Nickel phosphonate MOF as efficient water splitting photocatalyst

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 having bi-octahedra nickel nodes and a photo/electroactive tritopic phosphonate ligand. Remarkably, this material exhibits coordinatively unsaturated nickel(II) sites, free–POH and–POH acidic groups, a CO 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 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 µmol of H per gram using methanol as sacrificial agent, exhibiting stability, maintaining its crystal structure and allowing its recycling. Even more, 170 µmol of H 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 reduction. The present work opens new avenues for further optimization of the photocatalytic activity in this type of multifunctional materials. [Figure not available: see fulltext.].This work was supported by MOFseidon project (Retos project, PID2019-104228RB-I00, MICIU-AEI/FEDER, UE), and the Ramón Areces Foundation project H+MOFs. P. H. acknowledges the Spanish Ramón y Cajal Programme (2014-15039). S. N. thanks financial support by the Fundación Ramón Areces (XVIII Concurso Nacional para la Adjudicación de Ayudas a la Investigatión en Ciencias de la Vida y de la Materia, 2016), Ministerio de Ciencia, Innovatión y Universidades RTI2018–099482-A-I00 project and Generalitat Valenciana grupos de investigación consolidables 2019 (AICO/2019/214) project and Agència Valenciana de la Innovació (AVI, INNEST/2020/111) project. H. G. thanks financial support to the Spanish Ministry of Science and Innovation (Severo Ochoa and RTI2018-098237-CO21) and Generalitat Valenciana (Prometeo2017/083). In memory of our dear colleague, Prof. Emilio Morán, who recently passed away