Insights into the spontaneous multi-scale supramolecular assembly in an ionic liquid-based extraction system.

Herein, we report a four-step mechanism for the spontaneous multi-scale supramolecular assembly (MSSA) process in a two-phase system concerning an ionic liquid (IL). The complex ions, elementary building blocks (EBBs), [EBB]n clusters and macroscopic assembly (MA) sphere are formed step by step. The porous large-sized [EBB]n clusters in the glassy state can hardly stay in the IL phase and they transfer to the IL-water interface due to both electroneutrality and amphiphilicity. Then, the clusters undergo random collision in the interface driven by the Marangoni effect and capillary force thereafter. Finally, a single MA sphere can be formed owing to supramolecular interactions. To our knowledge, this is the first example realizing spontaneous whole-process supramolecular assembly covering microscopic, mesoscopic and macroscopic scales in extraction systems. The concept of multi-scale selectivity (MSS) is therefore suggested and its mechanism is revealed. The selective separation and solidification of metal ions can be realized in a MSSA-based extraction system depending on MSS. In addition, insights into the physicochemical characteristics of ILs from microscopic, mesoscopic to macroscopic scales are provided, and especially, the solvation effect of ILs on the large-sized clusters leading to the phase-splitting is examined. It is quite important that the polarization of uranyl in its complex, the growing of uranyl clusters in an IL as well as the glassy material of uranyl are investigated systematically on the basis of both experiment and theoretical calculations in this work.

Complexation of Cyclic Glutarimidedioxime with Cerium: Surrogating for Redox Behavior of Plutonium.

The complexation of cerium with glutarimidedioxime (H2L) was studied by potentiometry, ESI-mass spectrometry, and cyclic voltammetry. Crystallization of [CeIV(HL)3]+ from Ce3+ starting reactant indicated spontaneous complexation-driven oxidation. In aqueous solution, Ce3+ ions form three successive complexes, Ce(HL)2+, Ce(HL)2+, and Ce(HL)3 (where HL- stands for the singly deprotonated ligand). The interactions of glutarimidedioxime with metal ions are dominantly electrostatic in nature, and the stability constants of the complexes are correlated to the charge density of metal ions. Extrapolations of predicted stability constant (log ß) values were made from plotting effective charge and the ionic radius of the metal ion for Pu3+ and Pu4+. The stability constants of PuIV(HL)3+ and PuIII(HL)2+ are estimated to be 27.74 and 19.75, respectively. The differences of stability constants mean that glutarimidedioxime selectively binds Pu4+ over Pu3+ by a factor of about 8 orders of magnitude, suggesting Pu4+ would be stabilized by chelation with glutarimidedioxime. The mechanism of reduction of Pu4+ to Pu3+ in acidic solution is explained by decomposition of glutarimidedioxime through acid hydrolysis rather than a chelation-driven mechanism.

Complexation of Light Trivalent Lanthanides with N-(2-Hydroxyethyl)ethylenediamine-N,N',N'-triacetic Acid in Aqueous Solutions: Thermodynamic Analysis and Coordination Modes.

N-(2-Hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid (HEDTA, denoted as H3L) is a strong chelating ligand that is widely used in the separation of f elements as relevant to the nuclear fuel cycle. There is much to be known about the structure and composition of the coordination sphere of the complexes of HEDTA with lanthanides. The complexation of HEDTA with light lanthanides (La3+, Nd3+, and Eu3+) was investigated thermodynamically and structurally in aqueous solutions. Potentiometry and microcalorimetry were performed to acquire the complexation constants (25-70 °C) and enthalpies (25 °C), respectively, at I = 1.0 mol·L-1 NaClO4. Coordination modes of the complexes were analyzed by luminescence spectroscopy and NMR spectroscopy. The results indicate that there are two successive Ln3+/HEDTA complexes, LnLaq and Ln2(H-1L)22- (Ln3+ refers to La3+, Nd3+, and Eu3+; H-1L4- refers to deprotonation of the hydroxyl group) during titration. The hydroxyl group of HEDTA is coordinated in the Ln3+/HEDTA complex. The dinuclear Ln2(H-1L)22- complex is present as a carboxyl-bridged centrosymmetric dimer, and two carboxyl groups in bridging positions are coordinated to two adjacent Ln3+ cations. Complexation of NdLaq is exothermic, while formation of the hydrolytic complex Nd2(H-1L)22- is endothermic. Both NdLaq and Nd2(H-1L)22- complexes are driven by entropic force. These data will help to predict the behavior of lanthanides in the separation process, where HEDTA is used as the aqueous complexant.

Efficient and irreversible capture of strontium ions from aqueous solution using metal-organic frameworks with ion trapping groups.

Efficient and irreversible capture of radioactive nuclides is an important environmental protection task when disposing of nuclear wastewater. This paper uses an "ion trapping" concept to design an efficient adsorbent based on a metal-organic framework (MOF), for removal of radioactive strontium from nuclear wastewater. Two functionalized MOFs were achieved by the introduction of sulfate or oxalate into the pore structure of MOF-808, giving MOF-808-SO4 and MOF-808-C2O4, respectively. These functionalized MOF-808 materials exhibit excellent ability to remove Sr2+ from acidic solution due to their particular trapping action, with the maximum Sr2+ adsorption capacities of 176.56 mg g-1 and 206.34 mg g-1 for MOF-808-SO4 and MOF-808-C2O4, respectively, surpassing most other inorganic materials. Additionally, 99% of Sr2+ is removed by MOF-808-SO4 and MOF-808-C2O4 after reaching the equilibrium. Remarkably, these two functionalized MOF-808 materials exhibited selectivity for the removal of Sr2+ from simulated mixed nuclear wastewater, even when there are 10 times as many co-existing ions as Sr2+ ions, demonstrating that anchoring of the trapping groups is a good way to improve Sr2+ adsorption capacity on MOFs. Moreover, both functionalized MOF-808 materials trap Sr2+ ions irreversibly, suggesting these trapping groups have strong ability to bind with Sr2+. A mechanism study indicated no proton ion exchange occurred during the adsorption process, so the functionalized groups anchored to MOFs play an important role in Sr2+ adsorption. Our present study provides an efficient way to design new adsorbents for the removal of radioactive strontium and other radionuclides from nuclear wastewater.

Improving barium ion adsorption on two-dimensional titanium carbide by surface modification.

Recently, 2D-MXene materials have attracted much attention. However, their low adsorption capacities for metal ions have limited their application in nuclear wastewater disposal. Here, we describe the unprecedentedly high adsorption by Ti3C2Tx for the removal of radionuclides by a simple and efficient surface modification strategy. We have produced an Alk-Ti3C2Tx material possessing desirable properties such as wide layer spacing and abundant active adsorption sites, with excellent ability to remove barium ions from aqueous solution. Maximum Ba2+ adsorption by Alk-Ti3C2Tx is 46.46 mg g-1, almost three times higher than that of unmodified Ti3C2Tx and much higher than that reported in previous studies. The remarkable selectivity for the removal of Ba2+ from simulated mixed nuclear wastewater is highly desirable for application in environmental wastewater treatment.

Safe disposal of radioactive iodide ions from solutions by Ag2O grafted sodium niobate nanofibers.

Radioactive iodine isotopes are released into the environment by the nuclear industry and medical research institutions using radioactive materials, and have negative effects on organisms living within the ecosystem. Thus, safe disposal of radioactive iodine is necessary and crucial. For this reason, the uptake of iodide ions was investigated in Ag2O nanocrystal grafted sodium niobate nanofibers, which were prepared by forming a well-matched phase coherent interface between them. The resulting composite was applied as an efficient adsorbent for I(-) anions by forming an AgI precipitate, which also remained firmly attached to the substrates. Due to their one-dimensional morphology, the new adsorbents can be easily dispersed in liquids and readily separated after purification. This significantly enhances the adsorption efficiency and reduces the separation costs. The change in structure from the pristine sodium niobate to Ag2O anchored sodium niobate and to the used adsorbent was examined by using various characterization techniques. The effects of Ag(+) concentration, pH, equilibration time, ionic strength and competing ions on the iodide ion removal ability of the composite were studied. The Ag2O nanocrystal grafted sodium niobate adsorbent showed a high adsorption capacity and excellent selectivity for I(-) anions in basic solutions. Our results are useful for the further development of improved adsorbents for removing I(-) anions from basic wastewater.

[Preparation and optical properties of tantalum tungsten bronze].

Tantalum tungsten bronze(TaxWO3)nanowires were successfully synthesized via hydrothermal method using TaCl5 and Na2WO4 . 2H20 as raw materials. The morphology, crystal structure and optical properties of synthesized products were characterized by means of XRD, TEM, SEM, UV-Vis and Raman technologies. The XRD results showed that TaxWO3 nanowire exhibited hexagonal structure. By increasing the doping content, the cell parameter was kept increasing gradually till Ta/W= 0. 04, then it remained almost constant. The UV-Vis diffraction spectrum analysis showed that the absorption peaks redshifted, the band gap energy decreased with increasing the doping content. The Raman peaks moved with a downshift, and the peak gradually became broader, which further proved the influence of the tantalum doping for tungsten oxide. The reactions of decomposing liquid rhodamine B solution showed that the nanosized TaxWO3 had a high photo-catalytic activity.

Guanidine sulfate-assisted synthesis of hexagonal WO3 nanoparticles with enhanced adsorption properties.

Large surface area hexagonal phase WO3 (h-WO3) nanowires were synthesized by a hydrothermal route with the assistance of C2H12N6O4S. They were characterized by XRD, SEM, TEM, BET, FT-IR and XPS. It is shown that C2H12N6O4S not only acts as a stabilizer to facilitate the generation of a metastable hexagonal phase, but also functions as a structure directing agent to assist the construction of nanowires. The obtained h-WO3 possesses a large specific surface area and numerous adsorption functional groups such as -OH groups. These characteristics result in an excellent adsorption performance for the removal of strontium from acidic aqueous solutions. A maximum adsorption capacity of 52.93 mg g(-1) was achieved on the h-WO3 prepared in the presence of C2H12N6O4S. This value is almost two times higher than that of bare h-WO3 (no C2H12N6O4S). The effects of pH, contact time, initial Sr(2+) concentration and ion strength on Sr(2+) removal from the solution by h-WO3 were systematically investigated. The adsorption mechanism involving the combination of electrostatic attraction and ion exchange for the adsorption of Sr(2+) is proposed. Based on our results, h-WO3 with high adsorption capacity and good surface characteristics exhibits great potential for the removal of Sr(2+) from radioactive wastewater.

Strontium adsorption on tantalum-doped hexagonal tungsten oxide.

Hexagonal tungsten oxide (hex-WO3) has the potential to separate (137)Cs and (90)Sr from nuclear power plant or fission (99)Mo production waste. This study aims to increase the capacity of hex-WO3 to adsorb Sr(2+). Ta-doped hex-WO3 was synthesized by the hydrothermal treatment of sodium tungstate dihydrate and tantalum chloride in concentrated HCl, in the presence of ammonium sulfate. Incorporating Ta into the WO3 framework caused the interlayer spacing to expand, and the band gap to shift to higher energy. The Sr(2+) adsorption capacity of Ta-doped hex-WO3 was significantly higher than that of hex-WO3. Sr(2+) adsorption reached equilibrium within 2h in acidic solution. Maximum Sr(2+) removal occurred at pH 4. Sr(2+) uptake by hex-WO3 was described better by the Freundlich model than by the Langmuir model. Sr(2+) adsorption on hex-WO3 was spontaneous under the studied conditions.