Forum Article pubs.acs.org/IC
Preface for the Forum on Metal−Organic Frameworks for Energy Applications Wenbin Lin*,† and Jeffrey R. Long*,‡,§ †
Department of Chemistry, University of Chicago, 929 East 56th Street, Chicago, Illinois 60637, United States Department of Chemistry and Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720, United States § Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States ‡
M
pyridinecarboxylic acid and trans-3-fluoro-4-pyridineacrylic acid.13 They studied the effects of partial fluorination and isoreticulation of MOF structures and measured the resulting hydrogen adsorption capacities, observing no clear trend. Senkovska and co-workers systematically studied the innersurface functionalization of DUT-67, a zirconium-based MOF featuring Zr6O6(OH)2 nodes and 2,5-thiophenedicarboxylate bridging ligands.14 The coordinating acetate modulators were exchanged postsynthetically with a series of carboxylic acids of varying hydrophobicity. Such simple modulator exchanges systematically tune the hydrophobicity of the MOF inner surfaces and can help to stabilize the MOFs toward water removal compared to the parent DUT-67 material. Investigations of new MOFs intended for the storage or purification of small molecules provide the topic for four of the articles. Qian, Chen, and co-workers report the synthesis of ZJU-40, a copper MOF incorporating the 5,5′-(pyrazine-2,5diyl)diisophthalic acid linker.15 Because of its high porosity, moderate pore size, and noncoordinated Lewis basic nitrogen sites, this MOF exhibits a high acetylene uptake capacity. The nitrogen sites, however, have almost no effect on the CO2 uptake. Consequently, ZJU-40 displays a high adsorption selectivity of 12−17 for C2H2/CO2 separations at ambient temperature. Ibarra, Schröder, Zou, and co-workers detail a study of the competitive CO2/N2 adsorption in two scandium MOFs based on biphenyl-3,3′,5,5′-tetracarboxylate and thiophene-2,5-dicarboxylate ligands.16 Canonical Monte Carlo and density functional theory (DFT) computational analyses of CO2 and hydrocarbon uptake in both MOFs reveal preferential adsorption sites due to supramolecular interactions between the framework and adsorbate. Liu, Cui, and co-workers report the synthesis of chiral, porous zinc and cadmium MOFs incorporating enantiopure (R)-2,3-dihydroimidazo[1,2-a]pyridine ligands, together with an examination of their enantioselective adsorption properties toward chiral sulfoxides.17 The zinc MOF exhibits a modest enantioselectivity of 12−47 in adsorbing either R or S enantiomers from racemic sulfoxide mixtures. Allendorf and co-workers highlight their efforts on using MOF−guest interactions to study the fundamental aspects of energy applications.18 They describe efforts toward hydrogen
etal−organic frameworks (MOFs) have emerged as a promising new class of porous materials with widely varying, and sometimes tunable, structures and properties.1 Although earlier concepts of extended coordination networks were advanced by Robson and co-workers in the late 1980s,2 the field of MOFs did not catch the imagination of the broader scientific community until the mid-1990s, when seminal contributions from Yaghi,3 Kitagawa,4 Ferey,5 and others6 demonstrated that such structures could exhibit permanent porosity and possess interesting functionalities. The initial excitement about MOFs was mainly driven by their enormous internal surface areas and their potential for storing hydrogen at high densities, a critical need for hydrogen-based clean energy technologies.7 Extensive efforts over the past 2 decades have led to the synthesis of a large number of highly porous MOFs, and many of these materials have been examined for the storage of key gaseous molecules, including hydrogen, methane, and carbon dioxide.8 In addition, the ability to achieve selective adsorption by adjusting the surface chemistry has raised the possibility of employing MOFs to improve the efficiency of some energy-intensive separation processes, including the removal of carbon dioxide from flue gases9 and the separation of hydrocarbon mixtures.10 More recently, by taking advantage of the extraordinary tunability of both the organic and inorganic building units, a number of designer MOFs have been examined for other clean energy applications, such as using MOFs as model structures for studying essential steps in solar energy utilization, including energy transfer, light-harvesting, water oxidation, and proton reduction.11 This Forum features a collection of articles that encompass many aspects of MOF research relating to the possible development of new clean energy technologies. A number of articles address the design and modification of MOF architectures. Serre, Devic, and co-workers describe the design and synthesis of four crystalline titanium(IV) carboxyphenolate MOFs synthesized using the 2,5-dihydroxyterephthalic acid (H4dobdc) linker.12 Because of the strong coordination ability of the α-hydroxycarboxylate moieties, these MOFs feature extended network structures built from single Ti4+-ion metal-connecting points that are connected solely by the dobdc4− ligands. As a result of the ligand-to-metal charge transfer arising from Ti−phenolate bonds, these MOFs strongly absorb visible light. Titanium MOFs also mediate hydrogen evolution in the presence of trimethylamine under UV irradiation. Banerjee and co-workers synthesized manganese, cobalt, and cadmium MOFs based on linkers derived from 3-fluoro-4© 2016 American Chemical Society
Special Issue: Metal-Organic Frameworks for Energy Applications Received: July 13, 2016 Published: August 1, 2016 7189
DOI: 10.1021/acs.inorgchem.6b01680 Inorg. Chem. 2016, 55, 7189−7191
Forum Article
Inorganic Chemistry
highlight molecular MOF catalysts for hydrogen evolution and CO2 reduction. Finally, they report their original research on the design of new MOFs based on squaramide ligands that can provide second-sphere interactions with the metal center, position substrates through hydrogen bonding, or even perform a complementary (i.e., tandem) organocatalytic reaction. Ma and co-workers report their research on the synthesis of a Zn-(Zn-porphyrin) MOF of pcu topology.24 The MOF adopts 4-fold interpenetration due to the highly elongated nature of the porphyrin ligand. The Zn-porphyrin moieties provide Lewis acidic sites for catalysis of the reaction of CO2 with epoxides to form cyclic carbonates. Wu and co-workers report the synthesis of a metalloporphyrin−polyoxometalate (POM) hybrid material for the synergistic activation of O2.25 Specifically, they demonstrate a turnover frequency of 6 s−1 together with an exceptionally high turnover number of 220000 for the metalloporphyrin−POM hybrid in the epoxidation of styrene using isobutyraldehyde and O2. Finally, Kobayashi, Mitsuka, and Kitagawa highlight their research efforts on the synthesis and applications of hybrid materials composed of metal nanoparticles and MOFs.26 The synthetic strategies for several metal@MOF systems are surveyed, including Pd@HKUST-1, Pd−Au@ ZIF-8, and Cu@MIL-100-Cr. They also discuss hydrogen storage in Pd@HKUST-1, alcohol oxidation by Pd−Au@ ZIF-8, and CO2 reduction to methanol by Cu@MIL-100-Cr, while further reporting their original research on the one-pot synthesis of the new composite materials Pd/ZIF-8 and Ni@MOF-74. As illustrated in the Forum Articles, the design and synthesis of MOFs with extraordinarily high porosity has witnessed significant advancement in the past 2 decades. The practical application of MOFs in the storage of gases such as hydrogen and methane still faces some critical challenges, including limitations in volumetric capacity at ambient temperatures, tolerance toward impurities, and potentially a relatively high cost. On the other hand, the implementation of MOFs in replacing energy-intensive gas separations may be closer to reality, owing to some significant potential advantages over other solid adsorbents and absorptive solutions.27 The studies of MOFs in energy-efficient lighting, energy conversion, energy storage, and small-molecule activation all benefit from the synthetic tunability of MOFs, a unique advantage of MOFs over other crystalline solid-state materials. Such synthetic versatility can be leveraged to design MOF materials for other important applications, including chemical sensing,28 earthabundant element catalysis,29 and disease diagnosis and treatment.30
and noble gas storage, hydrogenolysis of biomass, light harvesting, and conductive materials. In particular, they show how, by treating guest molecules as integral design elements for guest@MOF constructs, interesting insights can be gained in the development of clean energy technologies. Luminescence, energy transfer, and electron transport are also important topics for potential energy applications of MOFs. Li and co-workers discuss the use of fluorescent MOFs as energy-efficient and lanthanide metal-free lighting phosphors.19 They report the design and synthesis of a series of highly fluorescent zinc MOFs based on 1,1,2,2-tetrakis[4-(4carboxyphenyl)phenyl]ethene and 1,1,2,2-tetrakis[4-(pyridin-4yl)phenyl]ethene ligands, demonstrating greater than 75% fluorescence quantum yields for many of the materials. The enhanced quantum efficiency and thermal stability of luminescent MOFs over the organic ligands are attributed to chromophore rigidification in the MOFs. The luminescence properties of these MOFs can be further tuned through the choice of coligands. MOFs thus provide an interesting platform for the design of lanthanide metal-free phosphors for energyefficient solid-state lighting applications. Shustova and co-workers discuss recent advances in efficient multiple-chromophore coupling in structurally defined MOFs.20 In particular, because of their structural regularity and synthetic tunability, MOFs offer an excellent platform for engineering molecular assemblies that mimic protein systems with exceptionally high energy-transfer efficiency. These authors also report the synthesis of 16 dye molecules based on the benzylidene imidazolinone core that can be encapsulated inside the rigid scaffold of Zn3(BTC)2 to lead to novel noncoordinative MOF mimics of protein β-barrels. Hendon, Walsh, and Dincă describe a potentially promising approach to the design of porous and conductive MOFs based on DFT calculations.21 They propose the possibility of overcoming the poor electronic communication between metal clusters and the organic ligands in MOFs by extending the dimensionality of the inorganic components. The calculations indicate that the alkaline-earth oxides SrO and BaO can be transformed to form porous solids with acetate and trifluoroacetate ligands, leading to changes in the frontier crystalline orbital composition, band dispersion, and dielectric constants. The insights gained from such DFT analyses could prove instructive in the design of hybrid solids with tunable band structures. Baldansuren, D’Alessandro, and co-workers report the electrochemical properties of the redox-active tris[4-(pyridine4-yl)phenyl]amine (NPy3) ligand and a zinc-containing MOF based on this ligand.22 Through comprehensive in situ UV/vis/ near-IR, electron paramagnetic resonance, and fluorescence spectroelectrochemical experiments, they determined that NPy3 forms a highly delocalized radical cation upon one-electron oxidation both in solution and in the MOF framework. Significantly, the authors establish the utility of in situ spectroelectrochemical methods in the study of electroactive MOFs. The remainder of the articles deal with one of the most challenging potential applications of MOFs: combining their porosity and functionalities to effect molecular transformations that are of importance to energy conversion and utilization. Cohen and co-workers discuss the use of MOFs as single-site metal catalysts for small-molecule transformations.23 They introduce the general aspects of the design of catalytic MOFs, survey common molecular metal catalysts in MOFs, and
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Views expressed in this editorial are those of the author and not necessarily the views of the ACS.
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REFERENCES
(1) Furukawa, H.; Cordova, K. E.; O’Keeffe, M.; Yaghi, O. M. Science 2013, 342, 974. (2) Robson, R. Dalton Trans. 2008, 37, 5113. (3) Yaghi, O. M.; Li, H.; Eddaoudi, M.; O’Keeffe, M. Nature 1999, 402, 276.
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DOI: 10.1021/acs.inorgchem.6b01680 Inorg. Chem. 2016, 55, 7189−7191
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Inorganic Chemistry (4) Kondo, M.; Yoshitomi, T.; Matsuzaka, H.; Kitagawa, S.; Seki, K. Angew. Chem., Int. Ed. Engl. 1997, 36, 1725. (5) (a) Férey, G. Chem. Soc. Rev. 2008, 37, 191. (b) Férey, G.; Mellot-Draznieks, C.; Serre, C.; Millange, F.; Dutour, J.; Surblé, S.; Margiolaki, I. Science 2005, 309, 2040. (6) (a) Evans, O. R.; Lin, W. Acc. Chem. Res. 2002, 35, 511. (b) Bradshaw, D.; Claridge, J. B.; Cussen, E. J.; Prior, T. J.; Rosseinsky, M. M. Acc. Chem. Res. 2005, 38, 273. (c) Bourne, S. A.; Lu, J.; Mondal, A.; Moulton, B.; Zaworotko, M. J. Angew. Chem., Int. Ed. 2001, 40, 2111. (7) (a) Murray, L. J.; Dincă, M.; Long, J. R. Chem. Soc. Rev. 2009, 38, 1294. (b) Suh, M. P.; Park, H. J.; Prasad, T. K.; Lim, D.-W. Chem. Rev. 2012, 112, 782. (8) Mason, J. A.; Veenstra, M.; Long, J. R. Chem. Sci. 2014, 5, 32. (9) (a) Sumida, K.; Rogow, D. L.; Mason, J. A.; McDonald, T. M.; Bloch, E. D.; Herm, Z. R.; Bae, T.-H.; Long, J. R. Chem. Rev. 2012, 112, 724−781. (b) Li, J.-R.; Sculley, J.; Zhou, H.-C. Chem. Rev. 2012, 112, 869. (10) Herm, Z. R.; Bloch, E. D.; Long, J. R. Chem. Mater. 2014, 26, 323. (11) Wang, J.-L.; Wang, C.; Lin, W. ACS Catal. 2012, 2, 2630. (12) Assi, H.; Pardo Perez, L. C.; Mouchaham, G.; Ragon, F.; Nasalevich, M.; Guillou, N.; Martineau, C.; Chevreau, H.; Kapteijn, F.; Gascon, J.; Fertey, P.; Elkaim, E.; Serre, C.; Devic, T. Inorg. Chem. 2016. (13) Pachfule, P.; Garai, B.; Banerjee, R. Inorg. Chem. 2016, DOI: 10.1021/acs.inorgchem.6b00758. (14) Drache, F.; Bon, V.; Senkovska, I.; Marschelke, C.; Synytska, A.; Kaskel, S. Inorg. Chem. 2016, DOI: 10.1021/acs.inorgchem.6b00829. (15) Wen, H.-M.; Wang, H.; Li, B.; Cui, Y.; Wang, H.; Qian, G.; Chen, B. Inorg. Chem. 2016, DOI: 10.1021/acs.inorgchem.6b00748. (16) Ibarra, I. A.; Mace, A.; Yang, S.; Sun, J.; Lee, S.; Chang, J.-S.; Laaksonen, A.; Schrö d er, M.; Zou, X. Inorg. Chem. 2016, DOI: 10.1021/acs.inorgchem.6b00035. (17) Zhang, J.; Li, Z.; Gong, W.; Han, X.; Liu, Y.; Cui, Y. Inorg. Chem. 2016, DOI: 10.1021/acs.inorgchem.6b00894. (18) Ullman, A. M.; Brown, J. W.; Foster, M. E.; Léonard, F.; Leong, K.; Stavila, V.; Allendorf, M. D. Inorg. Chem. 2016, DOI: 10.1021/ acs.inorgchem.6b00909. (19) Lustig, W. P.; Wang, F.; Teat, S. J.; Hu, Z.; Gong, Q.; Li, J. Inorg. Chem. 2016, DOI: 10.1021/acs.inorgchem.6b00897. (20) Dolgopolova, E. A.; Rice, A. M.; Smith, M. D.; Shustova, N. B. Inorg. Chem. 2016, DOI: 10.1021/acs.inorgchem.6b00835. (21) Hendon, C. H.; Walsh, A.; Dincă, M. Inorg. Chem. 2016, DOI: 10.1021/acs.inorgchem.6b00979. (22) Hua, C.; Baldansuren, A.; Tuna, F.; Collison, D.; D’Alessandroa, D. M. Inorg. Chem. 2016, DOI: 10.1021/acs.inorgchem.6b00981. (23) Cohen, S. M.; Zhang, Z.; Boissonnault, J. A. Inorg. Chem. 2016, DOI: 10.1021/acs.inorgchem.6b00828. (24) Gao, W.-Y.; Tsai, C.-Y.; Wojtas, L.; Thiounn, T.; Lin, C.-C.; Ma, S. Inorg. Chem. 2016, DOI: 10.1021/acs.inorgchem.6b00937. (25) Zhu, S.-L.; Xu, X.; Ou, S.; Zhao, M.; He, W.-L.; Wu, C.-D. Inorg. Chem. 2016, DOI: 10.1021/acs.inorgchem.6b00971. (26) Kobayashi, H.; Mitsuka, Y.; Kitagawa, H. Inorg. Chem. 2016, DOI: 10.1021/acs.inorgchem.6b00911. (27) McDonald, T. M.; Mason, J. A.; Kong, X.; Bloch, E. D.; Gygi, D.; Dani, A.; Crocellà, V.; Giordanino, F.; Odoh, S.; Drisdell, W.; Vlaisavljevich, B.; Dzubak, A. L.; Poloni, R.; Schnell, S. K.; Planas, N.; Lee, K.; Pascal, T.; Wan, L. F.; Prendergast, D.; Neaton, J. B.; Smit, B.; Kortright, J. B.; Gagliardi, L.; Bordiga, S.; Reimer, J. A.; Long, J. R. Nature 2015, 519, 303. (28) Campbell, M. G.; Liu, S. F.; Swager, T. M.; Dincă, M. J. Am. Chem. Soc. 2015, 137, 13780. (29) Zhang, T.; Manna, K.; Lin, W. J. Am. Chem. Soc. 2016, 138, 3241. (30) He, C.; Liu, D.; Lin, W. Chem. Rev. 2015, 115, 11079.
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