Characterization of titanosilicate ETS-4 crystals grown from synthesis mixtures of different alkalinity

Synthesis of large ETS-4 crystals in the Na and Na/K systems: the effects of alkali metal ion and synthesis mixture alkalinity

“…The Ti content of these ETS-4 crystals increased with increasing pH [9]. This was hypothesized to be due to the relatively smaller number of Ti vacancies (i.e., more ordered structure) [9]. In the present contribution, the effects of synthesis mixture Si/Ti ratio and initial pH, type of pH modifier, and utilization of K ions in a pure Na system on ETS-4 crystal size and morphology is reported.…”

“…The central location of the spiral hillocks suggests that the screw type line defects were generated at the early stages of growth. Growth spirals were observed on the {1 0 0} surfaces of ETS-4 crystals synthesized by utilizing both organic and inorganic precursors, and the characteristic step height was measured to be $1.1 nm by AFM [8,9,[12][13][14]. This value is equal to the half unit cell length in the {1 0 0} direction, which is also equivalent to the combination of two building units forming the ETS-4 framework: a titanosilicate chain containing octahedral titanium, and a bridging unit containing semi-octahedral titanium [12,13].…”

“…This value is equal to the half unit cell length in the {1 0 0} direction, which is also equivalent to the combination of two building units forming the ETS-4 framework: a titanosilicate chain containing octahedral titanium, and a bridging unit containing semi-octahedral titanium [12,13]. The presence of growth spirals on the {1 0 0} surfaces of the monolithic crystals was attributed to the relatively low supersaturation levels in their syntheses [8,9,[12][13][14][15]. This occurs at least during the final stages of crystallization and is hypothesized to result in the growth of the {1 0 0} surfaces only by the flow of spiral steps generated at surface defects.…”

“…However, their method involved the initial formation of another crystalline phase, GTS-1, followed by its recrystallization [4]. We have previously reported the direct synthesis of ETS-4 crystals with controlled morphology [8] and their physicochemical characterization [9]. The initial pH of the synthesis mixture was varied in the range of 11.50-12.90 by modifying the sulfuric acid content [8].…”

“…As a result, a progressive change of ETS-4 morphology from spherulitic particles of submicron crystallites to monolithic crystals with rectangular prism morphology and relatively small average dimensions $1 Â 15 Â 2 mm was achieved [8]. The Ti content of these ETS-4 crystals increased with increasing pH [9]. This was hypothesized to be due to the relatively smaller number of Ti vacancies (i.e., more ordered structure) [9].…”