Hydrothermal Synthesis of Metal Oxide Nanoparticles at Supercritical Conditions

Hydrothermal synthesis of CeO₂ and AlO(OH) were conducted using a flow type apparatus over the range of temperature from 523 to 673 K at 30 MPa. Nanosize crystals were formed at supercritical conditions. The mechanism of nanoparticle formation at supercritical conditions was discussed based on the metal oxide solubility and kinetics of the hydrothermal synthesis reaction. The reaction rate of Ce(NO₃)₃ and Al(NO₃)₃ was evaluated using a flow type reactor. The Arrhenius plot of the first order rate constant fell on a straight line in the subcritical region, while it deviated from the straight line to the higher values above the critical point. The solubility of Ce(OH)₃ and AlO(OH) was estimated by using a modified HKF model in a wide range of pH and temperature. In acidic conditions, where hydrothermal synthesis reaction is concerned, solubility gradually decreased with increasing temperature and then drastically dropped above the critical point. The trend of the solubility and the kinetics around the critical point could be explained by taking account of the dielectric constant effect on the reactions. There are two reasons why nanoparticle are formed at supercritical conditions. Larger particles are produced at subcritical conditions due to Ostwald ripening; that could not be observed in supercritical water because of the extremely low solubility. Second reason is the faster nucleation rate in supercritical water because of the lower solubility and the extremely fast reaction rate.     

A Theoretical Study of Correlation between Hydrogen‐Bond Stability and J‐Coupling through a Hydrogen Bond

trans‐Hydrogen‐bond hyperfine splitting via magnetic interaction, which is observed as J‐coupling in NMR experiments, was theoretically studied. trans‐Hydrogen‐bond hyperfine splitting should be closely related to the orbital interaction between the lone‐pair orbital of the H‐bond acceptor and the antibond orbital of the H‐bond donor. A linear relationship was observed between magnetic interaction hyperfine splitting through a H‐bond and the H‐bond strength. The relationship was dependent on the type of the nucleus forming the H‐bond; linear correlation was observed in N H⋅⋅⋅O/N type or O H⋅⋅⋅N type H‐bonded complexes, but not in O H⋅⋅⋅O type H‐bonded complexes.     

“Three-dimensional analysis of the pyrolysis behavior of solid fuel by ultra high-speed X-ray CT”

In this research, microscopic visualization of pyrolysis in woody biomass was conducted by using the BL20B2 beamline at “SPring-8,” a large synchrotron radiation facility. Changes in shape and internal structure of the woody biomass were visualized by ultra high-speed CT. The samples were made of Japanese cypress wood; they had a height and a diameter of 5 mm. We used radiation as the heat source to achieve a high heat flux. When the heat flux was high, the samples expanded. Gaps were observed inside the samples. By comparing our results with the experimental results obtained under a low heat flux in a previous study, we could observe an entirely different aspect. Considering that the increase in pressure due to the rapid generation of pyrolysis gas created gaps in the samples, the samples were drilled, and experiments were performed on them. The hole in the center of the wood alone did not create an escape route for the pyrolysis gas, and the pyrolysis behavior was the same as that observed in the unprocessed wood.     

Syntheses and thermal analyses of curium trichloride

Curium trichloride was synthesized by the solid state reaction of curium nitride with cadmium chloride heated up to 748 K in a dynamic vacuum. The product was hexagonal ²⁴⁴CmCl₃, of which lattice parameters were determined to be a = 0.7385 ± 0.0005 and c = 0.4201 ± 0.0005 nm. The melting temperature of the ²⁴⁴CmCl₃ sample was determined to be 970 ± 3 K by differential thermal analyses using a gold crucible. These values are close to those reported in literature. The results show that mg-scale CmCl₃ samples for thermochemical measurements were prepared from the purified oxide sample without the use of corrosive reagents.     

Decomposition kinetics of 2-propylphenol in supercritical water

The decomposition of 2-propylphenol (PP) at 673 K and a water density of 0–0.5 g cm⁻³ yielded 2-isopropylphenol (IPP), phenol and 2-cresol. Gas products were methane, carbon dioxide, ethylene and propene. The decomposition was found to occur through rearrangement and alkylation, that is, (1) rearrangement of the propyl functional group from PP to IPP, (2) dealkylation of PP to phenol, (3) dealkylation of PP to 2-cresol. The decomposition probably occurred by a free-radical mechanism. The reaction rate constants of each pathway were determined and it was found that these were invariant over all the water densities studied at the given temperature.     

Basis set effects on the intermolecular interaction of the H2-H2 system obtained using ab initio molecular orbital calculations with the Møller-Plesset perturbation correction

The intermolecular interaction potential of the H₂-H₂ system was calculated by an ab initio molecular orbital method using several basis sets (up to 6-31 lG(3pd)) with inclusion of the electron correlation correction of the Møller-Plesset perturbation method and the basis set superposition error (BSSE) correction of the counterpoise method in order to evaluate the basis set effect. The calculated interaction energies depend strongly on the basis set used. Whereas the interaction energies of the repulsive and coulombic energy components calculated at the Hartree-Fock level are not affected by a change of basis set, the dispersion energy component depends strongly on the basis set used. Parameters of an exp-6-1 type non-bonding interaction potential were optimized on the basis of the MP4(SDTQ)/6-311G(3p) level intermolecular interaction energies of the H₂-H₂ system.     

Transparent CoAl2O4 hybrid nano pigment by organic ligand-assisted supercritical water

Transparent types of inorganic pigments are important as they can be used in a variety of applications, such as metallic finishing, contrast enhancing luminescent pigments, high-end optical filters, and so on. Currently, the difficulty in producing monodisperse and stable binary metal oxide nano pigments at low temperature hampers the applicability and realization of transparent blue nano pigments. Here, for the first time, we report organic ligand capped CoAl2O4 hybrid transparent nano pigment, which has a particle size less than 8 nm with well-stabilized single nanocrystals, using organic ligand-assisted supercritical water as the reaction medium. The organic ligand capping could effectively inhibit the particle growth and also control the size of nanocrystals. This helps to diminish the scattering effect of the nano blue pigment, realizing a transparent cobalt blue nano pigment without any postheat treatment.     

Organocatalytic, enantioselective intramolecular [6+2] cycloaddition reaction for the formation of tricyclopentanoids and insight on its mechanism from a computational study

Diphenylprolinol silyl ether was found to be an effective organocatalyst for promoting the asymmetric, catalytic, intramolecular [6 + 2] cycloaddition reactions of fulvenes substituted at the exocyclic 6-position with a δ-formylalkyl group to afford synthetically useful linear triquinane derivatives in good yields and excellent enantioselectivities. The cis-fused triquinane derivatives were obtained exclusively; the trans-fused isomers were not detected among the reaction products. The intramolecular [6 + 2] cycloaddition occurs between the fulvene functionality (6π) and the enamine double bond (2π) generated from the formyl group in the substrates and the diphenylprolinol silyl ether. The absolute configuration of the reaction products was determined by vibrational circular dichroism. The reaction mechanism was investigated using molecular orbital calculations, B3LYP and MP2 geometry optimizations, and subsequent single-point energy evaluations on model reaction sequences. These calculations revealed the following: (i) The intermolecular [6 + 2] cycloaddition of a fulvene and an enamine double bond proceeds in a stepwise mechanism via a zwitterionic intermediate. (ii) On the other hand, the intramolecular [6 + 2] cycloaddition leading to the cis-fused triquinane skeleton proceeds in a concerted mechanism via a highly asynchronous transition state. (iii) The fulvene functionality and the enamine double bond adopt the gauche-syn conformation during the C-C bond formation processes in the [6 + 2] cycloaddition. (iv) The energy profiles calculated for the intramolecular reaction explain the observed exclusive formation of the cis-fused triquinane derivatives in the [6 + 2] cycloaddition reactions. The reasons for the enantioselectivity seen in these [6 + 2] cycloaddition reactions are also discussed.     

Magnitude and nature of carbohydrate-aromatic interactions in fucose-phenol and fucose-indole complexes: CCSD(T) level interaction energy calculations

The CH/π contact structures of the fucose-phenol and fucose-indole complexes and the stabilization energies by formation of the complexes (E(form)) were studied by ab initio molecular orbital calculations. The three types of interactions (CH/π and OH/π interactions and OH/O hydrogen bonds) were compared and evaluated in a single molecular system and at the same level of theory. The E(form) calculated for the most stable CH/π contact structure of the fucose-phenol complex at the CCSD(T) level (-4.9 kcal/mol) is close to that for the most stable CH/π contact structure of the fucose-benzene complex (-4.5 kcal/mol). On the other hand the most stable CH/π contact structure of the fucose-indole complex has substantially larger E(form) (-6.5 kcal/mol). The dispersion interaction is the major source of the attraction in the CH/π contact structures of the fucose-phenol and fucose-indole complexes as in the case of the fucose-benzene complex. The electrostatic interactions in the CH/π contact structures are small (less than 1.5 kcal/mol). The nature of the interactions between the nonpolar surface of the carbohydrate and aromatic rings is completely different from that of the conventional hydrogen bonds where the electrostatic interaction is the major source of the attraction. The distributed multipole analysis and DFT-SATP analysis show that the dispersion interactions in the CH/π contact structure of fucose-indole complex are substantially larger than those in the CH/π contact structures of fucose-benzene and fucose-phenol complexes. The large dispersion interactions are responsible for the large E(form) for the fucose-indole complex.     

Quantitative analysis of trivalent uranium and lanthanides in a molten chloride by absorption spectrophotometry

As an analytical application for pyrochemical reprocessing using molten salts, quantitative analysis of uranium and lanthanides by UV/Vis/NIR absorption spectrophotometry was performed. Electronic absorption spectra of LiCl–KCl eutectic at 773 K including trivalent uranium and eight rare earth elements (Y, La, Ce, Pr, Nd, Sm, Eu, and Gd as fission product elements) were measured in the wavenumber region of 4,500–33,000 cm^?1. The composition of the solutes was simulated for a reductive extraction condition in a pyroreprocessing process for spent nuclear fuels, that is, about 2 wt% U and 0.1–2 wt% rare earth elements. Since U(III) possesses strong absorption bands due to f–d transitions, an optical quartz cell with short light path length of 1 mm was adopted in the analysis. The quantitative analysis of trivalent U, Nd, Pr, and Sm was possible with their f–f transition intensities in the NIR region. The analytical results agree with the prepared concentrations within 2σ experimental uncertainties.