Seiichi Takami

Green materials synthesis with supercritical water

This paper describes the chemistry of green materials synthesized with supercritical fluids. First, the properties and some specific features of supercritical water are summarized. Then, supercritical hydrothermal synthesis of nanoparticles is explained, and various applications of green materials are described. The surface control of nanoparticles in supercritical water is also explained. Green processes involving chemical recycling of waste polymers and a combination of hydrothermal synthesis and supercritical water oxidation are also discussed. Finally, commercialization of supercritical water processes is discussed.

Extra-Low-Temperature Oxygen Storage Capacity of CeO2 Nanocrystals with Cubic Facets

Herein we demonstrate the extra-low-temperature oxygen storage capacity (OSC) of cerium oxide nanocrystals with cubic (100) facets. A considerable OSC occurs at 150 °C without active species loading. This temperature is 250 °C lower than that of irregularly shaped cerium oxide. This result indicates that cubic (100) facets of cerium oxide have the characteristics to be a superior low-temperature catalyst.

SUPERCRITICAL WATER TREATMENT OF BIOMASS FOR ENERGY AND MATERIAL RECOVERY

ABSTRACT Supercritical water liquefaction and gasification is reviewed with the introduction of some recent findings by the authors. Supercritical water gasification is suitable for recovery of energy from wet biomass while supercritical water liquefaction opens the door to effective treatment of biomass species in terms of material recovery. Cellulose, one of the main components of biomass, is completely dissolved in supercritical water. Once dissolved, reaction of cellulose can take place swiftly by hydrolysis and pyrolysis. The hydrolysis reaction, otherwise slower than pyrolysis due to the mass transfer limitation, is faster than decomposition in supercritical water, and a possibility of efficient glucose recovery has been shown. Once dissolved, super saturation is kept when the solution is cooled down, and swift hydrolysis by enzyme is also possible. Lignin can be also converted into specialty chemicals by using supercritical cresol/water mixture as a solvent. Dissolution of cellulose also enables efficient gasification of biomass. Complete gasification of biomass has been realized with production of combustible gas including hydrogen, carbon monoxide, and methane.

Enhanced optical properties of metal‐coated nanoparticles

Metal‐coated, nanometer‐size particles are modeled with a realistic distribution of coating thicknesses. General expressions are given for the local‐field enhancement, absorption, and nonlinear optical response. In addition, heuristic arguments are used to determine the effects of a diffuse, rather than a sharp interface. The linear and nonlinear optical properties are discussed within the context of the effective medium theory for small volume fractions. An efficient method of solution is used with the flexibility to handle an arbitrary number of coatings.

Supercritical hydrothermal synthesis of hydrophilic polymer-modified water-dispersible CeO2 nanoparticles

We have succeeded in the simple and rapid synthesis of the hydrophilic polymer-modified CeO2 nanoparticles using a supercritical hydrothermal method. To prepare the nanoparticles, Ce(OH)4 as precursor was treated in a batch-type reactor with supercritical water in the presence of either polyvinyl alcohol (PVA) or polyacryl acid (PAA) as surface modifiers. The hydrophilic polymers attached to the surface of the CeO2 nanoparticles by the coordination bond between the functional groups, such as hydroxyl (–OH) or carboxyl (–COOH), of the polymers and the Ce atoms. The amount of the attached polymers on the surface of the CeO2 nanoparticles tended to increase with a decrease in the molecular weight of the polymer. The morphology and the particle size of the nanoparticles were cuboctahedral and about 20 nm, respectively. The nanoparticles were dispersed in water by virtue of the functional groups on the polymers. Notably, the ζ potential of PAA-modified CeO2 nanoparticles did not become zero in the measured pH range between 3 and 11. Interestingly, the surface modification by the polymers controlled the band gap of the nanoparticles, suggesting the possibility of tuning the electronic and the optical properties of the metal oxide nanoparticle by modifying their surface with organic molecules.

Efficient conversion of lignin into single chemical species by solvothermal reaction in water-p-cresol solvent

Lignin was selectively converted into single chemical species in water–p-cresol mixtures at 673 K. Complete depression of char formation was realized in a mixture of 1.8 g of water and 2.5 g of p-cresol. The frame structure of lignin was efficiently decomposed within a reaction time of 4 min. The species obtained had a molecular weight of 214 (M+) assigned by gas chromatography–mass spectroscopy and was identified as hydroxylphenyl-(hydroxyltolyl)-methane (HPHTM) by 1H and 13C nuclear magnetic resonance. Its yield approached the maximum of 80% C at min of reaction time. HPHTM was presumably produced by the addition of p-cresol at the most active C α position of the hydroxyphenylpropane derivative that was formed by the hydrolysis of lignin.

Direct and selective immobilization of proteins by means of an inorganic material-binding peptide: discussion on functionalization in the elongation to material-binding peptide.

Using an artificial peptide library, we have identified a peptide with affinity for ZnO materials that could be used to selectively accumulate ZnO particles on polypropylene-gold plates. In this study, we fused recombinant green fluorescent protein (GFP) with this ZnO-binding peptide (ZnOBP) and then selectively immobilized the fused protein on ZnO particles. We determined an appropriate condition for selective immobilization of recombinant GFP, and the ZnO-binding function of ZnOBP-fused GFP was examined by elongating the ZnOBP tag from a single amino acid to the intact sequence. The fusion of ZnOBP with GFP enabled specific adsorption of GFP on ZnO substrates in an appropriate solution, and thermodynamic studies showed a predominantly enthalpy-dependent electrostatic interaction between ZnOBP and the ZnO surface. The ZnOBPs binding affinity for the ZnO surface increased first in terms of material selectivity and then in terms of high affinity as the GFP-fused peptide was elongated from a single amino acid to intact ZnOBP. We concluded that the enthalpy-dependent interaction between ZnOBP and ZnO was influenced by the presence of not only charged amino acids but also their surrounding residues in the ZnOBP sequence.

Electronic structures and spectroscopic properties of dimers Cu2, Ag2, and Au2 calculated by density functional theory

Abstract Electronic structures and spectroscopic properties of dimers Cu2, Ag2, and Au2 have been studied by density functional theory (DFT). The relativistic effects increase with the increment in electronic number. Zero order regular approximation (ZORA) relativistic correlation gives reliable parameters of electronic structures. By applying B3LYP as the exchange–correlation functional, a same sequence of orbital levels is obtained for Cu2, Ag2, and Au2. The fully filled d-electrons are not completely inert. The contributions of d-electrons to the frontier molecular orbitals are different in these three molecules. A strong interaction between d- and s-electrons causes an up-shift of d-type and a down-shift of s-type molecular orbitals. For Cu2 and Au2, the separation in d- and s-type molecular orbitals is close and small, which account for the much similar characteristics of the excitation states. For Ag2, a big separation in d- and s-type molecular orbitals is shown owing to the extremely small contribution of d electrons to the frontier molecular orbitals. By TDDFT and DSCF, the spectroscopic terms are assigned and explained in terms of the contributions of s- and d-electrons on the excitations. The prediction based on the present calculation matches well with the experimental data.

Combinatorial computational chemistry approach to the design of deNOx catalysts

Abstract Combinatorial chemistry is an efficient technique for the synthesis and screening of a large number of compounds. Recently, we introduced the combinatorial approach to computational chemistry for catalyst design and proposed a new method called ‘combinatorial computational chemistry’. In the present study, we have applied this combinatorial computational chemistry approach to the design of deNO x catalysts. Various ion-exchanged ZSM-5 are candidates as catalysts for the removal of nitrogen oxides (NO x ) from exhaust gases in the presence of excess oxygen. Here, we describe the screening of the exchange cations in ion-exchanged ZSM-5 which are strong against poisons. We investigated the adsorption energies of NO and water on various ion-exchanged ZSM-5 catalysts. Cu + , Ag + , Au + , Fe 2+ , Co 2+ , Ni 2+ , Pd 2+ , Pt 2+ , Cr 3+ , Fe 3+ , Ir 3+ and Tl 3+ were found to have high resistance to water molecules during the deNO x reaction.

Combinatorial computational chemistry approach as a promising method for design of Fischer–Tropsch catalysts based on Fe and Co

Abstract The combinatorial computational chemistry approach was applied to design new types of catalysts, which can be used in the Fisher–Tropsh (FT) synthesis for the production of ecologically high-quality transportation fuels. For this purpose, the density functional theory (DFT) was used to investigate the CO adsorption on Fe- and Co-based multi-component catalysts. The energetic, electronic and structural properties of CO on the catalyst surfaces were calculated. It was found that Mn, Mo, and Zr could be used as additional elements in the Fe- and Co-based catalysts, since one cannot observe a degradation of the adsorption properties of the active sites as well as showing a high sulfur tolerance. For the Co-based catalyst, the same tendency is also found in the case of the Si promoter. The obtained results are in agreement with available experimental data that confirmed the validity of combinatorial computational chemistry approach.