The Performance Of Iodine Adsorption In Zr-Based Metal-Organic Frameworks

Metal-organic frameworks(MOFs)have been reported as the promising candidates for iodine adsorption because of their uniform pore structure,large pore volumes,and easy modification.However,MOFs usually have the low stability,which limits their further application.In order to solve this problem,zirconium-based metal-organic framework materials(Zr-MOFs)with high stability were selected as the research object.The work was dedicated to the study of the volatile iodine capture using several typical Zr-based MOFs,focusing on the relationship between the adsorption performance and structural stability and the species forms of adsorbed iodine.MOF-808 with the high structural stability and large adsorption capacity was selected to synthesis beads for iodine capture.The results show that the iodine adsorption properties of Zr-MOFs are closely related to their structural stability.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.When iodine enters Zr-MOFs,the initial adsorbed iodine is mainly caused by the internal boundary of the Zr-MOFs framework to form iodine anion,then the entering iodine interacts with the iodine molecule itself,which tends to form a dense packing structure of iodine.Beads were synthesisd by phase transfer method with MOF-808 and Polyvinylidene fluoride(PVDF).The crystal structure MOF-808 and its iodine adsorption capacity were maintained effectively in the beads.The adsorption capacity of 70%MOF-808 beads was 1350 mg/g at 80?.After 12 hours of N₂ purging,the adsorption capacity of MOF-808 was still as high as 910 mg/g,indicating that MOF-808 has a high affinity for iodine and high application prospect for iodine capture.