Iodine Capture Using Zr-Based Metal–Organic Frameworks (Zr-MOFs): Adsorption Performance and Mechanism

Abstract

The effective capture of radioiodine, produced or released from nuclear-related activities, is of paramount importance for the sustainable development of nuclear energy. Here, a series of zirconium-based metal−organic frameworks (Zr-MOFs), with a Zr 6 (μ 3 -O) 4 (μ 3 -OH) 4 cluster and various carboxylate linkers, were investigated for the capture of volatile iodine. Their adsorption kinetics and recyclability were investigated in dry and humid environments. The structural change of Zr-MOFs during iodine trapping was studied using powder X-ray diffraction and pore structure measurements. Experimental spectra (Raman and X-ray photoelectron spectroscopy) and density functional theory (DFT) calculations for the linkers and Zr clusters were performed to understand the trapping mechanism of the framework. When interacting with iodine molecules, MOF-808, NU-1000, and UiO-66, with highly connected and/or rigid linkers, have better structural stability than UiO-67 and MOF-867, which have flexible linkers with less connectivity. Particularly, MOF-808, with a rigid and tritopic benzenetricarboxylate linker, has the highest iodine adsorption capacity (2.18 g/g, 80 °C), as well as the largest pore volume after iodine elution. In contrast, UiO-67, with long linear ditopic linkers, exhibits the weakest stability and lowest adsorption capacity (0.53 g/g, 80 °C) because of its most serious collapse of pore structures. After incorporating with strong electron-donating imidazole/pyridine ligands, both the stability and adsorption capacity of MOF-808/NU-1000 decrease. DFT calculations verify that the N-heterocycle groups could enhance the affinity toward iodine by strong charge transfer. DFT calculations also suggest that the terminal −OH in MOF-808 has a strong affinity toward iodine (−54 kJ/mol I 2 ) and water (−63 kJ/mol H 2 O) and a weak affinity toward NO 2 (−27 kJ/mol NO 2 ). With high adsorption capacity and excellent stability, MOF-808 shows great potential for the sustainable removal of radioiodine.

Pyrene-based metal organic frameworks: from synthesis to applications

“…While SION-8 is an insulator, the I 2 -adsorbed SION-8 (SION-8*I 2 ) showed electrical conductivity, proving the donor-acceptor charge transfer. Similarly, NU-1000 has been studied for the capture of volatile I 2 by Chen et al 224 NU-1000 could adsorb 1.45 g I 2 /g MOF at 80 1C, thanks to the presence of the -OH groups of Zr 6 nodes and enriched p-conjugated electron clouds on pyrene. Pyrene can donate abundant negative charges, making NU-1000 convenient to host iodine.…”

Porous MOF-808@PVDF beads for removal of iodine from gas streams

“…4(b), the three 808-PVDFx beads have a lower weight gain, exhibiting the similar patterns as their powder counterparts, due to the hydrophilic Zr nodes in the MOFs. 13 Because of the huge difference in molecular weights of iodine and water molecules, the weight ratio of adsorbed water is very small. 34,35 Besides, there may be a cooperative adsorption effect between H 2 O and iodine molecules.…”

“…Raman mapping of area integral intensities was detected to explore the species of the adsorbed iodine on the external surfaces of the beads. Two typical bands, which are centered at 110 cm À1 and 170 cm À1 , ascribed to I 3 À species and packed iodine solid, respectively, 13,40 were recorded and integrated. The Raman mapping images of 808-PVDF0.7 with low loading amount (5% wt) of iodine, 808-PVDF0.7-5% I, are shown as Fig.…”

“…[10][11][12] In our previous study, the development and potential application of Zr-MOFs are driven by their capture performance of iodine, and the Zrbased MOF-808 has excellent adsorption capacity and structural stability, displaying its great prospect for the sustainable capture of iodine. 13 Like the other MOFs, in terms of conventional solvothermal processes, MOF-808 is oen isolated as polycrystalline powders in a small scale. The MOFs with the form of tiny powder, are not suitable for industrial applications, due to operating problems, such as dirtiness, mass loss, and difficulties in simply storage and transport.…”

Co-Oligomerization of Electroconductive Monomers in a Cyclodextrin-Based Metal–Organic Framework

“…is is caused by the disorder of the crystal structure and the scattering of the iodine element remaining in the crystal during polymerization. Cheng et al (2020) reported that the intensity of all the peaks for the porous MOF-808 crystal decreases gradually, because of the increased di use scattering of the absorbed iodine. In addition, SEM images of these cubic CD-MOF crystals showed hardly any change.…”