(198e) Facile Synthesis of Cd-Substituted Zeolitic-Imidazolate Framework Cd-ZIF-8 and Mixed-Metal Cdzn-ZIF-8

Facile Synthesis of Cd-substituted Zeolitic-imidazolate
Framework Cd-ZIF-8 and Mixed-metal CdZn-ZIF-8

Jingze Sun,¹ Liya Semenchenko,² Woo Taik Lim,³ and Hae-Kwon Jeong*^{1, 4}

¹Artie McFerrin Department of Chemical Engineering and ⁴Department of Materials
Science and Engineering, Texas A&M University, College Station, TX
77843-3122

²Department of Chemical Engineering, University of Florida,

Gainesville, FL 32611

³Department of Applied Chemistry, College of Natural Science,
Andong National University, 388 Song-chon Dong, Kyungpook 760-749, Korea

*
Corresponding author: hjeong7@tamu.edu

Zeolitic-imidazolate frameworks (ZIFs),¹ are
of great practical interest due to their stable chemical nature and ultra-microporosities. ZIFs are composed of tetrahedrally coordinated
transition-metals (i.e., Zn, Co, Cd,) and bridged by imidazolate-derived
linkers. Among many ZIFs, ZIF-8,¹ constituted of zinc and
2-methylimidazole (hereafter mIm) forming sodalite (SOD) topology, has been most extensively
studied for its use in gas separation applications^{2, 3} mainly due to its
robust synthesis protocols, thermal/chemical stability, and well-defined
aperture size. ZIF-8 has shown to be extremely effective for the kinetic separation
of propylene from propane.^{2, 4}

As with
any other crystalline molecular sieves such as zeolites, the available aperture
sizes of ZIFs are fixed and discrete, thereby limiting their gas separation
applications. For example, while high-quality ZIF-8 membranes show impressive
propylene/propane selectivity (as high as ~ 200),⁵ their ethylene/ethane separation
performances are negligible.⁶

Various
strategies have been applied for changing the effective aperture size of ZIF-8
systematically, including varying organic linkers, varying metal nodes, thermal
treatment for removing methyl groups,⁷ and mixed linker approaches.⁸ Jeong and his
co-workers⁹ have demonstrated mixed metal approach to be effective by
introducing Co centers along with Zn centers in ZIF-8 (i.e., mixed metal
CoZn-ZIF-8). However, mixed metal approach is limited by the number of metal
elements that can be incorporated into ZIF-8 framework.

Cadmium
can be added into the toolbox for mixed metal approaches to systemically vary
the effective apertures of ZIF-8 and its iso-structures. There is, however, only one synthesis recipe¹⁰reported
for Cd-ZIF-8 (formally as CdIF-1). Unfortunately, the reported recipe is not
compatible with those recipes for Zn- and Co-ZIF-8 (formally named ZIF-67),
thereby limiting its use in mixed metal approach.

Here, we
would like to present a facile solvothermal recipe for phase-pure Cd-ZIF-8 in methanol, thereby
compatible with the recipes of Zn- and Co-ZIF-8. The presence of an organic
base, tetraethylamine (TEA), was found
critical not only for the formation of Cd-ZIF-8 but also for the inhibition of
phase transformation from Cd-ZIF-8 into other phases. The single crystal X-ray
structure of Cd-ZIF-8 was solved performed and compared with those of Zn-ZIF-8
and Co-ZIF-8 at the same condition. Finally, for the first time, mixed-metal
CdZn-ZIF-8 crystals with a various Cd/Zn ratio were solvothermally synthesized, demonstrating
the opportunity for varying the effective aperture sizes of ZIF-8 iso-structures.

References
and Notes:

(1)           
Park, K. S.; Ni, Z.; Cote, A. P.; Choi, J. Y.; Huang, R. D.; Uribe-Romo, F. J.; Chae, H. K.; O'Keeffe, M.; Yaghi, O.
M., Exceptional chemical and thermal stability of zeolitic imidazolateframeworks. PNAS 2006, 103, (27), 10186-10191.

(2)           
Kwon, H. T.; Jeong,
H. K., Highly propylene-selective supported zeolite-imidazolate framework (ZIF-8) membranes
synthesized by rapid microwave-assisted seeding and secondary growth. Chem. Commun. 2013, 49, (37), 3854-6.

(3)           
Zhang, K.; Lively, R. P.; Zhang, C.; Koros, W. J.; Chance, R. R., Investigating the Intrinsic
Ethanol/Water Separation Capability of ZIF-8: An Adsorption and Diffusion
Study. J. Phys. Chem. C 2013, 117, (14), 7214-7225.

(4)           
Pan, Y. C.; Li, T.; Lestari, G.; Lai, Z. P., Effective separation of
propylene/propane binary mixtures by ZIF-8 membranes. J. Membr. Sci. 2012, 390, 93-98.

(5)           
Lee, M. J.; Kwon, H. T.; Jeong, H. K., Defect-dependent stability of highly
propylene-selective zeolitic-imidazolate framework
ZIF-8 membranes. J. Membr. Sci. 2017, 529, 105-113.

(6)            Bux, H.; Chmelik, C.;
Krishna, R.; Caro, J., Ethene/ethane separation by the MOF membrane ZIF-8:
molecular correlation of permeation, adsorption, diffusion. J. Membr. Sci. 2011, 369, (1), 284-289.

(7)            Gadipelli,
S.; Travis, W.; Zhou, W.; Guo, Z., A thermally derived and optimized structure from
ZIF-8 with giant enhancement in CO 2 uptake Energ. Environ. Sci.

 2014, 7, (7), 2232-2238.

(8)           
Liao, Y. T.; Dutta, S.; Chien, C. H.; Hu, C. C.; Shieh, F. K.; Lin, C. H.; Wu, K.
C. W., Synthesis of Mixed-Ligand Zeolitic Imidazolate Framework
(ZIF-8-90) for CO2 Adsorption. J. Inorg. Organomet. Polym.
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(9)           
Hillman, F.; Zimmerman, J. M.; Paek, S.-M.; Hamid, M. R. A.; Lim, W. T.; Jeong,
H.-K., Rapid microwave-assisted synthesis of hybrid zeolitic_imidazolate frameworks
with mixed metals and mixed linkers. J.
Mater. Chem. A 2017, 5, (13), 6090-6099.

(10)         Tian, Y. Q.;
Yao, S. Y.; Gu,
D.; Cui, K. H.; Guo, D. W.; Zhang, G.; Chen, Z. X.; Zhao, D. Y., Cadmium imidazolate frameworks with polymorphism, high
thermal stability, and a large surface area. Chemistry 2010, 16, (4), 1137-41.