Naoki Hirayama

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.

An 8-sulfonamidoquinoline derivative with imidazolium unit as an extraction reagent for use in ionic liquid chelate extraction systems

To evaluate the superiority of using a task-specific onium salt (TSOS), a novel TSOS reagent 1-methyl-3-[2-(8-quinolinylaminosulfonyl)ethyl]imidazolium chloride (HmimesqCl) was synthesized, and its performance in extraction of different divalent metal cations was investigated. This TSOS reagent has both a cationic imidazolium unit and an anionic (proton-dissociable) complexation unit for the extraction of metal cations into an ionic liquid. In the use of HmimesqCl, relatively high extraction of metals resulted in comparison with the use of its non-imidazolium analogs, without changing the extraction selectivity.

Electrocatalytic Reduction of Free Chlorine at an N,N-Diethylaniline-grafted Carbon Electrode for Improved Sensitivity in Amperometric Detection

The electrocatalytic activity of an N,N-diethylaniline-grafted carbon (DEA/PFC) electrode was utilized to improve the sensitivity in the cathodic detection of free chlorine. Voltammetric curves showed a well-defined cathodic peak of free chlorine on DEA/PFC, lowering the overlap with that of dissolved oxygen. Amperometric measurements were applied for the determination of free chlorine for a concentration range of 4 orders of magnitude. The results showed that measurements of the amperometric response with DEA/PFC can be used as the basis for a simple, accurate, and rapid method to determine free chlorine.

Formation of Minimal Third Phase in Ionic Liquid Extraction System with Trioctylphosphine Oxide and Its Possible Application to Extraction Concentration

The third-phase formation behavior in ionic liquid (IL) extraction system using trioctylphosphine oxide (TOPO) was investigated. In the use of a relatively less-lipophilic IL, such as 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C4mimTf2N), the third phase was formed between the aqueous phase and the IL phase. The third phase seems to have a relatively high lipophilicity compared to the IL phase. The main components of the third phase were suggested as being (H3O)TOPO+, IL anion (Tf2N-), IL cation (C4mim+) and free TOPO. In addition, the third phase showed an extraction concentration ability for the Fe(III)-thiocyanato complex.

Effect of the Elemental Composition of Precursors from Amino Acids and Their Binary Mixtures on the Photoluminescent Intensity of Carbon Nanodots

We report on the photoluminescent (PL) properties of carbon nanodots (CNDs) doped with nitrogen and sulfur obtained by the pyrolytic carbonization of amino acids as precursors. Prepared CNDs exhibit stable PL emission under a wide variety of aqueous conditions. The results also provided the way to tune a PL intensity of CNDs by varying the amount of heteroatoms in precursors with a binary mixture of amino acids. The PL quantum yields of the obtained CNDs were determined to be from 0.079 to 0.571.