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.