The effects of inorganic anions (SO42-, H2PO4-, HCO3-, F-) on the photoactivity of surface bond-conjugated TiO2/SiO2 and Fe-TiO2/SiO2 for the photodegradation of Acid Red B were investigated. The introduction of iron changed the chemical environment of lattice titanium and the surface charge properties of TiO2/SiO2. Fe-TiO2/SiO2 inhibited the negative role of the selected inorganic anions. The effects of different light sources and dyes of various structure, with a sulfonate group, on the role of F- in decolorization of Acid Red B were examined. F- has the same negative influence on the photoactivity of TiO2/SiO2 with the blacklight lamp and solar irradiation, but shows no influence upon irradiation with the 254 nm lamp. The tested inorganic anions affected the photodegradation of dyes by controlling their adsorption onto the surface of the catalyst and by trapping h(+) and (OH)-O-.. (C) 2004 Society of Chemical Industry.