On the crystallization mechanism of ETS-10 titanosilicate synthesized in gels containing TAABr

Thermal analysis of the products resulted during crystallization of ETS-10 by using starting co gels with molar composition 5.0 Na2O–3.0 KF–TiO2–6.4 HCl–TAABr–7.45 SiO2–197.5 H2O, where tetralkylammonium (TAA) are tetramethyl (TMA), tetraethyl (TEA), tetrapropyl (TPA) and tetrabutylammonium (TBA), was performed. The effect of TAA+ cations (ionic radius in hydrated forms, shapes and hydrophilic/hydrophobic character) on the crystallization of ETS-10 is evident from the induction time, ti (TMA+ ≪ TEA+ < TPA+ < TBA+), the rate of crystallization, R (TMA+ < TEA+ < TPA+ < TBA+), morphology and size of crystallites. Organic cations play a “pore filling” role rather than as a “structure-directing” agent. The relatively flexible molecules of the symmetric tetraalkylammonium cations mixed with alkali cations (Na+, K+) participate directly at prenucleation and nucleation steps by their interaction with the silicate and titanate in aqueous colloidal dispersion.