Effects of Interlayer Cation Species and Layer Charge on Formation and Properties of Titania Pillared Fluorine Micas

Abstract

In order to clarify the influence of interlayer cation species and layer charge upon formation and properties of titania pillared fluorine micas, synthetic expandable fluorine micas having different interlayer cations, such as Li⁺, Na⁺, K⁺, and layer charges [M_xMg_3-xLi_xSi₄O₁₀F₂(M=Li, Na, K, x=0.4, 0.5, 0.6, 0.8)] were reacted with titania sol prepared by hydrolyzing titanium tetraisopropoxide (TTIP)with hydrochloric acid. Based on specific surface area measurements for pillared micas, the most appropriate reaction conditions of complex formation were decided to be [TTIP/HC1] ratio of 4, concentration of HCl used being 1 mol/dm³ with reaction time of 180 min. Interlayer cation species of host micas had the profound influence on complex formation, resulting in different titania contents and surface areas of pillared micas in the order of K⁺±Na⁺ ± Li⁺. This is due to the difference in expandability of host micas since interlayer cation determines swelling characteristics and intercalation process. In addition, layer charge had also the influence on titania contents and surface areas of pillared micas. Especially, Na_x-system was greatly influenced by layer charge, giving a maximum of titania content at x_??_0.6. Such an appearance of the maximum can be explained in terms of the decrease in swelling ability and the increase in cation exchange capacity with increasing layer charge. Thermal durability of titania pillared fluorine micas depended on titania content, being about 500 °C for Li_x-system having maximum titania content. Part of interlayer titania was expelled from interlayer region onto crystal surface of mica to precipitate as anatase at higher temperatures.