Construction of polyoxometalate-based metal−organic frameworks through covalent bonds for enhanced visible light-driven coupling of alcohols with amines

Abstract

Broad spectral response and rapid carrier transport are essential in making efficient photocatalysts. In this work, we utilized Keggin-type polyoxometalates (POMs) [CoIIW12O40]6– as metal-to-metal charge transfer (MMCT) chromophores and assembled them into metal–organic frameworks (MOFs) to construct visible-light-responsive, noble metal-free crystalline POM-based MOFs (POMOFs) (CoW-1 and CoW-2). The precise introduction of MMCT chromophores extending the light absorption of POMOFs to the visible region and improving the solar energy utilization efficiency, meanwhile, the Cu-O-W covalent bonds constructed in CoW-1 makes the framework structure more robust, reduces the interfacial contact resistance, facilitates the electron transfer, suppresses the recombination of the electron-hole pairs, improves the charge carriers separation efficiency, and boosts the quantum efficiency, thus achieving high catalytic activity in the coupling reaction of benzyl alcohol with aniline under visible light irradiation (>400 nm). In the presence of CoW-1, the reaction conversion yield was measured as 92.6 % with turnover frequency reaching 374.4 h−1, and the apparent quantum yield at 595 nm was calculated as 17.5 %, besides, CoW-1 also exhibited high catalytic stability and reusability. To the best of our knowledge, this is the first work describing the enhanced photocatalytic performance of POMOFs based on the synergistic effect of MMCT and covalent linkage.