Photocatalytic Conversion of CO2 by H2O over Ag-Loaded SrO-Modified Ta2O5

We found that incorporation of alkaline earth metal oxides into Ag-loaded Ta2O5 (Ag/Ta2O5) suppresses the H-2 production from overall water splitting for the photocatalytic conversion of CO2 by using H2O as an electron donor. Four different combinations of the photocatalysts (Ag/MO/Ta2O5 (M = Mg, Ca, Sr, or Ba)) were utilized; of these, the highest amount of CO was generated over Ag-loaded SrO-modified Ta2O5 (Ag/SrO/Ta2O5) with the evolution of a stoichiometric amount of O-2. It was demonstrated that the presence of low quantities of SrO considerably enhanced the selectivity toward CO evolution. We also confirmed that a Ag cocatalyst increased the selectivity toward CO evolution and relatively small Ag nanoparticles maximized the selectivity toward CO evolution. It was therefore concluded that the particle size of the Ag cocatalysts should be controlled, and alkaline earth metal oxides should be introduced into Ag/Ta2O5 in order to achieve high conversion of CO2 and good selectivity toward O-2 evolution.