Targeted synthesis of a high-stability cationic porous aromatic framework for highly efficient remediation of 99TcO4−

Efficient removal of 99TcO4− from nuclear wastewater is of great significance for the safe development of nuclear energy. In this work, a viologen-based cationic porous aromatic framework (TZ-PAF) was prepared as a novel sorbent for TcO4−. With 4,4′-bipyridine as the linker units, tetraphenylmethane was selected as the knot units to construct the diamond-like topology structure of TZ-PAF, which was benefit to its outstanding structural stability (thermal stability and acid resistance). The batch sorption experiments showed that TZ-PAF possessed fast sorption kinetics, higher sorption capacity (982 mg g−1 for ReO4−) and a highest removal depth (Kd for TcO4− was 5.02 × 106 mL g−1), which could be attributed to the low-density skeleton of TZ-PAF resulting in the high density of sorption sites. XPS and SEM analyses revealed that the mechanism of TcO4−/ReO4− capture was attributed to an anion-exchanged process in which Cl− of TZ-PAF was replaced by ReO4−. And more, the excellent reusability to capture ReO4− from a highly acidic solution (64.6%) and a simulated nuclear wastewater (77.6%) were obtained. In general, this work exhibited a new sorbent for the highly efficient and deep removal of TcO4− form nuclear wastewater, and would provide a valuable insight into designing novel high-stability sorbents for wastewater treatment.