Tadafumi Adschiri

Nanoparticles synthesis using supercritical fluid technology - towards biomedical applications.

Supercritical fluid (SCF) technology has become an important tool of materials processing in the last two decades. Supercritical CO(2) and H(2)O are extensively being used in the preparation of a great variety of nanomaterials. The greatest requirement in the application of nanomaterials is its size and morphology control, which determine the application potential of the nanoparticles, as their properties vary significantly with size. Although significance of SCF technology has been described earlier by various authors, the importance of this technology for the fabrication of inorganic and hybrid nanomaterials in biomedical applications has not been discussed thoroughly. This review presents the nanomaterial preparation systematically using SCF technology with reference to the processing of biomedical materials. The basic principles of each one of the processes have been described in detail giving their merits and perspectives. The actual experimental data and results have been discussed in detail with respect to the selected nanomaterials for biomedical applications. The SCF synthesis of nanoparticles like phosphors, magnetic materials, carbon nanotubes, etc. have been discussed as they have potential applications in bio-imaging, hyperthermia, cancer therapy, neutron capture therapy, targeted drug delivery systems and so on. The more recent approach towards the in situ surface modification, dispersibility, single nanocrystal formation, and morphology control of the nanoparticles has been discussed in detail.

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.

Continuous production of phosphor YAG:Tb nanoparticles by hydrothermal synthesis in supercritical water

Phosphor YAG:Tb ((Y{sub 2.7}Tb{sub 0.3})Al{sub 5}O{sub 12}) nano particles were synthesized by a hydrothermal method at supercritical conditions (400 deg. C and 30 MPa) using a flow reactor. Hydroxide sol solutions formed by stoichiometric aluminum nitrate, yttrium nitrate, terbium nitrate and potassium hydroxide solutions. The relationship between particle size and experimental variables including pH, concentration of coexistent ions and hydroxide sol were investigated. Particles were characterized by XRD, TEM and photo-luminescence measurements. Particle size of YAG:Tb became finer as pH was increased or potassium nitrate concentration of the starting metal salt solution was increased. By removing the coexisting ions (NO{sub 3}{sup -}, K{sup +}) from the metal salt solution, single phase YAG:Tb particles with 20 nm particle size were obtained. The emission spectra of YAG:Tb particles of 14 nm shows a blue shift.

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.

Phase equilibrium study for the separation and fractionation of fatty oil components using supercritical carbon dioxide

Abstract Bharath, R., Inomata, H., Adschiri, T. and Arai, K., 1992. Phase equilibrium study for the separation and fractionation of fatty oil components using supercritical carbon dioxide. Fluid Phase Equilibria , 81: 307-320. Vapor-liquid equilibria were measured for the binary systems oleic acid-carbon dioxide and triolein-carbon dioxide and for the ternary system oleic acid-triolein-carbon dioxide with the aim of separating the fatty acids and triglycerides. Experimental results showed that oleic acid can be selectively extracted using supercritical carbon dioxide as a solvent. Supercritical carbon dioxide was also considered for the fractionation of mixtures of triglycerides. High pressure vapor-liquid equilibria were measured for the systems palm kernel oil-carbon dioxide and sesame oil-carbon dioxide. Supercritical carbon dioxide was found to fractionate these triglyceride mixtures on the basis of the total carbon number of the constituent fatty acids of the triglyceride.

Partial oxidation of n-hexadecane and polyethylene in supercritical water

In this study, we show the results of partial oxidation experiments of n-hexadecane (n-C16) and polyethylene (PE) in supercritical water (SCW). The experiments were carried out at 673 or 693 K of reaction temperature and 5 or 30 min of reaction time using a 6 cm3 of a batch type reactor. Water density ranged from 0.1 to 0.52 g/cm3 (water pressure: 20–40 MPa). The loaded amount of oxygen was set to 0.3 of the ratio of oxygen atom to carbon atom. Some experiments were made using CO instead of oxygen for the partial oxidation of n-C16 and PE to explore the effect of water gas shift reaction. In the results of partial oxidation of n-C16, the yield of CO and some compounds containing oxygen atoms, such as aldehydes and ketones increased with increasing water density. Moreover, 1-alkene/ n-alkane ratio in the products decreased with increasing water density. The 1-alkene/n-alkane ratio was lower than that of pyrolysis in SCW. Also for the case of PE experiments, in dense SCW (0.42 g/cm3), the 1-alkene/n-alkane ratio in partial oxidation was lower than that in SCW pyrolysis. In the case of CO experiments for n-C16 and PE, 1-alkene/n-alkane ratio was a little lower than that of pyrolysis in SCW. These results show that the yield of n-alkane, which is a hydrogenated compound, was higher through water gas shift reaction in SCW and also through partial oxidation in SCW. Therefore, these results suggest the possibility of hydrogenation of hydrocarbon through partial oxidation followed by the water gas shift reaction.

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.

Phase equilibria of supercritical CO2 - fatty oil component binary systems

Abstract With the aim of separating fatty acids and triglycerides of different carbon numbers, fluid - liquid equilibria of supercritical CO2 - fatty acid(C6, C12, C16) and supercritical CO2 - triglyceride(C24, C36, C48) binary systems were measured using a static type apparatus for the temprature range of 313K–353K and pressures up to 30MPa. For both fatty acids and triglycerides, the solubility decreases with total carbon number of the compound, showing that they can be fractionated based on their carbon number using supercritical carbon dioxide. The measured fluid - liquid equilibrium data were correlated by a lattice-fluid EOS proposed by Kumar et al. and the commonly used Peng-Robinson EOS. The lattice-fluid EOS correlated both the liquid and vapor phases well compared to the Peng-Robinson EOS. The regressed binary interaction parameter of the latitce model EOS was found closely related to the total carbon number of fatty acids and triglycerides. Above results suggest that to establish a method to evaluate the interaction and size parameters of fatty oil components is required for developing a phase equilibrium prediction model for the supercritical CO2- fatty oil component systems based on the lattice - fluid EOS.

Refractive index control and Rayleigh scattering properties of transparent TiO2 nanohybrid polymer.

The surface of TiO2 nanoparticles (NPs) was modified by a coupling agent of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane to render them highly compatible with organic monomer mixtures avoiding aggregation. Such TiO2 NPs were then chemically attached with a prepolymer. The refractive index of hybrid TiO2 NPs-polymer was increased dramatically in comparison with that of pure polymer, and it can be controlled by adjusting the content of TiO2 NPs. The Rayleigh scattering of hybrid TiO2 NPs-polymer was size-dependent and increased with the increase of the TiO2 NPs content. When Rayleigh scattering of the hybrid material prepared with a milling and centrifuge process was significantly lowered, one can obtain a transparent sample, which is good for optical devices.