Heterogeneous photocatalytic activity of transition-metal cation impregnated TiO2

Abstract

Irradiation of aqueous Ti02 dispersions containing metal ions with light of energy equal or greater than the bandgap of the catalyst. leads to a deposition on the semiconductor particle surface. This photodeposition process may be a phtotoreduction or an irreversible photosorption process depending on the redox potential of the couples in the solution. In this study, preparation of Ti02 impregnated by some selected cations of the first transition series: ( Cr(III), Mn(II), Fe(III), Fe(Il), Co(II) and Ni(II)] using dark and photocatalytic impregnation methods has been demonstrated. and the photocatalytic activity of these samples in photodegradation of 4-chlorophenol in aerated aqueous solutions has beeinvestigated by gas chromatography techniques. The effect of sulfate anion on the degree of 4-chlorophenol photooxidation to C02 has also been studied by the same method. The addition of alcohols, which scavenge the holes of the illuminated TiO2 renders the photodeposition process more efficient by preventing the recombination of holes with electrons on the catalyst's surface. This effect has been examined by using methanol as a model hole scavenger. Finally, BET surface areas for Co(II) and Ni(II) impregnated Ti02 samples were measured in a Micromeritics Flowsorb II 2300 instrument.