Decolourising textile wastewater with modified titania: the effects of inorganic anions on the photocatalysis
In this study, the environment of the TiO2 photocatalyst modified with silver was investigated. The photocatalytic degradation of textile dye Astrazone Orange G was carried out in the presence and absence of common inorganic salts to determine the effect of the anionic species. It was shown that degradation of dyes in the first 20 min in the presence of anions exhibited different behaviour. While the catalytic activity of TiO2 was significantly retarded in the presence of common inorganic anions it was not affected or was promoted in many cases with Ag-loaded TiO2. In TiO2/UV system positive charged holes (h(+)) might be scavenged by the negatively charged anions and the adsorption of dyes on the surface of TiO2 was significantly inhibited. However, this inhibition effect was not observed with modified titania and possible mechanism was thought to be the trapping of the conductive band electrons by silver islands producing more positively charged holes as well as the reduction of the band gap energy. Additionally, the adsorption of the dye on the Ag-TiO2 catalyst surface was significantly increased in the presence of anions and this might be responsible for another promoting effect. (C) 2002 Elsevier Science B.V. All rights reserved.