NH₃-Assisted Flux-Mediated Direct Growth of LaTiO₂N Crystallites for Visible-Light-Induced Water Splitting

Photocatalytic overall water splitting on (oxy)nitrides under visible light is one of the interesting approaches to fulfill the growing demand for clean and renewable energy. The improvement of the fabrication method is however important for reducing the defect density of (oxy)nitride crystals. The present study aims to investigate the direct growth of the LaTiO₂N (LTON) crystallites with less defect density by an NH₃-assisted flux method and to demonstrate the visible-light-induced photocatalytic water oxidation activity in relation to their crystallite morphology. Single-phase LaTiO₂N crystallites (average size of 120 ± 39 nm) in round shape with smooth surface and high crystallinity were grown by an NH₃-assisted flux method using the KCl flux with the solute concentration of 5 mol % at 950 °C for 10 h. The photocatalytic water oxidation activity of bare and CoO_x-loaded LaTiO₂N crystallites grown directly by an NH₃-assisted flux method (1-step-LTON) was evaluated under visible light by comparing with the LaTiO₂N crystallites fabricated by a two-step method (2-step-LTON), converting La₂Ti₂O₇ to LaTiO₂N by high-temperature nitridation. Within the first 2 h of the photocatalytic water oxidation half-reaction, the O₂ evolution rates of bare and CoO_x-loaded 1-step-LTON crystallites were 82 μmol·h^-1 and 204 μmol·h^-1, respectively, which are much higher than that of bare and CoO_x-loaded 2-step-LTON crystallites (37 μmol·h^-1 and 177 μmol·h^-1) due to less defect density of the LaTiO₂N crystallites achieved by a direct fabrication route using KCl flux. An NH₃-assisted flux growth is a promising route for the direct fabrication of the LaTiO₂N crystallites with less defect density that is beneficial for the enhancement of photocatalytic water oxidation half-reaction.