Alkylammonium derivatives of layered alkali silicates and micro- and mesoporous materials: I. Lithium sodium silicate (silinaite)

The layered lithium sodium silicate silinaite exchanges alkylammonium ions for interlayer lithium and sodium ions. This exchange increases the disorde r of the structure and leads to transformation of many Q(3) silicon oxygen groups into Q(4) groups. Owing to their large size the alkylammonium ions d isplace only a part of the inorganic interlayer cations. The remaining lith ium and sodium ions are replaced by protons, and the silanol groups (Q(3) S i) call condense to siloxane groups (Q(4) Si). Calcination of the alkylammo nium derivatives at 350-550 degrees C yields mesoporous materials with meso pore volumes of between 130 and 390 mu L g(-1) and micropore Volumes of bet ween 25 and 110 mu L g(-1). The diameters of the mesopores lie between 1.7 and 2.9 nm (from mesopore volumes and surface areas). In the same way, poro us materials with similar properties were prepared from other silica source s like sodium metasilicalite, delta-Na(2)Si(2)o(5) (SKS-6), and even water glass solutions. A mechanism is proposed based on the aggregation of alkyla mmonium ions carrying caps of the fragmented layers.