Metal–Organic Cages as Porous Photosensitizers for Polyoxometalate Catalysts

Abstract Ionic metal–organic cages (MOCs) offer a unique platform to promote the reactivity of their functional counterions by forming “porous functional salts” (PFSs), but the role of MOCs has so far been limited to structuring and porogenic agent without strong coupling of properties. Herein, we report a new PFS, built from the assembly of the stable and noble-metal-free Keggin-type polyoxometalate (POM) SiW12O404– (SiW12) with a cationic Zr-based metal–organic cage (ZrT-NH2). While pristine SiW12 did not present any porosity or light absorption in the visible light region (above 400 nm), the PFS ZrT-NH2/SiW12 presented an appreciable surface area for a POM-based material (SBET(CO2) = 143 m2/g) as well as a photoinduced electron transfer from ZrT-NH2 to SiW12, which then enabled the formation of reactive species from dissolved dioxygen molecules. This combination made the PFS ZrT-NH2/SiW12 highly potent as a photocatalyst for environmental remediation (evaluated with the model pollutant rhodamine B), as porosity led to a pollutant preconcentration and improved accessibility to the SiW12 catalytic centers, while the photosensitizing effect enabled visible light photodegradation without the need for sacrificial reagents. This method of integrating POMs and functional MOCs offers a promising strategy for the development of functional materials with enhanced porosity and activity.