From Radioactive Effluent to Drinking Water: Efficient Removal of Trace 99TcO4−/ReO4− by Cationic Porous Aromatic Framework

Abstract

Efficient removal of ⁹⁹TcO₄⁻ from radioactive effluents while recovering drinking water remains a challenge. Herein, an excellent ReO₄⁻ (a nonradioactive surrogate of ⁹⁹TcO₄⁻) scavenger is presented through covalently bonding imidazolium poly(ionic liquids) polymers with an ionic porous aromatic framework (iPAF), namely iPAF-P67, following an adsorption-site density-addition strategy. It shows rapid sorption kinetics, high uptake capacity, and exceptional selectivity toward ReO₄⁻. Notably, the residual concentration of TcO₄⁻/ReO₄⁻ in the radioactive wastewater after iPAF-P67 treatment is as low as 0.046 ppb, fully meeting the drinking water standards of World Health Organization (WHO, 0.159 ppb) and United States Environmental Protection Agency (U.S. EPA, 0.053 ppb). Density functional theory (DFT) calculations show that the imidazolium groups in iPAF-P67 provide stronger electrostatic interactions and higher binding energies between iPAF-P67 and TcO₄⁻ anions, leading to its superior adsorption performance. Furthermore, the scale-up synthesized iPAF-P67 materials are shaped with polyethersulfone (PES) to fabricate PAF-P67/PES beads and nanofibers via phase inversion method and electrospinning technique, respectively. Both composites demonstrate outstanding ultra-purification abilities toward ReO₄⁻ to meet the WHO criteria even after multiple dynamic adsorption/desorption cycles. This work develops a design strategy for adsorbents applicable in the sequestration of low-concentration radioactive pollutants.