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

Oxynitrides are promising visible-light-responsive photocatalysts, but their structures are almost confined with three-dimensional (3D) structures such as perovskites. A phase-pure Li2LaTa2O6N with a layered perovskite structure was successfully prepared by thermal ammonolysis of a lithium-rich oxide precursor. Li2LaTa2O6N exhibited high crystallinity and visible-light absorption up to 500nm. As opposed to well-known 3D oxynitride perovskites, Li2LaTa2O6N supported by a binuclear Ru-II complex was capable of stably and selectively converting CO2 into formate under visible light (>400nm). Transient absorption spectroscopy indicated that, as compared to 3D oxynitrides, Li2LaTa2O6N 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.