Photocatalytic reduction of metals in presence of combustion synthesized nano-TiO2

The photocatalytic reduction of the metal ions, Cu(II) and Cr(VI), was investigated in presence of solution combustion synthesized (CS) nano-TiO2. The efficiency of this catalyst was compared with that of commercial titania, Degussa P-25. For the reduction of Cu2+, the first-order rate constants were 0.003 and 0.018 min(-1) in presence of Degussa P-25 and CS TiO2, respectively. For the reduction of Cr6+. the initial rate constants were 0.007 and 0.247 min(-1) in presence of Degussa P-25 and CS TiO2, respectively. Thus, the rate of reduction of Cu(II) and Cr(VI) is higher in CS TiO2 compared to Degussa P-25 TiO2. The effect of pH and the effect of initial concentration on the photocatalytic reduction of Cu(II) and Cr(VI) in presence of solution combustion synthesized TiO2) and Degussa P-25 catalyst were investigated. The variation of the photoreduction rate of Cu(II) and Cr(VI) with respect to pH correlates with the variation of the driving force, which is the difference between the standard reduction potential of the metal ion and the energy level of the electrons in the conduction band. The other metal ions like Zn(II), Cd(II), Pb(II) and Mn(II) could not be reduced in both the catalytic systems and this is attributed to the thermodynamic infeasibility of their reduction by photo generated electrons. (c) 2007 Elsevier B.V. All rights reserved.