Ryota Watanabe

Extension of size of monodisperse silica nanospheres and their well-ordered assembly

A liquid-phase method for preparing uniform-sized silica nanospheres (SNSs) 12 nm in size and their three-dimensionally ordered arrangement upon solvent evaporation have recently been pioneered by us. Here we report the successful control of the sphere sizes in the wide range from 14 to 550 nm by the seed regrowth method. In this method, the dispersion of SNSs 14 nm in size as seeds was prepared in the emulsion system containing Si(OEt)(4) (TEOS), water and arginine under weakly basic conditions (pH 9-10). An appropriate portion of this dispersion is added to the solution containing water, ethanol and arginine, and then TEOS is added. The additional TEOS introduced into the regrowth system contributed only to the resumed growth of the seeds, not to the formation of new silica particles. The size of interparticle pores was finely tuned by changing the size of the spheres. The preparation of three-dimensionally ordered porous carbons by using the colloidal array of silica nanospheres as a template is also reported.

Synthesis and application of colloidal nanocrystals of the MFI-type zeolites.

The colloidal dispersion containing the nanosized zeolites with the MFI topology has been successfully prepared. A pre-aging process of the mother gel at 80°C for 24 h before the crystallization was important for the formation of the nanosized zeolites. We have also found that silicalite-1 nanocrystals av. 62 nm in size were formed by the addition of acidic amino acids into the mother gel. The particle size of the zeolites can be controlled ranging from 62 to 530 nm by changing the amount of water, aging process, crystallization time and temperature and the addition of organic molecules. Furthermore, nanosized titanium silicalite-1 (TS-1) with the size of 50-130 nm has been successfully synthesized by the addition of a Ti source into the synthesis gel of the silicalite-1 nanocrystals. The nanosized TS-1 exhibits a higher catalytic activity in the epoxidation of cyclohexene than the microsized ones. Finally, we demonstrate the preparation of thin films of the silicalite-1 and TS-1 nanocrystals onto a silicon substrate by a dip-coating technique.

Synthesis of well-ordered nanospheres with uniform mesopores assisted by basic amino acids

Abstract We applied basic amino acids in place of NH 3 to the well-known Stober method for preparing silica spheres; the hydrolysis and condensation reactions of tetraethyl orthosilicate were conducted in the presence of basic amino acids such as L -lysine and L -arginine. The obtained silica spheres, which are of uniform size of 12 nm, are well-ordered, forming a cubic closed pack (ccp) structure, Fm-3m space group. The arrangement of uniform spheres simultaneously creates intraparticle uniform mesopores of about 3 nm. We also succeeded in the preparation of exact carbon replica with uniform mesopores by using the silica nanospheres as a template. The results shown here are the first example of the arrangement of silica nanospheres assisted by simple biomolecules, leading to the development of a novel family of ordered mesoporous materials, which will open up a wide range of possibilities for the synthesis of spontaneously assembled nano-structured materials.