Charge-regulated sequential adsorption of anionic catalysts and cationic photosensitizers into metal-organic frameworks enhances photocatalytic proton reduction

Abstract

We have developed a simple, general, and efficient method for constructing photocatalytic active metal-organic framework (MOF)-based composite materials for visible light-driven hydrogen production. Here, several transition metal-substituted Wells−Dawson-type polyoxometalates (POMs) were successfully immobilized into a Cr-MOF of the MIL-101 structure, resulting in a series of POM@MOF composite materials [POM=K8HP2W15V3O62·9H2O (P2W15V3), K8P2W17(NiOH2)O61·17H2O (P2W17Ni), K8P2W17(CoOH2)O61·16H2O (P2W17Co)]. We adjust the charge of MIL-101 framework by introducing Wells−Dawson-type POM anions with highly negative charge into the MOF. The MIL-101 framework absorbs the anionic POM, while the charge overcompensation in the POM@MOF composites allow them to efficiently adsorb cationic dyes. These composite materials accommodate and enrich cationic photosensitizer (PS) ruthenium(II) tris(bipyridyl) (Ru(bpy)32+) from the solution, allowing the PSs to surround the POM proton reduction catalysts, resulting in a heterogeneous catalytic device POM@PSs@MOF with much higher photocatalytic activity than that of the corresponding homogeneous catalytic system. POM@MIL-101 could also be readily recycled and reused in catalytic reaction. Furthermore, this strategy was extended to sequential adsorption of anionic Mo2S122− and cationic PSs to lead to highly active photocatalytic proton reduction system with a H2 evolution rate of up to 25578μmolh−1g−1 (corresponding to Mo2S122− catalyst) in 8h under visible light irradiation.