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

Abstract

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 LaTiO 2 N (LTON) crystallites with less defect density by an NH 3 -assisted flux method and to demonstrate the visible-light-induced photocatalytic water oxidation activity in relation to their crystallite morphology. Single-phase LaTiO 2 N crystallites (average size of 120 ± 39 nm) in round shape with smooth surface and high crystallinity were grown by an NH 3 -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 LaTiO 2 N crystallites grown directly by an NH 3 -assisted flux method (1-step-LTON) was evaluated under visible light by comparing with the LaTiO 2 N crystallites fabricated by a two-step method (2-step-LTON), converting La 2 Ti 2 O 7 to LaTiO 2 N by high-temperature nitridation. Within the first 2 h of the photocatalytic water oxidation half-reaction, the O 2 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 LaTiO 2 N crystallites achieved by a direct fabrication route using KCl flux. An NH 3 -assisted flux growth is a promising route for the direct fabrication of the LaTiO 2 N crystallites with less defect density that is beneficial for the enhancement of photocatalytic water oxidation half-reaction.

The contrasting effect of the Ta/Nb ratio in (111)-layered B-site deficient hexagonal perovskite Ba5Nb4−xTaxO15 crystals on visible-light-induced photocatalytic water oxidation activity of their oxynitride derivatives

“…Clearly, all samples showed absorption peaks at 15 000 cm −1 assignable to photogenerated holes. Similarly, absorption peaks located in the visible light region were also observed previously for LaTiO 2 N, 21,22 BaTaO 2 N, 38 and Ta 3 N 5 . 34 The intensity of the absorption peaks at 15 000 cm −1 was notably changed with the Ta content (Fig.…”

NH3-Assisted Flux Growth of Cube-like BaTaO2N Submicron Crystals in a Completely Ionized Nonaqueous High-Temperature Solution and Their Water Splitting Activity

“…The details of TAS measurements were reported elsewhere. 42,43 Figure 11 shows the TA spectra of 1-step-BTON and 2-step-BTON. The observed transient absorption from 20000 to 1500 cm -1 can be divided into three parts: a relatively sharp peak at ~ 16000 cm -1 , broad absorption at 13000-6000 cm -1 , and 3000-1500 cm -1 .…”

KCl flux-induced growth of isometric crystals of cadmium-containing early transition-metal (Ti 4+ , Nb 5+ , and Ta 5+ ) oxides and nitridability to form their (oxy)nitride derivatives under an NH 3 atmosphere for water splitting application

“…For the nitrided crystal samples, the slope of the UV-Vis spectra became steeper with increasing the nitridation temperature and time due to the gradual conversion of the mixed phases of TaON and Ta 3 N 5 to single-phase Ta 3 N 5 . Meantime, the intensity of the background absorption beyond the absorption edge increased with increasing the nitridation temperature and time, which is generally indicative of the presence of increased defects associated with the reduced tantalum species and anion deficiency[29,30]. It can be deduced that highly porous Ta 3 N 5 crystalline structures with their retained isometric shapes and high crystallinity are expected to show better photocatalytic activity for water splitting and the decomposition of organic pollutants under visible light irradiation.21The chemical composition analysis was conducted by EDS, XPS, and ICP for the detailed investigation of the amounts of cadmium, potassium, and nitrogen as well as the oxidation state of tantalum in the flux-grown Cd 2 Ta 2 O 7 crystals and as-convertedTa3 N 5 crystalline structures, and the results are compiled in Figure 7.…”