Ammonothermal synthesis and photocatalytic activity of lower valence cation-doped LaNbON2

Abstract

Highly crystalline pure perovskite-type LaNbON2 powders were synthesized in supercritical ammonia using sodium hydroxide as an oxygen source. Additionally, doping LaNbON2 with cations of lower valence than that of the parent cation was performed to inhibit reduction of Nb5+. Various characterization methods indicated that crystallinity, particle morphology, and absorption edge of the product, that is, the factors possibly affecting photocatalytic activity, were not significantly changed by the doping of a lower-valence cation. Nevertheless, the doped LaNbON2 synthesized using the ammonothermal method evolved hydrogen, suggesting that this type of doping decreases the formation of reduced niobium species and consequently enhances the photocatalytic activity of LaNbON2. In case of doped LaNbON2 synthesized using conventional method, no hydrogen evolution was observed. This difference is probably due to the higher crystallinity of ammonothermally synthesized LaNbON2. Therefore, we successfully produced LaNbON2 with improved potential for photocatalytic activity for hydrogen evolution under visible light irradiation using ammonothermal synthesis and lower-valence cation doping.