image: (a) Deep purification of 99TcO4– species in LAW streams by CPFs composite beads to produce drinking water. (b) The optimization strategy inspired by the challenges of CPFs sorbents and commercial resin in practical applications.
Credit: ©Science China Press
Tianjin Normal University and Southeast Normal University teams developed a scalable strategy to integrate 17 types of crystalline porous frameworks (CPFs) with hydrophilic poly(acrylic acid) (PAA) or hydrophobic polyether sulfone (PES), fabricating 34 millimeter-scale composite beads (CPFs beads). Through a microdroplet shaping technique, materials such as PG-HOF-2 were uniformly embedded into polymer matrices with high loading efficiency, forming mechanically stable porous structures. This strategy combined the high adsorption efficiency of powdered materials with the engineering applicability of resin granules, preserving crystallinity while preventing microparticle leakage through polymer networks—effectively addressing industrial challenges such as reactor clogging, material recovery, and the long-standing trade-off between adsorption performance and mechanical stability.
PG-HOF-2/PES beads demonstrated exceptional adsorption capabilities, including efficient adsorption kinetics (>99.99% within 10 minutes, Kd = 1.471 × 107 mL/g), impressive capacity (976.9 mg/g), and accurate selectivity. The hydrophobic surface preferentially captured less hydrophilic TcO4–/ReO4– by overcoming Hofmeister bias, highlighting both industrial durability and lifecycle cost efficiency.
In continuous-flow column tests, 1 g of PG-HOF-2/PES beads processed 4.8 L of pre-treated low-activity waste (LAW), reducing Re/Tc concentrations far below the WHO (0.159 ppb) and U.S. EPA (0.053 ppb) drinking water standards. In contrast, commercial resin Purolite A530E yielded a residual Re concentration of 8.498 ppb under identical conditions. The composite beads demonstrated excellent reusability over multiple adsorption-desorption cycles, validating their reliability in real-world applications.
To understand the adsorption mechanism at the molecular level, density functional theory (DFT) calculations were performed to model the local charge structures. The simulations revealed strong binding interactions between PG-HOF-2/PES and TcO4–/ReO4– species. This strong binding interaction significantly outperformed that of quaternary ammonium resins, demonstrating that PG-HOF-2 is more favorable to sequester trace TcO4– than commercial resins. Furthermore, the purification performance of various CPF-X powders and their CPF-X/PES composites was analyzed. The CPF-X/PES beads consistently outperformed their parent CPF-X powders in deep purification, corroborating the universality of this strategy.