Co@NH2-MIL-125(Ti): Cobaloxime-derived Metal-Organic Framework-based Composite for Light-driven H2 Production Nasalevich, M.A.; Becker, R.; Ramos-Fernandez, E.V.; Castellanos, S.; Veber, S.L.; Fedin, M.V.; Kapteijn, F.; Reek, J.N.H.; van der Vlugt, J.I.; Gascon, J. Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. We present a synthetic strategy for the efficient encapsulation of a derivative of a well-defined cobaloxime proton reduction catalyst within a photoresponsive metal-organic framework (NH 2 -MIL-125(Ti)). The resulting hybrid system Co@MOF is demonstrated to be a robust heterogeneous composite material. Furthermore, Co@MOF is an efficient and fully recyclable noble metal-free catalyst system for lightdriven hydrogen evolution from water under visible light illumination. Broader contextThe development of new strategies for the efficient valorization of solar light is one the most important challenges we face nowadays. Among the different possibilities, dihidrogen molecule is considered as one of the possible future energy carriers allowing for CO 2 -free energy cycle. Although the photocatalytic water splitting was the rst photocatalytic reaction to be discovered, no photocatalytic systems for this reaction have been industrially applied. This is both due to the fact that most discovered catalysts rely on the use of noble metals and to the low activities achieved so far by alternative catalysts. The application in this eld of materials such as metal-organic frameworks (MOFs) can be a game changer in this research eld. MOFs have been proven to be photoactive and their optical properties can be easily tuned towards visible light operation. The current challenge lies in the development of more appropriate active sites for the desired photocatalytic cycle. In this manuscript, we report a new strategy to achieve this goal. By introducing a derivative of the well-known molecular Co-based electrocatalyst Co-dioxime-diimine into the pores of a photo-active NH 2 -MIL-125(Ti) following a 'Ship-in-a-bottle' strategy, we were able to synthesize a highly active photocatalyst composite free of noble metals, and fully recyclable. Because of the novelty and the implications of this work, we feel that it might appeal to the interdisciplinary readership of energy and environmental science. The journal has previously been an important forum for the research topics touched upon in this paper (new earth abundant materials and their application in (photo) catalysis and hydrogen evolution from water under visible light illumination). We would be glad t...

Metal-organic frameworks (MOFs) containing d0 metals such as NH2-MIL-125(Ti), NH2-UiO-66(Zr) and NH2-UiO-66(Hf) are among the most studied MOFs for photocatalytic applications. Despite structural similarities, we demonstrate that the electronic properties of these MOFs are markedly different. As revealed by quantum chemistry, EPR measurements and transient absorption spectroscopy, the highest occupied and lowest unoccupied orbitals of NH2-MIL-125(Ti) promote a long lived ligand-to-metal charge transfer upon photoexcitation, making this material suitable for photocatalytic applications. In contrast, in case of UiO materials, the d-orbitals of Zr and Hf, are too low in binding energy and thus cannot overlap with the π* orbital of the ligand, making both frontier orbitals localized at the organic linker. This electronic reconfiguration results in short exciton lifetimes and diminishes photocatalytic performance. These results highlight the importance of orbital contributions at the band edges and delineate future directions in the development of photo-active hybrid solids.

Hybrid materials bearing organic and inorganic motives have been extensively discussed as playgrounds for the implementation of atomically resolved inorganic sites within a confined environment, with an exciting similarity to enzymes. Here, we present the successful design of a site-isolated mixed-metal Metal Organic Framework that mimics the reactivity of soluble methane monooxygenase enzyme and demonstrates the potential of this strategy to overcome current challenges in selective methane oxidation. We describe the synthesis and characterisation of an Fe-containing MOF that comprises the desired antiferromagnetically coupled high spin species in a coordination environment closely resembling that of the enzyme. An electrochemical synthesis method is used to build the microporous MOF matrix while integrating the atomically dispersed Fe active sites in the crystalline scaffold. The model mimics the catalytic C-H activation behaviour of the enzyme to produce methanol, and shows that the key to this reactivity is the formation of isolated oxobridged Fe units.