Effects of Layer Charge on Formation of Chromia Pillared Fluorine Micas

Abstract

In order to synthesize pillared micas with controlled microporous properties, expandable Li⁺exchanged fluorine micas having different layer charges (x)[Li_xMg_3-x Li_xSi₄O₁₀F₂(x=0.5, 0.8)] were allowed to react with various polynuclear hydroxochromium (III) solutions having different OH/Cr ratios and aging conditions, and the effects of layer charge on formation and properties of chromia pillared fluorine micas were studied. When host mica crystals had larger layer charge (x=0.8), Cr(III) monomer and Cr(III)-oligomers such as dimer and trimer having smaller cross sectional area per a positive charge were selectively intercalated into the interlayer region of mica. On the other hand, when host micas had smaller layer charge (x=0.5), highly polymerized Cr(III)-species with larger cross sectional area were selectively intercalated. Furthermore, intercalated Cr species were not only dependent On layer charge but also the containing ratios of Cr(III)-ion species in solutions. When pillared micas having larger layer charge were heated at 200∼300 °C, micropores were formed, resulting in larger specific surface area and pore volume. However, the pillared micas with smaller layer charge, as the result of intercalated large polymers, had larger basal spacings and thermal stability than the ones having larger layer charge, exhibiting relatively larger surface area and pore volume at high temperatures.