Template-free synthesis and structural evolution of discrete hydroxycancrinite zeolite nanorods from high-concentration hydrogels

Abstract

We report the synthesis and characterization of hydroxycancrinite zeolite nanorods by a simple hydrothermal treatment of aluminosilicate hydrogels at high concentrations of precursors without the use of structure-directing agents. Transmission electron microscopy (TEM) analysis reveals that cancrinite nanorods, with lengths of 200-800 nm and diameters of 30-50 nm, exhibit a hexagonal morphology and are elongated along the crystallographic c direction. The powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) and TEM studies revealed sequential events of hydrogel formation, the formation of aggregated sodalite nuclei, the conversion of sodalite to cancrinite and finally the growth of cancrinite nanorods into discrete particles. The aqueous dispersion of the discrete nanorods displays a good stability between pH 6-12 with the zeta potential no greater than -30 mV. The synthesis is unique in that the initial aggregated nanocrystals do not grow into microsized particles (aggregative growth) but into discrete nanorods. Our findings demonstrate an unconventional possibility that discrete zeolite nanocrystals could be produced from a concentrated hydrogel.

Exploratory Synthesis of Low-Silica Nanozeolites through Geopolymer Chemistry

“…For example, highly crystalline cancrinite (CAN) nanorods (diameter <40 nm) could be obtained by geopolymer gels by simply heating a geopolymer gel at temperatures between 90 and 120 °C. 18 By extending our previous work, we herein report exploration of geopolymeric synthetic conditions of nanozeolites and a resulting quaternary kinetic phase diagram of Na−Al−Si−H 2 O geopolymer system which show how compositional parameters influence the structure and morphology of the products.…”

“…On the basis of the BET analysis on the N 2 gas desorption isotherm (Figure S5), the product showed a high surface area (168 m 2 /g) and a large pore volume (0.84 cm 3 /g), which is mostly from the textural mesopores among the nanocrystallites. The micropore volume was negligible (0.008 cm 3 /g), as the micropores in the CAN structure are not accessible by N 2 gas molecules. , Our previous work showed that the CAN zeolite can be obtained as discrete nanorods with a high crystallinity upon longer heating (7 days) at a higher temperature (120 °C) …”

“…While geopolymerization process has been studied in the area of ceramics and cements, our studies have demonstrated that the innate gel structure of the products and their close relationship with the zeolite system , can be taken advantage of in producing nanozeolites in a convenient and straightforward manner. For example, highly crystalline cancrinite (CAN) nanorods (diameter <40 nm) could be obtained by geopolymer gels by simply heating a geopolymer gel at temperatures between 90 and 120 °C . By extending our previous work, we herein report exploration of geopolymeric synthetic conditions of nanozeolites and a resulting quaternary kinetic phase diagram of Na–Al–Si–H 2 O geopolymer system which show how compositional parameters influence the structure and morphology of the products.…”

“…26,27 Our previous work showed that the CAN zeolite can be obtained as discrete nanorods with a high crystallinity upon longer heating (7 days) at a higher temperature (120 °C). 18 In Figure 2C, SOD zeolites also appear as submicron-sized aggregates of nanosized primary nanocrystallites. The average diameter of the nanocrystallites is estimated to be 20 nm by applying the Scherrer equation to the PXRD pattern.…”

“…Recently, we have reported new synthetic routes for production of nanozeolites from high-concentration aluminosilicate gel. , This so-called “geopolymer gel” is produced through a geopolymerization process in which a high volume of amorphous aluminosilicate solid particles is dissolved in an alkaline solution . While geopolymerization process has been studied in the area of ceramics and cements, our studies have demonstrated that the innate gel structure of the products and their close relationship with the zeolite system , can be taken advantage of in producing nanozeolites in a convenient and straightforward manner.…”