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Chenfeng Ke1

1, Dartmouth College, Hanover, New Hampshire, United States

Covalent organic frameworks (COFs) are prominent in gas storage/separation, catalysis, and energy-related applications. The crystalline nature of COFs with defined pore sizes allows for a precise structural design to sequester environmental pollutants such as radioactive wastes. The chemical stability of COFs, in general, limits their practical application for adsorbing ions/molecules that are environmentally impactful. Compared with COFs, highly crystalline porous molecular materials, such as hydrogen bonded organic frameworks1 (HOFs) and porous organic molecules2,3 that rely on weak interactions to stabilize their frameworks, are often too labile for their wide adoption under environmental settings. Developing hydrogen-bonded crosslinked organic frameworks4 (HCOFs), will leverage the advantages of both COFs and HOFs, thus affording high chemical stability for selectively adsorbing environmentally impactful guests. We report the design and synthesis of HCOF-1 through a single crystal to single crystal (SCSC) transformation from molecular precursor via photo-irradiated thiol-yne reactions. HCOF-1 adsorbs I2 rapidly in an aqueous environment with high uptake capacity and efficiency, associated with an increase in the density of the material that simplifies its isolation. Interestingly, the adsorbed I2 can interrupt the crystallinity of HCOF-1, which expands its void space to accommodate more I2 beyond its theoretical capacity. The crystallinity of HCOF-1 can be recovered by releasing the enriched I2 after solvent evacuation, demonstrating the elastic and recyclable properties of HCOF-1 and its potential in practical application for the active enrichment and removal of radioactive iodine isotopes (129I and 131I) that are liberated during nuclear fuel treatment and nuclear accidents such as the Fukushima nuclear disaster.
References:
(1) He, Y., Xiang, S., Chen, B. J. Am. Chem. Soc., 2011, 133, 14570-14573.
(2) Zhang, G., Presly, O., White, F., Oppel, I. M., Mastalerz, M. A Angew. Chem. Int. Ed, 2014, 53, 1516-1520.
(3) Hasell, T., Cooper, A. I. Nat. Rev. Mater., 2016, 1, 16053.
(4) Lin, Y., Jiang, X., Kim, S. T., Alahakoon, S. B., Hou, X., Zhang, Z., Thompson, C. M., Smaldone, R. A., Ke, C. J. Am. Chem. Soc., 2017, 139, 7172–7175.

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