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Zirconium metal-organic cages for iodine adsorption: Effect of substituted groups and pore structures
Bin Xue1, Yingtong Lv2, Weimin Xuan3
1State Key Laboratory of Advanced Fiber Materials, College of Chemistry and Chemical Engineering, Donghua University, Shanghai 201620, China; Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, PR China.
Abstract:
Zirconium metal-organic cages (MOCs) have emerged as potential adsorbents for radioactive iodine absorption, one of key fission products of concern in nuclear fuel cycles. Herein a series of substituted groups functionalized Zr-MOCs were employed to investigate the influence of substituted group on iodine adsorption, in which ZrT-1-(NH2)2 showed the highest improvement on both iodine vapor and solution-based absorption. Thereafter, five longer linkers functionalized with amino groups were chosen to construct five isoreticular MOCs for iodine absorption. Among them, ZrT-2-3,3'-(NH2)2 and ZrT-3-2,2''-(NH2)2 exhibited comparable iodine vapor absorption capacity compared with ZrT-1-(NH2)2. Impressively, iodine vapor adsorption capacities (2.62 g/g and 2.50 g/g) of ZrT-1-(NH2)2 and ZrT-3-2,2''-(NH2)2, represent the second highest among all the MOCs. These five isoreticular MOCs displayed higher iodine uptake capacities via solution-based process than ZrT-1-(NH2)2. The iodine/cyclohexane uptake capacities of ZrT-2-3-NH2 and ZrT-2-3,3'-(NH2)2 and ZrT-3-2,2''-(NH2)2 are the highest among all the MOCs. Raman and XPS demonstrate the strong charge transfer from the amino-substituted linkers to absorbed iodine. Synchrotron X-ray single-crystal diffraction provides the possible iodine species distribution in the cage, clarifying the host-guest interactions between the trapped iodine and MOCs. This work may motivate the rational design of MOCs with optimized structures to enhance the adsorption properties.
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