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
analogs, 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.