Unique phase transformation behavior and visible light photocatalytic activity of titanium oxide hybridized with copper oxide

The nanoscale hybridization of titanium oxide with copper oxide was carried out to control the phase transformation behavior of titanium oxide and develop a new photocatalyst active in visble light. Analysis by X-ray diffraction, electron microscopy, and nitrogen adsorption-desorption isotherm to gauge pore size distribution showed that intercalative hybridization between copper oxide and titanium oxide produced a mesoporous layer-by-layer interstratified heterostructure with a repeating distance of ∼24.2 Å and an average pore size of ∼52 Å. X-ray absorption spectroscopy at Cu K- and Ti K-edges clearly demonstrated that divalent copper oxides were interstratified with lepidocrocite-type titanium oxide. As a result of the modification of band structure, the resulting nanohybrids showed high activity for photoinduced degradation of organic dye molecules under visible light illumination. Heat-treatment of the nanohybrids at 500°C produced anatase TiO₂ at the expense of intermediate rutile TiO₂ formed in the lower temperature region (300-400°C). This suggests a phase transition from rutile TiO₂ to anatase TiO₂. This phenomenon is related to the variation in the surface energy of titania caused by the redox process of hybridized copper oxide and by the phase transition of co-existing Ti-deficient titanium oxide.