Hirochika Naganawa

Thermochromic properties of low-melting ionic uranyl isothiocyanate complexes

Temperature-dependent yellow-to-red colour changes of uranyl thiocyanate complexes with 1-alkyl-3-methylimidazolium cations have been studied by different spectroscopic methods and this phenomenon is attributed to changes in the local environment of the uranyl ion, including the coordination number, as well as to cation-anion interactions.

Cooperative intramolecular interaction of diazacrown ether bearing β-diketone fragments on an ionic liquid extraction system

A novel extractant beta-diketone-substituted diaza-18-crown-6 demonstrated very efficient extraction of Sr(2+) due to an intramolecular synergistic effect on the ionic liquid extraction system and recovery of Sr(2+) from the ionic liquid was successfully achieved under acidic conditions.

Specific Cooperative Effect of a Macrocyclic Receptor for Metal Ion Transfer into an Ionic Liquid

An intramolecular cooperative extraction system for the removal of strontium cations (Sr(2+)) from water by use of a novel macrocyclic receptor (H(2)βDA18C6) composed of diaza-18-crown-6 and two β-diketone fragments in ionic liquid (IL) is reported, together with X-ray spectroscopic characterization of the resulting extracted complexes in the IL and chloroform phases. The covalent attachment of two β-diketone fragments to a diazacrown ether resulted in a cooperative interaction within the receptor for Sr(2+) transfer, which remarkably enhanced the efficiency of Sr(2+) transfer relative to a mixed β-diketone and diazacrown system. The intramolecular cooperative effect was observed only in the IL extraction system, providing a 500-fold increase in extraction performance for Sr(2+) over chloroform. Slope analysis and potentiometric titration confirmed that identical extraction mechanisms operated in both the IL and chloroform systems. Extended X-ray absorption fine structure spectroscopy revealed that the average distance between Sr(2+) and O atoms in the Sr(2+) complex was shorter in IL than in chloroform. Consequently, Sr(2+) was held by H(2)βDA18C6 more rigidly in IL than in chloroform, representing an important factor dominating the magnitude of the intramolecular cooperative effect of H(2)βDA18C6 for Sr(2+). Furthermore, competitive extraction studies with alkaline earth metal ions revealed that the magnitude of the intramolecular cooperative effect depended on the suitability between metal ion size and the cavity size of H(2)βDA18C6. Sr(2+) was successfully recovered from IL by controlling the pH in the receiving phase, and the extraction performance of H(2)βDA18C6 in IL was maintained after five repeated uses.

Temporal variations in metal enrichment in suspended particulate matter during rainfall events in a rural stream

We studied enrichment of heavy metals (V, Zn, Cr, Ni, Cu, Pb, As, Sb, and Cd) in a rural stream of the Kuji River basin in central Japan in suspended particulate matter, and associated transport flux during two rainfall events (in November 2003 and in April 2008). The concentration of heavy metals in suspended particulate matter (SPM) exhibited a distinctive temporal variation, wherein the concentrations decreased with increasing water discharge and then increased as the discharge decreased. Concentration of dissolved metal forms showed a slight increase with scatters around the flow rate peak. Enrichment factors for those metals in the SPM decreased sharply as the flow rate increased, making an obvious concave shaped curve (the November 2003 rainfall event). The metal enrichment factors under low flow conditions had a similarity to those found in atmospheric deposits at a foot of the Kuji River basin, suggesting atmospheric source would contribute to enriching the SPM with those metals in part. Mineralogical analyses and carbon content analysis (the April 2008 rainfall event) of the SPM suggests the SPM matrix became more lithological as the flow rate increased. The changes observed in the matrix are thought to be directly related to progressive changes in metal enrichment within the SPM. Concerning the transport phase of several heavy metals, a dynamic change in transport phase partitioning within a rainfall event was suggested. The present enrichment factor study and the SPM matrix characterization implied the partitioning change is due to an increase in lithologic solids during high flow conditions.

Role of Tf2N− anions in the ionic liquid–water distribution of europium(III) chelates

The role of bis(trifluoromethanesulfonyl)imide (Tf2N−) anions in the ionic liquid–water distribution systems of Eu(III) chelates with 2-thenoyltrifluoroacetone (Htta) was investigated by liquid–liquid distribution and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The extraction constants of neutral Eu(tta)3 and anionic Eu(tta)4− chelates in 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Cnmim][Tf2N]) were determined by analyzing the distribution equilibrium. The effect of the ionic liquids on the distribution constant of the neutral Eu(tta)3 chelate was evaluated by the regular solution theory. The distribution constant of Eu(tta)3 in [Cnmim][Tf2N] was increased dramatically by the solvation effects of Eu(tta)3 in [Cnmim][Tf2N]. TRLFS for [Eu(tta)3(H2O)3] synthesized revealed that the Eu(tta)3 chelate was almost completely dehydrated in a series of [Cnmim][Tf2N] (n = 2–10). The Eu(tta)3 chelate exists as di- or tri-hydrates in 1-ethyl-3-methylimidazolium perchlorate ([C2mim][ClO4]) containing 20 mol dm−3 water, whereas mono-hydrated chelate was formed in [C2mim][Tf2N, ClO4] in the presence of 0.50 mol dm−3 Tf2N− and 20 mol dm−3 water. These results show that the coordinated water molecules of [Eu(tta)3(H2O)3] were replaced by the Tf2N− anions. In fact, an anionic adduct, [Eu(tta)3(Tf2N)]−, was observed by electrospray ionization mass spectrometry in the presence of [C4mim][Tf2N].

Increase in rare earth element concentrations controlled by dissolved organic matter in river water during rainfall events in a temperate, small forested catchment

The distributions of dissolved rare earth elements (REEs) in river water during rainfall events in a forested catchment were studied to contribute to understandings of TRUs behavior. Variations in the concentrations of dissolved REEs and several elements (As, Sb, and V) apparently correlated well with peak intensities in the optical spectra (ultraviolet absorption and fluorescence emission) of the river water. The optical properties were considered to represent humic substances in dissolved organic matter (DOM). Similar hysteretic loops were found for the REE concentrations and optical intensities as a function of the water discharge. This result indicates that the mobile REEs and DOM likely shared flow paths from the soil to the stream during these events. An ultrafiltration study revealed that colloidal REEs present in a size fraction of 10–30 kilodaltons comprised the major component of the dissolved REEs and increased under high water flow. Considering these observations and model interpretations in the precedent literature, complexation of the dissolved REEs with DOM was suggested to occur during the studied rainfall events. A high correlation between the size-fractionated REE concentrations and specific ultraviolet absorbance was observed, suggesting that the aromaticity of DOM plays a role in its complexation with dissolved REEs.

Continuous Liquid–Liquid Extraction of Uranium from Uranium-containing Wastewater Using an Organic Phase-refining-type Emulsion Flow Extractor

A previously reported emulsion flow (EF) extraction system does not equip the refining device for any used organic phase. Therefore, the processing of large quantities of wastewater by using the EF extractor alone could lead to the accumulation of extracted components into the organic phase, and a lowering of the extraction performance. In the present study, we developed an organic phase-refining-type EF system, which is equipped with a column for refining a used organic phase to prevent accumulation, and successfully applied it for treating uranium-containing wastewater.