Photocatalytic removal of bromates with noble metal-modified titanium dioxide

TiO₂ modified with nobel metals (M/TiO₂, M = Pt, Pd, Ru, Rh, Ir, Au, Ag) was prepared by an impregnation method. The photocatalytic activity of M/TiO₂ for bromate removal was studied under UV or visible light. The results show that high loading of Pt and Ag improves the photocatalytic activity of TiO₂ on the removal of bromates up to 4.6 and 2.9 times, respectively. The photosensitization of the active species of the PtCl₄ at the surface of Pt/TiO₂ significantly improves the photocatalytic activity of TiO₂. Ag mainly existed on the surface of TiO₂ in the form of Ag⁰. During the photocatalytic removal process, Ag⁰ reacted with Br^- to form AgBr with visible light activity. Similar to PtCl₄, AgBr greatly improves the photocatalytic activity of TiO₂ for bromate removal under visible light. However, Pd/TiO₂, Ru/TiO₂, Au/TiO₂, Ir/TiO₂, Rh/TiO₂ and Ag/TiO₂ with low Ag loading can not enhance the separation efficiency of photogenerated electron and hole, or generate the active species with visible activity directly or indirectly. These materials become the recombination centers of the charge carriers, thus inhibits the photocatalytic activity of TiO₂ for bromate removal.