Effects of Coapplication of Rh-Doping and Ag-Substitution on the Band Structure of Li2TiO3 and the Photocatalytic Property

Formation of impurity levels by doping and control of valence bands by substitution with suitable elements into photocatalyst materials are useful strategies for sensitization of metal oxide photocatalysts with a wide band gap to visible light. In the present study, we demonstrated energy gap narrowing of a metal oxide photocatalyst by coapplication of the doping and the substitution. Rh-doped and Ag(I)-substituted Li2TiO3 (AgLi1/3Ti2/3O2:Rh, 2.2-2.3 eV) was successfully synthesized from Rh-doped Li2TiO3 (Li2TiO3:Rh, 3.0-3.2 eV) with a molten AgNO3 treatment. The AgL1/3Ti2/3O2:Rh possessed a narrower energy gap than either Li2TiO3:Rh or Ag(I)-substituted Li2TiO3 (AgL1/3Ti2/3O2, 2.8 eV). The AgLi1/3Ti2/3O2:Rh showed the activity for photocatalytic O-2 evolution from an aqueous AgNO3 solution under irradiation of light with wavelength longer than 480 nm under which AgLi1/3Ti2/3O2 did not show the activity. The photocatalytic activity of AgLi1/3Ti2/3O2:Rh for the sacrificial O-2 evolution became similar to 4 times greater by Sb-codoping. The optimum doping levels of Rh and Sb were 1% and 2% in Li1/3Ti2/3O2 layers of AgLi1/3Ti2/3O2:Rh,Sb, respectively.