Preparation of highly porous silica nanocomposites from clay mineral: a new approach using pillaring method combined with selective leaching

Abstract

A silica xerogel was synthesized from a clay mineral by a new approach using a pillaring method combined with a selective leaching method. Preparation was conducted by applying an HCl/ethanol treatment after intercalation and condensation of tetraethoxysilane (TEOS) and/or methyltriethoxysilane (MTS) into cetyltrimethylammonium (CTA) ion-exchanged vermiculite. The products are porous nanocomposites consisting of TEOS and/or MTS-derived polysiloxane and hydrated silica, resulting from the selective leaching process of the inorganic constituents and the extraction of CTA ions from CTA-exchanged vermiculite after the intercalation of TEOS and/or MTS. The morphology remains similar to the originated vermiculite owing to the topotactic dissolution process. The products have high porosity with 1205–715 m 2 g −1 of BET surface area when prepared with up to 2 mol dm −3 HCl concentration. The pore size distributions of the products show a wide distribution from 1 nm to 4 nm in diameter due to the presence of micropores and mesopores. The HCl concentration dependence of the surface area suggests that the main porosity arises from the porous polysiloxane which is formed by the pillaring process. Water adsorption isotherms reveal that the products have a hydrophilic surface originating from silanol groups on the polysiloxane and the hydrated silica. However, the incorporation of MTS in the pillaring process results in successful surface modification of the products. This novel approach is advantageous for the synthesis of highly porous xerogels with different kinds of surface properties.