Core–shell-structured LaTaON${}_2$ transformed from LaKNaTaO${}_5$ plates for enhanced photocatalytic H${}_2$ evolution

LaTaON${}_2$ is a photocatalyst with intense visible light absorption up to 650 nm, but exhibits low H${}_2$ evolution activity owing to uncontrolled facets and high defect densities. In this work, core–shell-structured plate-like LaKNaTaO${}_5$/LaTaON${}_2$ was synthesized by nitriding a layered perovskite-type LaKNaTaO${}_5$. The volatilization of K and Na species during the nitridation promoted the rapid transformation of LaKNaTaO${}_5$ into LaTaON${}_2$ along [010] direction with the plate-like shape retained. This yielded high-quality LaTaON${}_2$ shells exposing (010) facets on the lattice-matched LaKNaTaO${}_5$ cores. After loading with a Rh co-catalyst, LaKNaTaO${}_5$/LaTaON${}_2$ showed photocatalytic H${}_2$ evolution activity four times greater than that obtained from conventional irregular-shaped LaTaON${}_2$ powders and utilized visible light up to 620 nm. This work provides a novel strategy yielding oxynitrides with well-defined facets and low defect densities by selecting lattice-matched oxide precursors containing volatile components. (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)