Effective and selective removal of TcO from aqueous solution is highly desirable for both waste partitioning and contamination remediation purposes in the modern nuclear fuel cycle, but is of significant challenge. We report here a hydrolytically stable and radiation-resistant cationic metal-organic framework (MOF), SCU-101, exhibiting extremely fast removal kinetics, exceptional distribution coefficient, and high sorption capacity toward TcO. More importantly, this material can selectively remove TcO in the presence of large excesses of NO and SO, as even 6000 times of SO in excess does not significantly affect the sorption of TcO. These superior features endow that SCU-101 is capable of effectively separating TcO from Hanford low-level waste melter off-gas scrubber simulant stream. The sorption mechanism is directly unraveled by the single crystal structure of TcO-incorporated SCU-101, as the first reported crystal structure to display TcO trapped in a sorbent material. A recognition site for the accommodation of TcO is visualized and is consistent with the DFT analysis results, while no such site can be resolved for other anions.

Tc is one of the most problematic radioisotopes in used nuclear fuel owing to its combined features of high fission yield, long half-life, and high environmental mobility. There are only a handful of functional materials that can remove TcO anion from aqueous solution and identifying for new, stable materials with high anion-exchange capacities, fast kinetics, and good selectivity remains a challenge. We report here an 8-fold interpenetrated three-dimensional cationic metal-organic framework material, SCU-100, which is assembled from a tetradentate neutral nitrogen-donor ligand and two-coordinate Ag cations as potential open metal sites. The structure also contains a series of 1D channels filled with unbound nitrate anions. SCU-100 maintains its crystallinity in aqueous solution over a wide pH range from 1 to 13 and exhibits excellent β and γ radiation-resistance. Initial anion exchange studies show that SCU-100 is able to both quantitatively and rapidly remove TcO from water within 30 min. The exchange capacity for the surrogate ReO reaches up to 541 mg/g and the distribution coefficient K is up to 1.9 × 10 mL/g, which are significantly higher than all previously tested inorganic anion sorbent materials. More importantly, SCU-100 can selectively capture TcO in the presence of large excess of competitive anions (NO, SO, CO, and PO) and remove as much as 87% of TcO from the Hanford low-level waste melter off-gas scrubber simulant stream within 2 h. The sorption mechanism is well elucidated by single crystal X-ray diffraction, showing that the sorbed ReO anion is able to selectively coordinate to the open Ag sites forming Ag-O-Re bonds and a series of hydrogen bonds. This further leads to a single-crystal-to-single-crystal transformation from an 8-fold interpenetrated framework with disordered nitrate anions to a 4-fold interpenetrated framework with fully ordered ReO anions. This work represents a practical case of TcO removal by a MOF material and demonstrates the promise of using this type of material as a scavenger for treating anionic radioactive contaminants during the nuclear waste partitioning and remediation processes.

Direct removal of 99TcO4− from the highly acidic solution of used nuclear fuel is highly beneficial for the recovery of uranium and plutonium and more importantly aids in the elimination of 99Tc discharge into the environment. However, this task represents a huge challenge given the combined extreme conditions of super acidity, high ionic strength, and strong radiation field. Here we overcome this challenge using a cationic polymeric network with significant TcO4− uptake capabilities in four aspects: the fastest sorption kinetics, the highest sorption capacity, the most promising uptake performance from highly acidic solutions, and excellent radiation-resistance and hydrolytic stability among all anion sorbent materials reported. In addition, this material is fully recyclable for multiple sorption/desorption trials, making it extremely attractive for waste partitioning and emergency remediation. The excellent TcO4− uptake capability is elucidated by X-ray absorption spectroscopy, solid-state NMR measurement, and density functional theory analysis on anion coordination and bonding.

Many environmental pollutants inherently exist in their anionic forms and are therefore highly mobile in natural water systems. Cationic framework materials that can capture those pollutants are highly desirable but scarcely reported. Here we present a mesoporous cationic thorium-based MOF (SCU-8) containing channels with a large inner diameter of 2.2 nm and possessing a high surface area of 1360 m2 g−1. The anion-exchange properties of SCU-8 were explored with many anions including small oxo anions like ReO4 − and Cr2O7 2− as well as anionic organic dyes like methyl blue and the persistent organic pollutant, perfluorooctane sulfonate (PFOS). Both fast uptake kinetics and great sorption selectivity toward PFOS are observed. The underlying sorption mechanism was probed using quantum mechanical and molecular dynamics simulations. These computational results reveal that PFOS anions are immobilized in SCU-8 by driving forces including electrostatic interactions, hydrogen bonds, hydrophobic interactions, and van der Waals interactions at different adsorption stages.

Uranium is not only a strategic resource for the nuclear industry but also a global contaminant with high toxicity. Although several strategies have been established for detecting uranyl ions in water, searching for new uranium sensor material with great sensitivity, selectivity, and stability remains a challenge. We introduce here a hydrolytically stable mesoporous terbium(III)-based MOF material compound 1, whose channels are as large as 27 Å × 23 Å and are equipped with abundant exposed Lewis basic sites, the luminescence intensity of which can be efficiently and selectively quenched by uranyl ions. The detection limit in deionized water reaches 0.9 μg/L, far below the maximum contamination standard of 30 μg/L in drinking water defined by the United States Environmental Protection Agency, making compound 1 currently the only MOF material that can achieve this goal. More importantly, this material exhibits great capability in detecting uranyl ions in natural water systems such as lake water and seawater with pH being adjusted to 4, where huge excesses of competing ions are present. The uranyl detection limits in Dushu Lake water and in seawater were calculated to be 14.0 and 3.5 μg/L, respectively. This great detection capability originates from the selective binding of uranyl ions onto the Lewis basic sites of the MOF material, as demonstrated by synchrotron radiation extended X-ray adsorption fine structure, X-ray adsorption near edge structure, and first principles calculations, further leading to an effective energy transfer between the uranyl ions and the MOF skeleton.