Nickel phosphonate MOF as efficient water splitting photocatalyst

Abstract

[EN] A novel microporous two-dimensional (2D) Ni-based phosphonate metal-organic framework (MOF; denoted as IEF-13) has been successfully synthesized by a simple and green hydrothermal method and fully characterized using a combination of experimental and computational techniques. Structure resolution by single-crystal X-ray diffraction reveals that IEF-13 crystallizes in the triclinic space group P-i having bi-octahedra nickel nodes and a photo/electroactive tritopic phosphonate ligand. Remarkably, this material exhibits coordinatively unsaturated nickel(II) sites, free-PO3H2 and-PO3H acidic groups, a CO2 accessible microporosity, and an exceptional thermal and chemical stability. Further, its in-deep optoelectronic characterization evidences a photoresponse suitable for photocatalysis. In this sense, the photocatalytic activity for challenging H-2 generation and overall water splitting in absence of any co-catalyst using UV-Vis irradiation and simulated sunlight has been evaluated, constituting the first report for a phosphonate-MOF photocatalyst. IEF-13 is able to produce up to 2,200 mu mol of H-2 per gram using methanol as sacrificial agent, exhibiting stability, maintaining its crystal structure and allowing its recycling. Even more, 170 mu mol of H-2 per gram were produced using IEF-13 as photocatalyst in the absence of any co-catalyst for the overall water splitting, being this reaction limited by the O-2 reduction. The present work opens new avenues for further optimization of the photocatalytic activity in this type of multifunctional materials.