Regulating the iodine adsorption performances of two- and three-component β-ketoenamine-linked covalent organic frameworks through tuning the proportion of monomers

Abstract

Although significant progress in the development of functional covalent organic frameworks (COFs) as effective porous adsorbents for capturing radioactive iodine has been achieved, a systematic study on regulating the iodine adsorption performance of COFs by tuning the proportion of monomers is extremely scarce. Herein, a series of two- and three-component β-ketoenamine-linked COFs denoted as NH₂-Th_X-Mth_1−X-Tfp (X = 1, 0.75, 0.50, 0.25, and 0) with different contents of free amino groups have been synthesized by tuning the proportion of three monomers, 2-aminoterephthalohydrazide (NH₂-Th), 2,5-bis(2-methylbutoxy) dihydrazide terephthalate (Mth) and 1,3,5-trihydroxy phloroglycerol (Tfp). Then, these NH₂-Th_X-Mth_1−X-Tfp COFs have been utilized as adsorbents for iodine vapour capture. Apparently, owing to the change of the proportion of monomers, the content of amino groups, crystallinity and the specific surface area of the obtained COFs are different, which have remarkable regulation effects on their adsorption performances toward iodine vapour. With the decrease of the content of NH₂-Th, the crystallinity and specific surface area of COFs increased gradually. And the adsorption capacities of five NH₂-Th_X-Mth_1−X-Tfp COF materials (X = 1, 0.75, 0.50, 0.25, and 0) were determined to be 1.21, 1.32, 1.55, 2.30 and 1.73 g g⁻¹, respectively. Significantly, the NH₂-Th_0.25-Mth_0.75-Tfp COF containing 25% NH₂-Th exhibited the largest adsorption capacity for iodine vapour among the five as-synthesized COFs, and still maintained 70% adsorption capacity after six cycles. Moreover, the iodine adsorption kinetics of NH₂-Th_X-Mth_1−X-Tfp COFs (X = 0, 0.25, 0.50, and 0.75) were consistent with the pseudo-second-order simulations, while that of the NH₂-Th-Tfp COF fitted better with the pseudo-first-order simulations. This study uncovered that regulating the COF structures by tuning the proportion of monomers could greatly improve their iodine adsorption performances, which provided a reference for the design and development of new high-performance COF-based absorbents.