Layered Sodium Disilicates as Precursors of Mesoporous Silicas. Part I: Optimisation of the Synthesis Procedure of δ-Na₂Si₂O₅ and α-Na₂Si₂O₅

Optimization of the synthetic procedures described in literature aimed at preparing pure δ-Na₂Si₂O₅ has been carried out. The results show that a substantial shortening of the calcination time of amorphous silicate precursor is required, in order to minimize the appearance of the thermodynamically stable α-Na₂Si₂O₅. The use of commercial water glass solution rather than freshly synthesized silica/NaOH slurry is the preferred source of the starting amorphous silicate. Optimized preparative routes for synthesis of single-phase δ-Na₂Si₂O₅ and α-Na₂Si₂O₅ have been described.