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

Abstract

The layered lithium sodium silicate silinaite exchanges alkylammonium ions for interlayer lithium and sodium ions. This exchange increases the disorder of the structure and leads to transformation of many Q3 silicon oxygen groups into Q4 groups. Owing to their large size the alkylammonium ions displace only a part of the inorganic interlayer cations. The remaining lithium and sodium ions are replaced by protons, and the silanol groups (Q3 Si) can condense to siloxane groups (Q4 Si). Calcination of the alkylammonium derivatives at 350–550°C yields mesoporous materials with mesopore volumes of between 130 and 390 µL g−1 and micropore volumes of between 25 and 110 µL 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, porous materials with similar properties were prepared from other silica sources like sodium metasilicalite, δ-Na2Si2O5 (SKS-6), and even water glass solutions. A mechanism is proposed based on the aggregation of alkylammonium ions carrying caps of the fragmented layers.