Visible‐Light‐Induced Water Oxidation Mediated by a Mononuclear‐Cobalt(II)‐Substituted Silicotungstate |
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| Authors: | Rui Xiang Prof?Dr Yong Ding Prof?Dr Junwei Zhao |
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| Institution: | 1. State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000 (China), Fax: (+86)?931‐8912582;2. State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029 (China);3. Henan Key Laboratory of Polyoxometalate Chemistry, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, Henan 475004 (P. R. China) |
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| Abstract: | A mononuclear‐cobalt(II)‐substituted silicotungstate, K10Co(H2O)2(γ‐SiW10O35)2] ? 23 H2O (POM‐ 1 ), has been evaluated as a light‐driven water‐oxidation catalyst. With in situ photogenerated Ru(bpy)3]3+ (bpy=2,2′‐bipyridine) as the oxidant, quite high catalytic turnover number (TON; 313), turnover frequency (TOF; 3.2 s?1), and quantum yield (ΦQY; 27 %) for oxygen evolution at pH 9.0 were acquired. Comparison experiments with its structural analogues, namely Ni(H2O)2(γ‐SiW10O35)2]10? (POM‐ 2 ) and Mn(H2O)2(γ‐SiW10O35)2]10? (POM‐ 3 ), gave the conclusion that the cobalt center in POM‐ 1 is the active site. The hydrolytic stability of the title polyoxometalate (POM) was confirmed by extensive experiments, including UV/Vis spectroscopy, linear sweep voltammetry (LSV), and cathodic adsorption stripping analysis (CASA). As the Ru(bpy)3]2+/visible light/sodium persulfate system was introduced, a POM–photosensitizer complex formed within minutes before visible‐light irradiation. It was demonstrated that this complex functioned as the active species, which remained intact after the oxygen‐evolution reaction. Multiple experimental parameters were investigated and the catalytic activity was also compared with the well‐studied POM‐based water‐oxidation catalysts (i.e., Co4(H2O)2(α‐PW9O34)2]10? (Co4‐POM) and CoIIICoII(H2O)W11O39]7? (Co2‐POM)) under optimum conditions. |
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| Keywords: | cobalt oxidation photochemistry polyoxometalates water chemistry |
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