A new strategy for the synthesis of pillared clays with super galleries: Direct intercalation of metal oxide sols (DIMOS)

The direct intercalation of metal oxide sols (DIMOS) is a promising new route to pillared clays with highly expanded super galleries, as judged from the properties of products obtained from the reaction of silica sols with Na⁺-montmorillonite. Silica-clay compositions in the range 1:1 to 10:1 (wt./wt.) were prepared by allowing mixtures of positively charged sol (pH=3.0) and clay to evaporate in air at room temperature. A stabilized commercial sol (Nalco 1115, ∼40 Å) and a sol freshly prepared by tetraethylorthosilicate hydrolysis gave products with similar XRD, thermogravimetric, and N₂ BET surface area properties. Although regular intercalation was not observed for any of the products, complete segregation of the clay and silica into separate phases was precluded by surface area values (250–460 m²/g) that were substantially larger than those from the pure silica (176–259 m²/g) and clay (50 m²/g) components. Thus, specific sol-clay interactions stabilize the sol particles against further particle growth during reaction. Such interactions are essential for the successful implementation of DIMOS routes to pillared clays with very large gallery heights. Additional pre-requisites for efficient DIMOS pathways to new generations of super gallery clays are identified and discussed.