A Hexadecanuclear Cobalt-Added Tungstogermanate Containing Counter Cobalt Hydrates: Synthesis, Structure and Photocatalytic Properties

Abstract

The synthesis and exploration of the properties of structurally-new polyoxometalates (POMs) has been attracting considerable research interest. In this work, a hexadecanuclear cobalt-added tungstogermanate, H31(NH4)5Na16{CoⅢ(H2O)6}4{[CoⅡ4(μ3-OH)3(PO4)]4(A-α-GeW9O34)4}2·23-H2O (1), was synthesized under hydrothermal conditions and characterized by various techniques. Compound 1 can effectively drive the heterogeneous photocatalytic hydrogen evolution reaction in the presence of [Ir(ppy)2(dtbbpy)][PF6] as the photosensitizer, with triethanolamine (TEOA) and N-Hydroxy succinimide (NHS) used as the dual sacrificial reagents. Control experiments revealed the important role of NHS in enhancing the hydrogen-evolution activities. Under optimal catalytic conditions, a hydrogen yield of 54.21 μmol was achieved after 10-h photocatalysis, corresponding to a hydrogen evolution rate of 1807.07 μmol·g−1·h−1. Stability studies demonstrated that catalyst 1 can be isolated and reused for three successive photocatalytic cycles with negligible decline of the H2 yield, indicating the stability and recycling robustness of catalyst 1.