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Controllable Preparation of Nanoscale Metal−Organic Frameworks by Ionic Liquid Microemulsions Weizhong Zheng,† Xiaolei Hao,† Ling Zhao,†,‡ and Weizhen Sun*,† †

State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China Shanghai Key Laboratory of Multiphase Materials Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China



S Supporting Information *

ABSTRACT: With particle sizes down to the nanoscale, nanometal−organic frameworks (NMOFs) with well-controllable dimensions exhibit many potential applications in drug delivery, biosensing, and biomedical imaging. Although the microemulsion method provides an efficient approach for preparing nanoparticles, the synthesis of NMOFs with narrow size distribution is a great challenge. In this work, nanoscale zeolitic imidazolate frameworks (NZIFs), considered as a subclass of MOFs, were synthesized by the ionic liquid-containing microemulsion system of H2O/BmimPF6/ TX-100. The obtained NZIFs have extremely small size of no more than 2.3 nm, narrow distribution of less than 0.5 nm, and good thermal stabilities. By addition of ethanol into the H2O/BmimPF6/ TX-100 system, [Cu3(BTC)2(H2O)3]n (HKUST-1) was successfully synthesized with nanodimensions similar to those of NZIFs. The molecule dynamic simulation reveals that one new microemulsion was formed in which the ethanol and water molecules were capsuled by the surfactant TX-100 and BmimPF6. This new microemulsion is beneficial to the dissolution of organic ligand 1,3,5benzenetricarboxylic acid. This work hopefully provides new insights into the green production of nanoscale MOFs. with well-controlled sizes.5,19,20 In our recent work, nanoscale zeolitic imidazolate frameworks (ZIFs) with well-controllable size distributions were prepared in a conventional reverse microemulsion.21 Although such a conventional reverse microemulsion is confirmed to be an efficient means to synthesize NMOFs, the large amount of spent heptane causes serious environmental pollution, and its recovery is cost-intensive, particularly for large-scale production of NMOFs. Herein, we employ a green method to synthesize NMOFs using ionic liquid microemulsions (ILMEs), which are considered as an environmentally friendly system to construct nanoscale materials because ILs possess many excellent properties, including outstanding dissolution performance, designable combination of cations and anions, negligible vapor pressure, and easy recovery.22−24 In the pioneering work, Han et al. synthesized La(BTC)(H2O)6 with different nanoscale shapes by using H2O/TX-100/BmimPF6 microemulsions, which provided a possible environmentally friendly system to achieve the production of NMOFs.20 They emphasized that the shape of the dispersed phase has a crucial effect on determining the morphology of the MOF nuclei

1. INTRODUCTION Metal−organic frameworks (MOFs), constructed with the selfassembly of metal ions or metal clusters and organic bridging ligands, are a novel class of crystalline porous materials.1−4 To date, porous MOFs with high surface area and designable structures have attracted tremendous attention owing to their potential applications in gas sorption,5 energy storage,6 catalysis,7 selective separation8 etc. With particle sizes down to the nanoscale, MOFs with well-controllable dimensions exhibit additional potential applications in catalysis,9 drug delivery,10 biosensing,11 and biomedical imaging.12 Until now, two major strategies regarding the synthesis of nanoscale MOFs (NMOFs) have been reported according to previous research.13−16 One strategy concerns the controlled precipitation of MOFs, including via ultrasounds,14 thermal conditions,17 and surfactant-directed control,12 and the other strategy is related to the self-assembly of MOFs such as templates and microemulsions.18 Due to the existence of many factors that affect the precipitation of precursors, it is challenging to synthesize different kinds of NMOFs in the same or similar reaction conditions. In contrast, microemulsions provide an efficient approach for preparing NMOFs. In microemulsions, the dispersed phase is considered as numerous nanoreactors that can easily control the growth of the particles. However, the dissolution of organic ligands in microemulsions is still an obstacle for synthesizing NMOFs © 2017 American Chemical Society

Received: Revised: Accepted: Published: 5899

February 17, 2017 April 12, 2017 May 2, 2017 May 2, 2017 DOI: 10.1021/acs.iecr.7b00694 Ind. Eng. Chem. Res. 2017, 56, 5899−5905

Article

Industrial & Engineering Chemistry Research

Figure 1. Schematic illustration for the process of MOF synthesis.

The detailed synthesis procedures of BmimPF6 and MOFs are described in the Supporting Information. The whole schematic illustration for the process of MOF synthesis is shown in Figure 1. 2.2. Molecular Dynamics (MD) Simulation. The quaternary component system composed of water, ethanol, TX-100, and BmimPF6 was investigated via MD simulation to confirm the location of ethanol in ILME-2. The initial simulated box was built and maintained at the size of 6.0 × 6.0 × 6.0 nm3 using PACKMOL software.31 To reduce the computational cost, water and ethanol molecules were initially wrapped by the TX-100, and BmimPF6 was placed in the most outside layer of the built box with the corresponding molecule numbers of 300, 100, 80, and 400, respectively. The obtained box was simulated using GROMACS 4.5 package. First, the energy minimum was performed for 5000 steps to eliminate the overlap in the initial box. Then, 8 ns quenching simulation was carried out under the Canonical ensemble (NVT) with Hoover-Nose thermostat using the relaxation time of 0.5 ps from 300 to 500 K and then back to 300 K. Afterwards, the quenched box was simulated under isothermal−isobaric ensemble (NPT) with Parrinello−Rahman barostat for 60 ns to equilibrate. Periodic boundary conditions (PBC) were employed in three directions. The particle mesh Ewald method was used to deal with long-range electrostatic interactions with a cutoff of 1.2 nm. The CGenFF force field was used to describe the interaction of water, ethanol, TX-100,32 and BmimPF6.33 Water molecules were described by the extended simple point charge (SPC/E) model. 2.3. Characterization of MOFs. In this work, power X-ray diffraction (PXRD) patterns of MOFs were characterized through the Bruker D8 Advance X-ray powder diffractometer using Cu Kα radiation (λ = 1.54059 Å) at 40 kV and 40 mA at room temperature. In addition, transmission electron microscopy (TEM) images of MOFs were characterized by the FEI Tecnai G2 spirit BioTwin at 300 kV. The SDT Q600 thermal analyzer with a ramp rate of 10 °C/min from room temperature up to 800 °C in the nitrogen atmosphere was used to characterize thermogravimetric analysis (TGA) of MOFs. Meanwhile, the nitrogen adsorption−desorption was characterized by the Micromeritics ASAP 2020 M analyzer at 77 K.

formed at the beginning, which further controls the shape of the final MOFs. Nevertheless, the mean particle size of MOFs obtained in their work seems to be larger than 200 nm with slightly poor particle size distribution, which was ascribed to the fact that the coordination reaction proceeds at the water/IL interface because metal ions and organic ligands are dissoluble in water and IL phases, respectively. In the H2O/TX-100/ BmimPF6 microemulsion, some nanoparticles with the mean size of about 3−5 nm such as Pd25 and Pd4Au26 were successfully synthesized. However, it is still a challenge to synthesize MOFs with extremely small size less than 10 nm in such microemulsion, especially when the organic ligands constructing the MOFs are not water-soluble. In the present work, nanoscale ZIF-8 and ZIF-67 with wellcontrollable dimensions and uniform particle size distribution were successfully synthesized on the basis of the H2O/TX-100/ BmimPF6 microemulsion. By addition of ethanol into the H2O/TX-100/BmimPF6 system to improve the dissolution of organic ligands, the [Cu3(BTC)2(H2O)3]n (HKUST-1) was further synthesized with nanodimensions similar to those of NZIFs. The mechanism of controlling the crystal growth in the dispersed phase was proposed and further confirmed by molecular dynamics simulation. In addition, from the industry of interest, a green method of demulsification and the recycling of ILs were presented. Hopefully, the process introduced here can confine the growth of nanoparticles and provide a new environmentally friendly way to produce nanoscale MOFs on a large scale.

2. EXPERIMENTAL SECTION 2.1. Synthesis of MOFs in ILMEs. Ionic liquid microemulsion containing water, TX-100, and BmimPF6 was constructed according to a previous report27 and denoted as ILME-1. The BmimPF6 was synthesized based on the pioneering work.28 The ZIF-8 and ZIF-67 nanocrystals (NZIF-8 and NZIF-67) were synthesized in ILME-1 using a direct mixing method.21,29 The quaternary component system composed of water, ethanol, TX-100, and BmimPF6 (denoted as ILME-2) was formed by adding ethanol in ILME-1. Similarly, the HKUST-1 nanocrystal (NHKUST-1 b) was synthesized in ILME-2 using a direct mixing method.29,30 For comparison, HKUST-1 nanocrystal (NHKUST-1a) was synthesized in ILME-1. To remove the solvent, the samples were immersed in dichloromethane (CH2Cl2) and ethanol solution (V:V = 1:1) with stirring at room temperature for 48 h.

3. RESULTS AND DISCUSSION 3.1. XRD of MOFs Synthesized in ILMEs. The powder XRD patterns of MOFs synthesized in ionic liquid micro5900

DOI: 10.1021/acs.iecr.7b00694 Ind. Eng. Chem. Res. 2017, 56, 5899−5905

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Industrial & Engineering Chemistry Research

Figure 2. PXRD patterns of MOFs synthesized in ILMEs.

Figure 3. TEM images of (a) NZIF-8 synthesized in ILME-1, (b) NZIF-67 synthesized in ILME-1, (c) NHKUST-1b synthesized in ILME-2, and (d) NHKUST-1a synthesized in ILME-1.

It can be seen that the NZIF particles (Figures 3a and 3b) with remarkably small mean particle size and extremely narrow particle size distribution synthesized in the ILME-1 (including water, TX-100, and BmimPF6) are well-dispersed and regularly spherical. The mean particle sizes of NZIF-8 and NZIF-67 are 2.2 nm (σ = 0.5) and 2.3 nm (σ = 0.4), respectively. The NZIF particles obtained in this work possess remarkably smaller mean particle sizes than the corresponding samples obtained in water and methanol but are comparative to those obtained from the conventional reverse microemulsion.21 In addition, compared with the La-MOFs prepared by Han,20 the NZIF-8 and NZIF67 synthesized in the ILME-1 have a smaller size (only 1/100 of La-MOFs particles). This should be ascribed to the different mechanism of controlling the crystal growth in the coordination reaction of metal ions and organic ligands.

emulsions are presented in Figure 2. A good agreement can be seen between the XRD patterns of NZIFs (NZIF-8 and NZIF67) and NHKUSTs (NHKUST-1a and NHKUST-1b) synthesized in the ILMEs and those of the corresponding reported and simulated patterns.34−36 For example, the major peaks of the XRD patterns synthesized in the ILMEs, corresponding to the planes (011), (022), (112), (022), (013), and (222) for NZIFs and the planes (200), (220), (222), (400), (331), and (333) for NHKUST-1, agree well with those of the samples’ XRD patterns. Furthermore, the peak broadening can be observed compared to the samples’ XRD pattern. Therefore, it can be concluded that both of NZIFs and NHKUSTs are formed in ILMEs. 3.2. TEM Image of the Nanoparticles. TEM images of the nanoparticles synthesized in ILMEs are shown in Figure 3. 5901

DOI: 10.1021/acs.iecr.7b00694 Ind. Eng. Chem. Res. 2017, 56, 5899−5905

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Industrial & Engineering Chemistry Research Using ILME-1 as reaction media, the NHKUST-1a was synthesized. From the TEM image of NHKUST-1a (Figure 3d), the particles size is large (almost about 100 nm or even bigger). However, for the NHKUST-1b (Figure 3c) synthesized in the ILME-2 (including water, ethanol, TX-100, and BmimPF6), the nanoparticles are well-dispersed and regularly spherical. The mean particle size of NHUKST-1b is 1.6 nm (σ = 0.4). Compared with the NHKUST-1a, the nanoparticles prepared in the ILME-2 prove that the ethanol as an additive in ILME-2 plays a decisive role in the particle size control. 3.3. Thermal Stability. Figure 4 presents the TGA traces of NZIF-8, NZIF-67, and NHKUST-1b synthesized in ILMEs.

Table 1. Porosity Properties of MOFs Synthesized in ILMEs sample

solvent

SBET (m2/g)

Vmicro (cm3/g)

Da (nm)

NZIF-8 NZIF-67 NHKUST-1b

ILME-1 ILME-1 ILME-2

799.7 675.2 700.9

0.222 0.225 0.260

0.6 0.6 0.8

a

The pore diameter is referred to as the pore size corresponding to the peak position on the pore size distribution curve.

have smaller surface areas compared with those synthesized at high temperatures.38−40 Indeed, the surface areas of MOFs in this work are comparative to those of MOFs synthesized in aqueous room temperature conditions.40,41 On the other hand, for the synthesized MOFs in this work, some chemical substances, e.g., 2-MeIM, H3BTC, TX-100, and BmimPF6, may be adsorbed inside the pores of MOFs and cannot be easily removed through subsequent disposals such as washing and drying. 3.5. Growth Mechanism of the Nanoparticle Synthesized in ILMEs. In microemulsions, the dissolution of organic ligands into the dispersed phase plays an important role in controlling the particle size. For ZIFs, the building blocks, i.e., 2-methylimidazole (2-MeIM), can dissolve in water; thus, the coordination reaction proceeds within nano-water droplets, and the nanoscale ZIF-8 and ZIF-67 are synthesized in the ILME-1. However, most organic ligands such as trimesic acid (H3BTC), which is used to synthesize HKUST-1, are insoluble or slightly soluble in water. Therefore, a new method needs to be designed to dissolve organic ligands in the droplets of ILMEs. As excellent solvents, ethanol exhibits a good dissolving capacity for organic compounds. To reveal the important role of ethanol in the controlling mechanism of particle size, MD simulations were performed. By MD simulations, the microemulsion system can be found to be well-established, and the ethanol is observed to be well-dispersed in the water droplet, as shown in Figure 6. Therefore, as an additive, ethanol is added into the ILME-1 to form a novel ionic liquid microemulsion (ILME-2) with quaternary component for improving the dissolution of organic ligands. The growth mechanism of HKUST-1 nanoparticles in ILME2 is similar to that of ZIF nanoparticles in the ILME-1 because, for both ILME-1 and ILME-2, the metal ions and organic ligands are dissolved into the water droplets. Therefore, the growth mechanism of HKUST-1 nanoparticles in ILME-2 is discussed as follows, as shown in Figure 7, and that of ZIF nanoparticle is presented in Figure S1 in the Supporting Information. Cu(NO3)2·3H2O and trimesic acid are dissolved into ethanol aqueous solution (50 wt %), respectively. Then, the above-obtained aqueous solutions are added into the mixture solution of TX-100 and BmimPF6, respectively, to construct ILME-2 (ILME-2A: dissolved metal ions; ILME-2B: dissolved organic ligands). Finally, the ILME-2A and ILME-2B are blended with vigorous stirring. In the microemulsion, water droplets undergo a dynamic process of coalescence and separation. When the water droplet containing metal ions collides with the one composed of organic ligands, the compounds between the two droplets exchange, and the coordination reaction further occurs. At the beginning, the MOF nuclei are formed by self-coordination of metal ions and organic ligands in the water droplets. The water droplets constrain the growth of MOFs and can control the particle size well.

Figure 4. TGA traces of MOFs synthesized in ILMEs.

The MOFs obtained in this work have thermal stabilities similar to those prepared in previous researches.34−36 The decomposition temperature of NZIF-8 and NZIF-67 reaches up to 520 and 410 °C, respectively, which is in good agreement with the previous work that ZIF-8 exhibits a higher thermal stability compared to ZIF-67.37 Additionally, NHKUST-1b is thermally stable up to 290 °C, which is also consistent with the previous report.36 3.4. Adsorption−Desorption Isotherms and Porosity Properties. The porous structure properties of MOFs synthesized in ILMEs were evaluated through the N 2 adsorption−desorption isotherm method, as shown in Figure 5. For NZIF-8, NZIF-67, and NHKUST-1b, the adsorption isotherms exhibit a trend similar to that of type IV, indicating that they have an obvious microporous structure. The BET surface area, microprobe volume and pore diameter of MOFs synthesized in ILMEs are shown in Table 1. The MOFs (NZIF-8, NZIF-67, and NHKUST-1b) synthesized in ILMEs exhibit a BET surface area in the range of 675−800 m2/ g. Actually, the MOFs synthesized at room temperature usually

Figure 5. N2 adsorption−desorption isotherms of MOFs synthesized in ILMEs. 5902

DOI: 10.1021/acs.iecr.7b00694 Ind. Eng. Chem. Res. 2017, 56, 5899−5905

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Figure 6. Equilibrated snapshot of ILME-2 by MD simulations.

conventional chemical demulsification, new organic solvents are usually added into microemulsions, which will contaminate the ILMEs and limit the reuse of the microemulsion. According to the water/TX-100/BmimPF6 ternary phase diagram,27 point A, the composition of ILMEs used in this work is close to the twophase region, as shown in Figure 8a. Thus, with the addition of a certain amount of water into the system, the composition of ILMEs can be adjusted to point B in the two-phase region. Then, by further centrifugation, the system will be divided into three phases (IL phase, water phase, and products phase). The MOF crystals are located in the intermediate layer, with the water phase at the upper layer and the BmimPF6 phase in the bottom layer (Figure 8b). The MOF crystals are constructed with metal clusters and organic bridging ligands. Thus, they are essentially composed of hydrophilic domains and hydrophobic ones, meaning that the MOF crystals tend to locate at the interface between the water phase and BmimPF6 phase. In particular, with the particle size of MOFs down to the nanoscale, the interface tension between MOF crystals, water, and the BmimPF6 phase plays a major role in determining the location of MOFs after centrifugation in the ILMEs, compared to the gravity of MOF crystals. The water phase was removed by syringe. The ionic liquid phase was collected by syringe and then evaporated under reduced pressure to remove water. The recovered IL (RIL) can be recycled for the next synthesis of MOFs. The products of MOFs stayed in the centrifuge tube and were washed for future use (see the Supporting Information for the detailed procedure).

Figure 7. Schematic representation of the growth mechanism of HKUST-1 nanoparticles synthesized in ILME-2.

3.6. Demulsification and Centrifugation of ILMEs at the End of the Reaction. Ionic liquid microemulsions where at least one constituent is IL are thermodynamically stable systems composed of two immiscible solvents stabilized by surfactants.42 At the end of the self-coordination reaction, the ILMEs need to be broken to obtain the MOFs. Due to the high stability of the ILMEs and extremely small mean particle size of the MOFs, it is difficult to collect the nanoscale MOFs from this system by direct centrifugation. In addition, for the

Figure 8. Phase diagram (a) of the ILME-1 ternary system at 25 °C27 and (b) the ternary system after demulsification and centrifugation. Point A is the composition of the ILME-1 where the ZIFs are synthesized; point B is the composition of the ternary system after demulsification by adding water, and points C and D are the IL phase and water phase, respectively. 5903

DOI: 10.1021/acs.iecr.7b00694 Ind. Eng. Chem. Res. 2017, 56, 5899−5905

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(7) Ma, L.; Falkowski, J. M.; Abney, C.; Lin, W. A series of isoreticular chiral metal-organic frameworks as a tunable platform for asymmetric catalysis. Nat. Chem. 2010, 2 (10), 838−846. (8) Li, J. R.; Sculley, J.; Zhou, H. C. Metal-organic frameworks for separations. Chem. Rev. 2012, 112 (2), 869−932. (9) Lee, J.; Farha, O. K.; Roberts, J.; Scheidt, K. A.; Nguyen, S. T.; Hupp, J. T. Metal-organic framework materials as catalysts. Chem. Soc. Rev. 2009, 38 (5), 1450−1459. (10) McKinlay, A. C.; Morris, R. E.; Horcajada, P.; Férey, G.; Gref, R.; Couvreur, P.; Serre, C. BioMOFs: metal−organic frameworks for biological and medical applications. Angew. Chem., Int. Ed. 2010, 49 (36), 6260−6266. (11) Lin, W.; Rieter, W. J.; Taylor, K. M. Modular synthesis of functional nanoscale coordination polymers. Angew. Chem., Int. Ed. 2009, 48 (4), 650−658. (12) Taylor, K. M. L.; Jin, A.; Lin, W. Surfactant-assisted synthesis of nanoscale gadolinium metal-organic frameworks for potential multimodal imaging. Angew. Chem. 2008, 120 (40), 7836−7839. (13) Peng, L.; Zhang, J. L.; Li, J. S.; Han, B. X.; Xue, Z. M.; Yang, G. Y. Surfactant-directed assembly of mesoporous metal-organic framework nanoplates in ionic liquids. Chem. Commun. 2012, 48 (69), 8688−8690. (14) Qiu, L. G.; Li, Z. Q.; Wu, Y.; Wang, W.; Xu, T.; Jiang, X. Facile synthesis of nanocrystals of a microporous metal-organic framework by an ultrasonic method and selective sensing of organoamines. Chem. Commun. 2008, 31, 3642−3644. (15) Carne, A.; Carbonell, C.; Imaz, I.; Maspoch, D. Nanoscale metal-organic materials. Chem. Soc. Rev. 2011, 40 (1), 291−305. (16) Flügel, E. A.; Ranft, A.; Haase, F.; Lotsch, B. V. Synthetic routes toward MOF nanomorphologies. J. Mater. Chem. 2012, 22 (20), 10119−10133. (17) Tsuruoka, T.; Furukawa, S.; Takashima, Y.; Yoshida, K.; Isoda, S.; Kitagawa, S. Nanoporous nanorods fabricated by coordination modulation and oriented attachment growth. Angew. Chem., Int. Ed. 2009, 48 (26), 4739−4743. (18) Rieter, W. J.; Taylor, K. M. L.; Lin, W. Surface modification and functionalization of nanoscale metal-organic frameworks for controlled release and luminescence sensing. J. Am. Chem. Soc. 2007, 129 (32), 9852−9853. (19) Rieter, W. J.; Taylor, K. M.; An, H.; Lin, W.; Lin, W. Nanoscale metal-organic frameworks as potential multimodal contrast enhancing agents. J. Am. Chem. Soc. 2006, 128 (28), 9024−9025. (20) Shang, W.; Kang, X.; Ning, H.; Zhang, J.; Zhang, X.; Wu, Z.; Mo, G.; Xing, X.; Han, B. Shape and size controlled synthesis of MOF nanocrystals with the assistance of ionic liquid mircoemulsions. Langmuir 2013, 29 (43), 13168−13174. (21) Sun, W. Z.; Zhai, X. S.; Zhao, L. Synthesis of ZIF-8 and ZIF-67 nanocrystals with well-controllable size distribution through reverse microemulsions. Chem. Eng. J. 2016, 289, 59−64. (22) Welton, T. Room-temperature ionic liquids. Solvents for synthesis and catalysis. Chem. Rev. 1999, 99 (8), 2071−2084. (23) Rogers, R. D.; Seddon, K. R. Ionic liquids-solvents of the future? Science 2003, 302 (5646), 792−793. (24) Petkovic, M.; Seddon, K. R.; Rebelo, L. P. N.; Pereira, C. S. Ionic liquids: a pathway to environmental acceptability. Chem. Soc. Rev. 2011, 40 (3), 1383−1403. (25) Zhang, G.; Zhou, H.; Hu, J.; Liu, M.; Kuang, Y. Pd nanoparticles catalyzed ligand-free Heck reaction in ionic liquid microemulsion. Green Chem. 2009, 11 (9), 1428−1432. (26) Zhang, G.; Zhou, H.; An, C.; Liu, D.; Huang, Z.; Kuang, Y. Bimetallic palladium−gold nanoparticles synthesized in ionic liquid microemulsion. Colloid Polym. Sci. 2012, 290 (14), 1435−1441. (27) Gao, Y. A.; Han, S. B.; Han, B. X.; Li, G. Z.; Shen, D.; Li, Z. H.; Du, J. M.; Hou, W. G.; Zhang, G. Y. TX-100/water/1-butyl-3methylimidazolium hexafluorophosphate microemulsions. Langmuir 2005, 21 (13), 5681−5684. (28) Dupont, J.; Consorti, C. S.; Suarez, P. A.; de Souza, R. F. Preparation of 1-butyl-3-methyl imidazolium-based room temperature ionic liquids. Org. Synth. 2003, 79, 236−241.

4. CONCLUSIONS In summary, nanoscale MOFs, including ZIF-8, ZIF-67, and HKUST-1, were prepared in ionic liquid microemulsions. Through use of ionic liquid microemulsions, MOFs crystals with small particle size, uniform size distribution, and thermal stability were prepared. With addition of ethanol into ILME-1 to dissolve organic ligands into the microemulsion, the quaternary component system of water/ethanol/TX-100/ BmimPF6 was demonstrated to be a novel microemulsion. This kind of ILME provides a potential method to enrich the synthesis strategies of MOFs, and ethanol as an additive in ILME-2 plays a very important role in particle size control. Furthermore, the synthesis process is environmentally friendly and requires less energy due to the use of green solvent (ionic liquid) and the simple demulsification method. Additionally, ionic liquid is easily recycled to synthesize MOFs. This work provides a promising green method to synthesize nanoscale MOFs on a large scale.



ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.7b00694. Further experimental details and grown mechanism (PDF)



AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]; Telephone: +86 21 64253027. ORCID

Weizhen Sun: 0000-0002-9957-3620 Notes

The authors declare no competing financial interest.



ACKNOWLEDGMENTS The financial support by the National Natural Science Foundation of China (91434108) and the Shanghai Excellent Technical Leaders Program (14xd1425500) is gratefully acknowledged.



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DOI: 10.1021/acs.iecr.7b00694 Ind. Eng. Chem. Res. 2017, 56, 5899−5905

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DOI: 10.1021/acs.iecr.7b00694 Ind. Eng. Chem. Res. 2017, 56, 5899−5905