Photocatalytic activity of Cu-doped titania prepared by controlling the Cu distribution

抄録

Cu-doped titania powders were prepared from the sol–gel reaction systems containing titanium tetraisopropoxide (TTIP) and copper(II) nitrate with different compositions. The copper(II) nitrate was added to the sol containing TTIP after a specific reaction period of the TTIP polymerization in order to control the Cu distribution in the titania. The Cu localization on the titania nanoparticle surface was indirectly estimated by the Cu chelation of 8-hydroxylquinoline on the surface. The photocatalytic activities of the samples concerning the decomposition of organic substances were quantified by the amount of the hydroxyl radical formed during ultraviolet (UV) and visible irradiations. The titania with dispersed Cu on the surface demonstrated a higher activity than that with dispersed Cu inside the bulk titania. The electrons in the titania conduction band caused by the UV photoexcitation were effectively transferred to the impurity states of Cu²⁺ on the titania surface. Some electrons in the titania valence band were directly transferred to the impurity states of Cu²⁺ upon the visible photoexcitation. Consequently, these processes suppressed the electron–hole charge recombination in the titania. It was confirmed again that a slight amount of the Cu highly dispersed only on the titania surface rather than inside the titania bulk was favorable for its high photocatalytic performance.