Halogen bonding and hydrophobic interactions: A new strategy for synergistically enhancing ReO4−/99TcO4− binding

Abstract

Efficient removal of 99TcO4− from strongly acidic and alkaline nuclear wastewater is essential due to environmental protection and nuclear fuel cycle issues associated with the nuclear industry. However, the combined features of anion exchange materials with decent acid/base stability, high capacity, and high selectivity toward ReO4−/99TcO4− have not yet been achieved. Here, we explore a new strategy to overcome the aforementioned challenges by pre-organizing pyridinium-based cationic polymer network (TFTA-BPD) with sigma-holes and strongly hydrophobic fluorine atoms, which can effectively form strong halogen bonding and enhance hydrophobic interactions for selective ReO4−/99TcO4− binding. This emerging strategy not only significantly enhances the stability of the adsorbent, but also remarkably strengthens the specific affinity toward ReO4−/99TcO4− due to the synergistic effect of halogen bonding and hydrophobic interactions, compared to reported cationic polymer networks. More importantly, our TFTA-BPD exhibit fast removal kinetics, high capacity, excellent removal selectivity, and encouraging reusability, enabling efficient removal of ReO4− from simulated low activity waste (LAW) at Hanford and high-level waste (HLW) at the Savannah River Site in both dynamic column separation and batch experiments. Experimental and computational results indicate that the halogen-functionalized TFTA-BPD can regulate the electron distribution of adjacent N atoms and enhance charge separation through the halogen electron traction effect. This work demonstrates the enormous potential of halogen bonding and hydrophobic interactions in synergistically enhancing ReO4−/99TcO4− binding and paves the way for constructing high-performance adsorbents for HLW and LAW treatment.