Photocatalytic Reduction of Carbon Dioxide over Ag Cocatalyst-Loaded ALa4Ti4O15 (A = Ca, Sr, and Ba) Using Water as a Reducing Reagent

Ag cocatalyst-loaded ALa(4)Ti(4)O(15) (A = Ca, Sr, and Ba) photocatalysts with 3.79-3.85 eV of band gaps and layered perovskite structures showed activities for CO2 reduction to form CO and HCOOH by bubbling CO2 gas into the aqueous suspension of the photocatalyst powder without any sacrificial reagents. Ag cocatalyst-loaded BaLa4Ti4O15 was the most active photocatalyst. A liquid-phase chemical reduction method was better than impregnation and in situ photodeposition methods for the loading of the Ag cocatalyst. The Ag cocatalyst prepared by the liquid-phase chemical reduction method was loaded as fine particles with the size smaller than 10 nm on the edge of the BaLa4Ti4O15 photocatalyst powder with a plate shape during the CO2 reduction. CO was the main reduction product rather than H-2 even in an aqueous medium on the optimized Ag/BaLa4Ti4O15 photocatalyst. Evolution of O-2 in a stoichiometric ratio (H-2+CO: O-2 = 2:1 in a molar ratio) indicated that water was consumed as a reducing reagent (an electron donor) for the CO2 reduction. Thus, an uphill reaction of CO2 reduction accompanied with water oxidation was achieved using the Ag/BaLa4Ti4O15 photocatalyst.