Photosensitizing metal–organic polyhedra combined with Co catalytic sites for CO2 photoreduction

Abstract

Metal–organic frameworks (MOFs) are excellent photocatalysts due to their high designability and have been intensively investigated over the last decade. However, the catalytically active sites inside bulk MOFs may not absorb light and therefore fail to work, resulting in a waste of catalytically active sites. Based on this, in recent years, metal–organic polyhedra (MOP), which are structurally similar to MOFs but more dispersible, have been developed as more promising photocatalysts. Herein, we created a zirconium-based MOP (abbreviated MOP-Ru) containing [Ru(bpy)₃]²⁺ (bpy = 2,2′-bipyridine) photosensitive units and bipyridine units. MOP-Ru can combine with Co²⁺ easily to form MOP-Ru-Co. After MOP-Ru-Co is dissolved in methanol, it disperses into discrete cages, greatly facilitating the active sites’ light absorption. In CO₂ photoreduction experiments, dispersed MOP-Ru-Co exhibits better catalytic activity than the analogous MOF and the undispersed MOP-Ru-Co. MOP-Ru and MOP-Ru-Co show interesting color changes when exposed to intense light. Based on this phenomenon and other characterization results, the mechanism of this CO₂ photoreduction reaction is that the Ru photosensitive units in MOP-Ru-Co absorb light and transfer the photogenerated electrons to the Co catalytic sites, thereby achieving efficient CO₂ photoreduction.