Enhanced Water Oxidation on Ta3N5 Photocatalysts by Modification with Alkaline Metal Salts
Enhanced Water Oxidation on Ta3N5 Photocatalysts by Modification with Alkaline Metal Salts
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DOI：
10.1021/ja3095747
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发表时间：
2012-12-12
影响因子：
15
通讯作者：
Domen, Kazunari
中科院分区：
文献类型：
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作者：
Ma, Su Su Khine;Hisatomi, Takashi;Domen, Kazunari
氮化钽（Ta3N5）是用于太阳能水分解的有前景的氮化物半导体光催化剂，因为其具有能够在可见光（λ <590 nm）下从水中产生氢和氧的带边电势。然而，Ta3N5的光催化性能远低于预期，因为氧化物前体热氮化时的不充分结晶增强了不期望的电荷复合，限制了光催化反应的量子效率。在本研究中，通过用少量碱金属（AM）盐对起始Ta2O5的表面进行改性，成功地纠正了这个问题。与传统的Ta3N5相比，AM盐改性的Ta2O5氮化的Ta3N5具有更好的结晶度和更小的颗粒，更光滑的表面，最重要的是，在可见光下的光催化活性提高了6倍。AM盐改性与O-2析出助催化剂如CoOx的负载相容，在500 - 600 nm处产生5.2%的表观量子效率。这表明AM改性的效果归因于Ta3N5的结晶度和形貌的变化，而不是催化效果。详细表征的Na2CO3-改性的Ta3N5建议部分溶解Ta2O5和成核NaTaO3在氮化的早期阶段，这引起了特征的颗粒形态和提高氮化产物的结晶度。这项研究表明，对起始材料进行简单的预处理可以大大提高光催化剂的物理和光催化性能，从而能够开发用于太阳能水分解的先进光催化剂。
Tantalum nitride (Ta3N5) is a promising nitride semiconductor photocatalyst for solar water splitting because it has band edge potentials capable of producing hydrogen and oxygen from water under visible light (lambda < 590 nm). However, the photocatalytic performance of Ta3N5 has been far below expectations because insufficient crystallization upon thermal nitridation of the oxide precursors enhances undesirable charge recombination limiting the quantum efficiency of the photocatalytic reaction. This problem was successfully rectified in this study by modifying the surface of the starting Ta2O5 with a small amount of alkaline metal (AM) salts. Compared with conventional Ta3N5, Ta3N5 nitrided from AM salt-modified Ta2O5 had better crystallinity and smaller particles with smoother surfaces and, most importantly, demonstrated a 6-fold improvement in photocatalytic activity for O-2 evolution under visible light. AM salt modification was compatible with the loading of an O-2 evolution cocatalyst, such as CoOx, yielding an apparent quantum efficiency of 5.2% at 500-600 nm. This indicates that the effects of AM modification were attributable to the changes in the crystallinity and the morphology of Ta3N5 rather than to catalytic effects. Detailed characterization of the Na2CO3-modified Ta3N5 suggested partial dissolution of Ta2O5 and nucleation of NaTaO3 in the early stages of nitridation, which gave rise to the characteristic particle morphologies and improved the crystallinity of the nitridation products. This study demonstrates that a facile pretreatment of a starting material can improve the physical and photocatalytic properties of photocatalysts drastically, enabling the development of advanced photocatalysts for solar water splitting.