Photocatalytic activities of Cu_3xLa_1-xTa ₇O₁₉ solid solutions for H₂ evolution under visible light irradiation

Development of new visible-light-driven oxide photocatalysts for H ₂ evolution was conducted with a concept of formation of solid solutions containing Cu(i) ions. Band gaps of Cu_3xLa _1-xTa₇O₁₉ solid solutions were 2.57-2.71 eV being remarkably narrower than that of LaTa₇O₁₉ (x = 0, 4.14 eV). The remarkable narrowing of the band gaps was due to the contribution of Cu 3d orbitals to valence bands. The solid solutions were capable of photocatalytic H₂ evolution under visible light irradiation in the presence of methanol as an electron donor. Interestingly, the solid solutions with x = 0.2-0.8 showed higher activities than that of a native Cu(i)-tantalate, Cu₃Ta₇O₁₉ (x = 0). Among the solid solutions, the x = 0.6 sample, Cu_1.8La_0.4Ta₇O ₁₉, exhibited the highest activity. The apparent quantum yield of the optimized photocatalyst was 0.48% at 420 nm. Moreover, the good stability of Cu(i) ions in the solid solutions was proven through the investigation of photocatalytic properties and the XPS analysis. Thus, new visible-light-driven oxide photocatalysts capable of H₂ evolution were developed by the formation of the Cu_3xLa_1-xTa₇O₁₉ solid solutions.