Satoko Tezuka

Studies on selective adsorbents for oxo-anions. Nitrate ion-exchange properties of layered double hydroxides with different metal atoms

Layered double hydroxides (LDHs) with different kinds of metal ions (Mg–Al, Co–Fe, Ni–Fe, and Mg–Fe) in the brucite layers were prepared and their anion exchange properties were studied by measurements of distribution coefficient (Kd) and ion exchange capacity. The basal spacing of LDHs varied depending on the kind of metal ions in the brucite layer. A relatively high Kd value for NO3− ions was observed on Ni–Fe type LDHs, and a markedly high Kd value for the hydrothermally-treated Ni–Fe type LDHs (Ni–Fe (HT)), prepared at 120 °C. These high Kd values correlated with the basal spacing of 0.81 nm observed for this sample, where the interlayer distance (0.33 nm) is suitable for the stable fixing of NO3− ions (ionic size = 0.33 nm). A chemical analysis study showed a Cl−/NO3− ion-exchange mechanism for NO3− adsorption on Ni–Fe (HT). The NO3− uptake by Ni–Fe (HT) was nearly constant (NO3/Fe = 0.7) over a pH range between 5 and 10, which also supports the adsorption mechanism of Cl−/NO3− ion exchange. The Ni–Fe (HT) could remove NO3− ions from seawater effectively (NO3− uptake = 168 μmol g−1) even though seawater contains an extremely large amount of coexisting anions. This novel adsorbent thus has a NO3− ion-sieve property and will prove beneficial for the selective removal of NO3− ions from industrial effluents and seawater to clean the environment.

Uptake properties of phosphate on a novel Zr–modified MgFe–LDH(CO3)

We prepared a novel Zr-modified MgFe-LDH(CO(3)) composite by adding a mixed solution of MgCl(2), FeCl(3), and ZrOCl(2) and another mixed solution of 1mol/dm(3) NaOH and 1mol/dm(3) Na(2)CO(3) to distilled water at a constant pH of 10. The composite exhibited only a poorly crystalline structure, resembling that of layered double hydroxides (LDH) from X-ray diffraction. The phosphate uptake is dependent on pH, decreasing with an increase in pH. This composite shows a much greater uptake of phosphate ions in P-enriched seawater (0.33mg-P/dm(3)) than amorphous zirconium oxide and MgFe-LDH(CO(3)). The uptake isotherm was fitted with a Freundlich relation. These phosphate-uptake behaviors closely resemble those of the relevant Zr-MgAl-LDH, which is estimated to be a composite of MgAl-LDH with amorphous zirconium hydroxide on the surface from X-ray absorption spectroscopy. Therefore, a similar structure of Zr-modified MgFe-LDH(CO(3)) composite probably causes the marked increase in phosphate uptake from P-enriched seawater.

NH3 desorption and decomposition behavior on microporous hollandite-type hydrous manganese oxide

Abstract In order to figure out the catalytic property of hollandite-type hydrous manganese oxide (H-Hol) to remove NH3, the desorption and decomposition properties of NH3 from NH3-chemically adsorbed H-Hol were examined and these properties and NH3 adsorptivity were compared with those of other manganese oxides and a de-NOx catalyst. It was found that the presence of NO accelerates the oxidation of NH3 to form N2 at a lower temperature. Comparison of NH3 pulse reaction in a flow containing NO on H-Hol with those on a high surface area-manganese oxide and a commercial de-NOx catalyst shows that H-Hol has the greatest N2 production, but less selectivity to form N2. H-Hol has a comparable amount of the strong H+ sites with the high surface area manganese oxide, which have relationship with NH3 decomposition.