Core–shell Ag@polypyrrole for synchronous pre-enrichment and immobilization of iodine (I−, IO3−) from liquid radioactive wastes

Abstract

Radioiodine is of great concern owing to its high mobility in the environment and long-term radiotoxicity, and effective techniques for the simultaneous removal of iodide (I⁻) and iodate (IO₃⁻) from aqueous solutions remain a significant challenge. Here, Ag@polypyrrole core–shell nanoparticles (Ag@PPy) were synthesized in situ and constructed by synergistic enrichment and immobilization as a desirable iodine nano-adsorbent. Its performance benefits from the ability for anions to be pre-enriched on the surface of Ag@PPy via electrostatic force through the positively charged polypyrrole with nitrogen-containing groups and then immobilized in the core–shell nanostructure with nanosilver as a reactive center. These efforts gave rise to Ag@PPy exhibiting an ultrahigh iodide adsorption capacity (788.7 mg g⁻¹) and desirable iodate uptake capacity (133.9 mg g⁻¹). More importantly, in the low-concentration region, Ag@PPy is able to almost completely remove I⁻ and IO₃⁻ from aqueous solution even in the presence of competitive anions such as Cl⁻, SO₄²⁻, NO₃⁻ and CO₃²⁻, with a distribution coefficient K_d of up to 3.90 × 10⁵ and 2.30 × 10⁵ mL g⁻¹, respectively. Unexpectedly, this core–shell nanostructure endows silver-based materials with high stability under acid–base conditions, and reduces the leaching rate approximately 10-fold compared to silver powder at near-neutral pH. This work highlights the feasibility of using Ag-containing nanomaterials to separate radioiodine from liquid environments.