Molten salt-assisted carbonized zeolite imidazolate framework on nickel foam for highly efficient iodide capture in fluoride molten salts

Abstract

Removing radioactive iodide ions from molten salt nuclear fuel in fourth-generation molten salt reactors is essential for nuclear and environmental safety. In the present work, a synthesis strategy as synthesised in molten salt was utilized by employing. A two-dimensional nanoscale carbon membrane with a hierarchical pore structure (HNPC@NF) was successfully prepared via molten salt-assisted carbonized three-dimensional ZIF-8 grown in situ on nickel foam, which showed the maximum adsorption capacity of 55.6 mg/g for iodide ions in LiF-BeF2 molten salt within 8 h under static adsorption experiments. HNPC@NF was capable of effectively adsorbing iodide ions even in the presence of various cations and anions such as Cs+, Sr2+, Nd3+, Sm3+and Br- and also adsorbed coexisting ions. The different-sized pores of HNPC@NF act as filters, sieving, and occluding for these ions. Radioactive tracer experiments have confirmed that HNPC@NF could adsorb 131I in simulated spent nuclear fuel salt and captured radionuclides 99mTc, 99Mo, 239Np, and 132Te within 4 h without interacting with 237U. The adsorption mechanism was determined by combining kinetic fitting, XRD, XPS, and simulation calculations using the Adsorption Locator and CASTEP module of BIOVIA Materials Studio based on density functional theory (DFT). On the macroscopic scale, iodide ions covered by molten salt diffused the surface of HNPC@NF through physisorption and occluded in the pores. On the atomic scale, charge-shift bonds formed between carbon atoms and iodide ions, allowing for stable adsorption at the hollow sites within the carbon network. The coexistence of cations increased the adsorption energy of iodide ions, which benefited the reaction. Based on these results, HNPC@NF showed the potential application as an adsorbent for radioactive iodide in the fluoride molten salt system.