Size Control of LaNbON 2 Particles for Enhanced Photocatalytic Water Oxidation Under Visible Light Irradiation

Perovskite‐type LaNbON 2 has the longest wavelength onset of visible light absorption—up to approximately 740 nm—among (oxy)nitrides based on transition metals Ti, Ta, and Nb. Water oxidation using visible‐light‐responsive LaNbON 2 is challenging because the synthesis of the oxynitride has rarely been studied. Herein, we report the synthesis of small LaNbON 2 particles and their size effect on photocatalytic water oxidation under visible light illumination. The small scheelite‐type LaNbO 4 , prepared by a polymerized complex method, was transformed into less‐defective LaNbON 2 during nitridation as compared with that nitrided from LaNbO 4 via a solid‐state reaction method. The small LaNbON 2 particles, capable of absorbing intense visible light 700 nm above, improved the O 2 evolution during 5 h of water oxidation under 300 W Xe light irradiation (λ > 420 nm). This enhancement was attributed to the size reduction of LaNbON 2 particles, leading to increased surface area and encouragement of mild nitridation.