Immobilizing [FeFe]-hydrogenase mimics to metal–organic frameworks for enhanced hydrogen production Science Bulletin 64 (2019) 1476–1477 Contents lists available at ScienceDirect Science Bulletin journal homepage: www.elsevier.com/locate/scib Research Highlight Immobilizing [FeFe]-hydrogenase mimics to metal–organic frameworks for enhanced hydrogen production https://doi.org/10.1016/j.scib.2019.08.018 2095-9273/� 2019 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved. E-mail address: dfsun@upc.edu.cn Daofeng Sun School of Materials Science and Engineering, College of Science, China University of Petroleum (East China), Qingdao 266580, China Production of hydrogen from water by solar-energy conversion has long been considered a promising way to solve the climate change and energy crisis [1]. However, some critical issues at this stage, such as catalysts for hydrogen evolution with high efficiency and low cost, definitely hinder the practical application of photo- catalytic hydrogen production from water. [FeFe]-hydrogenase, an excellent natural biological enzyme catalyst bearing unique organometallic clusters with noble-metal-free element, is most efficient in reducing protons to hydrogen and demonstrates remarkable turnover frequencies (TOF 6000–9000 s�1 per active site) [2]. With the crystal structural elucidation of [FeFe]-hydroge- nase, numerous [FeFe]-hydrogenase mimics have been synthesized to develop photocatalytic systems for hydrogen generation [3–5]. To date however, there are still no artificial [FeFe]-hydrogenase mimics that can reproduce the high reactivity of natural [FeFe]- hydrogenase, largely because of the low stability of [FeFe]-hydro- genase in photocatalytic process. Therefore, considering the fact that a natural [FeFe]-hydrogenase is deeply embedded within the protein matrix, it is important to explore the external matrix of the [FeFe]-hydrogenase mimics. Emerging as an intriguing class of porous crystalline materials, metal–organic frameworks (MOFs) can be easily functionalized at the molecular level [6]. Pioneering works on the incorporation of [FeFe]-hydrogenase mimics into MOFs to create heterogeneous catalysts has been demonstrated improved photocatalytic activity and stability for hydrogen production [7–9]. Among these previously reported studies, [FeFe]-hydrogenase mimics were incorporated into a photosensitizing zirconium-porphyrin MOF by direct coordination or into a non-photosensitizing MOF by post-synthetic exchange/covalent bond with [Ru(bpy)3] 2+ as a pho- tosensitizer. Although some achievements have been made in combination of [FeFe] catalyst and MOFs, immobilizing [FeFe] catalyst to photosensitizing MOF by covalent bonds is still a challenging task. Recently, Yuan’s group [10] reported the incorporation of an [FeFe]-hydrogenase mimics into an [Ru(bpy)3] 2+-derived photo- sensitizing UiO-type MOF by a facile click reaction to generate a new hydrogen evolution catalyst UiO-MOF-Fe2S2 (Fig. 1) [10]. In this work, the construction of photosensitizer and [FeFe] catalytic active site in the same framework could enhance the electron transfer process in a local microenvironment by comparison to [Ru(bpy)3] 2+ as a photosensitizer. Besides, the incorporation of [FeFe] catalytic active site via click reaction is more efficient com- pared with ligand exchange or weakly coordination strategy. After 50 h of photocatalytic reaction, the UiO-MOF-Fe2S2 produced a total of 32 lmol H2 with ascorbic acid as a proton source and a sac- rificial electron donor. The good performance of UiO-MOF-Fe2S2 can be ascribed to greatly improved stability by the protection from the framework, as well as the efficient electron transfer between the photosensitizer and the [FeFe] catalytic site. In summary, this work may provide a new solution for incorpo- ration of the [FeFe] catalytic center into a photosensitizing MOF by judicious design of the ligands. Meanwhile, the good performance of this artificial [FeFe]-hydrogenase mimics system demonstrates that this approach is a promising strategy to stabilize the [FeFe] catalyst and improve the photocatalytic efficiency of hydrogen evolution in water. Conflict of interest The author declares that he has no conflict of interest. https://doi.org/10.1016/j.scib.2019.08.018 mailto:dfsun@upc.edu.cn https://doi.org/10.1016/j.scib.2019.08.018 http://www.sciencedirect.com/science/journal/20959273 http://www.elsevier.com/locate/scib Fig. 1. Modification of UiO-MOF via a click reaction for incorporating [FeFe] catalytic sites to form new catalysts UiO-MOF-Fe2S2. Reprouduced with permission from Ref. [10]. Copyright 2019 Elsevier. D. Sun / Science Bulletin 64 (2019) 1476–1477 1477 References [1] Gray HB. Powering the planet with solar fuel. Nat Chem 2009;1:7. [2] Frey M. Hydrogenases: hydrogen-activating enzymes. ChemBioChem 2002;3:153–60. [3] Adams MW, Stiefel EI. Biological hydrogen production: not so elementary. Science 1998;282:1842–3. [4] Cammack R. Hydrogenase sophistication. Nature 1999;397:214–5. [5] Tard C, Pickett CJ. Structural and functional analogues of the active sites of the [Fe]-, [NiFe]-, and [FeFe]-hydrogenases. Chem Rev 2009;109:2245–74. [6] Cohen SM. Postsynthetic methods for the functionalization of metal�organic frameworks. Chem Rev 2012;112:970–1000. [7] Pullen S, Fei H, Orthaber A, et al. Enhanced photochemical hydrogen production by a molecular diiron catalyst incorporated into a metal�organic framework. J Am Chem Soc 2013;135:16997–7003. [8] Sasan K, Lin Q, Mao C, et al. Incorporation of iron hydrogenase active sites into a highly stable metal�organic framework for photocatalytic hydrogen generation. Chem Commun 2014;50:10390–3. [9] Roy S, Pascanu V, Pullen S, et al. Catalyst accessibility to chemical reductants in metal�organic frameworks. Chem Commun 2017;53:3257–60. [10] Wang W, Song XW, Hong Z, et al. Incorporation of iron hydrogenase active sites into a stable photosensitizing metal-organic framework for enhanced hydrogen production. Appl Catal B Environ 2019;258:117979. Daofeng Sun obtained his M.S. degree from Liaocheng Normal University, China in 1998, and graduated from Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences with a Ph.D. degree under the supervision of Rong Cao and Maochun Hong in 2003. After finishing three-year postdoctoral fellowship at Miami University, he joined Shandong University as a full professor in January 2007, then moved to China University of Petroleum (East China) in January 2013. 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