Photocatalytic properties of thin films of ruthenium metallopolymers/gold nanoparticle: Polyoxometalate composites using visible excitation

Abstract

Thin layers of an electrostatically associated adduct RuPVP-AuNP:POM formed between the polyoxomolybdate, [S₂Mo₁₈O₆₂]⁴⁻, the polycationic metallopolymer [Ru(bpy)₂(PVP)₁₀](ClO₄)₂ and DMAP-protected gold nanoparticle have been deposited onto electrodes using two separate methods, alternate immersion layer-by-layer assembly and pre-assembled drop-casting; PVP is poly(4-vinylpyridine), BPY is 2,2′-bipyridyl, and DMAP is 4-dimethylaminopyridine. Significantly, the efficiency of the photocatalysis depends markedly on the structure of the [RuPVP-AuNP:POM] even when photonic properties are very similar. Strikingly, despite their similar photonic properties, an additional optical transition is observed in UV-vis and the Raman spectra of pre-assembled drop cast [RuPVP-AuNP:POM], which was not seen in dip coated [RuPVP-AuNP:POM]. Importantly, this electronic communication enhances the photocatalytic oxidation of benzaldehyde by a factor of more than four. While there is clear evidence for photosensitisation in the drop cast not present for the dip coated systems, the magnitude of the photocurrent, i.e., (82.2±6.6) nA·cm⁻² for pre-assembled drop cast [RuPVP-AuNP:POM] at a ruthenium to Au nanoparticle mole ratio of 48:1, is twice as large as that those found in [Ru-PVP:POM] film.