Ryo Sasai

Dielectric Mismatch Mediates Carrier Mobility in Organic-Intercalated Layered TiS2.

The dielectric constant is a key parameter that determines both optical and electronic properties of materials. It is desirable to tune electronic properties though dielectric engineering approach. Here, we present a systematic approach to tune carrier mobilities of hybrid inorganic/organic materials where layered two-dimensional transition-metal dichalcogenide TiS2 is electrochemically intercalated with polar organic molecules. By manipulating the dielectric mismatch using polar organic molecules with different dielectric constants, ranging from 10 to 41, the electron mobility of the TiS2 layers was changed three times due to the dielectric screening of the Coulomb-impurity scattering processes. Both the overall thermal conductivity and the lattice thermal conductivity were also found to decrease with an increasing dielectric mismatch. The enhanced electrical mobility along with the decreased thermal conductivity together gave rise to a significantly improved thermoelectric figure of merit of the hybrid inorganic/organic materials at room temperature, which might find applications in wearable electronics.

Synthesis of copper nanoparticles within the interlayer space of titania nanosheet transparent films

We report the first in situ synthesis of copper nanoparticles (CuNPs) within the interlayer space of inorganic layered semiconductors (titania nanosheet films) through the following steps. A sintered titania nanosheet (s-TNS) film was synthesised, forming a transparent, layered semiconductor film (∼2 μm thick). A considerable amount of copper ions (ca. 68% relative to the cation exchange capacity of TNSs) was intercalated in the s-TNSs using the methyl viologen-containing s-TNSs as the intermediate. The resultant copper-containing s-TNS (TNS/Cu2+) film was treated with an aqueous solution of NaBH4, resulting in a colour change. Extinction spectra of NaBH4-treated films exhibited a wide extinction band at λmax (the extinction band maximum) = 683 nm. The spectral shapes and λmax were similar to those for copper nanoparticles on TiO2 surfaces. Transmission electron microscopy analysis demonstrated the wide distribution of electron dense particles on the titania sheet of NaBH4-treated TNS/Cu2+. XRD analysis and absorption/extinction analysis with different amounts of TNSs suggest that CuNPs were formed within the interlayer space rather than the surface of TNSs through NaBH4 treatment. Repeatable oxidation and reduction behaviour, i.e. colouration and decolouration cycles of the copper species within TNS films, was investigated.

Multinuclear solid-state NMR spectroscopy of a paramagnetic layered double hydroxide

NMR spectroscopy is rarely utilized when analytes include paramagnetic ions. We show that multinuclear solid-state NMR is actually potentially useful for investigating nanostructures of a layered double hydroxide (LDH) containing paramagnetic Ni2+ cations. In particular, 13C NMR spectra of interlayer carbonate anions are well resolved by using conventional MAS/DD.

Technique for recovering rare-earth metals from spent sintered Nd-Fe-B magnets without external heating

Abstract To selectively recover rare-earth metals with higher purity from spent sintered Nd-Fe-B magnets without external heating, we investigated the mechano-chemical treatment of spent sintered Nd-Fe-B magnet powder with a reaction solution of HCl and (COOH)2 at room temperature. The results of various experiments showed that the mechano-chemical treatment with HCl and (COOH)2 is very effective for recovering the rare-earth metals contained in spent sintered Nd-Fe-B magnet powder; the recovery rate and purity of the rare-earth metals were 95.3 and 95.0 mass%, respectively, under optimal conditions ([HCl] = 0.2 mol/dm3 and [(COOH)2] = 0.25 mol/dm3).

Preparation of Stable Silver Nanoparticles Having Wide Red-To-Near-Infrared Extinction

Abstract The synthesis of silver nanoparticles (AgNPs) within the interlayer space of transparent layered titania nanosheet (TNS) films is investigated. A considerable number of silver ions (≈70% against the cation exchange capacity of the TNS) are intercalated in the TNS films using methyl‐viologen‐containing TNSs as a precursor. The silver ion (Ag+)‐containing TNS films are treated with aqueous sodium tetrahydroborate (NaBH4), resulting in a gradual color change to bright blue. Various structural analyses clearly show that crystalline AgNPs are generated within the interlayer space of the TNSs. The NaBH4‐treated films show intense and characteristic near‐infrared (NIR) extinction spectra up to 1800 nm. The stability of the AgNPs within the TNS against oxygen and moisture is also investigated, and 96% and 82% of the AgNPs remain after standing in air for 1 month and 1 year, respectively. The NIR extinctions of the AgNP‐containing TNS films are further extended by employing different preparation procedures, for example, using sintered TNS films as starting materials and irradiating the Ag+‐containing TNSs with ultraviolet (UV) light. The obtained AgNP‐containing TNS films exhibit photochemical activities in the production of hydrogen from ammonia borane under visible‐light irradiation and the decomposition of nitrogen monoxide under UV‐light irradiation.

Effects of Rh-doping on the photooxidative degradation activity of titanate nanosheets

To investigate the Rh-doping effect on the photooxidative degradation activity of titanate nanosheets prepared by exfoliation of an H2Ti3O7 crystal in aqueous media, a colloidal aqueous suspension of titanate nanosheets doped with Rh atoms at the Ti sites (TiNS:Rhz, z = amount of Rh, [Ti3−zRhzO7]2−) was prepared. Oxidative degradation of methylene blue (MB) by TiNS:Rhz in aqueous media under UV light irradiation was studied. Using X-ray diffraction, diffuse reflection spectroscopy, and photoelectrochemical measurements, the electronic band structure of TiNS:Rhz was elucidated and was shown not to change with the amount of Rh doping at the Ti sites. However, the degradation of MB increased with an increase in Rh doping. From these results, it is suggested that the redox reaction between Rh3+ and Rh4+ strongly contributes to the oxidative degradation of MB in the presence of TiNS:Rhz under UV light irradiation.

Assessment of soil remediation technologies by comparing health risk reduction and potential impacts using unified index, disability-adjusted life years

The assessment methodology of soil remediation technologies including citizen’s opinions about environmental policy was developed to enable direct comparison between the resident health risk reduction by carrying out remediation (decreased primary risk) and the potential impacts of chemicals emitted during the remediation on national health, social assets, and primary production (secondary risk). Both risks were quantified with an unified index, disability-adjusted life years (DALYs), by employing life cycle costingxa0(LCC), economic input–output life cycle assessmentxa0(EIO-LCA), and life cycle impact assessmentxa0(LCIA) database. Four remediation technologies were considered: excavation–disposal, high temperature thermal desorption (HTTD), biopile, and landfarming. There was almost no difference in the decreased primary risk among the four technologies, apart from landfarming, which had the smallest decreased primary risk. The secondary risk of the biological technologies (biopile, landfarming) was smaller than that of the physical and chemical technologies (excavation–disposal, HTTD). The ratio of the decreased primary risk to the secondary risk was largest in case of landfarming, which indicated that landfarming was most effective. The sum of the residual primary risks and secondary risk was small in the biological technologies, indicating that the biological technologies had smaller environmental impacts. Indexing both of decreased primary risk and secondary risk with DALYs enables non-experts who prioritize resident’s health to assess the soil remediation technologies and would facilitate the decision making in the selection of remediation technologies.

Optical Humidity Sensing Using Transparent Hybrid Film Composed of Cationic Magnesium Porphyrin and Clay Mineral

A transparent hybrid film composed of cationic magnesium porphyrin and clay mineral was developed, and its chromic behavior depending on relative humidity (RH) was investigated. The hybrid film was obtained via intercalation of magnesium porphyrin into clay film; magnesium porphyrin was intercalated into the interlayer spaces of the clay mineral without aggregation. The absorption spectra of the hybrid film showed red shifts compared to the aqueous solution of magnesium porphyrin because of the π-conjugated system extension with coplanarization of the meso-substituted pyridinium group and porphyrin ring. The absorption maximum of the hybrid film was gradually shifted to a shorter wavelength, and the color of the hybrid film was changed with increasing RH. The X-ray diffraction measurement suggested that the basal space of clay was expanded with increasing RH, indicating that the interlayer space of clay was expanded by water adsorption, and the spectral shift was induced by the change in coplanarization degree between the porphyrin ring and meso-substituted pyridinium groups.

Molecular Sensing Ability of Layered Inorganic/Luminous Organic Nano Hybrid Solid Materials

To apply titanate nanosheet/decyltrimethlammonium/rhodamine 3B (TNS/C10TMA/R3B) hybrid material with highly luminescent ability to high performance sensor or indicator, spectroscopic properties in the absence and presence of water and/or NH3 vapors were investigated. The TNS/C10TMA/R3B hybrid material exhibited tone change of photoadsorption and photoluminescence in the presence of water vapor. Moreover, this material exhibited remarkable quenching in the presence of NH3 vapor under humid condition. It was found that this quenching was caused by an intramolecular cyclization reaction of incorporated R3B. This photoluminescence intensity decreased with an increase in NH3 concentration. This fact is that the present hybrid material has a high potential for molecular sensor or indicator.

Recovery of SiC powder from sintered DPF using hydrothermal treatment combined with ball-milling technique

In the present work, hydrothermal treatment combined with ball-milling technique (HTBT) was attempted to recover SiC powder from bulk sintered DPF. Various parameters including the material and size of the milling-ball, the type of the solvent medium, the rotation speed, the ratio of solvent/DPF, the treatment temperature and time were optimized. The pulverization rate, impurity content and the particle size of the recovered SiC powder were investigated to assess the effect of HTBT. Dilute HF solution was selected as the main solvent and SiC milling-ball was the most suitable for pulverization of the sintered DPF. The rotation speed played a significant role for the pulverization rate and more than 90% of bulk sintered DPF was recovered as SiC powder using SiC balls (5 mm in diameter) in the mixed aqueous solutions of HF (0.05 mol/dm3) and H2O2 (0.25 mol/dm3) with rotation speed ≥ 275 rpm and solvent/DPF = 1.5 at 200°C after 20 h HTBT . Generally the average grain size of the recovered SiC powder was less than 1.5 μm and decreased with the extended treatment time and the increased rotation speed. The result of purity analysis showed that the recovered SiC powder totally met the demand of the raw SiC powder for DPF production under the optimized conditions.