Akinari Sonoda

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.

High electron mobility in a columnar phase of liquid-crystalline perylene tetracarboxylic bisimide bearing oligosiloxane chains

A liquid-crystalline (LC) semiconductor based on perylene tetracarboxylic bisimide (PTCBI) bearing four 1,1,1,3,3-pentamethyldisiloxane chains was synthesized. This LC PTCBI derivative exhibits ordered columnar phases and the low temperature columnar phase is retained below room temperature. The electron mobility in the ordered columnar phase of this compound at room temperature exceeds 0.1 cm2 V−1 s−1. Moreover, this compound is soluble in various organic solvents, except alcohols, and thin films in which the columnar aggregates are aligned parallel to the substrates are produced by spin-coating. In particular, LC thin films in which the columnar stacks are uniaxially oriented can be produced by a friction transfer method.

Fe-Al layered double hydroxides in bromate reduction: Synthesis and reactivity

This study presents a rare use of layered double hydroxides of Fe(II) and Al(III) (Fe-Al LDH), as reported for the first time for bromate removal from aqueous solutions. The Fe-Al LDH samples were prepared with Fe/Al molar ratios of 1-4 using a co-precipitation method at pH 7, with subsequent hydrothermal treatment at 120°C. The Fe-Al LDH (molar ratio of Fe/Al=1, 2) with a layered structure exhibited nearly complete removal of bromate from initial concentration of 100μmol/dm(3) at a wide pH range of 4.0-10.5 over a 2h reaction period; the residual bromate concentration in the solution was lower than the detection limit of 0.07μmol/dm(3) (9μg-BrO(3)(-)/dm(3)). During the reaction period, bromide was released into the solution via a reduction process. Reactivity of Fe-Al LDH with a Fe/Al molar ratio of 2 did not decrease the bromate reduction efficiency during 30days.

Photofabrication of Fullerene-Shelled Quantum Dots Supramolecular Nanoparticles for Solar Energy Harvesting

Quantum dots-based electron donor-acceptor systems play a rising role in the design of renewable and carbon-free energy harvesting technologies. In this article, we discuss the photofabrication of fullerene-shelled quantum dots supramolecular nanoparticles, in which the fullerene shell acts as not only a well-defined electron acceptor but also a robust protecting layer against the photocorrosion of the quantum dot core. We evaluate the ensemble and single-molecule electron transfer from the core to the shell in the nanoparticles and the photocurrent response of a photoelectrochemical cell constructed using the nanoparticles. The supramolecular nanoparticle has been prepared by the covalent tethering of a fullerene-thiol monolayer to the quantum dot followed by the photochemical reactions of free fullerene-thiol to the tethered monolayer. The nanoparticles are characterized using scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Correlated single-photon emission and the two-state ON-OFF photoluminescence show that single quantum dots are included in the supramolecular nanoparticles. The fullerene-shells suppress the blinking of single quantum dots by acting as well-defined electron traps, without allowing the transfer of Auger electrons to unknown traps. Electron transfer from the quantum dot-core to the fullerene-shell is apparent from the short ON and OFF durations in the photoluminescence intensity trajectories of single quantum dots, quenching of the photoluminescence intensity and lifetime of quantum dots at the ensemble level, and the characteristic transient absorption band of the anion radical of fullerene. We next construct a photoelectrochemical cell using the supramolecular nanoparticles, and the transferred electron is externally driven in the cell to generate ∼400 μA/cm(2) photocurrent. Electron transfer from the highly stable quantum dots to the protecting fullerene-shells places the supramolecular nanoparticles among the most promising antenna systems for the construction of cost-effective and stable next generation solar energy harvesting systems.

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.

Synthesis of a novel layered double hydroxides [MgAl4(OH)12](Cl)2·2.4H2O and its anion-exchange properties

A novel layered double hydroxide of Mg and Al with composition [Mg(0.96)Al(4.00)(OH)(12)]Cl(1.86)(CO(3))(0.03)·2.4H(2)O, designated as MgAl(4)-Cl, was synthesized by mixing crystalline gibbsite (γ-Al(OH)(3)) and solid MgCl(2)·6H(2)O with subsequent hydrothermal treatment at 160 °C for 72h. The MgAl(4)-Cl exhibited a crystalline material of a layered structure, as evidenced from X-ray diffraction. Anion uptake experiments with the MgAl(4)-Cl showed that Cl(-) in the interlayer space can be exchanged with anions such as Br(-), H(2)PO(4)(-), CO(3)(2-) or dodecyl sulfate (DS(-)) from aqueous solutions with preservation of the layered structure. Uptake of NO(3)(-), BrO(3)(-) or SO(4)(2-) on the MgAl(4)-Cl showed different behavior; these anions can be exchanged within 1h maintaining the layered structure, but a release of Mg(2+) cations from the sample was observed with increased reaction time, resulting in collapse of the layered structure and formation of the gibbsite phase, as determined from chemical analyses and X-ray diffraction.

A liquid-crystalline perylene tetracarboxylic bisimide derivative bearing a triethylene oxide chain and complexation of the derivative with Li cations

A liquid-crystalline (LC) perylene tetracarboxylic bisimide (PTCBI) derivative bearing a triethylene oxide chain as well as two pentamethyldisiloxane chains was synthesized. This compound exhibits an ordered lamellar phase at room temperature, and the LC phase is retained when the sample is cooled to -100 °C. Due to the presence of extended π-conjugated perylene rings, efficient electron transport occurs in the lamellar phase and the electron mobility exceeds 1 × 10(-3) cm(2) V(-1) s(-1) at room temperature. Moreover, this PTCBI derivative can form a complex with lithium triflate because of the polar triethylene oxide chain. Lithium triflate can be mixed with it up to 3 mol%. Up to this concentration, the lamellar LC structure and the electron transport properties are not perturbed by the presence of the ionic species.

Temperature-Independent Hole Mobility of a Smectic Liquid-Crystalline Semiconductor based on Band-Like Conduction

A liquid-crystalline (LC) phenylterthiophene derivative, which exhibited an ordered smectic phase at room temperature, was purified by vacuum sublimation under a flow of nitrogen. During the sublimation process, thin plates with sizes of 1 mm grew on the surface of the vacuum tube. The crystals exhibited the same X-ray diffraction patterns as the ordered smectic phase of the LC state that was formed through a conventional recrystallization process by using organic solvents. Because of the removal of chemical impurities, the hole mobility in the ordered smectic phase of the vacuum-grown thin plates increased to 1.2×10(-1) cm(2) V(-1) s(-1) at room temperature, whereas that of the LC precipitates was 7×10(-2) cm(2) V(-1) s(-1). The hole mobility in the ordered smectic phase of the vacuum-sublimated sample was temperature-independent between 400 and 220 K. The electric-field dependence of the hole mobility was also very small within this temperature range. The temperature dependence of hole mobility was well-described by the Hoesterey-Letson model. The hole-transport characteristics indicate that band-like conduction affected by the localized states, rather than a charge-carrier-hopping mechanism, is a valid mechanism for hole transport in an ordered smectic phase.

Liquid-crystalline perylene tetracarboxylic bisimide derivatives bearing cyclotetrasiloxane moieties

Liquid-crystalline perylene tetracarboxylic bisimide derivatives bearing heptamethylcyclotetrasiloxane moieties have been synthesized. Compound 2 bearing four heptamethylcyclotetrasiloxane moieties exhibits a rectangular columnar phase at room temperature. In the columnar phase, the cyclotetrasiloxane rings interdigitate into neighbouring columns and their interaction promotes the formation of the columnar mesomorphic structure. A time-of-flight measurement reveals that the electron mobility in the columnar phase of compound 2 is on the order of 10−2 cm2 V−1 s−1 at room temperature. Compound 2 is soluble in various organic solvents except for alcohol.

Ferroelectric liquid-crystalline semiconductors based on a phenylterthiophene skeleton: effect of the introduction of oligosiloxane moieties and photovoltaic effect

Ferroelectric liquid-crystalline phenylterthiophene derivatives bearing a decenyl group, disiloxane chain, and cyclotetrasiloxane ring were synthesized. These compounds exhibited a chiral smectic C (SmC*) phase. The spontaneous polarizations of the compounds exceeded 50 nC cm−2. The hole mobilities determined by the time-of-flight method were in the order of 1 × 10−4 cm2 V−1 s−1. The compound with a decenyl group exhibited an anomalous photovoltaic effect in the SmC* phase although the conversion efficiency was lower than 0.01%. Notably, even the compound bearing a bulky cyclotetrasiloxane ring exhibited an enantiotropic SmC* phase.