Pillaring Puckered Layer Silicates

Upon acid leaching or alkylammonium intercalation, KHSi2O5 is transformed into a silicic acid or a silicic acid intercalate, where in the structure pairs of SiO4 tetrahedra are alternately pointing on both sides of the basal hexagonal network of oxygens. A fraction of the layers is bound by siloxane bridges as shown by Si-29 MAS NMR, resulting in an interstratified structure. Pillaring with aluminum polyhydroxy polymers yields an interstratification of open and siloxane-bridged galleries having a surface area as high as 400 m(2)/g after drying at 100 degrees C and 200 m(2)/g after calcination at 500 degrees C. The galleries opened by the aluminum polyhydroxy polymers have cross sections between 10 and 30 angstrom and their volume is on the order of 0.12 mL/g in the favorable cases. High-resolution Al-27 magic-angle-spinning (MAS) NMR detects three distinct resonance lines corresponding to three kinds of aluminum sites. One is a "framework" tetrahedral Al within a Si Q(4) 5678(1Al) environment. The other two lines at 0 and 30 ppm belong to "nonframework" aluminum. The 0 ppm line is that of octahedral Al, whereas the third resonance at similar to 30 ppm may be assigned either to strongly distorted tetrahedral Al or to pentacoordinated Al. The pillaring mechanism, which is very different from that observed for clay minerals, is discussed.