Flux‐Assisted Synthesis of Prism‐like Octahedral Ta₃N₅ Single‐Crystals with Controllable Facets for Promoted Photocatalytic H₂ Evolution

Abstract

Crystal facet engineering has emerged as one of the most important strategies for designing highly efficient photocatalysts with improved charge separation efficiency. Tantalum nitride (Ta3N5) is one of the most popular visible‐light‐responsive photocatalysts, but the controllable synthesis of well‐shaped Ta3N5 single‐crystals with clear facets is still challenging due to the harsh synthesis conditions. Herein, the first demonstration is given that prism‐like octahedral Ta3N5 single crystals with preferential exposure of {001}, {010}, and {102} facets can be synthesized via the mixed KCl–LiCl flux. Meanwhile, the effects of flux type (KCl, LiCl, and KCl–LiCl), flux ratio, nitridation time, etc. on the phase composition, crystallinity, and morphology of Ta3N5 are studied. Detailed structural characterizations verify its high crystallinity and relatively low defect density. Furthermore, growth of the Ta3N5 single crystal with controllable facets is demonstrated to follow a bottom‐up growth mechanism involving dissolution, recrystallization, and precipitation processes. As a probe test, the as‐obtained Ta3N5 single crystals exhibit about five times the promoted photocatalytic H2 evolution rate with respect to the conventional Ta3N5 nanoparticles, demonstrating the advantages of the specific facet‐defined structure. This finding offers a new avenue to prepare (oxy)nitrides with facets exposed for promising solar energy conversion.

Nanostructure Engineering and Modulation of (Oxy)Nitrides for Application in Visible‐Light‐Driven Water Splitting

“…Reproduced with permission. [39] Copyright 2020, Wiley-VCH. Ta 3 N 5 single crystals with preferential exposure of (001), (010), and (102) facets have been successfully synthesized (Figure 7d).…”

“…Thus, the enhanced photocatalytic H 2 evolution activity is achieved because of high crystallinity and decreased defect density. [ 39 ]…”

“…d) Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images of prism-like Ta 3 N 5 crystals. Reproduced with permission [39]. Copyright 2020, Wiley-VCH.…”

Strategies and Methods of Modulating Nitrogen-Incorporated Oxide Photocatalysts for Promoted Water Splitting

“…23 The addition of flux salts is expected to reduce the nitridation temperature and serve as a useful variable for tuning the chemical and physical properties of the final (oxy)nitrides. 24,25 Chloride salts of alkali metals such as NaCl, KCl, RbCl, and CsCl have been widely used as flux salts, and the morphology of the (oxy)nitrides could be modulated by the Cl − adsorption. 26,27 As revealed by Hojamberdiev et al, the KCl flux salt will induce the formation of cubelike BTON with high crystallization (Figure 4a−c), and the melting of the molten salt provides a highly reactive solvent environment because its high mobility and volatility characteristics facilitate the crystal growth process of BTON.…”

Metallic Powder Promotes Nitridation Kinetics for Facile Synthesis of (Oxy)Nitride Photocatalysts

“…[2] Among these methodologies, the flux salt-assisted nitridation strategy has received significant attention, in which flux salts, such as NaCl, KCl, RbCl, and CsCl, have been employed as reaction solvents to effectively promote nitrogen diffusion during the high-temperature nitridation process. [14][15][16][17] However, one limitation of the flux salt-assisted nitridation methods is that the residue of certain flux salts may negatively affect the photocatalytic performance of the (oxy)nitride semiconductors, [18] even after several washings. Additionally, flux salts may also react with nitridation precursors, producing certain impurities.…”