Visible Light Activity of Photocatalytic Composites Composed of Metal Oxides

CuxBiyOz particles were prepared by sintering at 973 K in air after mixing CuO and Bi2O3 particles. CuxBiyOz particles over 50 mol% of CuO content were composed of CuBi2O4 and CuO crystalline phases. Absorbance in wavelength range above 460 nm increased with increasing CuO content in CuxBiyOz. Composites of CuxBiyOz and WO3 particles could decompose 2-propanol into CO2 under visible light irradiation, whereas CuxBiyOz and WO3 particles did not show independently such visible light activity. The visible light activity in WO3/CuxBiyOz, composite increased with increasing WO3 content in the region of weight ratio WO3/CuxBiyOz of 1/2 to 2/1. It will be realized in the composites that an electron photoexited to the conduction band of WO3 can transfer to combine with a hole formed on the valence band of photoexcited CuxBiyOz, whereas an electron and a hole left in the photoexcited CuxBiyOz and WO3, respectively, bring about redox reaction. As the quantum yield of WO3 is approached to that of CuxBiyOz in the composite, the transfer efficiency of photoexcited electron from WO3 to CuxBiyOz will increase to result in an increase in the visible light activity.