Transformation of Porous Organic Cages and Covalent Organic Frameworks with Efficient Iodine Vapor Capture Performance

Abstract

The reaction of 5,5′-([2,2′-bipyridine]-5,5′-diyl)diisophthalaldehyde (BPDDP) with cyclohexanediamine and [benzidine (BZ)/[2,2′-bipyridine]-5,5′-diamine (BPDA)], respectively, affords a nitrogen-rich porous organic cage BPPOC and two two-dimensional (2D) covalent organic frameworks (COFs), USTB-1 and USTB-2 (USTB = University of Science and Technology Beijing), under suitable conditions. Interestingly, BPPOC with a single-crystal X-ray diffraction structure is able to successfully transform into USTB-1 and USTB-2 (newly converted COFs denoted as USTB-1c and USTB-2c, respectively) upon exchange of the imine unit of cyclohexanediamine in the cage by BZ and BPDA. Such a transformation also enables the isolation of analogous COFs (USTB-3c and USTB-4c) on the basis of an isostructural organic cage, BTPOC, which is derived from 5,5′-([2,2′-bithiophene]-4,4′-diyl)diisophthalaldehyde (BTDDP) and cyclohexanediamine. However, the conventional solvothermal reaction between BTDDP and BPDA leads to an impure phase of USTB-4 containing incompletely converted aldehyde groups due to the limited solubility of the building block. The newly prepared COFs have been characterized by nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. In particular, BPPOC is able to absorb the iodine vapor with an uptake of 5.64 g g −1 , breaking the porous organic cage's (POC's) record value of 3.78 g g −1 . Nevertheless, the cage-derived COFs exhibit improved iodine vapor adsorption capability in comparison with the directly synthesized counterparts, with the highest uptake of 5.80 g g −1 for USTB-1c. The mechanism investigation unveils the superiority of nitrogen atoms to sulfur atoms for POCs in iodine vapor capture with the assistance of definite crystal structures. This, in combination with porosity, synergistically influences the iodine vapor capture capacity of COFs.

In Situ Confined Synthesis of a Copper-Encapsulated Silicalite-1 Zeolite for Highly Efficient Iodine Capture

“…Currently, the capture of iodine with solid adsorbents has been demonstrated to be a feasible method for commercial application compared to wet scrubbing of iodine-containing off-gas streams using alkaline solutions. 9 A variety of porous adsorbents, including activated carbon, 10−13 zeolites, 14−17 aerogels, 18,19 covalent organic frameworks (COFs), 3,20,21 metal−organic frameworks (MOFs), 22−25 etc., with intrinsic properties of their porous structure, high specific surface area, and uniformly dispersed functional groups showed exceptional advantages in capturing radioactive iodine. 26−28 Originating from the diverse structural units and modifiable functional groups of organic polymer materials, it exhibits a strong affinity between iodine and the active site of sorbents through Lewis acid−base interactions and superior physicochemical stability.…”

“…Currently, the capture of iodine with solid adsorbents has been demonstrated to be a feasible method for commercial application compared to wet scrubbing of iodine-containing off-gas streams using alkaline solutions . A variety of porous adsorbents, including activated carbon, − zeolites, − aerogels, , covalent organic frameworks (COFs), ,, metal–organic frameworks (MOFs), − etc., with intrinsic properties of their porous structure, high specific surface area, and uniformly dispersed functional groups showed exceptional advantages in capturing radioactive iodine. − Originating from the diverse structural units and modifiable functional groups of organic polymer materials, it exhibits a strong affinity between iodine and the active site of sorbents through Lewis acid–base interactions and superior physicochemical stability. − However, their complicated preparation process and high cost limit their large-scale applications. Activated carbon is widely used as an iodine adsorbent in the nuclear industry due to its high degree of porosity, but its application is limited on account of weaknesses such as low autoignition temperature, aging problems, and lack of selectivity between water and iodine molecules. , Zeolite molecular sieves are a class of aluminosilicate crystal material with a microporous structure, which is extensively used in the field of gas separation due to its large specific surface area, uniform pore size distribution, excellent thermal stability, and hydrothermal stability .…”

Facile Preparation of MCM-41/Ag2O Nanomaterials with High Iodide-Removal Efficiency

“…The high-resolution I3d spectra of 5-Ag 2 O@MCM-41-I along with their fitting results are presented in Figure 6 c. The I3d5/2 peak of 5-Ag 2 O@MCM-41-I were deconvoluted into two components occurring at 619.7 eV and 620.3 eV. The signal at 619.7eV was attributed to I − in AgI [ 42 ], while the peak at 620.3 eV could be ascribed to I 2 [ 43 ], which was formed due to the partial oxidation of iodide by the dissolved oxygen. Li et al and Mao et al have, respectively, reported that iodide could be partially oxidized by dissolved oxygen, forming I 2 [ 42 , 44 ].…”

Energy‐Efficient Iodine Uptake by a Molecular Host⋅Guest Crystal

“…The numerous C−H⋅⋅⋅I and C−O⋅⋅⋅I interactions are probably in part responsible for this surprising guest exchange in a water‐saturated crystal. While iodine capture usually requires energy‐intensive material activation, [68–70, 88, 98] PHGC‐1 could be advantageous due to (i) the absence of energy devoted to its synthesis, (ii) its moisture insensitivity, (iii) its absence of energy‐intensive activation step, (iv) the adsorption possible at room temperature and (v) the I 2 /H 2 O selectivity. The dynamics of water motion inside the crystals was probed by DOSY NMR as a function of water replacement by iodine molecules.…”

“…All techniques converged toward a � 30 % weight of iodide absorbed which is comparable to the capacity of some zeolites. [88] Iodine uptake capacities of POC based on macrocycles alone clearly exceed the performances of PHGC-1, [68][69][70] but adsorption capacities are recorded at 75 °C and these materials are activated prior to measurements. Beside high recording temperature, it is important to note that material activation is an energy-intensive step, usually followed by unwanted water uptake (for most porous materials) [71,89] thereby limiting their capacity in real conditions, and so restricting their use.…”