Feasibility Study of Using Bi-mna Metal–Organic Frameworks as Adsorbents for Radioiodine Capture at High Temperature

In this study, a bismuth-based metal–organic framework (Bi-MOF) was investigated in its applicability as an iodine adsorbent at high temperatures for possible applications under severe accidents in a nuclear power plant. Bi-mna was selected among Bi-MOF candidates based on its thermodynamic characteristics, which expected to allow chemisorption of iodine by bismuth. Its iodine adsorption performance was compared with zeolitic imidazolate framework-8 and Cu-BTC and other MOFs which were chosen due to their diversity in iodine adsorption mechanisms. Bi-mna was synthesized at the laboratory scale, and the aforementioned three MOFs were tested for iodine adsorption at various temperatures from 350 to 600 K. The adsorption mechanism of Bi-mna was investigated by conducting various analyses including thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller. The results showed that Bi-mna has good adsorption performance (700 mg-I/g-adsorbent) while maintaining good thermal stability even at a high temperature (up to 575–600 K). The iodine capture performance of Bi-mna is better, especially at high temperature, in comparison with those of non-MOF adsorbents such as silver-exchanged zeolites and bismuth-embedded SBA-15. Analysis results confirmed that Bi-mna chemically captured iodine by breaking bonds between bismuth and sulfur to form new chemical bonds between iodine and the bismuth in Bi-mna. The results indicate that Bi-mna has the potential to be used in capturing radioiodine at high-temperature environments, such as during nuclear severe accident management. Its use should also be considered as a potential candidate for waste form development.