Photocatalytic water oxidation by persulfate (Na2S2O8) with [Ru(bpy)3]2+ (bpy=2,2′-bipyridine) as a photocatalyst provides a standard protocol to study the catalytic reactivity of water oxidation catalysts. The yield of evolved oxygen per persulfate is regarded as a good index for the catalytic reactivity because the oxidation of bpy of [Ru(bpy)3]2+ and organic ligands of catalysts competes with the catalytic water oxidation. A variety of metal complexes act as catalysts in the photocatalytic water oxidation by persulfate with [Ru(bpy)3]2+ as a photocatalyst. Herein, the catalytic mechanisms are discussed for homogeneous water oxidation catalysis. Some metal complexes are converted to metal oxide or hydroxide nanoparticles during the photocatalytic water oxidation by persulfate, acting as precursors for the actual catalysts. The catalytic reactivity of various metal oxides is compared based on the yield of evolved oxygen and turnover frequency. A heteropolynuclear cyanide complex is the best catalyst reported so far for the photocatalytic water oxidation by persulfate and [Ru(bpy)3]2+, affording 100 % yield of O2 per persulfate.
Bibliographical noteFunding Information:
The authors gratefully acknowledge the contributions of their collaborators and coworkers mentioned in the cited references, and support by ALCA and SENTAN projects (to S.F.) from Japan Science and Technology Agency (JST), Japan, JSPS KAKENHI (Grant Nos. 24350069 and 15K14223 to Y.Y., 24655044 to T. K.), and the NRF of Korea through CRI (NRF-2012R1A3A2048842 to W.N.) and GRL (NRF-2010-00353 to W.N.).
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- heterogeneous catalysis
- homogeneous catalysis
- water oxidation