Temperature and time controlled crystallization in Na2O–SiO2–TiO2–H2O system

Abstract

Phase formation upon hydrothermal crystallization of sodium titanosilicates has been studied in detail. It was shown that an excessive amount of Na and Si with respect to Ti affects the crystallization. It demonstrates that in a clear starting solution, high crystalline microporous titanosilicate (CST, Na 2 Ti 2 SiO 7 ·2H 2 O) with sitinakite structure can be formed in 6 h and the crystallization is controlled by nucleation. With less amount of water, CST can be formed in 2 h. At low NaOH content, ETS-4 forms in 2 h at 230 °C. By simply increasing NaOH content in starting mixture, the crystallinity of CST improved. With increasing synthesis time CST re-crystallized to AM-4 with unusual hierarchal morphology. The synthesis temperature has a clear influence on the phase formation. At low synthesis temperature, a material with ivanyukite structure (GTS-1) was obtained in 4 h at 150 °C. Additionally, we discussed evidence for CST/GTS-1 intergrowths. The rapid crystallization of the microporous titanosilicates CST (TAM-5), GTS-1, ETS-4, and layered AM-4 can be achieved by adjusting NaOH content, synthesis temperature and time. • The rapid crystallization of the microporous titanosilicates CST (TAM-5), GTS-1, ETS-4, and layered AM-4 has been achieved. • The rapid formation of high crystalline CST from clear synthesis solution is controlled by nucleation. • The first observation of CST to AM-4 phase transformation is revealed. • The evidences of temperature controlled CST/GTS-1 intergrowth are provided.