Sensitizing the Photocatalytic Ability of Dawson-Wells Polyoxometalates in Solution and Thin Films

Abstract

Heteropolyoxomolybdate anions exhibit rich redox and photochemistry enabled by the capacity of polyoxomolybdate to act as both electron and proton relays. They are widely investigated for application across domains involving photooxidation and photocatalysis. A key limitation though is that polyoxometallates such as [S2M18O62]4-, where M is W or Mo, are not signifantly activated by visible light. This presentation describes investigations into the sensitization of Dawson polyoxometallates photochemistry [S2Mo18O62]4- and [S2W18O62]4- by ruthenium(II)polypyridine complexes in solution and at modified electrodes. Electrostatically associated supramolecular structures comprising of ruthenium polypyridyl cations and polyoxoanions can be readily isolated as charge neutral adducts by combining the cation and anion in solution. For [Ru(bpy)3]2+ with [S2Mo18O62]4- or [S2W18O62]4- the polyoxometallate adducts are remarkably photostable. And [Ru(bpy)3]2+ the resulting clusters sensitises the very efficient photooxidation of organic substrates such as DMF and benzylalcohol by the polyoxometalates under visible irradiation, between 355 and 490 nm.. Resonance Raman spectroscopy was used to identify a charge transfer transition between Ru and polyoxometallate which suggests significant electronic communication in these cluster complex. Exploiting resonance Raman spectroscopy to identify the presence of the CT transition we took a combinatorial approach to identifying potentially sensitized Ru(II)-POM pairs and assemble the resulting pairs into layer by layer electrostatic assemblies at electrodes. The photoelectrochemical response of these systems, with a range of organic donors, including persistent pollutants diclofenac and ibuprofen is described. References Nigel Fay, Victoria M. Hultgren, Anthony G. Wedd, Tia E. Keyes, Deirdre Leane, Alan M. Bond, Dalton Trans, 2006, 4218 - 4227.Visible Light Sensitized Photocurrent Generation from Electrostatically Assembled Thin Films of [Ru(bpy)3]2+ and the polyoxometalate [W18O54(SO4)2]4-; Optimizing Performance in a low electrolyte media, James J Walsh; Jie Zhu; Alan M Bond; Robert J Forster, Tia E Keyes, 2013, Journal of Electroanal. Chem., 2013, 706, 93-101Hybrid Polyoxometalate Materials for Photo(electro-) chemical Applications., J. Walsh, A.M. Bond, R.J. Forster, T.E. Keyes, Coord. Chem Rev., Volume 306, Part 1, 1 January 2016, Pages 217–234 Figure 1