Micropore Formation by Acid Treatment of Antigorite

Abstract

Microporous materials are prepared by H{sub 2}SO{sub 4} treatment of antigorite (Mg{sub 3}Si{sub 2}O{sub 5}(OH){sub 4}) and characterized mainly by SEM observation, a gas adsorption method, and {sup 29}Si MAS NMR spectroscopy. The microtexture of the acid-treated products retains the morphology of the original pore composed of antigorite-like platy masses. Micropores 1 nm in size are formed between the layers of SiO{sub 4}-tetrahedron by Mg{sup 2+} dissolution. The micropore structure is changed by a condensation of silanol groups occurring in the pores. The maximum specific surface area is around 400 m{sup 2}/g, pore volume is 0.22 mL/g, and mean pore diameter is 1.2 nm. Around 5% MgO is necessary to stabilize the micropore structure and achieve a specific surface area of over 300 m{sup 2}/g. Mg{sup 2+} dissolution finally leads to formation of an amorphous silica with more than 99% SiO{sub 2} content of which the specific surface area, pore volume and mean pore diameter are 170 m{sup 2}/g, 0.08 mL/g, and 2.0 nm, respectively. 10 refs., 10 figs., 1 tab.