Molecular Dye-Sensitized Photocatalysis with Metal-Organic Framework and Metal Oxide Colloids for Fuel Production

Colloidal dye-sensitized photocatalysis is a promising route toward efficient solar fuel production by merging properties of catalysis, support, light absorption, and electron mediation in one. Metal-organic frameworks (MOFs) are host materials with modular building principles allowing scaffold property tailoring. Herein, we combine these two fields and compare porous Zr-based MOFs UiO-66-NH 2 (Zr) and UiO-66(Zr) to monoclinic ZrO 2 as model colloid hosts with co-immobilized molecular carbon dioxide reduction photocatalyst fac -ReBr(CO) 3 (4,4′-dcbpy) (dcbpy = dicarboxy-2,2′-bipyridine) and photosensitizer Ru(bpy) 2 (5,5′-dcbpy)Cl 2 (bpy = 2,2′-bipyridine). These host-guest systems demonstrate selective CO 2 -to-CO reduction in acetonitrile in presence of an electron donor under visible light irradiation, with turnover numbers (TONs) increasing from ZrO 2 , to UiO-66, and to UiO-66-NH 2 in turn. This is attributed to MOF hosts facilitating electron hopping and enhanced CO 2 uptake due to their innate porosity. Both of these phenomena are pronounced for UiO-66-NH 2 (Zr), yielding TONs of 450 which are 2.5 times higher than under MOF-free homogeneous conditions, highlighting synergistic effects between supramolecular photosystem components in dye-sensitized MOFs.