Abstract:

Copper and tungsten codoped NaTaO₃(NaTaO₃: Cu/W) photocatalysts were prepared by a high-temperature solid state synthetic method. The effects of the molar ratio of Cu to W and the total doping amount on the phase structure, morphology, optical absorption properties as well as photocatalytic activities for hydrogen production from methanol aqueous solutions under visible light were studied. The results show that the metallic dopants exist in forms of Cu(Ⅱ) and W(Ⅵ) in NaTaO₃:Cu/W, respectively. The codoping of Cu and W into NaTaO₃ does not affect the crystal structure, but distorts the crystal lattice and decreases the characte-ristic steps on the surface. With increasing the total doping amount at a constant Cu/W molar ratio, the increased doping ions make the (020) diffraction peak gradually shift to higher angles as well as the red shift of the absorption edge to the visible light range. However, further increase of total doping amount results in the shift of the (020) diffraction peak to lower angle. This indicates that excessive metallic ions can not be doped into the lattice effectively. There is a maximum doping amount for the codoping of Cu, W into NaTaO₃. When the molar ratios of Cu to W are 1: 2, 1: 3 and 1: 4, the maximum total doping amount are 8%, 6% and 4%, respectively. NaTaO₃: Cu/W exhibits the enhanced photocatalytic activity for hydrogen evolution at the maximum total doping amount and obtains the highest activity when the molar ratios of Cu to W is 1: 4, the total doping amount is 4%. It indicates that the codoping of Cu and W ions into NaTaO₃ at an appropriate Cu/W molar ratio can maintain the charge balance to a great extent, suppress the formation of oxygen defects in the lattice and inhibit the recombination of photogenerated electrons and holes so that the photocatalytic activity for hydrogen production is improved.

Key words: High-temperature solid state synthetic method, NaTaO₃, Codoping, Photocatalytic hydrogen evolution