title: Micropore to macropore structure-designed silicas with regulated condensation of silicic acid nanoparticles.
abstract: A new preparation method for porous silica particles was developed using activated silica sols which are called nano-silica solutions in this paper. Several kinds of organic and inorganic acids are employed to neutralize diluted sodium silicate solutions to form the nano-silica solutions: formic acid, acetic acid, propionic acid, oxalic acid, succinic acid, dl-malic acid, citric acid, and tricarballylic acid as carboxylic acids, and sulfuric acid and hydrochloric acid as inorganic acids. The effect of salts in the nano-silica solution is also studied. The products were investigated using a field emission scanning electron microscope, an X-ray diffractometer, the nitrogen adsorption technique, and a mercury porosimeter. Microporous silicas were produced when carboxylic acids were applied; the formation of micropores was influenced by the pH of the nano-silica solutions and molecular sizes of the carboxylic acids. Addition of a salt in a citric acid solution increased the mesopore volume. Macropores were formed when inorganic acids including salts were applied; the salt nanoparticles which were crystallized in silica spheres acted as templates. The anion types and salt concentrations in the nano-silica solutions affected the aggregation condition of silica nanoparticles, following the Schulze-Hardy rule.
authors.affiliation: Fuji Chemical Company, Ltd., 1683-1880 Nasubigawa, Nakatsugawa 509-9132, Japan. isobe@fuji-chemical.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Isobe
authors.forename: Shigenori
authors.initials: S
authors.lastname: Utsumi
authors.forename: Kohzoh
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Kanoh
authors.forename: Katsumi
authors.initials: K
authors.lastname: Kaneko