photoreactor under visible and solar light, and compared with TiO 2 (anatase) suspensions. The layers’ photocatalytic behaviour was evaluated taking into account different experimental variables, such as: (i) layer thickness; (ii) operation time; (iii) TiO 2/polyester ink weight ratio and (iii) dye solution concentration and pH. A better performance was attained for layers having a 1:1 weight ratio of TiO 2 and polyester ink and a thickness of 60 μm (100 g/m 2). These layers showed an interesting discolouration performance: an attenuation degree of 95% and discolouration rate, assuming an apparent first order reaction, reaching 2.2 × 10 −3 min −1. These results were attained for the naturally resulting dye solution pH of ≈7, and for the lowest dye concentration of 20 mg/L. Therefore, neither alkalinisation or acidification of the dye solution nor the utilization of high-concentration solutions is recommended. Despite the slower kinetics, the dye degradation level achieved is similar to that obtained for TiO 2 powder suspensions. Thus, these treated layered aluminium pieces can be considered as a serious alternative to photocatalytic suspensions of the oxide, with the advantage of excluding the removal of the photocatalyst at the end of the process.