Observation of Photocatalytic Dissociation of Water on Terminal Ti Sites of TiO2(110)-1 x 1 Surface
Observation of Photocatalytic Dissociation of Water on Terminal Ti Sites of TiO2(110)-1 x 1 Surface
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TiO2(110)-1 x 1 表面末端 Ti 位点光催化解离水的观察
DOI：
10.1021/ja211919k
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发表时间：
2012-06-20
影响因子：
15
通讯作者：
Hou, J. G.
中科院分区：
文献类型：
--
作者：
Tan, Shijing;Feng, Hao;Hou, J. G.
基于TiO 2光催化剂的水裂解反应是氢能技术中具有重要意义的基础过程之一，已得到广泛的研究。然而，在理解水裂解的反应序列中，一个长期令人困惑的问题是，初始反应步骤是否是光催化过程以及它是如何发生的。在此，我们使用低温扫描隧道显微镜（STM）在80 K下进行，观察到在波长短于400 nm的紫外光照射下，在还原的TiO 2（110）-1 X 1表面的5重配位Ti（Ti-5c）位点处的单独吸附的水分子解离1 h，或者说其能量大于金红石型TiO 2的3.1eV的带隙。因此，这一发现清楚地表明了产生两种羟基物质的光催化解离过程的参与。一个总是存在于相邻的桥接氧位点，即OHbr，另一个要么发生在远离原始的Ti-5c位点的OHt，甚至从表面脱附。相比之下，针尖诱导的水的解离只能在原始Ti-5c位点上产生OHt或氧吸附原子，而没有痕量的OHbr。这种差异清楚地表明，水的光催化解离经历了一个过程，显着不同于由尖端注入的电子的附着。我们的研究结果表明，在紫外光照射下的水离解的初始步骤可能不会被电子还原，但最有可能被光子产生的空穴氧化。
The water splitting reaction based on the promising TiO2 photocatalyst is one of the fundamental processes that bears significant implication in hydrogen energy technology and has been extensively studied. However, a long-standing puzzling question in understanding the reaction sequence of the water splitting is whether the initial reaction step is a photocatalytic process and how it happens. Here, using the low temperature scanning tunneling microscopy (STM) performed at 80 K, we observed the 1 h dissociation of individually adsorbed water molecules at the 5-fold coordinated Ti (Ti-5c) sites of the reduced TiO2 (110)-1 X 1 surface under the irradiation of UV lights with the wavelength shorter than 400 nm, or to say its energy larger than the band gap of 3.1 eV for the rutile TiO2. This finding thus clearly suggests the involvement of a photocatalytic dissociation process that produces two kinds of hydroxyl species. One is always present at the adjacent bridging oxygen sites, that is, OHbr, and the other either occurs as OHt at Ti-5c sites away from the original ones or even desorbs from the surface. In comparison, the tip-induced dissociation of the water can only produce OHt or oxygen adatoms exactly at the original Ti-5c sites, without the trace of OHbr. Such a difference clearly indicates that the photocatalytic dissociation of the water undergoes a process that differs significantly from the attachment of electrons injected by the tip. Our results imply that the initial step of the water dissociation under the UV light irradiation may not be reduced by the electrons, but most likely oxidized by the holes generated by the photons.