Nariyuki Tomonaga

Rapid Room Temperature Synthesis of Hexagonal Mesoporous Silica Using Inorganic Silicate Sources and Cationic Surfactants under Highly Acidic Conditions

The room-temperature synthesis of mesoporous silica was investigated by using cationic surfactants and inorganic Si sources, like sodium silicate and colloidal silica. Mesoporous silica analogous to the hexagonal MCM-41 could be obtained over a wide range of pH below ca. 11 within short synthesis time (3 h), when the Q4-state Si was absent in the Si source solution prior to mixing with an aqueous solution of cationic surfactants. It was suggested that the strongly acidic conditions (pH < 1) were favorable to give mesoporous silica materials with higher surface area and larger mesopore volume.

Synthesis and characterization of tin oxide-modified mesoporous silica by the repeated post-grafting of tin chloride

Abstract Modification of mesoporous silica with tin oxide was investigated by the repeated post-grafting method, which consisted of the repetition of the cycle of hydroxylation of the surface, grafting of tin(IV) chloride through the reaction with surface hydroxyl groups and calcination in air. The singly SnO2-modified material showed extremely high thermal stability up to 950°C as well as the stability against the treatment in basic solution (pH=10). With increasing the number of cycles, XRD peak intensity characteristic to the hexagonal mesophase decreased gradually, but the mesoporous structure was maintained up to the third modification. The optical absorption due to tin oxide was emerged by the modification and its absorbance increased with an increase in the modification cycles. The repeated modification with tin oxide caused progressive decreases in specific surface area, mesopore volume and diameter, while no significant change of the hexagonal cell parameter was observed. It was suggested from the enhanced stabilities and the pore-structure change that inner wall and outer surfaces of the mesoporous silica was progressively coated with the tin oxide layer.

Widely Tunable Operation of Ti:Sapphire Lasers under Optimum Coupling Condition

Widely tunable operation of Ti:sapphire lasers under the optimum coupling condition was investigated. The rate equation analysis on the pulsed Ti:sapphire laser shows that the tunable range can be extended by increasing the cavity-Q value and the pump laser fluence, and this was demonstrated with a Nd:YAG laser-pumped Ti:sapphire laser. If a coupling mirror has a wavelength-dependent reflectivity which increases in shorter and longer wavelengths of the tunable region, the entire spectral region can be tuned under the optimum coupling condition. A dielectric-coated coupling mirror with such wavelength dependence was developed, and a pulsed Ti:sapphire laser was operated under the nearly optimum condition over its tunable range of 690-960 nm without exchanging the mirror. The conversion efficiency was 30% at the maximum point.

Molecular sieve effect of chemically modified Na-A type zeolite and its molecular dynamic simulation

Summary In this study, the precise window shrinkage of Na-A type zeolite (Na-A) in the order of 0.1by calcination after rehydration, a partial K exchange and low temperature adsorption was evaluated[1],[2],[3]. It was understood that the precise window shrinkage of thermally and chemically modified Na-A was related to the behavior of Na located in the center of 8 oxygen members ring. Following the adsorption evaluation of oxygen selectivity based on an oxygen/nitrogen binary system and CO2 selectivity based on CO2/nitrogen binary system, a more precise relationship between the window shrinkage and the behavior of Na located at the center of 8 oxygen members ring was studied with an MAS-NMR, a single crystal X-ray diffraction (SCXD) and a molecular dynamic simulation (MD).