新規エネルギー変換型光触媒による水分解のダイナミクス

K_4Nb_6O_<17>是一种层状光催化剂，可以将水分解成氧和氢。二维夹层为化学反应提供了极大的空间。在层与层之间插入合适的染料分子，实现光催化反应的可见光响应。在这些情况下，层和染料分子之间的电荷转移被认为是整个光催化化学反应中重要的初级过程。利用飞秒瞬态吸收光谱研究了K_4Nb_6O_<17>和染料插层K_4Nb_6O_<17>中光激发诱导的超快过程。阐明了带隙激发产生的载流子的动力学，如电子-空穴复合和电子转移。研究了Ru(bpy)_3^<2+>插层在K_4Nb_6O_<17>中的动力学，以明确快速的前后电子转移过程是如何发生的。在K_4Nb_6O_<17>中发现了一个覆盖整个可见光区域的较宽的瞬态吸收带。二阶动力学分析表明，载流子在二维层中迁移，发生电子-空穴复合。寿命长于纳秒的物种也被观察到，这对于高催化活性是重要的。以Ru(bpy)_3^<2+>插层的k4nb_6o_ <17>薄膜为例，在400 nm处激发发现Ru(bpy)_3^<2+>的基态吸收带发生了瞬态漂白，而K_4Nb_6O_<17>不能被激发。Ru(bpy)_3^<2+>的漂白表现出与水中不同的快速非指数衰减。从该样品在可见光照射下表现出光催化反应性来看，Ru(bpy)_3^<2+>的电子转移应该是通过Ru(bpy)_3^<2+>的光激发进行的。因此，观察到的动力学可以从发生在皮秒和纳秒以上的时间区域的相对快速的电子转移和随后的重组来讨论。超快光谱技术可以成功地揭示实际应用的光催化剂中一些重要的初级事件。这些结果有望为新型催化剂的设计提供参考。少

K_4Nb_6O_<17> is known to be a layered photocatalyst to split water into oxygen and hydrogen. The two-dimensional interlayer provides an extremely large area for chemical reactions. Intercalation of suitable dye molecules between the layers achieves visible light response for the photocatalytic reaction. In these cases, charge transfer between the layer and dye molecules is considered to be an important primary process in a whole photocatalytic chemical reaction. By using femtosecond transient absorption spectroscopy, we have investigated ultrafast processes induced by photoexcitation in K_4Nb_6O_<17> and dyeintercalated K_4Nb_6O_<17>. Dynamics of charge carriers generated by bandgap excitation, such as electron-hole recombination and electron transfer was elucidated. The dynamics of Ru(bpy)_3^<2+> intercalated in K_4Nb_6O_<17> was investigated to make clear how fast forward and back electron transfer processes take place.A broad transient absorption band covering the whole visible reg … More ion, which could be ascribed to trapped electrons in K_4Nb_6O_<17>, was observed. The decay was essentially analyzed by second order kinetics, which indicates that the carriers can migrate in the two-dimensional layer and then electron-hole recombination occurs. Long lifetime species surviving longer than nanoseconds was also observed, which would be important for high catalytic reactivity. It the case of the K_4Nb_6O_<17> film intercalated with Ru(bpy)_3^<2+>, transient bleaching of the ground state absorption band of Ru(bpy)_3^<2+> was observed by excitation at 400 nm which cannot excite K_4Nb_6O_<17>. The bleaching of Ru(bpy)_3^<2+> showed fast and non-exponential decay different from that in water. From the fact that this sample shows photocatalytic reactivity under visible light irradiation, electron transfer from Ru(bpy)_3^<2+> should take place by photoexcitation of Ru(bpy)_3^<2+>. Therefore, observed dynamics can be discussed in terms of relatively fast electron transfer and following recombination occurring in the time regions of picosecond and longer than nanosecond.Ultrafast spectroscopy could successfully reveal some important primary events in the practically used photocatalysts. These results are expected to contribute for design of new catalysts. Less