Thermal Treatment of a Keggin‐Type Diplatinum(II)‐Coordinated Polyoxotungstate: Formation of Hydrophilic Colloidal Particles and Photocatalytic Hydrogen Production

Abstract

Hydrophilic platinum‐polyoxotungstate colloidal particles formed by a self‐assembly of Cs4[{Pt(OH)2}2·SiW12O40] were successfully obtained by calcining a cesium salt of α‐Keggin‐type diplatinum(II)‐coordinated silicotungstate, Cs4[α‐SiW11O39{cis‐PtII(NH3)2}2]·11H2O (Cs‐Si‐Pt), in air at 300 °C. During the thermal treatment, the structure of the mono‐lacunary Keggin‐type silicotungstate ligand {SiW11O39} transformed to that of {SiW12O40}, and the diplatinum sites in Cs‐Si‐Pt transformed to the platinum hydroxides with the elimination of the ammonia molecules coordinated to the platinum sites. All four cesium ions in Cs4[{Pt(OH)2}2·SiW12O40] could be ion‐exchanged by four tetramethylammonium ions, and hydrophilic [(CH3)4N]4[{Pt(OH)2}2·SiW12O40] colloidal particles were also formed in aqueous solution. The calcined sample acted as a photocatalyst for hydrogen evolution from aqueous triethanolamine (TEOA) under visible light irradiation (λ = ≥440 nm) in the presence of Eosin Y, K5[α‐SiW11{Al(OH2)}O39]·7H2O, and titanium dioxide. Although relatively rapid deactivation was observed, the turnover frequency was 3588 h–1 after 20 min, and the turnover number exceeded 4600 after 3 h of light irradiation.