Two Cu-Based Phosphonate Metal-Organic Frameworks as Efficient Water-Splitting Photocatalysts

Two novel three-dimensional metal-organic frameworks(MOFs)based on the photoactive pyrene tetraphosphonate ligand and copper(denoted as IEF-8 and IEF-9) have been hydrothermally synthesizedand fully characterized (XRD, FTIR, TGA, SEM, XPS, etc.). Their crystalstructures were unveiled by single-crystal X-ray diffraction. Remarkably,these materials exhibit coordinatively unsaturated copper (II) sites,free -PO3H2 and -PO3H acidic groups, and good thermal and chemical stability. Further,their optoelectronic characterization evidenced a photoresponse suitablefor photocatalysis. In this sense, the photocatalytic activity ofpyrene phosphonate MOFs was evaluated for the first time for the challenginghydrogen evolution reaction. In particular, IEF-8 exhibited a catalyticefficiency higher than that of the benchmarked Ti carboxylate photocatalystMIL-125-(Ti)-NH2, producing 1800 mu mol center dot g(-1) after 22 h under UV-vis irradiation in theabsence of any co-catalyst. Furthermore, this material presented goodreusability (at least up to 4 cycles), preserving its activity andstructural integrity.