Polymorphic Covalent Organic Frameworks: Molecularly Defined Pore Structures and Iodine Adsorption Property

Abstract

Radioactive iodine-capturing materials are urgently needed for the emerging challenges in nuclear waste disposal. The various pore structures of covalent organic frameworks (COFs) render them promising candidates for efficient iodine adsorption. However, the detailed structure–property relationship of COFs in iodine adsorption remains elusive. Herein, two polymorphic COFs with significantly different crystalline structures are obtained based on the same building blocks with varied molecular ratios. The two COFs both have high crystallinity, high specific surface area, and excellent chemical and thermal stability. Compared with the [C4+C4] topology (PyT-2) with an AA stacking form, the [C4+C2] topology (PyT-1) with an AB stacking form has more twisted pore channels and complex ink-bottle pores. At ambient conditions, PyT-1 and PyT-2 both exhibit good adsorption properties for iodine capture either in a gaseous or liquid medium. Remarkably, PyT-1 presents an excellent maximum adsorption capacity (0.635 g g−1), and the adsorption limit of PyT-2 is 0.445 g g−1 in an n-hexane solution with an iodine concentration of 400 mg L−1, which is highly comparable to the state-of-the-art iodine absorption performance. This study provides a guide for the future molecular design strategy toward novel iodine adsorbents.

Expanding the horizons of covalent organic frameworks: sub-stoichiometric synthesis as an emerging toolkit for functional COFs

“…11A). 149 While both the COFs exhibited good thermal, solvent, acid–base stabilities, PyT-1 was found to have comparably higher BET surface area (1186.94 m 2 g −1 ) and pore volume (0.89 cm 3 g −1 ). Significant iodine vapour adsorption was observed for both PyT-1 and PyT-2 for the first 10 h and attained saturation around 90 h (>3.4 g g −1 , Fig.…”

“…This interaction of water with residual carbonyls was established via spectroscopic techniques and a water-uptake value as high as 14.0 mmol g −1 (0.25 g g −1 ) was observed for COF-SMU-1 at 11A). 149 While both the COFs exhibited good thermal, solvent, acid-base stabilities, PyT-1 was found to have comparably higher BET surface area (1186.94 m 2 g −1 ) and pore This journal is © The Royal Society of Chemistry 2023 volume (0.89 cm 3 g −1 ). Signicant iodine vapour adsorption was observed for both PyT-1 and PyT-2 for the rst 10 h and attained saturation around 90 h (>3.4 g g −1 , Fig.…”

“…Since the rst report on sub-stoichiometric COFs, there are only three instances of polymorphism reported. 116,149,152 These reports on Type III COFs involve the use of tetratopic monomers and rhombic topologies. In these attempts, COFs with unreacted carbonyls were realized just by changing the solvent(s) rather than the stoichiometry of the monomers.…”

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

“…[19][20][21][22][23] Particularly, the design and construction of functional COFs as porous adsorbents for iodine adsorption have received much attention in recent years. [24][25][26][27][28][29][30] For example, Chen et al explored crystallization of a stable nitrogen-containing TAPA-PDA COF, which exhibited high iodine capture performance up to 5.09 g g À1 . 24 A new cationic C-TP-BPDA-COF prepared through post-synthetic modification by the Mi group exhibited an excellent iodine adsorption capacity up to 6.11 g g À1 .…”

“…27 In the work by the Wang group, two polymorphic PyT COFs with different stacking modes, namely AA- and AB-types, were obtained from the same building blocks but under different reaction conditions, and the iodine capture results of them revealed that the AB-stacking PyT COF (0.635 g g −1 ) possessed a bit larger iodine adsorption capacity in hexane solution as compared to the AA-stacking PyT COF (0.445 g g −1 ). 28 Additionally, Guo et al reported the oriented syntheses and iodine capture application of a series of TPT-DHBD x COFs ( X = 0, 25, 50, 75, and 100) with different intra-layer hydrogen bonds, showing the highest capture capacity up to 5.43 g g −1 . 29 Interestingly, the iodine adsorption capacity of TPT-DHBD X COFs decreased gradually with the increase of the monomer TPT-DHBD containing potential hydrogen bonding sites.…”