Rim-Based Binding of Perfluorinated Acids to Pillararenes Purifies Water

Per- and polyfluoroalkyl substances (PFAS) pose a rapidly increasing global problem as their widespread use and high stability lead worldwide to water contamination, with significant detrimental health effects.[1] Supramolecular chemistry has been invoked to develop materials geared towards the specific capture of PFAS from water,[2] to reduce the concentration below advisory safety limits (e.g., 70 ng/L for the sum of perfluorooctane sulfonic acid, PFOS and perfluorooctanoic acid, PFOA). Scale-up and use in natural waters with high PFAS concentrations has hitherto posed a problem. Here we report a new type of host-guest interaction between deca-ammonium-functionalized pillar[5]arenes (DAF-P5s) and perfluoroalkyl acids. DAF-P5 complexes show an unprecedented 1 : 10 stoichiometry, as confirmed by isothermal calorimetry and X-ray crystallographic studies, and high binding constants (up to 106 M-1) to various polyfluoroalkyl acids. In addition, non-fluorinated acids do not hamper this process significantly. Immobilization of DAF-P5s allows a simple single-time filtration of PFAS-contaminated water to reduce the PFOS/PFOA concentration 106 times to 15-50 ng/L level. The effective and fast (<5 min) orthogonal binding to organic molecules without involvement of fluorinated supramolecular hosts, high breakthrough capacity (90 mg/g), and robust performance (>10 regeneration cycles without decrease in performance) set a new benchmark in PFAS-absorbing materials.

Selective Adsorption Behavior and Mechanism for Cd(II) in Aqueous Solution with a Recoverable Magnetie-Surface Ion-Imprinted Polymer

A novel recoverable magnetic Cd(II) ion-imprinted polymer was synthesized on the surface of silica-coated Fe₃O₄ particles via the surface imprinting technique and chemical grafting method. The resulting polymer was used as a highly efficient adsorbent for the removal of Cd(II) ions from aqueous solutions. The adsorption experiments revealed that Fe₃O₄@SiO₂@IIP had a maximum adsorption capacity of up to 29.82 mg·g^-1 for Cd(II) at an optimal pH of 6, with the adsorption equilibrium achieved within 20 min. The adsorption process followed the pseudo-second-order kinetic model and the Langmuir isotherm adsorption model. Thermodynamic studies showed that the adsorption of Cd(II) on the imprinted polymer was spontaneous and entropy-increasing. Furthermore, the Fe₃O₄@SiO₂@IIP could rapidly achieve solid-liquid separation in the presence of an external magnetic field. More importantly, despite the poor affinity of the functional groups constructed on the polymer surface for Cd(II), we improved the specific selectivity of the imprinted adsorbent for Cd(II) through surface imprinting technology. The selective adsorption mechanism was verified by XPS and DFT theoretical calculations.

α-Aminophosphonates, -Phosphinates, and -Phosphine Oxides as Extraction and Precipitation Agents for Rare Earth Metals, Thorium, and Uranium: A Review

α-Aminophosphonates, -phosphinates, and -phosphine oxides are a group of organophosphorus compounds that were investigated as extraction agents for rare earth (RE) metals and actinoids for the first time in the 1960s. However, more systematic investigations of their extraction properties towards REs and actinoids were not started until the 2010s. Indeed, recent studies have shown that these α-amino-functionalized compounds can outperform the commercial organophosphorus extraction agents in RE separations. They have also proven to be very efficient extraction and precipitation agents for recovering Th and U from RE concentrates. These actinoids coexist with REs in some of the commercially important RE-containing minerals. The efficient separation and purification of REs is becoming more and more important every year as these elements have a pivotal role in many existing technologies. If one also considers the facile synthesis of α-amino-functionalized organophosphorus extractants and precipitation agents, it is expected that they will be increasingly utilized in the extraction chemistry of REs and actinoids in the future. This review collates α-aminophosphonates, -phosphinates, and -phosphine oxides that have been utilized in the separation chemistry of REs and actinoids, including their most relevant synthetic routes and molecular properties. Their extraction and precipitation properties towards REs and actinoids are also discussed.

New tetradentate N,O-hybrid phenanthroline-derived organophosphorus extractants for the separation and complexation of trivalent actinides and lanthanides

Comparison of the extraction and separation properties between two novel phenanthroline-derived organophosphorus ligands, Et-Ph-BPPhen and Et-Ph-PIPhen.

Selective Separation of Am(III)/Eu(III) by the QL-DAPhen Ligand under High Acidity: Extraction, Spectroscopy, and Theoretical Calculations

Although 1,10-phenanthroline-based ligands have recently shown vast opportunities for the separation of trivalent actinides (Ans(III)) from lanthanides (Lns(III)), the optimization and design of the extractant structure based on the phenanthroline framework remain hotspots for further improving the separation. Following the strategy of hard and soft donor atom combination, for the first time, the quinoline group was attached to the 1,10-phenanthroline skeleton, giving a lipophilic ligand, 2,9-diacyl-bis((3,4-dihydroquinoline-1((2H)-yl)-1),10-phenanthroline (QL-DAPhen)), for Am(III)/Eu(III) separation. In the presence of sodium nitrate, the ligand can effectively extract Am(III) over Eu(III) in HNO₃ solution, with the separation factor (SF_Am/Eu) ranging from 29 to 44. The coordination chemistry of Eu(III) with QL-DAPhen was investigated by slope analysis, NMR titration, UV-vis titration, Fourier transform infrared spectroscopy, electrospray ionization-mass spectrometry, and theoretical calculations. The experimental results unanimously confirm that the ligand forms both 1:1 and 1:2 complexes with Eu(III), and the stability constants (log β) of each of the two complexes were obtained. Density functional theory calculations show that the Am-N bonds have more covalent characteristics than the Eu-N bonds in the complexes, which reveals the reason why the ligand preferentially bonds with Am(III). Meanwhile, the thermodynamic analysis reveals that the 1:1 complex is more thermodynamically stable than the 1:2 complex. The findings of this work have laid a solid theoretical foundation for the application of phenanthroline-based ligands in the separation of An(III) from practical systems.

Specific recognition, intracellular assay and detoxification of fluorescent curcumin derivative for copper ions

Recognition and excretion of metal ions play an important role in the diagnosis and treatment of various diseases and poisoning. Although copper (Cu) is a cofactor of many key enzymes in the human body, its accumulation caused by genetic ATP7B mutation or environmental pollution can lead to hepatotoxicity, renal failure, Wilson's disease, inflammation, and even Parkinson's disease (PD) and Alzheimer's disease (AD). Therefore, in this work, a difluoroboron curcumin derivative (DF-Cur) was used for the specific recognition of copper ions (Cu²⁺). DF-Cur could be further used to as a rapid diagnostic agent for the copper detection in cells and zebrafish at the nanomolar level. DF-Cur could significantly reduce the toxic damage caused by high Cu²⁺ dose. Inductively coupled plasma-mass spectrometry (ICP-MS) analysis indicated that DF-Cur could promote the excretion of copper ions in the urine and bile and reduce the accumulation of copper ions in vivo. In addition, DF-Cur could selectively detect cholesterol in the blood and adipose tissue in vivo by fluorescent staining. These results demonstrated that this molecule might represent a new and promising diagnostic and therapeutic agent to combat diseases related to copper ions accumulation.

Endowing 2,6-bis-triazolyl-pyridine of poor extraction with superior efficiency for actinide/lanthanide separation at high acidity by anchoring to a macrocyclic scaffold

Exploring nitrogen-containing extractants for recovering hazardous minor actinides that are workable in solutions of high acidity has been a challenge in nuclear waste treatment. Herein, we report our findings that 2,6-bis-triazolyl-pyridine (PyTri), which is ineffective as a hydrophobic ligand for minor actinide separation, turns into an excellent extractant that exhibits unexpectedly high efficiency and selectivity (SF_Am/Eu = 172, 1 M HNO₃) when attaching to pillar[5]arene platform. Surprisingly, the distribution ratio of Am(III) (D_Am) is 4300 times higher than that of the acyclic PyTri ligand. The solvent extraction performance of this pillar[5]arene-achored PyTri not only far exceeds the best known pillar[5]arene ligands reported to date, but also stays comparable to other reported outstanding extractants. Slope analysis indicates that each P[5]A-PyTri can bind two metal ions, which is further corroborated by spectroscopic characterizations. Thermodynamic studies imply that the extraction process is exothermic and spontaneous in nature. Complexation investigation via EXAFS technique and DFT calculations strongly suggest that each Eu(III) ion is coordinated to three PyTri arms through a nine-coordination mode. This work provides a N-donor extractant that can operate at high acidity for minor actinide partitioning and implicates a promising approach for transforming poor extractants into superior ones.

Influence of a N-Heterocyclic Core on the Binding Capability of N,O-Hybrid Diamide Ligands toward Trivalent Lanthanides and Actinides

N,O-hybrid diamide ligands with N-heterocyclic skeletons are one of the promising extractants for the selective separation of actinides over lanthanides in a highly acidic HNO₃ solution. In this work, three hard-soft donor mixed diamide ligands, pyridine-2,6-diylbis(pyrrolidin-1-ylmethanone) (Pyr-PyDA), 2,2'-bipyridine-6,6'-diylbis(pyr-rolidine-1-ylmethanone) (Pyr-BPyDA), and (1,10-phenanthroline-2,9-diyl)bis(pyrrolidin-1-ylmethanone) (Pyr-DAPhen), were synthesized and used to probe the influence of N-heterocyclic cores on the complexation and extraction behaviors with trivalent lanthanides and actinides. ¹H NMR titration experiments demonstrated that 1:1 metal-to-ligand complexes were mainly formed between the three ligands and lanthanides, but 1:2 type complexes were also formed between tridentate Pyr-PyDA and Lu(III). The stability constants (log β) of these three ligands with two typical lanthanides, Nd(III) and Eu(III), were determined through spectrophotometric titration. It is found that Pyr-DAPhen formed the most stable complexes, while Pyr-PyDA formed the most unstable complexes with lanthanides, which coincided well with the following solvent extraction results. The solid-state structures of 1:1 type complexes of these three ligands with La(III), Nd(III), and Er(III) in nitrate media were identified by a single-crystal X-ray diffraction technique. Nd(III) and Er(III) were 10-coordinated with Pyr-PyDA, Pyr-BPyDA, and Pyr-DAPhen via one ligand molecule and three nitrate ions. La(III), because of its larger ionic radius, was 11-coordinated with Pyr-DAPhen through one ligand molecule, three nitrate ions, and one methanol molecule. Solvent extraction experiments showed that the preorganized phenanthroline-derived Pyr-DAPhen had the best extraction performance for trivalent actinide among the three ligands tested. This work provides some experimental insights into the design of more efficient ligands for trivalent actinide separation by adjusting the N-heterocyclic cores.

Highly efficient actinide(III)/lanthanide(III) separation by novel pillar[5]arene-based picolinamide ligands: A study on synthesis, solvent extraction and complexation

Selective extraction of highly radiotoxic actinides(III) is an important and challenging task in nuclear wastewater treatment. Many proposed ligands containing S or P atoms have drawbacks including high reagent consumption and possible secondary pollution after incineration. The present work reports five novel pillar[5]arene-based extractants that are anchored with picolinamide substituents of different electronic nature by varying spacer. These ligands reveal highly efficient separation of actinides(III) over lanthanides(III). Specifically, almost all of these ligands could extract Am(III) over Eu(III) selectively at around pH 3.0 (SF_Am/Eu>11) with fast extraction kinetics. Variation of the pyridine nitrogen basicity via changing para-substitution leads to an increase in the distribution ratios by a factor of over 300 times for Am(III) with an electron-withdrawing group compared to those with an electron donating group. Investigation of complexation mechanism by slope analysis, NMR, IR, EXAFS, and DFT techniques indicates that each ligand binds two metal ions by pyridine nitrogen and amide oxygen. Finally, these ligands do not show obvious decrease in both extraction and separation ability after being exposed to 250 kGy absorbed gamma radiation. These results demonstrate the potential application of pillar[5]arene-picolinamides for actinide(III) separation.

Unfolding the Extraction and Complexation Behaviors of Trivalent f-Block Elements by a Tetradentate N,O-Hybrid Phenanthroline Derived Phosphine Oxide Ligand

In this work, a tetradentate N,O-hybrid 2,9-bis(diphenylphosphine oxide)-1,10-phenanthroline (Ph₂-BPPhen) ligand was studied for the coextraction of trivalent f-block elements from nitric acid media. The extraction as well as the complexation behaviors of Ph₂-BPPhen with f-block elements were thoroughly investigated using ³¹P and ¹H NMR spectrometry, UV-vis spectrophotometry, single crystal X-ray diffraction, and density functional theoretical (DFT) calculation. Ph₂-BPPhen exhibits remarkably extraction ability for both Am(III) and Eu(III) and more than 99.5% of Am(III) and Eu(III) were extracted from 1.0 M HNO₃ solution. Slope analysis suggests that both 2:1 and 1:1 ligand/metal complexes were probably formed during the extraction. The 1:1 and 2:1 Ln(III) complexes with Ph₂-BPPhen were also identified in CH₃OH solution by NMR spectrometry, and the stability constants were determined via UV-vis spectrophotometry. Structures of the 1:1 Eu(Ph₂-BPPhen)(NO₃)₃ and Am(Ph₂-BPPhen)(NO₃)₃ complexes were further elucidated by single X-ray crystallography and DFT calculations. The higher extractability of Ph₂-BPPhen toward trivalent Am(III) and Eu(III) compared with the previously reported phenanthroline-derived amide and phosphonate ligands was attributed to the stronger affinity of the -P═O(R)₂ group to metal ions. The results from this work indicate that the N,O-hybrid 1,10-phenanthroline derived phosphine oxide ligand can serve as a new and promising candidate for coextraction of trivalent f-block elements in the treatment of nuclear waste.

Radiolytic stability of pillar[5]arene-based diglycolamides

Radiolytic stability of pillar[5]arene-based diglycolamides (P5DGAs) against gamma irradiation up to 1000 kGy adsorbed dose was studied. The results reveal the increase of radiation damage degree on P5DGAs with dose. The radiolysis products of P5DGAs including the gaseous and solid products were fully characterized by 1H NMR, HR-ESI-MS, GC, and HPLC techniques. It was found that the main radiolytic gas products of P5DGAs under argon are H2, N2, CO and gaseous hydrocarbons. The solid degradation products contain phenolic hydroxyl groups and secondary amine groups. In addition, solvent extraction toward Eu(III) was performed with P5DGAs, in which about 50% decrease on extraction efficiency was observed for irradiated P5DGAs with dose of 1000 kGy in comparison with the non-irradiated one. A radiolytic degradation pathway was also proposed based on the above results. This is the first time to investigate the radiolytic stability of neat P5DGAs and P5DGAs in molecular diluent in detail and provides useful information for further application of P5DGAs in practical applications for spent fuel reprocessing.

Light-controlled switchable complexation by a non-photoresponsive hydrogen-bonded amide macrocycle

A light controlled switchable host–guest system based on a non-photoresponsive H-bonded macrocycle and pyridinium salts was developed using a photoacid.

Effect of ionic liquid on the extraction of uranium with pillar[5]arene-based phosphine oxide from nitric acid solutions

The extraction of U(VI) from aqueous nitric acid solutions with pillar[5]arene-based phosphine oxide (L) and [C8mim][NTf2] ionic liquid dissolved in 1,2-dichloroethane was explored. A great positive impact in this system was observed. The effect of IL concentration in the organic phase and HNO3 concentration in the aqueous phase is considered. The distribution ratios of U(VI) were significantly enhanced upon adding a small amount of ionic liquid as compared with organic diluent. The extraction system was also examined for its ability towards extraction of lanthanides and Th4+. The results revealed higher separation factors towards UO2 2+ over Th4+ in the presence of ionic liquid compared with organic diluent. Other factors such as C8mim+ and NTf2 − have also been considered. This extraction system has shorter equilibrium time as compared with in IL diluent. Stripping experiments showed almost quantitative back extraction of UO2 2+ within two stages. With high selectivity towards UO2 2+ and efficient back extraction, this new POP5A-ionic liquid-organic diluent system shows promise for future application of uranium recovery.

Novel cyanide supramolecular fluorescent chemosensor constructed from a quinoline hydrazone functionalized-pillar[5]arene

Herein, we report a simple and novel approach for the design of fluorescent chemosensor through the self-assembly of functionalized monomer molecules. According to these approach, a novel supramolecular fluorescent chemosensor (SPMS) was successfully constructed by self-assembly of a quinoline hydrazone functionalized pillar[5]arene monomer PM. Interestingly, upon the addition of CN^-, the solution of SPMS instantly shows dramatic fluorescent enhancement and emitting bright blue emission. Meanwhile, the fluorescence quantum yields show distinct increase from 0.0582 of SPMS to 0.3952 of SPMS + CN^-. The detection limit (LOD) of SPMS for CN^- is 9.70 × 10^-8 M, which indicated high sensitivity. Moreover, the SPMS is selective for CN^- even in the presence of other anions, the fluorescent detection process of SPMS for CN^- was not interfered by other competitive anions (F^-, Cl^-, Br^-, I^-, N₃^-, OH^-, SCN^-, HSO₄^-, AcO^-, H₂PO₄^- and ClO₄^-). Notably, in the CN^- sensing process, the self-assembly structure of the supramolecular chemosensor SPMS didn't show any disassembly. This work provides a novel approach for instant detection of CN^- through a self-assembled supramolecular fluorescent chemosensor in aqueous system. Moreover, the test strips based on SPMS were fabricated, which could serve as convenient and efficient CN^- test kits.

Radiation stability of phosphine oxide functionalized pillar[5]arenes

The radiation stability of three phosphine oxide functionalized pillar[5]arenes (POP5A) was studied by an electron accelerator with dose up to 5 MGy in air at room temperature. The structures of both irradiated and unirradiated pillar[5]arenes samples were comparatively characterized by Micro-FTIR, NMR, UV-vis, ESI-HRMS and HPLC techniques. The results revealed different degrees of radiation damage at different doses for POP5A, and the degradation products are mainly composed of organic species containing hydroxyl groups and carbonyl groups. The possible radiolytic degradation pathway was proposed. In addition, extraction of uranyl ion with irradiated POP5A samples was examined. The distribution ratio of uranyl ion was found to increase at low radiation dose and decrease until 3000 kGy. This is the first time that the irradiation stability of pillar[5]arenes derivative extractants has been studied in detail and it provides reliable data support for further application of pillar[5]arenes extractants in practical applications.

Pillararenes as macrocyclic hosts: a rising star in metal ion separation

Pillararenes are macrocyclic oligomers of alkoxybenzene akin to calixarenes but tethered at the 2,5-positions via methylene bridges. Benefiting from their unique pillar-shaped architecture favorable for diverse functionalization and versatile host-guest properties, pillararenes decorated with chelating groups worked excellently as supporting platforms to construct extractants or adsorbents for metal ion separation. This feature article provides a detailed summary of pillararenes in Ln/An separation by liquid-liquid extraction and heavy metal separation by solid-liquid extraction. The preorganization effect of the rigid pillararene framework has a profound impact on the extraction of metal ions, and a unique extraction mechanism is observed when employing ionic liquids as solvents. The rich host-guest chemistry of pillararenes enables construction of a wide variety of supramolecular materials as metal ion adsorbents. We also discuss the differences between pillararenes and several well-known macrocycles, with a focus on the metal-ligand coordination and its influencing factors. We hope this review will provide useful information and unleash new opportunities in this field.

Supramolecular ligands for the extraction of lanthanide and actinide ions

A selection of supramolecular ligands designed to extract f-elements.

Unique reversibility in extraction mechanism of U compared to solvent extraction for sorption of U(VI) and Pu(IV) by a novel solvent impregnated resin containing trialkyl phosphine oxide functionalized ionic liquid

Novel Solvent Impregnated Resin (SIR) material was prepared by impregnating a trialkyl phosphine oxide functionalized ionic liquid (IL) into an inert polymeric material XAD-7. A series of SIR materials were prepared by varying the IL quantity. Sorption of both U(VI) and Pu(IV) were found to increase with increasing IL concentration in SIR up to an optimum IL concentration of 435 mg g^-1 of SIR beyond which no effect of IL concentration was observed. A change of mechanism of sorption for U(VI) by SIR was observed in comparison to solvent extraction. The dependency of U(VI) sorption with nitric acid concentration showed a reverse trend compared to solvent extraction studies while for Pu(IV) the trend remained same as observed with solvent extraction. Sorption of both the radionuclides was found to follow pseudo second order mechanism and Langmuir adsorption isotherm. Distribution co-efficient measurements on IL impregnated SIR showed highly selective sorption of U(VI) and Pu(IV) over other trivalent f-elements and fission products from nitric acid medium.

Unusual binding selectivity with non-selective homoditopic pillar[5]arene oxime: serendipitous discovery of a unique approach to heterobinuclear metalation in solution

A heterobinuclear complexation strategy on homoditopic pillar[5]arene was developed by using a pillar[5]arene with two rims decorated with benzaldehyde oximes. The unique selective recognition process was found to result from vesicular formation based on a controllable self-assembly, leading to binding of thorium(iv) only onto one rim, with the other rim being unoccupied for subsequent complexation of a second different metal ion.

Understanding the complexation of Eu3+ with potential ligands used for preferential separation of lanthanides and actinides in various stages of nuclear fuel cycle: A luminescence investigation

A systematic photoluminescence based investigation was carried out to understand the complexation of Eu³⁺ with different ligands (TBP: tri-n-butyl phosphate, DHOA: di-n-hexyl octanamide, Cyanex 923: tri-n-alkyl phosphine oxide and Cyanex 272: Bis (2,4,4 trimethyl) pentyl phosphinic acid) used for preferential separation of lanthanides and actinides in various stages of nuclear fuel cycle. In case of TBP and DHOA complexes, 3 ligand molecules coordinated in monodentate fashion and 3 nitrate ion in bidentate fashion to Eu³⁺ to satisfy the 9 coordination of Eu. In case of Cyanex 923 and Cyanex 272 complexes, 3 ligand molecules, 3 nitrate ion and 3 water molecules coordinated to Eu³⁺ in monodentate fashion. The Eu complexes of TBP and DHOA were found to have D_3h local symmetry while that for Cyanex 923 and Cyanex 272 were C_3h. Judd-Ofelt analysis of these systems revealed that the covalency of EuO bond followed the trend DHOA>TBP>Cyanex 272>Cyanex 923. Different photophysical properties like radiative and non-radiative life time, branching ratio for different transitions, magnetic and electric dipole moment transition probabilities and quantum efficiency were also evaluated and compared for these systems. The magnetic dipole transition probability was found to be almost independent of ligand field perturbation while electric dipole transition probability for ⁵D₀-⁷F₂ transition was found to be hypersensitive with ligand field with a trend DHOA>TBP>Cyanex 272>Cyanex 923.

A water-soluble pillar[5]arene-based chemosensor for highly selective and sensitive fluorescence detection of l-methionine

Cationic pillar[5]arene (AWP5) was employed as a water-soluble chemosensor for recognition of amino acids. AWP5 could fluorescently detect l-methionine in water with high selectivity and sensitivity.

A novel iodination-triggered competitive coordination mechanism: indirect detection of Hg2+and I−using a simple copillar[5]arene-based fluorometric sensor

Proposed mechanism for the detection of Hg²⁺and I⁻byDBP5.

A copillar[5]arene-based fluorescence “on–off–on” sensor is applied in sequential recognition of an iron cation and a fluoride anion

A copillar[5]arene-based [c2]daisy-chain dimer is applied in sequential detection of Fe³⁺ and F⁻ through a competitive complexation reaction.

Diglycolamic acid-functionalized multiwalled carbon nanotubes as a highly efficient sorbent for f-block elements: experimental and theoretical investigations

Diglycolamic acid-functionalized carbon nanotubes were employed for the efficient and selective separation of Pu⁴⁺, PuO₂²⁺ and Am³⁺.

Diglycolamide-functionalized poly(propylene imine) diaminobutane dendrimers for sequestration of trivalent f-elements: synthesis, extraction and complexation

Three generations of diglycolamide-functionalized poly(propylene imine)diaminobutane dendrimers were synthesized and evaluated for their complexation ability towards trivalent actinides/lanthanides.

A novel functionalized pillar[5]arene-based selective amino acid sensor forl-tryptophan

The sensing mechanism of the sensorBTAP5forl-Trp.

Pillar[5]arene-based fluorescent polymer for selective detection and removal of mercury ions

A novel pillar[5]arene-based fluorescent polymer has been synthesized, and it is used for fluorescence detection and removal of the toxic mercury ions.

Ligands for f-element extraction used in the nuclear fuel cycle

This review describes the latest advances regarding the development, modification and application of suitable ligands for the liquid–liquid extraction of actinides and lanthanides from nuclear waste.