Molecular Hosts for the Sensing and Separation of 99TcO4. Chemistry 2024;30:e202401551. [PMID: 38779975 DOI: 10.1002/chem.202401551] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

In recent years, European Union member states have hastened energy policy deliberations to address supply and sustainability concerns, placing a significant emphasis on nuclear energy as a means to achieve decarbonization goals. However, despite its significant role in power generation, nuclear energy faces significant challenges linked to fuel reprocessing and waste disposal, that hinder its broader expansion. In this context, the separation of technetium represents a concerning issue. Indeed, technetium's catalytic activity can impede the extraction of uranium, neptunium, and plutonium, affecting waste reprocessing efficiency. Additionally, the stable form of technetium in aerobic conditions, pertechnetate (TcO4 -), poses risks of groundwater contamination due to its mobility and solubility. Hence, sensing and separation of TcO4 - is imperative for both nuclear fuel processing and minimising radioactive contamination in the environment. However, the binding of TcO4 - and its separation from contaminated solutions present challenges due to the acidic (or basic) waste components and the high ionic strength in real matrices. Supramolecular chemists have addressed these issues by designing receptors inspired by molecular recognition principles. This article explores recent advancements and future directions in TcO4 - sensing and separation (using extraction and sorption) with a focus on molecular hosts. Metal-organic receptors will also be discussed.

Recent applications of organic cages in sensing and separation processes in solution

Organic cages are three-dimensional polycyclic compounds of great interest in the scientific community due to their unique features, which generally include simple synthesis based on the dynamic covalent chemistry strategies, structural tunability and high selectivity. In this feature article, we present the advances over the last ten years in the application of organic cages as chemosensors or components in chemosensing devices for the determination of analytes (pollutants, analytes of biological interest) in complex aqueous media including wine, fruit juice, urine. Details on the recent applications of organic cages as selective (back-)extractants or masking agents for potential applications in relevant separation processes, such as the plutonium and uranium recovery by extraction, are also provided. Over the last ten years, organic cages with permanent porosity in the liquid and solid states have been highly appreciated as porous materials able to discriminate molecules of different sizes. These features, combined with good solvent processability and film-forming tendency, have proved useful in the fabrication of membranes for gas separation, solvent nanofiltration and water remediation processes. An overview of the recent applications of organic cages in membrane separation technologies is given.

Functional Carbon Capsules Supporting Ruthenium Nanoclusters for Efficient Electrocatalytic 99 TcO4 - /ReO4 - Removal from Acidic and Alkaline Nuclear Wastes

The selective removal of the β-emitting pertechnetate ion (99 TcO4 - ) from nuclear waste streams is technically challenging. Herein, a practical approach is proposed for the selective removal of 99 TcO4 - (or its surrogate ReO4 - ) under extreme conditions of high acidity, alkalinity, ionic strength, and radiation field. Hollow porous N-doped carbon capsules loaded with ruthenium clusters (Ru@HNCC) are first prepared, then modified with a cationic polymeric network (R) containing imidazolium-N+ units (Ru@HNCC-R) for selective 99 TcO4 - and ReO4 - binding. The Ru@HNCC-R capsules offer high binding affinities for 99 TcO4 - /ReO4 - under wide-ranging conditions. An electrochemical redox process then transforms adsorbed ReO4 - to bulk ReO3 , delivering record-high removal capacities, fast kinetics, and excellent long-term durability for removing ReO4 - (as a proxy for 99 TcO4 - ) in a 3 m HNO3 , simulated nuclear waste-Hanford melter recycle stream and an alkaline high-level waste stream (HLW) at the U.S. Savannah River Site (SRS). In situ Raman and X-ray absorption spectroscopy (XAS) analyses showed that adsorbed Re(VII) is electrocatalytically reduced on Ru sites to a Re(IV)O2 intermediate, which can then be re-oxidized to insoluble Re(VI)O3 for facile collection. This approach overcomes many of the challenges associated with the selective separation and removal of 99 TcO4 - /ReO4 - under extreme conditions, offering new vistas for nuclear waste management and environmental remediation.

Converting pH probes into "turn-on" fluorescent receptors for anions

Recognition of anions by synthetic receptors is an integral part of supramolecular chemistry continuing to expand and find new application areas in our daily life. Many applications require visualization of anion recognition events, and the generated analytical signal is used to quantify anions in solution. Transferring a binding event to a measured signal is a challenging task. The design of a synthetic receptor must involve not only the perfectly positioned binding sites with complementary noncovalent interactions for a guest but should also realize the sensing mechanism that generates a strong analytical response upon guest binding. This feature article outlines the design concept for the construction of "turn-on" fluorescent receptors for anions involving fluorescent pH probes. Applications of this concept for the construction of synthetic fluorescent receptors for inorganic anions and nucleotides are described. Features of the obtained receptors and possible competing binding and sensing processes in solution are analyzed to understand the scope and limitations of the approach.

Pyridinium salt-based covalent organic framework with well-defined nanochannels for efficient and selective capture of aqueous 99TcO4. Sci Bull (Beijing) 2022;67:924-932. [PMID: 36546027 DOI: 10.1016/j.scib.2022.02.012]

Ionic covalent organic framework (COF) materials with high specific surface areas and well-defined pore structures are desired for many applications yet seldom reported. Herein, we report a cationic pyridinium salt-based COF (PS-COF-1) with a Brunauer-Emmett-Teller (BET) surface area of 2703 m2 g-1, state-of-the-art for an ionic COF. Aided by its ordered pore structure, chemical stability, and radiation resistance, PS-COF-1 showed exceptional adsorption properties toward aqueous ReO4- (1262 mg g-1) and 99TcO4-. Its adsorption performance surpassed its corresponding amorphous analogue. Importantly, PS-COF-1 exhibited fast adsorption kinetics, high adsorption capacities, and selectivity for 99TcO4- and ReO4- at high ionic strengths, leading to the successful removal of 99TcO4- under conditions relevant to low-activity waste streams at US legacy Hanford nuclear sites. In addition, PS-COF-1 can rapidly decontaminate ReO4-/99TcO4- polluted potable water (∼10 ppb) to drinking water level (0 ppb, part per billion) within 10 min. Density functional theory (DFT) calculations revealed PS-COF-1 has a strong affinity for ReO4- and 99TcO4-, thereby favoring adsorption of these low charge density anions over other common anions (e.g., Cl-, NO3-, SO42-, CO32-). Our work demonstrates a novel cationic COF sorbent for selective radionuclide capture and legacy nuclear waste management.

Recent Progress in Metal-Organic Framework Based Fluorescent Sensors for Hazardous Materials Detection

Population growth and industrial development have exacerbated environmental pollution of both land and aquatic environments with toxic and harmful materials. Luminescence-based chemical sensors crafted for specific hazardous substances operate on host-guest interactions, leading to the detection of target molecules down to the nanomolar range. Particularly, the luminescence-based sensors constructed on the basis of metal-organic frameworks (MOFs) are of increasing interest, as they can not only compensate for the shortcomings of traditional detection techniques, but also can provide more sensitive detection for analytes. Recent years have seen MOFs-based fluorescent sensors show outstanding advantages in the field of hazardous substance identification and detection. Here, we critically discuss the application of MOFs for the detection of a broad scope of hazardous substances, including hazardous gases, heavy metal ions, radioactive ions, antibiotics, pesticides, nitro-explosives, and some harmful solvents as well as luminous and sensing mechanisms of MOF-based fluorescent sensors. The outlook and several crucial issues of this area are also discussed, with the expectation that it may help arouse widespread attention on exploring fluorescent MOFs (LMOFs) in potential sensing applications.

Chiroptical sensing of perrhenate in aqueous media by a chiral organic cage

A chiral cage is proposed as an effective chiroptical sensor for perrhenate (surrogate for 99TcO4-) in water, fruit juice and artificial urine medium. The key mechanism for the chiroptical sensing...

Luminescent 2D Pillared-Bilayer Metal-Organic Coordination Networks for Selective Sensing of ReO4- in Water

For the preference in nuclear energy, one of the high-level liquid waste materials in the form of pertechnetate anion (TcO₄^-) has become an environmental hazard due to its mobility into groundwater and soil. For its sequestration, numerous efforts have been reported in recent years. However, its selective sensing, even using its nonradioactive surrogate oxidizing perrhenate ion (ReO₄^-), in aqueous media is very limited. To develop novel materials for such a purpose, we have designed an amino acid-functionalized bent dicarboxylic acid, 4-(((4-((carboxymethyl)carbamoyl)phenyl)amino)methyl)benzoic acid (H₂hipamifba), for the strategic room-temperature synthesis of two isostructural and highly luminescent two-dimensional (2D) metal-organic coordination networks (MOCNs), {[Cu(hipamifba)(4,4'-azbpy)]·2CH₃OH·2H₂O}_n (1) and {[Zn(hipamifba)(4,4'-azbpy)]·2CH₃OH·2H₂O}_n (2), where 4,4'-azobipyridine (4,4'-azbpy) as a pillar linker imparts luminescent properties in the architectures. The single-crystal X-ray structural analysis demonstrates that 1 and 2 have pillared-bilayer 2D networks with the sq1/Shubnikov tetragonal plane net topology. These multiresponsive luminescent materials were gainfully employed for the selective sensing of ReO₄^- in water with a detection limit of 3.4 and 5.4 ppm for 1 and 2, respectively. It is noteworthy to point out that these are the first neutral sensors for such study as the only other two sensors reported in the literature are cationic in nature. Their suitability (selectivity, stability, and recyclability) as excellent water-stable sensors was established through the competitive analyte test and a comparison of pristine and spent samples by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). Further, the mechanism of selective detection is explained by the time-resolved studies and density functional theory (DFT) calculations.

Applications of MOFs as Luminescent Sensors for Environmental Pollutants

The environmental pollution has become a serious issue because the pollutants can cause permanent damage to the DNA, nervous system, and circulating system, resulting in various incurable diseases, such as organ failure, malformation, angiocardiopathy, and cancer. The effective detection of environmental pollutants is urgently needed to keep them far away from daily life. Among the reported pollutant sensors, luminescent metal-organic frameworks (LMOFs) with tunable structures have attracted remarkable attention to detect the pollutants because of their excellent selectivity, sensitivity, and recyclability. Although lots of metal-organic framework (MOF)-based luminescent sensors have been summarized and discussed in previous reviews, the detection of environmental pollutants, especially radioactive ions and heavy metal ions, still have not been systematically presented. Here, the sensing mechanisms and construction principles of luminescent MOFs are discussed, and the state-of-the-art MOF-based luminescent sensors of environmental pollutants, including pesticides, antibiotics, explosives, VOCs, toxic gas, toxic small molecules, radioactive ions, and heavy metal ions are highlighted. This comprehensive review may further guide the development of luminescent MOFs and promote their practical applications for sensing environmental pollutants.

Unveiling the Uncommon Fluorescent Recognition Mechanism towards Pertechnetate Using a Cationic Metal-Organic Framework Bearing N-Heterocyclic AIE Molecules

As one of most problematic radionuclides, technetium-99, mainly in the form of anionic pertechnetate (TcO₄ ^- ), exhibits high environmental mobility, long half-life, and radioactive hazard. Due to low charge density and high hydrophobicity for this tetrahedral anion, it is extremely difficult to recognize it in water. Seeking efficient and selective recognition method for TcO₄ ^- is still a big challenge. Herein, a new water-stable cationic metal-organic framework (ZJU-X8) was reported, bearing tetraphenylethylene pyrimidine-based aggregation-induced emission (AIE) ligands and attainable silver sites for TcO₄ ^- detection. ZJU-X8 underwent an obvious spectroscopic change from brilliant blue to flavovirens and exhibited splendid selectivity towards TcO₄ ^- . This uncommon fluorescent recognition mechanism was well elucidated by batch sorption experiments and DFT calculations. It was found that only TcO₄ ^- could enter into the body of ZJU-X8 through anion exchange whereas other competing anions were excluded outside. Subsequently, after interaction between TcO₄ ^- and silver ions, the electron polarizations from pyrimidine rings to Ag⁺ cations significantly lowered the energy level of the π* orbital and thus reduced the π-π* energy gap, resulting in a red-shift in the fluorescent spectra.

Optimizing Strategy for Enhancing the Stability and 99TcO4 - Sequestration of Poly(ionic liquids)@MOFs Composites

Metal-organic frameworks (MOFs) are a class of promising sorbents for effective sequestration of radioactive ⁹⁹TcO₄ ^- anions. However, their poor stability and slow sorption kinetics in the industrial condition pose a great challenge. Herein, we demonstrate an optimizing strategy via in situ polymerization of ionic liquids (ILs) encapsulated in the pores of MOFs, forming polyILs@MOFs composites with greatly enhanced TcO₄ ^- sequestration compared with the pristine MOFs. Notably, the cross-linked polymerization of ILs facilitates the formation of both the inside ionic filler as the active sites and outside coating as the protective layers of MOFs, which is significantly beneficial to obtain the optimized sorption materials of exceptional stability under extreme conditions (e.g., in 6 M HNO₃). The final optimized composite shows fast sorption kinetics (<30 s), good regeneration (>30 cycles), and superior uptake performance for TcO₄ ^- in highly acidic conditions and simulated recycle stream. This strategy opens up a new opportunity to construct the highly stable MOF-based composites and extend their applicability in different fields.

A Porous Aromatic Framework Functionalized with Luminescent Iridium(III) Organometallic Complexes for Turn-On Sensing of 99TcO4. ACS APPLIED MATERIALS & INTERFACES 2020;12:15288-15297. [PMID: 32131587 DOI: 10.1021/acsami.0c01929]

Contamination of ⁹⁹TcO₄^-, a problematic radioactive anion in the nuclear fuel cycle, in groundwater has been observed in a series of legacy nuclear sites, representing a notable radiation hazard and environmental concern. The development of convenient, rapid, and sensitive detection methods is therefore critical for radioactivity control and remediation tasks. Traditional detection methods suffer from clear demerits of either the presence of large interference from coexisting radioactive species (e.g., radioactivity counting methods) or the requirement of extensive instrumentation and analysis procedure (e.g., mass spectrometry). Here, we constructed a luminescent iridium(III) organometallic complex (Ir(ppy)₂(bpy)⁺; ppy = 2-phenylpyridine, bpy = 2,2^'-bipyridine)-grafted porous aromatic framework (Ir-PAF) for the first time, which can be utilized for efficient, facile, and selective detection of trace ReO₄^-/TcO₄^- in aqueous solutions. Importantly, the luminescence intensity of Ir-PAF is greatly enhanced in the presence of ReO₄^-/TcO₄^-, giving rise to a distinct turn-on sensor with the detection limit of 556.9 μg/L. Such a superior detection capability originates from the highly selective and strong interaction between ReO₄^-/TcO₄^- and Ir(ppy)₂(bpy)⁺, leading to an efficient pre-enrichment of ReO₄^-/TcO₄^- during analysis and subsequently a much weaker nonradiative decay of the luminescence of Ir(ppy)₂(bpy)⁺, as illustrated by density functional theory (DFT) calculation as well as quantum yield and fluorescence lifetime measurements. Successful quantification of trace ReO₄^- in simulated Hanford low-activity waste (LAW) solution containing large excess of Cl^-, NO₃^-, and NO₂^- was demonstrated, highlighting the bright future of luminescent PAFs in the area of chemical sensing.

A Highly Efficient Coordination Polymer for Selective Trapping and Sensing of Perrhenate/Pertechnetate

A porous cationic Ag(I) coordination polymer, [Ag(1,2,4,5-p4b)](SbF₆) (TJNU-302) with the ligand 1,2,4,5-p4b (1,2,4,5-tetra(pyridin-4-yl)benzene), is reported that shows high sorption capacity (211 mg g^-1) and distribution coefficient K_d (5.8 × 10⁵ mL g^-1) as well as outstanding selectivity in 500 times excess of CO₃^2- or PO₄^3- anion for perrhenate removal. TJNU-302 can act as a crystalline turn-off sensor for perrhenate upon UV radiation. In this way, a test paper strip for sensing ReO₄^- could be produced. In water solution, TJNU-302 shows an efficient fluorescence quenching response to ReO₄^- ion, with the highest quenching percentage (86%) among all reported ReO₄^- sensors. These results could be elucidated by the bonding properties of single-crystal structures of TJNU-302 before and after perrhenate sorption, as well as density functional theory (DFT) calculations.

Redox-Based Electrochemical Affinity Sensor for Detection of Aqueous Pertechnetate Anion

Rapid, selective, and in situ detection of pertechnetate (TcO₄^-) in multicomponent matrices consisting of interfering anions such as the ubiquitous NO₃^- and Cl^- or the isostructural CrO₄^2- is challenging. Present sensors lack the selectivities to exclude these interferences or the sensitivities to meet detection limits that are lower than the drinking water standards across the globe. This work presents an affinity-based electrochemical sensor for TcO₄^- detection that relies on selective reductive precipitation of aqueous TcO₄^- induced by a 1,4-benzenedimethanethiol capture probe immobilized on an electrode platform. This results in a direct decrease in the electron transfer current, the magnitude of the decrease being proportional to the amount of TcO₄^- added. Using this approach, a detection limit of 1 × 10^-10 M was achieved, which is lower than the drinking water standard of 5.2 × 10^-10 M set by United States Environmental Protection Agency. The proposed approach shows selectivity to the TcO₄^- anion, allowing detection of TcO₄^- from a multicomponent groundwater sample obtained from a well at the Hanford site in Washington (well 299-W19-36) that also contained NO₃^-, Cl^-, and CrO₄^2-, without discernably affecting the detection limits.

Selective and efficient removal of perrhenate by an imidazolium based hexapodal receptor in water medium

This work reports a new cationic imidazolium based hexapodal receptor, [L.6Br], for selective and efficient removal of perrhenate (ReO₄⁻) as [L.6ReO4] from 100% aqueous medium via extraction through precipitation.

Anthracene-Based Receptors with a Turn-on Fluorescence Response for Nitrate

Herein we describe the design, synthesis, and anion binding properties of bicyclic receptors with two or three anthracenes, which show a turn-on fluorescence response in the presence of nitrate and chaotropic anions in a buffered aqueous solution. The receptor with two anthracenes binds nitrate with 10³ M^-1 affinity and stabilizes it in the inner cavity though electrostatic, hydrogen bonding, and anion-π interactions.

Phase-transfer extraction for the fast quantification of perchlorate anions in water

Supramolecular approaches for the quantitative anion analysis in water remain scarce due to the lack of receptors that effectively bind anions in this medium. Herein, we present a novel, fast and easy, supramolecular approach for a selective and quantitative analysis of perchlorate anions in water, coupling the UV-Vis spectroscopic method and phase-transfer extraction of anions by a water-insoluble anion receptor.

Optimizing radionuclide sequestration in anion nanotraps with record pertechnetate sorption

The elimination of specific contaminants from competitors poses a significant challenge. Rather than relying on a single direct interaction, the cooperation of multiple functionalities is an emerging strategy for adsorbents design to achieve the required affinity. Here, we describe that the interaction with the target species can be altered by modifying the local environment of the direct contact site, as demonstrated by manipulating the affinity of pyridinium-based anion nanotraps toward pertechnetate. Systematic control of the substituent effect allows the resulting anion nanotraps to combine multiple features, overcoming the long-term challenge of TcO₄^- segregation under extreme conditions of super acidity and basicity, strong irradiation field, and high ionic strength. The top material exhibits the highest sorption capacity together with record-high extraction efficiencies after a single treatment from conditions relevant to the used nuclear fuel (Hanford tank wastes, 95%) and legacy nuclear wastes (Savannah River Sites, 80%) among materials reported thus far.

Anion-adaptive crystalline cationic material for 99TcO4- trapping

Efficient anion recognition is of great significance for radioactive 99TcO4- decontamination, but it remains a challenge for traditional sorbents. Herein, we put forward a tactic using soft crystalline cationic material with anion-adaptive dynamics for 99TcO4- sequestration. A cucurbit[8]uril-based supramolecular metal-organic material is produced through a multi-component assembly strategy and used as a sorbent for effective trapping of TcO4-. Excellent separation of TcO4-/ReO4- is demonstrated by fast removal kinetics, good sorption capacity and high distribution coefficient. Remarkably, the most superior selectivity among metal-organic materials reported so far, together with good hydrolytic stability, indicates potential for efficient TcO4- removal. The structure incorporating ReO4- reveals that the supramolecular framework undergoes adaptive reconstruction facilitating the effective accommodation of TcO4-/ReO4-. The results highlight opportunities for development of soft anion-adaptive sorbents for highly selective anion decontamination.

Chiral Cryptates Derived from a Hexaazamacrocycle

The reactions of hexaazamacrocycle 1 with 2,6-bis(bromomethyl)pyridine or 2,6-bis[(tosyloxy)methyl)]pyridine in the presence of appropriate carbonates result in the formation of derivatives of cryptand 6: enantiopure azacryptates of sodium and potassium. Crystal structures of these compounds indicate interaction of a metal ion with four pyridine nitrogen atoms and four tertiary amine atoms. The competition reactions monitored by NMR spectroscopy indicate preferential binding of Na⁺ over K⁺ as well as higher affinity of 6 for Na⁺ in comparison with the [2.2.1] cryptand.

Molecular recognition and activation by polyaza macrocyclic compounds based on host-guest interactions

The design and syntheses of supramolecular hosts for the recognition and activation of molecules and anions are one of the most active research fields in supramolecular chemistry, in which polyaza macrocyclic ligands and their complexes have drawn particular attention due to their strong host-guest interactions. This review mainly focuses on the recent progress in the recognition of molecules and anions by polyaza macrocyclic compounds including polyaza macrocycles, polyaza macrobicycles and polyaza macrotricycles, as well as the activation of molecules by polyaza macrocyclic ligands and their metal complexes.

Finding a receptor design for selective recognition of perrhenate and pertechnetate: hydrogen vs. halogen bonding

Receptors bearing hydrogen and halogen bond donor sites for recognition of perrhenate and pertechnetate were designed and studied.

Selective perrhenate recognition in pure water by halogen bonding and hydrogen bonding alpha-cyclodextrin based receptors

Alpha-cyclodextrin based anion receptors containing halogen and hydrogen bond donor motifs display selective association of perrhenate in neutral aqueous media.

A bistren cryptand with a remote thioether function: Cu(ii) complexation in solution and on the surface of gold nanostars

A di-copper(ii) complex is formed in a bis-tren cage featuring a thioether function, capable of grafting on a monolayer of gold nanostars.

Removal of TcO4− ions from solution: materials and future outlook

The possibility of using ionic metal organic frameworks (i-MOFs) and related materials as next-generation ion exchange materials.

Metal containing cryptands as hosts for anions: evaluation of Cu(i)⋯X and π⋯X interactions in halide–tricopper(i) complexes through relativistic DFT calculations

More selective than crown ethers, cryptands arise as suitable hosts for several ions, with the size of the cavity and the behavior of the atoms belonging to the structure being the main factors governing their selectivity.

Superior perrhenate anion recognition in water by a halogen bonding acyclic receptor

The first example of perrhenate anion binding and fluorescence sensing in water by a halogen bond donor is reported.

A ratiometric fluorescent probe for in vivo tracking of alkaline phosphatase level variation resulting from drug-induced organ damage

Clinical drug-induced organ toxicity and damage have been recognized as an important public health issue, and an effective approach capable of in vivo detection of biomarkers resulting from drug-induced organ damage is being actively pursued. Herein, we demonstrate a ratiometric fluorescent probe that can trace the variation in alkaline phosphatase (ALP, an organ damage biomarker) levels spatially in vivo. The probe was synthesized by incorporating a phosphate group and an amine-N-oxide group on a 1,8-naphthalimide derivative. The presence of ALP cleaves the phosphate group from naphthalimide and remarkably alters the probe's photophysical properties, thus achieving ratiometric detection of ALP. The incorporation of amine-N-oxide ensures excellent water solubility and biocompatibility, which guarantees the ratiometric detection of ALP in aqueous media and in the cells overexpressed with ALP. With a detection limit of 0.38 U L^-1, the probe was successfully used in detecting ALP in human serum samples. Moreover, the probe can be employed to monitor and spatially map the endogenous variation in ALP levels in zebrafishes. This is the first observation, to our knowledge, of organ-scale ALP pattern in vivo as a result of clinical drug (APAP) induced damage.

Mixing the spacers in azacryptands: effects on halide recognition

Replacement of just one spacer in dicopper cryptates drastically alters the cavity's shape, thus affecting halide recognition.