Converting nonporous cationic polymeric networks to cationic porous aromatic frameworks for enhanced 99TcO4−/ReO4− elimination

High-efficiency capture of 99TcO4− from radioactive wastewater and natural aqueous environment is urgently in demand. In this study, nonporous cationic polymeric networks (CPN-n) were employed as the building units to construct the cationic porous aromatic frameworks (iPAF-10) through a molecular expansion strategy. This process was simple and efficient, in which iPAF-10 with fast mass transfer channels and high adsorption site utilization was achieved. In addition, this strategy could also improve the materials' stability in highly acidic and alkaline conditions. Remarkably, compared with CPN-n, iPAF-10 exhibited rapid kinetics (3 min) and a high adsorption capacity of 1287 mg g−1 toward ReO4− (a safe alternative to 99TcO4−), ranking iPAF-10 among the top in existing advanced 99TcO4−/ReO4− adsorbents. iPAF-10 also maintained the stable removal of ReO4− from excess competition anions (NO3− and SO42−), high acid/alkali (1 M HNO3 and 2 M NaOH) and radiation condition (200 kGy). As a result, iPAF-10 showed satisfying ReO4− elimination performance from simulated Hanford and Savannah River Site waste streams. The anion exchange mechanism during adsorption and desorption processes was clearly elucidated through experimental and computational analysis. This work demonstrated the synthesis of new cationic porous aromatic frameworks, which showed great potential for 99TcO4−/ReO4− removal from wastewater.