Double Doping of NaTaO₃ Photocatalysts with Lanthanum and Manganese for Strongly Enhanced Visible-Light Absorption

Perovskite-structured tantalates, NaTaO₃ in particular, have been at the forefront of solar energy conversion to generate hydrogen fuel via photocatalytic water splitting. However, their application as a photocatalyst remains impractical due to their inability to absorb long-wavelength light. One promising scheme for extending the material response to long-wavelength light is via the charge compensation of doped cations with lanthanum and a transition metal. In this research, NaTaO₃ is doubly doped with lanthanum and manganese, a 3d-block transition metal, for visible-light sensitization. Following the double doping, the light absorption is extended to the near-infrared region. The doubly doped samples not only strongly absorb visible light but also produce electrons under visible-light irradiation (420 < λ < 740 nm). EDX confirms the one-to-one ratio of dopant incorporation, and nanometer-resolution elemental mapping with TEM demonstrating that La and Mn are incorporated at approximately the same location in the particles. EXAFS furthermore reveals that La occupies the Na site, while Mn occupies the Ta site. These findings suggest that La pairs with Mn at the neighboring site to form a LaMnO₃–NaTaO₃ solid solution.