Flux-Assisted Synthesis of Prism-like Octahedral Ta_3N_5 Single-Crystals with Controllable Facets for Promoted Photocatalytic H_2 Evolution

摘要

Crystal facet engineering has emerged as one of the most important strategies for designing highly efficient photocatalysts with improved charge separation efficiency. Tantalum nitride (Ta_3N_5) is one of the most popular visible-lightresponsive photocatalysts, but the controllable synthesis of well-shaped Ta_3N_5 single-crystals with clear facets is still challenging due to the harsh synthesis conditions. Herein, the first demonstration is given that prism-like octahedral Ta_3N_5 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 Ta_3N_5 are studied. Detailed structural characterizations verify its high crystallinity and relatively low defect density. Furthermore, growth of the Ta_3N_5 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 Ta_3N_5 single crystals exhibit about five times the promoted photocatalytic H_2 evolution rate with respect to the conventional Ta_3N_5 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.