Synthesis of new carbazole derivative extractants and study on extraction of perrhenate/pertechnetate

Carbazole Framework as Functional Scaffold for the Design of Synthetic Receptors

Carbazole serves as a prominent framework in the design of synthetic receptors, being a valuable scaffold for supramolecular chemistry, thanks to its planarity, fluorescence and versatility. This review provides a comprehensive analysis of notable examples of carbazole-based receptors, highlighting the impact of structural modifications on binding affinity and selectivity toward different guests.

Selective Binding and Light-Driven Release of Fluorous PF6- and Radioactive 99TcO4- Anions for All-to-Nothing Liquid-Liquid Extraction

The removal of anions from aqueous media using molecular receptors in liquid-liquid extraction is a long-standing strategy to clean up contaminated water sources. Therein, high selectivity is needed to remove specific ions from mixtures of other ions, and high affinity provides extractions at low concentrations. However, the high affinity creates a conundrum by impeding the release of the ions in any stripping steps needed for further processing. To circumvent this problem, light-responsive receptors have been proposed as candidates for turning off the binding, but they are currently untested in liquid-liquid extraction. We tested the feasibility of light-driven release using a cyanostar macrocycle. We demonstrate the selective extraction of PF6- anions over large excesses of competing anions (Cl-, NO3-, SO42-) followed by photodriven release for quantitative isolation of the target. Release relies on photoisomerization of the macrocycle's five stilbenes generating distorted isomers to turn off binding. With modest reversibility, only a single-shot release was demonstrated, akin to photodriven uncaging. These methods were extended to the capture and photodriven release of ReO4- and radioactive 99TcO4- anions at ∼90% efficiency. Extraction was demonstrated down to the highly dilute 4 ppb levels of the 99TcO4- anion. This proof-of-concept demonstration verifies the use of a large change in affinity for the all-to-nothing capture and release of target anions between liquid phases.

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.

Silver 2,4'-Bipyridine Coordination Polymer for the High-Capacity Trapping of Perrhenate, A Pertechnetate Surrogate

Pertechnetate, the most stable form of the radionuclide 99Tc in aerobic aqueous systems, is a hazardous anion present in nuclear waste. Its high mobility in water makes the remediation of the anion challenging. In the past decade, significant effort has been placed into finding materials capable of adsorbing this species. Here, we present the synthesis and high-resolution crystal structure of the coordination polymer [Ag(2,4'-bipyridine)]NO3, which is capable of sequestering perrhenate─a pertechnetate surrogate─through anion exchange to form another new coordination polymer, [Ag(2,4'-bipyridine)]ReO4. Both the beginning and end structures were solved by single-crystal X-ray diffraction and the adsorption reaction was monitored through inductively coupled plasma-optical emission spectroscopy and UV-vis spectroscopy. The exchange reaction follows a pseudo-second-order mechanism and the maximum adsorption capacity is 764 mg ReO4/g [Ag(2,4'-bipyridine)]NO3, one of the highest recorded for a coordination polymer or metal-organic framework. A solvent-mediated recrystallization mechanism was determined by monitoring the ion-exchange reaction by scanning electron microscopy-energy-dispersive spectroscopy and powder X-ray diffraction.

Ultraselective Extraction Reprocessing of 99TcO4-/ReO4- with a Promising Carbamic Acid Extractant System

With the development of nuclear energy, the reprocessing of ⁹⁹TcO₄^-/ReO₄^- has become a very difficult problem due to environmental issues such as high output, long life, and easy leakage. In this study, three extraction systems containing carbamic acid were introduced into the reprocessing of ⁹⁹TcO₄^-/ReO₄^- for the first time. The results involving one of the three results show that N-[N,N-di(2-ethylhexyl) aminocarbonylmethyl] glycine (D2EHAG) has ultrahigh selectivity for removal to ⁹⁹TcO₄^-/ReO₄^-. When the extreme concentration ratio of SO₄^2- and Cl^- to ReO₄^- of D2EHAG is 10,000:1, the distribution coefficient of ReO₄^- still reaches 12.73 and 2.67, respectively. Additionally, the most hydrophilic NO₃^-, when the extreme concentration ratio of NO₃^- and ReO₄^- is 1000:1, still has a distribution coefficient close to 2.33, which is more than the most reported MOF adsorption materials. Moreover, the reaction kinetics, stripping rate, and reuse rate were studied. After five cycles, the removal rate is still 98.12%, with a decrease of less than 0.7%. The system containing carbamic acid is a potential extraction removal system to remove ⁹⁹TcO₄^-/ReO₄^- from nuclear radioactive wastewater.

Highly Selective Adsorption of 99TcO4-/ReO4- by a Novel Polyamide-Functionalized Polyacrylamide Polymer Material

The treatment of radioactive wastewater is one of the major problems in the current research. With the development of nuclear energy, the efficient removal of 99TcO4- in radioactive wastewater has attracted the attention of countries all over the world. In this study, a novel functional polyamide polymer p-(Amide)-PAM was synthesized by the two-step method. The experimental results show that p-(Amide)-PAM has good adsorptive properties for 99TcO4-/ReO4- and has good selectivity in the nitric acid system. The kinetics of the reaction of p-(Amide)-PAM with 99TcO4-/ReO4- was studied. The results show that p-(Amide)-PAM has a fast adsorption rate for 99TcO4-/ReO4-, the saturated adsorption capacity reaches 346.02 mg/g, and the material has good reusability. This new polyamide-functionalized polyacrylamide polymer material has good application prospects in the removal of 99TcO4- from radioactive wastewater.