Xiaoyong Xia,Jiaqing Huang,Qimeng Sun,Jinkai Qiu,Parada Weaoseng,Chanat Chokejaroenrat,Cheng Lian,Qingfeng Xu,Jianmei Lu
A cage-like multi-imidazolium sorbent is designed for 99 TcO 4 − /ReO 4 − capture. • Cooperative clamping in confined spaces enables ultrafast adsorption kinetics. • The sorbent exhibits a high ReO 4 − uptake capacity of 730 mg g −1 . • Excellent selectivity is achieved in highly competitive nuclear waste media. • Composite beads allow efficient fixed-bed removal with good regenerability. The efficient and selective removal of pertechnetate ( 99 TcO 4 − ) from water remains a significant challenge due to its high solubility, low charge density, and competition from coexisting anions. Herein, we report tetraphenylethene (TPE)-based, imidazolium-functionalized nanomicrospheres for pertechnetate ( 99 TcO 4 − )/perrhenate (ReO 4 − ) capture with high efficiency. The nonplanar, propeller-like TPE core stereospecifically arranges multiple imidazolium sites in a semi-encapsulating/polyhedral fashion, generating size-complementary pockets. Hierarchically confined nano-spaces enable cooperative multi-imidazolium clamping, where hydrophobic effects, electrostatic attraction, ion exchange, multipoint C–H···O hydrogen bonding, and geometric confinement act in concert to afford precise recognition and strong binding. Using ReO 4 − as a nonradioactive surrogate for 99 TcO 4 − , the sorbent delivers ultrafast kinetics (11.23 g mg −1 min −1 ), high capacity (730 mg g −1 ), and 86.5% removal from Hanford low-activity waste (LAW) stream. The powder is readily formed into mechanically robust granules and shows excellent regenerability in fixed-bed tests, retaining >95% efficiency after multiple cycles. This work demonstrates that cooperative multi-imidazolium clamping within confined nano-spaces amplifies multimechanism synergy, providing a general strategy for precise recognition and strong binding of weakly coordinating anions. Propeller-like TPE-based cage-like microspheres spatially organize multiple imidazolium sites into confined binding pockets, enabling cooperative multi-site clamping for rapid and selective ReO 4 − / 99 TcO 4 − capture through hydrogen bonding, electrostatic attraction, ion exchange, and hydrophobic confinement. Download: Download high-res image (184KB) Download: Download full-size image
99Tc is one of the most problematic fission products in the nuclear fuel cycle owing to its large inventory in used nuclear fuel, long half-life, potential radiation hazard, high environmental mobility of its major species 99TcO4−, and its redox-active nature. Ideally, 99TcO4− should be removed at the first stage, when the used fuel rods are dissolved in highly concentrated nitric acid solution, which can substantially reduce its interference with the solvent extraction process through catalytic redox reactions with the key actinides and diminish the chance of discharge into the environment as the volatile species during the waste vitrification process. However, this task cannot be achieved by any of the reported anion-scavenging materials including traditional polymeric anion-exchange resins, inorganic cationic framework materials, and recently developed cationic metal–organic framework materials, because they either are not stable under the extreme conditions of the combined high acidity and strong radiation field or do not possess the required uptake selectivity towards 99TcO4− in the presence of a huge excess of competing anions such as NO3− and SO42−. Herein, we present the first study of 99TcO4− removal under extreme conditions by a two-dimensional conjugated cationic covalent organic framework material, SCU-COF-1. This material exhibits ultrahigh acid stability, great resistance towards both large-dose β and γ irradiation and unprecedented 99TcO4− uptake capabilities including extremely fast sorption kinetics (sorption equilibrium can be reached within 1 min), ultrahigh uptake capacity (702.4 mg g−1 for the surrogate ReO4− at a slightly elevated temperature), and good anion-exchange selectivity towards 99TcO4−. These excellent features endow SCU-COF-1 with the practical capabilities of separating 99TcO4− from both simulant highly acidic fuel reprocessing solutions (3 M nitric acid) and low-activity waste streams at the US legacy nuclear site. The anion-exchange mechanism and the 99TcO4− uptake selectivity are further demonstrated and clearly visualized by the molecular dynamics simulation investigations.
危险品化学品经营许可证（带存储）