Communication pubs.acs.org/crystal
Synthesis of a Metal−Organic Framework, IronBenezenetricarboxylate, from Dry Gels in the Absence of Acid and Salt Imteaz Ahmed, Jaewoo Jeon, Nazmul Abedin Khan, and Sung Hwa Jhung* Department of Chemistry, Kyungpook National University, Daegu 702-701, Korea S Supporting Information *
ABSTRACT: A nanoporous metal−organic framework (MIL100(Fe)) has been synthesized by dry gel conversion for the first time from metallic iron and trimesic acid in the absence of any acid (excluding organic linker), salt, or fluoride.
acid),9,10 Fe(NO3)3·9H2O/H3-BTC/H2O,11 or FeCl3·6H2O/ H3-BTC/H2O.12 In each case, fluoride or salt was needed for the synthesis of the MIL-100(Fe). Recently, syntheses of porous materials from dry gels have attracted considerable attention. The synthesis of porous material with DGC (dry gel conversion) has potential advantages,13−16 including minimum waste disposal, reduced reactor size, reduced consumption of a template, the possibility of continuous production,14 etc. Moreover, DGC may be useful in producing a monolithic or shape-controlled porous material from preshaped gels.15 Very recently, ZIF-type materials (zeolite-imidazolate framework), such as ZIF-8 and ZIF-67, a subclass of MOFs, have been obtained from zinc or cobalt acetate and 2-methylimidazole with DGC for the first time (without any organic solvent).17 It has been concluded that ZIF-type materials can be synthesized under only DGC conditions in the absence of organic solvent; and water possibly has a structure-directing effect on the synthesis of the porous materials.17 However, the solubility of the precursors (especially cobalt acetate, which is water-soluble at room temperature) is very high; therefore, the efficiency of the DGC synthesis might not be high because of the dissolution of reagents under water. Moreover, to the best of our knowledge, MOFs (not ZIFs) synthesis by using the DGC method has not been reported so far. Herein, we present a facile crystallization of MOFs from precursors using the DGC method for the first time.
R
ecently, remarkable progress on porous materials has been achieved because of developments in metal−organic frameworks (MOFs),1−3 crystalline inorganic−organic porous materials. The importance of MOF-type materials is due to the huge porosity, the easy tunability of their pores, and the number of potential applications.1−3 A majority of the research on MOFs, so far, has been devoted mainly to the syntheses of new structures, the structure analysis, and the potential applications.1−3 Facile synthesis of MOFs is very important not only for fundamental understanding but also for viable applications. MOFs have been mainly synthesized with hydrothermal or solvothermal crystallization at relatively high temperature using conventional electrical (CE) heating.4 A few new techniques have been attempted in the synthesis of MOFs to decrease the reaction time or temperature and to find an effective alternative method. For example, ultrasounds have been applied to the preparations of several MOFs because of their rapid and low-temperature syntheses.5 Microwaves6 have been used for the synthesis of porous MOFs because they have several advantages, such as fast crystallization and phaseselectivity. MOFs have also been synthesized by mechanochemical methods,7 usually at room temperature without any solvent, and therefore, the method can be environmentally friendly. A few nonconventional methods,8 such as the electrochemical method8a and the “accelerated aging” approach,8b have also been used for the syntheses of MOFs. MIL-100(Fe), with the chemical formula Fe(III)3 O(H2O)2(OH or F){C6H3(CO2)3}2·nH2O (n ∼ 14.5), is a typical MOF having high porosity and coordinatively unsaturated sites,9 and it has various potential applications.10 MIL-100(Fe) is mainly obtained under hydrothermal conditions from Fe/HF/HNO3/H3-BTC/H2O (H3-BTC: trimesic © 2012 American Chemical Society
Received: September 28, 2012 Revised: November 1, 2012 Published: November 9, 2012 5878
dx.doi.org/10.1021/cg3014317 | Cryst. Growth Des. 2012, 12, 5878−5881
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Importantly, the synthesis was carried out in the absence of any salt, fluoride, or acid. In the present study, MIL-100(Fe) was synthesized from metallic iron (Fe0), H3-BTC (trimesic acid), and water in two ways. For the dry gel conversion, the reactor of Scheme 1 was Scheme 1. Schematic Drawing of the Reaction System for DGC To Synthesize MIL-100(Fe)
Figure 2. Relative crystallization curves of MIL-100(Fe)s obtained with DGC and CE heating at 165 °C.
and crystallinity increases with time up to a certain value and saturates at that time. As shown in the Figure 2, the crystallization of MIL-100(Fe) with DGC is quite rapid (about 2−3 times) compared with the conventional electric (or CE) synthesis. The morphology of MIL-100(Fe) obtained with DGC is very similar to that of MIL-100(Fe) synthesized with conventional electric heating, as shown in the SEM images of Supporting Information Figure S2. The adsorption isotherms of the fully crystallized samples for nitrogen (at liquid nitrogen temperature) and toluene (at 50 °C) are shown in Figure 3. The adsorbed amounts increased rapidly with pressure at low relative pressure, and after that relative pressure (P/P0 ≈ 0.15) the adsorption was nearly saturated. The BET surface areas and total pore volumes obtained with nitrogen adsorption isotherms are summarized in Table 1. Moreover, the adsorbed volumes of toluene are fairly agreeable with the pore volumes of the MIL-100(Fe) samples. On the basis of the XRD and adsorption (nitrogen and toluene) results, it may be concluded that the synthesis of the MIL-100(Fe) with DGC is more effective than that of the MIL100(Fe) with the CE heating method. In other words, the MOFs are rapidly obtained with DGC, and the porosity (for the fully crystallized samples) of the sample obtained with DGC is slightly higher than that of the sample synthesized with CE heating. There are two remarkable results in the present study. First is the successful synthesis of the MOF without any acid or salt. Second is the relatively rapid crystallization and high porosity with the DGC synthesis (compared with conventional hydrothermal/solvothermal synthesis). Both results were unexpected and are not easy to explain. So far, MIL-100(Fe) has been obtained from precursors (Fe/ H3-BTC) in acids (HF/HNO3)9,10 or from H3-BTC and salts such as Fe(NO3)311 or FeCl3.12 No results have been reported for the acid/salt/fluoride-free synthesis of the MIL-100(Fe). To the best of our knowledge, no MOF was synthesized from metal (not salt) in the absence of acids because metals are generally very unreactive. In this study, the MIL-100(Fe) was obtained, especially under DGC, from Fe/H3-BTC/H2O. However, it might be not easy to suggest the mechanism for the reactions of the MIL100(Fe) synthesis, since reactions under the studied conditions might be very complex. The following reactions might be considered as one of the possible reactions in the presence of water.
used and water in the bottom of the reactor was evaporated to the gel (Fe/H3-BTC) at the reaction temperature of 165 °C. For conventional electric (CE) heating, reactant having the molar composition of 1 Fe0:0.66 H3-BTC:280 H2O was used. The reactant mixture was loaded in a Teflon-lined autoclave and put in an oven preheated at 165 °C. After the crystallization, the product was recovered with separation (filtration), washed with water, and dried. More detailed information on the chemicals, syntheses, and characterization is shown in the Supporting Information. Figure 1 shows the XRD patterns of the fully crystallized MIL-100(Fe)s obtained by both DGC and CE syntheses for 4
Figure 1. XRD patterns of fully crystallized MIL-100(Fe)s obtained with DGC and CE heating for 4 and 10 days, respectively, at 165 °C.
and 10 days, respectively, at 165 °C. The XRD patterns are very similar to the reported results9−12 and do not show any impurity. Interestingly, the XRD intensity of the sample prepared by DGC is higher than that of the sample obtained with conventional electric heating even though the reaction time is shorter for DGC than that for CE heating. Figure 2 shows the relative crystallization curves (raw XRD patterns are shown in Supporting Information Figure S1) for the synthesis of MIL-100(Fe)s with both DGC and CE methods. In both cases, the crystallization curves are the typical sigmoid form5b,6c 5879
dx.doi.org/10.1021/cg3014317 | Cryst. Growth Des. 2012, 12, 5878−5881
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Figure 3. Adsorption isotherms of fully crystallized MIL-100(Fe)s obtained with DGC and CE heating for (a) nitrogen and (b) toluene.
synthesis from Fe(NO3)3/H3-BTC/H2O.11 Even though water is essential for the synthesis of MIL-100(Fe), highly diluted reactant might not be effective for the rapid crystallization of MIL-100(Fe). Therefore, it may be concluded that the synthesis of the MOF, MIL-100(Fe), with DGC is rapid in kinetics because of relatively high concentrations of iron and trimesic acid. However, water should be present for the ready crystallization of the MOF through reactions 1−4. Finally, the versatile applications of the DGC method should be checked in more detail by the synthesis of various MOFs. Moreover, it might be interesting to study whether there is any difference in physicochemical properties of the MOFs that were obtained with the synthesis methods (DGC vs hydrothermal or solvothermal synthesis) or not. It might also be interesting to study various applications of the MIL-100(Fe) obtained with DGC because of several potential applications of the MOF and relatively high porosity of the MIL-100(Fe) obtained with the DGC method. In summary, MOFs can be obtained from metals and linker materials when suitable reaction conditions are selected. Moreover, MIL-100(Fe) can be obtained rapidly from dry gels without any acid (excluding organic linker) and salt. This new synthesis method will pave a new and facile way for the synthesis of MOFs for viable applications.
Table 1. Synthesis Conditions and Textural Properties of Fully Crystallized MIL-100(Fe)s Obtained with DGC and CE Heating synth method
temp (°C)
time (d)
BET surf area (m2/g)
total pore vol (cm3/g)
vol ads toluenea (cm3/g)
DGC CE
165 165
4 10
1340 1190
0.63 0.56
0.53 0.50
a
Adsorbed volume obtained at P/P0 = 0.5.
2H3‐BTC → 2BTC3 − + 6H+
(1)
2Fe → 2Fe3 + + 6e−
(2)
6H+ + 6e− → 3H 2
(3) 3−
When the three reactions are combined, BTC (benzenetricarboxylate) and ferric ion may be obtained in the presence of water: 2H3‐BTC + 2Fe → 2BTC3 − + 3H 2 + 2Fe3 +
(4)
Finally, the obtained BTC3− may be coordinated onto Fe3+, leading to the MIL-100(Fe) structure via trimeric Fe3+.9 However, the contribution of water in the formation of μ3-O in trimeric iron should also be considered. Therefore, further work is necessary to understand the synthesis mechanism in more detail. From the successful synthesis of MIL-100(Fe) from metallic iron and H3-BTC, without any fluoride, acid (excluding organic linker), or salt, it may be concluded that some MOFs may be obtained from metals and linker materials (mainly carboxylic acids) when a suitable reaction condition is selected. DGC has generally been regarded to be slow in crystallization kinetics compared with CE synthesis in the preparation of aluminophosphates18,19 because of the low concentration of a template and water in the reaction mixture. In the preparation of MOFs in this study, unlike the synthesis of aluminophosphates, no template was used; therefore, water concentration can be considered to explain the rapid synthesis of MIL-100(Fe) with DGC. The concentration of water in reactants such as iron and trimesic acid will be low in the DGC, since only evaporated water can reach the reactants. On the other hand, in the case of CE synthesis, water concentration is surely high. Very recently, it has been reported that concentrated reactants, compared with diluted ones, were helpful to increase the crystallinity of MIL-100(Fe) in the
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ASSOCIATED CONTENT
S Supporting Information *
Synthesis and characterization procedures, raw XRD patterns, and SEM images of the MIL-100(Fe)s. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Fax: 82-53-950-6330. Tel: 82-53-950-5341. E-mail: sung@ knu.ac.kr. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors would like to express their sincere thanks to one anonymous reviewer who pointed out the contribution of water in the formation of μ3-O in trimeric iron. This research was supported by a Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the 5880
dx.doi.org/10.1021/cg3014317 | Cryst. Growth Des. 2012, 12, 5878−5881
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V. A.; Boissière, C.; Grosso, D.; Sanchez, C. Eur. J. Inorg. Chem. 2012, in press, DOI: 10.1002/ejic.201200710. (13) Xu, W.; Dong, J.; Li, J.; Li, J.; Wu, F. J. Chem. Soc., Chem. Commun. 1990, 755−756. (14) Matsukata, M.; Ogura, M.; Osaki, T.; Rao, P. R. H. P.; Nomura, M.; Kikuchi, E. Top. Catal. 1999, 9, 77−92. (15) Goergen, S.; Guillon, E.; Patarin, J.; Rouleau, L. Microporous Mesoporous Mater. 2009, 126, 283−290. (16) Hu, D.; Xia, Q.-H.; Lu, X.-H.; Luo, X.-B.; Liu, Z.-M. Mater. Res. Bull. 2008, 43, 3553−3561. (17) Shi, Q.; Chen, Z.; Song, Z.; Li, J.; Dong, J. Angew. Chem., Int. Ed. 2011, 50, 672−675. (18) Khan, N. A.; Park, J. H.; Jhung, S. H. Mater. Res. Bull. 2010, 45, 377−381. (19) Saha, S. K.; Waghmode, S. B.; Kubota, Y.; Sugi, Y. Mater. Lett. 2004, 58, 2918−2923.
Ministry of Education, Science and Technology (Grant Number 2012004528).
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ABBREVIATIONS DGC, dry gel conversion; MOF, metal−organic framework; ZIF, zeolite−imidazolate framework; CE, conventional electric heating
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REFERENCES
(1) (a) Férey, G. Chem. Soc. Rev. 2008, 37, 191−214. (b) Kitagawa, S.; Kitaura, R.; Noro, S.-I. Angew. Chem., Int. Ed. 2004, 43, 2334−2375. (c) Yaghi, O. M.; O’Keeffe, M.; Ockwig, N. W.; Chae, H. K.; Eddaoudi, M.; Kim, J. Nature 2003, 423, 705−714. (2) (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.; Ma, Y.; McCarthy, M. C.; Sculley, J.; Yu, J.; Jeong, H.-K.; Balbuena, P. B.; Zhou, H.-C. Coord. Chem. Rev. 2011, 255, 1791−1823. (c) Suh, M. P.; Park, H. J.; Prasad, T. K.; Lim, D.-W. Chem. Rev. 2012, 112, 782−835. (d) Wu, H.; Gong, Q.; Olson, D. H.; Li, J. Chem. Rev. 2012, 112, 836−868. (e) Li, J.-R.; Sculley, J.; Zhou, H.-C. Chem. Rev. 2012, 112, 869−932. (f) Jhung, S. H.; Khan, N. A.; Hasan, Z. CrystEngComm 2012, 14, 7099−7109. (3) (a) Horcajada, P.; Gref, R.; Baati, T.; Allan, P. K.; Maurin, G.; Couvreur, P.; Férey, G.; Morris, R. E.; Serre, C. Chem. Rev. 2012, 112, 1232−1268. (b) Uemura, T.; Yanai, N; Kitagawa, S. Chem. Soc. Rev. 2009, 38, 1228−1236. (c) Kurmoo, M. Chem. Soc. Rev. 2009, 38, 1353−1379. (d) Lee, J. Y.; Farha, O. K.; Roberts, J.; Scheidt, K. A.; Nguyen, S. T.; Hupp, J. T. Chem. Soc. Rev. 2009, 38, 1450−1459. (e) Rocha, J.; Carlos, L. D.; Paz, F. A. A.; Ananias, D. Chem. Soc. Rev. 2011, 40, 926−940. (f) Horike, S.; Shimomura, S.; Kitagawa, S. Nature Chem. 2009, 1, 695−704. (4) Stock, N.; Biswas, S. Chem. Rev. 2012, 112, 933−969. (5) (a) Qiu, L.-G.; Li, Z.-Q.; Wu, Y.; Xu, T.; Jiang, X. Chem. Commun. 2008, 3642−3644. (b) Haque, E.; Khan, N. A.; Park, J. H.; Jhung, S. H. Chem.Eur. J. 2010, 16, 1046−1052. (c) Khan, N. A.; Haque, E.; Jhung, S. H. Eur. J. Inorg. Chem. 2010, 4975−4981. (6) (a) Klinowski, J.; Paz, F. A. A.; Silva, P.; Rocha, J. Dalton. Trans. 2011, 40, 321−330. (b) Jhung, S. H.; Lee, J.-H.; Yoon, J. W.; Serre, C.; Férey, G.; Chang, J.-S. Adv. Mater. 2007, 19, 121−124. (c) Haque, E.; Khan, N. A.; Kim, C. M.; Jhung, S. H. Cryst. Growth Des. 2011, 11, 4413−4421. (d) Khan, N. A.; Jhung, S. H. Cryst. Growth Des. 2010, 10, 1860−1865. (7) (a) Pichon, A.; Lazuen-Garay, A.; James, S. L. CrystEngComm 2006, 8, 211−214. (b) Klimakow, M.; Klobes, P.; Thüunemann, A. F.; Rademann, K.; Emmerling, F. Chem. Mater. 2010, 22, 5216−5221. (8) (a) Müller, U.; Schubert, M.; Teich, F.; Puetter, H.; SchierleArndt, K.; Pastre, J. J. Mater. Chem. 2006, 16, 626−636. (b) Cliffe, M. J.; Mottillo, C.; Stein, R. S.; Bučar, D.-K.; Frišcǐ ć, T. Chem. Sci. 2012, 3, 2495−2500. (9) Horcajada, P.; Surblé, S.; Serre, C.; Hong, D.-Y.; Seo, Y.-K.; Chang, J.-S.; Grenèche, J.-M.; Margiolaki, I.; Férey, G. Chem. Commun. 2007, 2820−2822. (10) (a) Yoon, J. W.; Seo, Y.-K.; Hwang, Y. K.; Chang, J.-S.; Leclerc, H.; Wuttke, S.; Bazin, P.; Vimont, A.; Daturi, M.; Bloch, E.; Llewellyn, P. L.; Serre, C.; Horcajada, P.; Grenèche, J.-M.; Rodrigues, A. E.; Férey, G. Angew. Chem., Int. Ed. 2010, 49, 5949−5952. (b) Petit, C.; Bandosz, T. J. Adv. Funct. Mater. 2011, 21, 2108−2117. (c) Dhakshinamoorthy, A; Alvaro, M.; Hwang, Y. K.; Seo, Y.-K.; Corma, A.; Garcia, H. Dalton Trans. 2011, 40, 10719−10724. (d) Vermoortele, F.; Ameloot, R.; Alaerts, L.; Matthessen, R.; Carlier, B.; Fernandez, E. V. R.; Gascon, J.; Kapteijn, F.; De Vos, D. J. Mater. Chem. 2012, 22, 10313−10321. (e) Jeremias, F.; Khutia, A.; Henninger, S. K.; Janiak, C. J. Mater. Chem. 2012, 22, 10148−10151. (11) Seo, Y.-K.; Yoon, J. W.; Lee, J. S.; Lee, U.-H.; Hwang, Y. K.; Jun, C.-H.; Horcajada, P.; Serre, C.; Chang, J.-S Microporous Mesoporous Mater. 2012, 157, 137−145. (12) Márquez, A. G.; Demessence, A.; Platero-Prats, A. E.; Heurtaux, D.; Horcajada, P.; Serre, C.; Chang, J.-S.; Férey, G.; de la Peña-O’Shea, 5881
dx.doi.org/10.1021/cg3014317 | Cryst. Growth Des. 2012, 12, 5878−5881
