An unprecedented polyoxometalate-encapsulated organo–metallophosphate framework as a highly efficient cocatalyst for CO2 photoreduction

Abstract

The photocatalytic reduction of CO₂ to chemical fuels is attractive for addressing both the greenhouse effect and the energy crisis, but the key challenge is the design and synthesis of photocatalysts with remarkable performance under visible-light irradiation. Herein, we present two novel polyoxometalate-based organo–metallophosphate frameworks (POMPOs), formulated as [Zn₄(PO₄)(C₇H₈N₄)₆][BW₁₂O₄₀]·2H₂O (1) and [Co₄(PO₄)(C₇H₈N₄)₆][BW₁₂O₄₀]·1.5H₂O (2). According to the single crystal analysis, both compounds possess host organo–metallophosphate (OMPO) frameworks constructed with PO₄³⁻ anions, with the Keggin-type polyoxometalate H₅BW₁₂O₄₀ (BW₁₂) as a guest encapsulated in these size-matched frameworks. Due to the synergistic combination of the POMs and OMPO frameworks in the system of photocatalytic CO₂ reduction, compound 2 could act as a highly efficient cocatalyst in combination with the [Ru(bpy)₃]Cl₂ complex. The CO generation rate over compound 2 is 10 852 μmol g⁻¹ h⁻¹ with a high selectivity of 93.4%, which is superior to that of most reported POM-based or MOF-based catalysts for CO₂ photoreduction. To our knowledge, this is the first report of OMPO frameworks functionally combined with Keggin-type POMs being extended for the photoreduction of CO₂ and this affords a new pathway for the efficient photoconversion of CO₂ to CO.