Layered Perovskite Compound NaLaTiO<sub>4</sub> Modified by Nitrogen Doping as a Visible Light Active Photocatalyst for Water Splitting
Xiaoxiang Xu, Ran Wang, Xiaoqin Sun, Meilin Lv, Shuang Ni
Abstract
Sr2TiO4 and NaLaTiO4 are structural congeners with K2NiF4-type layered perovskite structure. However, nitrogen doping results in distinct modifications to their visible light absorption. Na/La ordering in the structure of NaLaTiO4 brings interesting structural features that are critical to a wealth of important factors such as nitrogen uptake, defect concentration, microstructures, and so forth. In sharp contrast to nitrogen-doped Sr2TiO4 (i.e., Sr2TiO4–xNy) whose photocatalytic activity is negligible under visible light illumination, nitrogen-doped NaLaTiO4 (i.e. NaLaTiO4–xNy) demonstrates very high activities for both photocatalytic water reduction and oxidation reactions. High apparent quantum efficiency ∼3.2% at 420 ± 20 nm has been recorded for NaLaTiO4–xNy, outperforming many other active metal oxynitride photocatalysts investigated under similar conditions. Theoretical calculations reveal that Na/La ordering incurs a strong electric field across Ti(O, N)6 octahedron layers and breaks the coplanar settlement of highest occupied molecular orbitals and lowest unoccupied molecular orbitals which are helpful to inhibit intralayer charge recombination.