Kimitaka Minami

Dealing with the aftermath of Fukushima Daiichi nuclear accident: decontamination of radioactive cesium enriched ash.

Environmental radioactivity, mainly in the Tohoku and Kanto areas, due to the long living radioisotopes of cesium is an obstacle to speedy recovery from the impacts of the Fukushima Daiichi Nuclear Power Plant accident. Although incineration of the contaminated wastes is encouraged, safe disposal of the Cs enriched ash is the big challenge. To address this issue, safe incineration of contaminated wastes while restricting the release of volatile Cs to the atmosphere was studied. Detailed study on effective removal of Cs from ash samples generated from wood bark, household garbage, and municipal sewage sludge was performed. For wood ash and garbage ash, washing only with water at ambient conditions removed radioactivity due to (134)Cs and (137)Cs, retaining most of the components other than the alkali metals with the residue. However, removing Cs from sludge ash needed acid treatment at high temperature. This difference in Cs solubility is due to the presence of soil particle originated clay minerals in the sludge ash. Because only removing the contaminated vegetation is found to sharply decrease the environmental radioactivity, volume reduction of contaminated biomass by incineration makes great sense. In addition, need for a long-term leachate monitoring system in the landfill can be avoided by washing the ash with water. Once the Cs in solids is extracted to the solution, it can be loaded to Cs selective adsorbents such as Prussian blue and safely stored in a small volume.

Estimation of the degree of hydrogen bonding between quinoline and water by ultraviolet–visible absorbance spectroscopy in sub- and supercritical water

UV–visible spectra of quinoline was measured in sub- and supercritical water (25 °C<T<430 °C and 0.1 MPa<P<40 MPa), and the degree of hydrogen bonding between quinoline and water was estimated from solvatochromic shifts in the π–π* absorbance band. Hydrogen bonding decreased with increasing temperature from 25 to 360 °C. At supercritical conditions (380 °C<T<400 °C), hydrogen bonding abruptly decreased where the isothermal compressibility of water was large (0.5<ρr<1.5). In this condition, local density around quinoline was lower than bulk density, namely negative solvation, and it led to the cleavage of hydrogen bonding between quinoline and water.

Historical Pigment Exhibiting Ammonia Gas Capture beyond Standard Adsorbents with Adsorption Sites of Two Kinds

Prussian blue is a historical pigment synthesized for the first time at the beginning of 18th century. Here we demonstrate that the historical pigment exhibits surprising adsorption properties of gaseous ammonia. Prussian blue shows 12.5 mmol/g of ammonia capacity at 0.1 MPa, whereas standard ammonia adsorbents show only 5.08-11.3 mmol/g. Dense adsorption was also observed for trace contamination in atmosphere. Results also show higher adsorption by Prussian blue analogues with the optimization of chemical composition. The respective capacities of cobalt hexacyanocobaltate (CoHCC) and copper hexacyanoferrate (CuHCF) were raised to 21.9 and 20.2 mmol/g, the highest value among the recyclable adsorbents. Also, CoHCC showed repeated adsorption in vacuum. CuHCF showed regeneration by acid washing. The chemical state of the adsorbed ammonia depends on the presence of the water in atmosphere: NH3, which was stored as in the dehydrated case, was converted into NH4(+) in the hydrated case.

Efficient synthesis of size-controlled open-framework nanoparticles fabricated with a micro-mixer: route to the improvement of Cs adsorption performance

We demonstrated an efficient method for size-controlled nanoparticles of the open framework coordination polymer potassium copper hexacyanoferrate (KCuHCF) using only aqueous solutions of the raw materials and a Y-type micro-mixer. Despite the high viscosity of the synthesized NP slurry, the micro-mixer provides continuous synthesis without clogging for a few hours with a high flow rate of 100 mL min−1, i.e. a linear velocity of 94 m s−1. The crystallite size, evaluated by the Scherrer equation using X-ray diffraction measurements, can be controlled by changing the flow rate. With the highest flow rate of 100 mL min−1, the smallest NPs with a size of ∼11 nm were obtained, less than half of the NP size obtained using the batch method. By downsizing the nanoparticles (NPs) using the micro-mixer synthesis, the Cs adsorption performance of potassium copper hexacyanoferrate (KCuHCF) was drastically improved. The KCuHCF with the smallest primary particles showed the fastest Cs adsorption: 1.4 times in the saturated capacity, 3.9 times in the distribution coefficient, and 7.7 times in the rate constant for the pseudo-second order adsorption theory, compared with the batch-synthesized sample.

Supercritical Hydrothermal Synthesis and In situ Organic Modification of Indium Tin Oxide Nanoparticles Using Continuous-Flow Reaction System

ITO nanoparticles were synthesized hydrothermally and surface modified in supercritical water using a continuous flow reaction system. The organic modification of the nanoparticles converted the surface from hydrophilic to hydrophobic, making the modified nanoparticles easily dispersible in organic solvent. The addition of a surface modifier into the reaction system impacted the crystal growth and particle size as well as dispersion. The particle size was 18 nm. Highly crystalline cubic ITO with a narrow particle size distribution was obtained. The advantages of short reaction time and the use of a continuous reaction system make this method suitable for industrial scale synthesis.

Improved adsorption properties of granulated copper hexacyanoferrate with multi-scale porous networks

Designed porous copper hexacyanoferrate micro-capsule beads (CuHCF-MCB) were prepared using freeze-drying (FD). Multi-scale porous networks composed of Angstrom, nanometer, and micrometer sizes were obtained in the desired shapes using a simple drying process. They provide special benefits such as fast kinetics and high capacity. The Cs adsorption equilibrium and kinetics fit the pseudo-second-order kinetic model well. The adsorption rate of FD-CuHCF-MCB was improved to about 15 times higher than that of the heat-drying process because of the highly multi-scale porous structure of FD-CuHCF-MCB, which facilitated solution flow and rapid ion-diffusion inside the MCB.

Determination of Kamlet-Taft solvent parameters π* of high pressure and supercritical water by the UV-Vis absorption spectral shift of 4-nitroanisole

Kamlet-Taft solvent parameters, pi*, of high pressure and supercritical water were determined from 16-420 degrees C based on solvatochromic measurements of 4-nitroanisole. For the measurements, an optical cell that could be used at high temperatures and pressures was developed with the specification of minimal dead space. The low dead space cell allowed us to measure the absorption spectra of 4-nitroanisole at high temperature conditions before appreciable decomposition occurred. The behavior of pi* in terms of water density (pi* = 1.77rho- 0.71) was found to be linear, except in the near critical region, in which deviations were observed that could be attributed to local density augmentation. Excess density, which was defined as the difference between local density and bulk density, showed a maximum near the critical density of water. The frequencies of UV-Vis spectra of 4-(dimethylamino)benzonitrile and N,N-dimethyl-4-nitroaniline were correlated with pi* based on a linear solvation energy relationship (LSER) theory. Local density augmentation around 4-nitroanisole and that around 4-(dimethylamino)benzonitrile were similar but the augmentation observed around N,N-dimethyl-4-nitroaniline was larger.

Mechanistic study on the synthesis of one-dimensional yttrium aluminum garnet nanostructures under supercritical hydrothermal conditions in the presence of organic amines

Novel one-dimensional nanostructures of yttrium aluminum garnet were synthesized under supercritical hydrothermal conditions in the presence of organic amine molecules. In addition, the effect of different reaction parameters such as the presence of organic amine molecules, pH of the precursor solution, and the state of water (sub- or supercritical conditions) on the morphology of the final product was investigated. In this paper, considering the simultaneous effects of these different parameters, a new electrostatic model is proposed to explain the formation mechanism of the obtained nanostructures.

Thermal dewetting behavior of polystyrene composite thin films with organic-modified inorganic nanoparticles.

The thermal dewetting of polystyrene composite thin films with oleic acid-modified CeO2 nanoparticles prepared by the supercritical hydrothermal synthesis method was investigated, varying the nanoparticle concentration (0-30 wt %), film thickness (approximately 50 and 100 nm), and surface energy of silanized silicon substrates on which the composite films were coated. The dewetting behavior of the composite thin films during thermal annealing was observed by an optical microscope. The presence of nanoparticles in the films affected the morphology of dewetting holes, and moreover suppressed the dewetting itself when the concentration was relatively high. It was revealed that there was a critical value of the surface energy of the substrate at which the dewetting occurred. In addition, the spatial distributions of nanoparticles in the composite thin films before thermal annealing were investigated using AFM and TEM. As a result, we found that most of nanoparticles segregated to the surface of the film, and that such distributions of nanoparticles contribute to the stabilization of the films, by calculating the interfacial potential of the films with nanoparticles.

Supercritical Hydrothermal Synthesis

This chapter describes specific features of a supercritical hydrothermal synthesis method. First, the some characteristic properties of supercritical water are summarized, and then the mechanism of supercritical hydrothermal synthesis is explained. Higher reaction rate and lower solubility are the key factors to synthesize nanosize crystals in a short reaction time. The flow reaction system to achieve rapid heating is explained. Some commercialized process is introduced. This method is useful to synthesize organic molecule modified nanoparticles (NPs). Since the organic molecules and metal–salt aqueous solutions are miscible under the supercritical state, and water molecule works as an acid/base catalyst for the reactions, organic–inorganic conjugate NPs can be synthesized under the condition. The mechanism of the conjugate forming reaction is explained. NPs’ superlattice structure and bioconjugate materials are also formed under the condition. The hybrid NPs show high affinity for the organic solvent or the polymer matrix, which leads to fabricate the organic–inorganic hybrid nanomaterials with the trade-off function (superhybrid nanomaterials). One of the applications is to fabricate a heat-conductive flexible hybrid-polymer sheet. By the surface modification of BN particles by supercritical method, affinity of BN and polymers could be improved so that high BN content of hybrid materials, thus high thermal conductivity materials, could be synthesized.