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

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.