Cationic Covalent Organic Nanosheets for Rapid and Selective Capture of Perrhenate: An Analogue of Radioactive Pertechnetate from Aqueous Solution

Capture of radioactive TcO₄⁻ from nuclear wastes is extremely desirable for waste disposal and environmental restoration. Here, we report the synthesis of hydrolytically stable cationic covalent organic nanosheets (iCON) for efficient uptake of ReO₄⁻, a nonradioactive surrogate of TcO₄⁻. The iCON combines cationic guanidine-based knots with hydroxyl anchored neutral edge units and chloride ions loosely bonded in the pores, rendering extremely fast exchange kinetics toward ReO₄⁻ with high uptake capacity of 437 mg g⁻¹ and prominent distribution coefficient of 5.0 × 10⁵. The removal efficiency remains stable over a pH range of 3-12 and allows selective capture of ReO₄⁻ in the presence of excessive competing anions such as NO₃⁻, CO₃²⁻, PO₄³⁻ and SO₄²⁻ with good removal efficiency for ReO₄⁻ in a simulated Hanford LAW Melter Recycle Stream. Anion exchange between the ReO₄⁻ in solution and the chloride ion in iCON plays dominant role in the adsorption of ReO₄⁻. The iCON shows promise for effective removal of radioactive ⁹⁹Tc from nuclear waste.