Undoped Layered Perovskite Oxynitride Li₂LaTa₂O₆N for Photocatalytic CO₂ Reduction with Visible Light

Abstract

Oxynitrides are promising visible-light-responsive photocatalysts, but their structures are almost confined with three-dimensional (3D) structures such as perovskites. A phase-pure Li₂ LaTa₂ O₆ N with a layered perovskite structure was successfully prepared by thermal ammonolysis of a lithium-rich oxide precursor. Li₂ LaTa₂ O₆ N exhibited high crystallinity and visible-light absorption up to 500 nm. As opposed to well-known 3D oxynitride perovskites, Li₂ LaTa₂ O₆ N supported by a binuclear Ru^II complex was capable of stably and selectively converting CO₂ into formate under visible light (λ>400 nm). Transient absorption spectroscopy indicated that, as compared to 3D oxynitrides, Li₂ LaTa₂ O₆ N possesses a lower density of mid-gap states that work as recombination centers of photogenerated electron/hole pairs, but a higher density of reactive electrons, which is responsible for the higher photocatalytic performance of this layered oxynitride.