Photocatalytic reactivity of zinc and cadmium ions in UV-irradiated titania suspensions

The reduction of Zn(II) and Cd(II) species to their corresponding metallic form is characterized by negative reduction potentials in aqueous media. Thus the direct reduction of these species by photogenerated electrons in UV-irradiated titania (Degussa, P 25) suspensions is difficult unless co-additives are present. This paper presents such scenarios involving nitrate and organic additives and describes conditions where facile conversion of Zn(II) and Cd(II) species can be secured. The photocatalysis reaction products depend on the conditions extant in the TiO2 dispersions and can be either the corresponding oxy-hydroxy compound or the metal. Interesting interfacial changes occur when formate ions are added to a TiO2 suspension containing Zn(II) species. Such changes were probed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.