PHOTOCATALYTIC REMOVAL OF NICKEL FROM AQUEOUS-SOLUTIONS USING ULTRAVIOLET-IRRADIATED TIO2

The photocatalytic removal of Ni(II) using ultraviolet (UV)-irradiated TiO2 suspensions is described. The photocatalytic reaction is shown t o be electron-mediated, and occurs both via direct electron transfer f rom the photoexcited TiO2 particles to Ni(II), and an indirect route a s described by previous authors. The latter requires the presence of a n organic additive (acetate, formate, or methanol) that generates an i ntermediate radical reductant via an initial hole-mediated reaction. T he effects of inorganic anions (chloride, sulfate) on the rate of Ni(I I) removal are described as are those of other variables including TiO 2 dose and solution pH. The direct electron-transfer route is shown to be kinetically sluggish, although it can be made fast by the addition of facile hole acceptors. The dark adsorption of Ni(II) on the TiO2 ( anatase) surface is also quantified in a chloride medium. The present data are discussed within the framework of previous studies on the UV/ TiO2 photocatalytic deposition of Ni(II) and other metal ions.