Insights into Decomposition Pathways and Fate of Ru(bpy)32+ during Photocatalytic Water Oxidation with S2O82–sup> as Sacrificial Electron Acceptor
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- 作者：Umme Sarmeen Akhtar ; Eunju Lee Tae ; Yu Sung Chun ; In Chul Hwang ; Kyung Byung Yoon
- 刊名：ACS Catalysis
- 出版年：2016
- 出版时间：December 2, 2016
- 年：2016
- 卷：6
- 期：12
- 页码：8361-8369
- 全文大小：561K
- ISSN：2155-5435
文摘
The most widely accepted system for homogeneous photocatalytic water oxidation process consists of a water oxidation catalyst, Ru<sup>IIsup>(bpy)3<sup>2+sup> as a photopump, and S2O8<sup>2–sup> as the sacrificial electron acceptor. However, this system is far less than ideal because Ru<sup>IIsup>(bpy)3<sup>2+sup> undergoes very rapid decomposition and as a result the process stops before all of the S2O8<sup>2–sup> is consumed. In this regard its decomposition pathways and the fate of Ru<sup>IIsup>(bpy)3<sup>2+sup> should be elucidated to design more efficient photocatalytic water oxidation systems. We found that two pathways exist for decomposition of Ru<sup>IIsup>(bpy)3<sup>2+sup> in the light–Ru<sup>IIsup>(bpy)3<sup>2+sup>–S2O8<sup>2–sup> system. The first is the formation of OH<sup>•sup> radicals at pH >6 through oxidation of OH<sup>–sup> by Ru<sup>IIIsup>(bpy)3<sup>3+sup> in the dark, which attack the bpy ligand of Ru<sup>IIsup>(bpy)3<sup>2+sup>. This is a minor, dark decomposition pathway. During irradiation not only Ru<sup>IIsup>(bpy)3<sup>2+sup> but also Ru<sup>IIIsup>(bpy)3<sup>3+sup> becomes photoexcited and the photoexcited Ru<sup>IIIsup>(bpy)3<sup>3+sup> reacts with S2O8<sup>2–sup> to produce an intermediate which decomposes into catalytically active Ru μ-oxo dimers when the intermediate concentration is low or into catalytically inactive oligomeric Ru μ-oxo species when the intermediate concentration is high. This is the major, light-induced decomposition pathway. When the Ru<sup>IIsup>(bpy)3<sup>2+sup> concentration is low, the light–Ru<sup>IIsup>(bpy)3<sup>2+sup>–S2O8<sup>2–sup> system produces O2 even in the absence of any added catalysts through the O2-producing dark pathway. When the Ru<sup>IIsup>(bpy)3<sup>2+sup> concentration is high, the system does not produce O2 because the overall rate for the light-induced decomposition pathway is much faster than that of the O2-producing dark pathway.