Micropore formation by acid treatment of antigorite

Microporous materials are prepared by H2SO4 treatment of antigorite (Mg3Si2O5(OH)(4)) and characterized mainly by SEM observation, a gas adsorption method, and Si-29 MAS NMR spectroscopy. The microtexture of the acid-treated products retains the morphology of the original ore composed of antigorite-like platy masses. Micropores 1 nm in size are formed between the layers of SiO4-tetrahedron by Mg2+ 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(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(2)/g. Mg2+ dissolution finally leads to formation of an amorphous silica with more than 99% SiO2 content of which the specific surface area, pore volume and mean pore diameter are 170 m(2)/g, 0.08 mL/g, and 2.0 nm, respectively.