title: Preparation of silica sphere with porous structure in supercritical carbon dioxide.
abstract: Silica sphere with porous structure has been synthesized in supercritical carbon dioxide. The structure originates from a delicate CO(2) trapping phenomenon intended for void formation in the inorganic framework. Silicate polymerization and subsequent removal of CO(2) by depressurization leaves the porous architecture. The key factor to obtain stable porous spherical structure was CO(2) pressure. Different characterization techniques such as X-ray diffraction, scanning and transmission electron microscopy and N(2) adsorption-desorption isotherm were used to determine the framework structure, morphology and porosity of the material. Microscopic visualization of calcined material suggested that the spherical structure was consisted of macroporous windows of diameter approximately 100 nm and the space between macropores presents a wormhole like mesoporous/microporous structure. The pore diameter of the mesoporous structure has been calculated as approximately 3 nm. X-ray diffraction and N(2) adsorption isotherm analysis confirmed the presence of micropores and also the macropores. In addition, the resulting material possess high thermal and hydrothermal stability associated with fully SiO(4) cross-linking. The spherical structure with different types of porosity was successfully obtained without using any molding agent.
authors.affiliation: Research Center for Compact Chemical Process, National Institute of Advanced Industrial Science and Technology, 4-2-1 Nigatake, Miyagino-ku, Sendai 983-8551, Japan. c-maya@aist.go.jp
authors.forename: Maya
authors.initials: M
authors.lastname: Chatterjee
authors.forename: Abhijit
authors.initials: A
authors.lastname: Chatterjee
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Ikushima
authors.forename: Hajime
authors.initials: H
authors.lastname: Kawanami
authors.forename: Takayuki
authors.initials: T
authors.lastname: Ishizaka
authors.forename: Masahiro
authors.initials: M
authors.lastname: Sato
authors.forename: Toshishige
authors.initials: T
authors.lastname: Suzuki
authors.forename: Toshirou
authors.initials: T
authors.lastname: Yokoyama