Synthesis, Ion-Exchange and Photocatalytic Properties of Layered Perovskite-Like CsBa<sub>2</sub>Nb<sub>3</sub>O<sub>10</sub> Niobate: Comparative Analysis with Related AA′<sub>2</sub>Nb<sub>3<

Layered perovskite-like niobate CsBa2Nb3O10 has been synthesized in a pure single-phase state for the first time using both nitrates and carbonates of cesium and barium. Unlike its Ca-, Sr- and Pb-containing analogues, the niobate obtained was shown not to undergo substitution of interlayer alkali cations with protons (protonation) upon acid treatments under various conditions. A potential reason for its chemical inactivity may consist in partial disordering of cesium and barium cations between the interlayer space and perovskite slab, hindering the interlayer ion exchange. Optical bandgap energy of CsBa2Nb3O10, being equal to 2.8 eV, potentially allows using visible light (λ 443 nm) for driving photocatalytic reactions. However, the photocatalytic potential of this niobate towards hydrogen production remains untapped since the activity of the interlayer space in protonation and hydration reactions, as shown earlier, is a fundamentally important factor determining the photocatalytic performance of ion-exchangeable layered perovskite-like oxides.