Takashi Toraishi

Adsorption behavior of IO3− by CO32−- and NO3−-hydrotalcite

Abstract For the improvement of radioactive waste disposal, the materials with high adsorption capacity for IO 3 − should be used. Hydrotalcite-type (HT) compounds are considered potential materials. The adsorption behavior of IO 3 − by hydrotalcite-type compounds with CO 3 − (HTCO 3 ) or NO 3 − (HTNO 3 ) interlayer anions was studied. Adsorption equilibrium was reached more quickly for HTCO 3 than for HTNO 3 . The adsorption isotherm for HTCO 3 consisted of two Langmuir type adsorption processes. The desorption behavior was quite different for HTCO 3 –HTNO 3 . The results suggested that IO 3 − is adsorbed on the external surface of HTCO 3 whereas IO 3 − is exchanged for interlayer NO 3 − .

Fluorescence characteristics of complex formation of europium(III)-salicylate

Summary The complexation of salicylate with Eu3+ was studied by means of time-resolved laser-induced fluorescence spectroscopy (TRLFS) using ultra-short pulses at a concentration of sodium salicylate of 1.00×10-4 M. Ionic media was kept constant at 0.1M NaClO4. pH was adjusted to 4.00. The concentration of Eu3+ was varied from 1.98×10-3 M to 1.31×10-2 M. From the fluorescence lifetime analysis of the salicylate, we confirmed that a dynamic quenching process did not take place, while static quenching proceeded under the experimental conditions. The Stern Volmer plots indicated only the formation of a 1:1 complex, and the stability constant was assigned to be logβ1,1= 2.08±0.02. This agrees with reported values, which have been determined by other techniques. This result shows that the studies on complex formation can be safely investigated quantitatively by means of TRLFS from not only the luminescence of Eu3+ but the fluorescence of salicylate.

Uptake mechanism of IO3- to NO3--hydrotalcite

Summary The FT-IR (Fourier transform infrared spectroscopy) spectrum of IO3− adsorbed in the interlayer of NO3− hydrotalcite (HTNO3) was determined. The v3 vibration modes of IO3− split into two peaks. All peaks caused by adsorbed IO3− were found to be shifted to the lower wavelength region relative to the peaks observed from IO3− in the KIO3 crystal. This suggested that IO3− adsorbed in the interlayer of HTNO3 has asymmetry different from the original C3v symmetrical structure of aqueous IO3−. The structural position of IO3− in the interlayer of HTNO3 was optimized using the CASTEP (Cambridge serial total energy package) code. This code is based on density functional theory (DFT) calculations for crystal structures. It was found that the hydroxyl groups bound to O atoms of IO3− are not uniform. This may lead to the structural change of adsorbed IO3−.

Luminescence and Potentiometric Studies on the Complexation of Europium(III) by Picolinate in an Aqueous Solution

The complexation of Eu3+ aquo ions by picolinic acid in an aqueous solution was investigated to describe the formation of polynuclear complexes that are uncommon for trivalent lanthanides. Potentiometric titration indicated that no polynuclear complexes formed via hydroxide bridges, even at high pH, and that the monomeric form [Eu(Pic)4_(H2O)]− was present when a large excess of a picolinate ligand was used. In addition, lifetime analysis of Eu3+ luminescence via time-resolved laser-induced fluorescence spectroscopy was performed under conditions where Eu(pic)2+ appears as the secondary dominant species. Strong quenching of the luminescence was detected, suggesting that polymeric complexes ([Eu(Pic)]m2m+) form, even at low pH, owing to a vicinal Eu–Eu interaction.