Disparate roles of doped metal ions in promoting surface oxidation of TiO2 photocatalysis

Abstract

The key standpoint favors the role of doped metal ions as electron traps in enhancing surface-charge separation during TiO2 photocatalysis. Besides that, this study demonstrated two disparate impacts of metal ion doping on reactive species generation during TiO2 photocatalysis. Ag+ and Cu2+ outperformed other dopants in photooxidation of oxalic acid (OA), while further increasing their doping amount from the optimum value produced a negligible impact on the photocatalytic performance. This implied other dominant roles of doped metal ions other than electron captors, because an excessive amount of traps can serve as charge-recombination centers and largely decrease the photocatalytic activity. N-2 purging and NaF (a scavenger for surface-radicals) markedly reduced the mineralization rate after Ag+ doping, verifying the significance of dissolved oxygen (DO) in reactive species generation upon TiO2 surface. Non-(OH)-O-center dot reactive oxygen species (ROS) were found to account for 75% in OA mineralization, attributed to enhanced DO adsorption towards TiO2 surface by Ag+ doping. However, Cu2+ doping could facilitate the oxidation by h(vb)(+) plus (OHads)-O-center dot, which took as dominant a part as 53%. Ag+-Cu2+ co-doping integrated these two positive sides and more inclined to the role of Ag+. Correspondingly, surface oxidation dominated whereas liquid-phase oxidation weakened. (C) 2015 Elsevier B.V. All rights reserved