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Removal of radioactive technetium‐99 (99TcO4−) from water by effective adsorbents is highly desired but remains a challenge. The currently used resin adsorbents possess several obstacles, such as slow adsorption kinetics and low adsorption capacity. To address these issues, herein a type of fibrous adsorbent with porosity and hyper‐branched quaternary ammonium groups, namely porous cationic electrospun fibers (PCE fibers), is successfully prepared. PCE fibers can remove 97% of 99TcO4− within 1 min and the equilibrium time of 99% removal is 20 min. The predicted maximum adsorption capacity toward the surrogate ReO4− can reach 826 mg g−1, which is higher than the state of art anion‐exchange resins and most of the other reported adsorbents. Furthermore, PCE fibers have good selectivity for ReO4− in the presence of competitive anions, and can retain ReO4− uptake under extreme conditions including high acid–base and gamma irradiation. Importantly, PCE fibrous adsorptive membrane is employed for dynamic ReO4− removal from simulated Hanford LAW stream with a processing capacity of 600 kg simulated stream per kilogram PCE fibers. The excellent performance highlights the advantages of PCE fibers over traditional resins in technetium removal. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel cationic electrospun nanofibers (NCE fibers) were designed and synthesized. • Specific anion traps with hydrophobic microenvironment were constructed. • NCE fibers exhibited fast kinetics and high uptake for ReO 4 −. • NCE fibers showed good removal depth and satisfying selectivity toward ReO 4 −. • The column adsorption was also conducted with the treatment capacity of 1540 BV. Developing cationic adsorbents for efficient radioactive pertechnetate (99TcO 4 −) removal from water is of great significance in both nuclear fuel management and nuclear-related environmental treatment fields. However, tremendous efforts should be taken to improve the comprehensive performance of the adsorbent materials. Herein, novel cationic electrospun nanofibers were synthesized via the blending electrospinning from the branched polyethylenimine based solution and the following quaternization reaction by benzyl bromide. Consequently, abundant specific anion traps with hydrophobic microenvironment were constructed on the fibers. The obtained fiber adsorbents were systematically investigated to remove perrhenate (ReO 4 −) ions (the nonradioactive surrogate for TcO 4 −), which exhibit satisfying adsorption performance in several aspects: high adsorption capacity (943 mg g−1), fast kinetics (30 min), good removal depth (distribution coefficient = 1.1 × 106 mL g−1), large dynamic column adsorption volume (1540 bed volume), and excellent ReO 4 − capture from solution with high ionic strength or acidity/alkalinity. The adsorption performance surpassed all macroscopic shapeable adsorbents and many powdery advanced porous materials, owing to their abundant adsorption sites, tailored anion traps and macroscopic fibrous structures. Overall, this work gives a useful insight into designing novel adsorbents for effective TcO 4 −/ReO 4 − capture. [ABSTRACT FROM AUTHOR]