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.