Can a Bismuth Aerogel Stop Radioactive Iodine?

A research team created a bismuth sulfide (Bi2S3) aerogel in a single-step hydrothermal process. The method uses water, bismuth, sulfur and moderate temperatures, without complex steps. The result is a lightweight sponge full of microscopic pores. Electron microscope images show a three‑dimensional network resembling a sea sponge. Thanks to this structure, the aerogel can absorb large amounts of iodine. In tests, it captured up to 1,204 milligrams of iodine per gram of material. The process follows a pseudo‑second‑order kinetic model, indicating surface chemistry is key. The Freundlich isotherm describes how iodine spreads across the pores. During adsorption, iodine shifts from gas to solid, forming stable BiI3. This locks iodine for long periods, lowering dispersion risk. The aerogel withstands high temperatures and harsh chemical conditions, showing rare robustness in capture materials. Moreover, the synthesis method is cheap and scalable, ideal for large‑scale use. In short, this new aerogel combines high capacity, stability and low cost, offering a sustainable solution for nuclear waste management.

The hydrothermal synthesis was performed at 180 °C for 12 hours, using Bi(NO3)3·5H2O and Na2S as precursors. Adding a chelating agent (EDTA) controlled crystal growth, promoting a porous network. BET analysis revealed a specific surface area of 350 m²/g and a pore volume of 0.8 cm³/g, with average pore sizes around 5 nm, typical of mesoporous aerogels. Iodine adsorption isotherms show a maximum capacity of 1 204 mg/g, far exceeding values of other carbon‑based or zeolite adsorbents. The pseudo‑second‑order kinetics (R² = 0.998) indicate that the rate depends on the availability of active sites on the Bi2S3 surface. The Freundlich isotherm (Kf = 210 mg·g⁻¹·(L·mg⁻¹)¹⁄n, n = 0.78) suggests multilayer interaction and a heterogeneous surface. XRD and Raman analyses confirmed in‑situ formation of BiI3 during adsorption, with nanometric crystals well distributed. Thermal tests showed the aerogel retains its structure up to 400 °C in an inert atmosphere and withstands acidic solutions (pH = 2) without significant degradation. Comparisons with other bismuth‑based adsorbents (Bi2O3, BiPO4) highlight a 30‑40 % higher capture capacity due to stronger S‑I chemical affinity. Process scalability is supported by 10 L reactors, with consistent yields and raw material costs below €5/kg of aerogel. These results pave the way for modular filtration systems in nuclear plants, where the aerogel can be placed in adsorption columns or portable filters for emergency response.