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

Abstract

As the 600 nm-class photocatalyst, BaTaO 2 N is one of the promising candidates of the perovskite-type oxynitride family for photocatalytic water splitting under visible light. The oxynitrides are routinely synthesized by nitriding corresponding oxide precursors under a high-temperature NH 3 atmosphere, causing an increase in the defect density and a decrease in photocatalytic activity. To improve the photocatalytic activity by reducing the defect density and improving the crystallinity, we here demonstrate an NH 3 -assisted KCl flux growth approach for the direct synthesis of the BaTaO 2 N crystals. The effects of various fluxes, solute concentration, and reaction time and temperature on the phase evolution and morphology transformation of the BaTaO 2 N crystals were systematically investigated. By changing the solute concentration from 10 to 50 mol %, it was found that phase-pure BaTaO 2 N crystals could only be grown with the solute concentrations of ≥ 10 mol % using the KCl flux, and the solute concentration of 10 mol % was solely favorable to directly grow cube-like BaTaO 2 N crystals with an average size of about 125 nm and exposed {100} and {110} faces at 950 °C for 10 h. The time-and temperature-dependent experiments were also performed to postulate the direct growth mechanisms of cube-like BaTaO 2 N submicron crystals. The BaTaO 2 N crystals modified with Pt and CoO x nanoparticles showed a reasonable H 2 and O 2 evolution, respectively, due to a lower defect density and higher crystallinity achieved by an NH 3 -assisted KCl flux method.

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.…”

“…39 Absorption in the mid-IR region (<4000 cm −1 ) is associated with free electrons and/or shallowly trapped electrons. 38 The number of surviving electrons observed at 1400 cm −1 was increased with increasing the Ta content up to 75 mol% and slightly decreased at 100 mol% (Fig. 9c).…”

Fabrication of well-shaped Sr2KTa5O15 nanorods with a tetragonal tungsten bronze structure by a flux method for artificial photosynthesis

“…The formation rate of CO increased and that of H 2 dramatically suppressed over Sr 2 KTa 5 O 15 fabricated by the flux method, as compared to that prepared by the SSR method. Flux method as a simple and cost-effective way to fabricate well-shaped and well-crystallized particles has been widely investigated [25,32,33]. Sr 2 KTa 5 O 15 nanorods fabricated in KCl flux in a lower calcination temperature and shorter time showed the highest photocatalytic activity and good selectivity toward CO evolution comparing with that of samples fabricated using SSR method.…”

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

“…In this study, we have attempted to experimentally validate the results of previous theoretical calculations predicting the possible formation of the CdTiO 3-x N y , CdNbO 2 N, and CdTaO 2 N phases by applying conventional one- [11] and two-step [12,13] [16] have already been reported, this study will seek to understand the flux-induced growth of their isometric crystals and conversion to their corresponding (oxy)nitride derivatives under high-temperature NH 3 atmosphere. The effects of solute concentration and cooling rate on the flux growth of the CdTiO 3 , Cd 2 Nb 2 O 7 , and Cd 2 Ta 2 O 7 crystals and the impacts of nitridation temperature and time on the formation of their corresponding (oxy)nitride derivatives under high-temperature NH 3 atmosphere were investigated.…”