(725b) Mixed-Linker MOF Synthesis and Remediation of Acid-Gas Degradation Using Linker-Exchange Techniques

Authors: 
Jayachandrababu, K. C. - Presenter, Georgia Institute of Technology
Bhattacharyya, S., Georgia Institute of Technology
Sholl, D., Georgia Institute of Technology
Nair, S., Georgia Institute of Technology
Solvent Assisted Linker Exchange (SALE) is known as a useful tool to modify existing MOFs and thereby obtain otherwise difficult-to-synthesize structures, or improve the stability and functional properties of MOFs. By partially exchanging the native linker in a MOF, this technique can also be used to synthesize mixed-linker MOFs. However, the structural properties of such materials, including the spatial distributions of linkers in these mixed-linker materials and how they differ from mixed-linker MOFs made via de novo routes, are not well known.

This work consists of two main parts. First, we compare and contrast a series of mixed-linker ZIF-8-90 materials made via both routes. 1H CRAMPS NMR spectroscopy, water and nitrogen adsorption, and native fluorescence confocal microscopy are used to elucidate the differences in the outcome of these syntheses routes. A generalizable mechanism for SALE in ZIFs is proposed by studying the impact of crystal size, temperature, and SALE duration. We observe that under moderate conditions, SALE in ZIFs is diffusion-limited, and results in a core-shell type structure. Harsher conditions lead to a deviation from this behavior including linker etching resulting in morphological changes to particles. Under appropriate reaction conditions, SALE techniques appear to be capable of producing controlled core-shell ZIF structures of good morphological quality that complement the well-mixed structures obtained by de novo routes.

Second, linker exchange was explored as a means of recovering crystallinity and porosity of ZIFs damaged by acid-gases. We developed a technique called Solvent Assisted Crystal Redemption (SACRED) wherein the damaged crystals of a ZIF are treated with a solution of its native linker. The structural damage to ZIFs induced by acid-gases were found to be partially or completely reversed by this treatment. The recovered material is shown to be chemically identical to the pristine material using FTIR spectroscopy and X-ray diffraction. Adsorption studies show that the functional performance of ZIF-8 is retained after the recovery. The use of deuterium-substituted linkers and 2H NMR spectroscopy provides mechanistic insight into the recovery process. This method has the potential to reduce costs and improve lifetime of ZIF-based adsorbents or membranes.

References

[1] Highly Tunable Molecular Sieving and Adsorption Properties of Mixed-Linker Zeolitic Imidazolate Frameworks; K. Eum, K.C. Jayachandrababu, F. Rashidi, K. Zhang, J. Leisen, S. Graham, R.P. Lively, R.R. Chance, D.S. Sholl, C.W. Jones, S. Nair; J. Am. Chem. Soc.; 2015; 137(12); 4191-4197

[2] Structure Elucidation of Mixed-Linker Zeolitic Imidazolate Frameworks by Solid-State 1H CRAMPS NMR Spectroscopy and Computational Modeling; K.C. Jayachandrababu, R.J. Verploegh, J. Leisen, R.C. Nieuwendaal, D.S. Sholl, S. Nair; J. Am. Chem. Soc.; 2016; 138(23); 7325-7336

[3] Structural and Mechanistic Differences in Mixed-Linker Zeolitic Imidazolate Framework Synthesis by Solvent Assisted Linker Exchange (SALE) and de novo Routes; K.C. Jayachandrababu, D.S. Sholl, S. Nair; J. Am. Chem. Soc.; 2017; Just Accepted Manuscript

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