Constructing Cationic Metal-Organic Framework Materials Based on Pyrimidyl as a Functional Group for Perrhenate/Pertechnetate Sorption

Cationic metal-organic framework (MOF) materials are widely used in the anion separation field, but there are few reports of pyrimidyl ligands as building units. In this work, three new cationic MOFs based on pyrimidyl as functional group ligands were synthesized for the removal of radioactive pertechnetate from aqueous solution. The pyrimidyl ligands were designed by incorporating pyrimidyl units into the skeletons of benzene, triphenylamine, and tetraphenylethylene, respectively. Taking advantage of multiple coordination sites of pyrimidyl groups, three cationic MOFs (ZJU-X11, ZJU-X12, and ZJU-X13) with diverse structures were solvothermally synthesized using silver ion as the metal node. Scanning electron microscopy-energy-dispersive spectroscopy mapping demonstrated that these three cationic MOFs could capture ReO₄^- via anion exchange, but the sorption capabilities were distinctly different. With 95% removal toward ReO₄^-, ZJU-X11 showed the strongest anion-exchange competence among the three MOFs. According to the results of batch experiments, ZJU-X11 could achieve sorption equilibrium within 10 min, remove 518 mg of ReO₄^- per 1 g of ZJU-X11, remove most of ReO₄^- after four recycles, and maintain satisfactory selectivity in the presence of excess competing anions, which is one of the best MOF materials for removing ReO₄^-/TcO₄^- among the three cationic MOFs. This work indicates that the pyrimidyl group is a promising multiple site to build versatile cationic MOFs.

A H-Bonding and Electrostatic Interaction Combined Strategy for TcO4- Separation by a Nitrotriacetate-Derived Amine-Amide Extractant

Effective and selective separation of technetium from acidic nuclear liquid waste is highly desirable for partitioning and transmutation but is of significant challenge. Highly efficient extraction of pertechnetate can be achieved by taking H-bonding and electrostatic interaction combined strategy. Base on this strategy, an amine-amide ligand NTAamide(n-Oct) was employed to extract TcO₄^- in HNO₃ solution. Using n-dodecane as a diluent, NTAamide(n-Oct) demonstrated excellent extractability and good selectivity toward TcO₄^- with a rapid extraction equilibrium that could be reached in less than 1 min. Its maximal loading capacity for TcO₄^- was almost 100 times as much as that of traditional amine extractant Aliquat-336 nitrate. Meanwhile, TcO₄^- could be efficiently stripped from the loaded organic phase by (NH₄)₂CO₃ solution. Slope analysis indicated the formation of a 1:1 complex of NTAamide(n-Oct) with TcO₄^-. The extraction conformed to the anion exchange extraction model, as confirmed by analyses of single-crystal X-ray diffraction, ¹H NMR titration, FTIR, and ESI-MS.

Novel Hybrid Nanoparticles: Synthesis, Functionalization, Characterization, and Their Application in the Uptake of Scandium (III)Ions from Aqueous Media

The aim of this study was to prepare novel supramolecular hybrid nanoparticles (HNPs) that can selectively separate and recover scandium metal ions, Sc(III), from an aqueous phase based on molecular recognition technology (MRT). Moreover, this approach is fully compatible with green chemistry principles. In this work, natural amorphous silica (SiO₂) nanoparticles were prepared by a precipitation method from Iraqi rice husk (RH) followed by surface modification with 3-amino-propyl triethoxysilane (APTES) as coupling agent and Kryptofix 2.2.2 (K2.2.2) as polycyclic ligand. To evaluate the potential of the hybrid nanoparticles, the prepared HNPs were used for the solid-liquid extraction of scandium, Sc(III), ions from model solutions due to the fact that K2.2.2 are polycyclic molecules. These polycyclic molecules are able to encapsulate cations according to the corresponding cavity size with the ionic radius of metal by providing a higher protection due their cage-like structures. Moreover, the authors set the objectives to design a high-technology process using these HNPs and to develop a Sc recovery method from the aqueous model solution prior to employing it in industrial applications, e.g., for Sc recovery from red mud leachate. The concentrations of Sc model solutions were investigated using the UV-Vis spectrophotometer technique. Different characterization techniques were used including scanning electron microscope (SEM), atomic force microscopy (AFM), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), X-ray fluorescence (XRF), and Fourier transform infrared (FTIR). The extraction efficiency of Sc varied from 81.3% to 96.7%. Moreover, the complexed Sc ions were efficiently recovered by HCl with 0.1 mol/L concentration. The stripping ratios of Sc obtained ranged from 93.1% to 97.8%.

Cationic Covalent Organic Nanosheets for Rapid and Selective Capture of Perrhenate: An Analogue of Radioactive Pertechnetate from Aqueous Solution

Capture of radioactive TcO₄^- from nuclear wastes is extremely desirable for waste disposal and environmental restoration. Here, we report the synthesis of hydrolytically stable cationic covalent organic nanosheets (iCON) for efficient uptake of ReO₄^-, a nonradioactive surrogate of TcO₄^-. The iCON combines cationic guanidine-based knots with hydroxyl anchored neutral edge units and chloride ions loosely bonded in the pores, rendering extremely fast exchange kinetics toward ReO₄^- with high uptake capacity of 437 mg g^-1 and prominent distribution coefficient of 5.0 × 10⁵. The removal efficiency remains stable over a pH range of 3-12 and allows selective capture of ReO₄^- in the presence of excessive competing anions such as NO₃^-, CO₃^2-, PO₄^3- and SO₄^2- with good removal efficiency for ReO₄^- in a simulated Hanford LAW Melter Recycle Stream. Anion exchange between the ReO₄^- in solution and the chloride ion in iCON plays dominant role in the adsorption of ReO₄^-. The iCON shows promise for effective removal of radioactive ⁹⁹Tc from nuclear waste.