A nanotrap infused ultrathin hybrid composite material for rapid and highly selective entrapment of 99TcO4−

Abstract

⁹⁹Tc is one of the potentially toxic radioactive substances owing to its long half-life and a high degree of environmental mobility. Hence, the sequestration of ⁹⁹Tc from radioactive waste has become enormously important and a contemporary research priority. However, selective extraction of this species in its stable oxoanionic form (⁹⁹TcO₄⁻) is very challenging on account of bottlenecks such as low charge density, less hydrophilic nature, etc. Herein, an ultrathin hybrid composite material has been strategically designed and fabricated by covalent anchoring of a chemically stable amino functionalized nanosized cationic metal–organic polyhedron with a positively charged robust ionic covalent organic framework. The resulting thin-layer-based hybrid composite presented multiple exfoliated exposed interactive sites, including a Zr(IV)-secondary building unit, amine and triaminoguanidine functional groups, which can selectively interact with TcO₄⁻ oxoanions through a synergistic combination of electrostatic, H-bonding and various other supramolecular interactions. Thus synthesized function-tailored composite, by virtue of its multiple unique characteristics, manifested an ultrafast and very selective, high distribution coefficient (∼10⁶ mL g⁻¹), as well as recyclable entrapment of TcO₄⁻ oxoanions from the complex mixture of superfluous (∼5000-fold) other interfering anions in both high and ultra-trace concentrations along with simulated nuclear waste and from different water systems. Dynamic flow-through experiments were conducted with the membrane of the hybrid material in simulated wastewater, which reduced the concentration of ReO₄⁻ (surrogate of radioactive TcO₄⁻) to below the WHO permissible level with rapid sequestration kinetics and excellent selectivity over excessive competing anions.