Nanozeolites:  Synthesis, Crystallization Mechanism, and Applications

Abstract

This review focuses on the synthesis, crystallization mechanism, and application of colloidal zeolites. The synthesis formulations and features of different zeolite-type structures prepared in nanosized form are summarized. Special attention is paid to zeolites prepared as stable colloidal suspensions. Next, new insights into zeolite crystallization mechanism gained by using colloidal zeolites as model systems are discussed. Further, the methods for deposition of zeolite nanocrystals from suspensions onto supports of different shapes and compositions used for the fabrication of zeolite films and membranes are reviewed. The use of colloidal zeolites for the fabrication of hierarchical macrostructures is also described. Other uses of nanozeolites for the preparation of functionalized materials, for the synthesis of mesoporous silicas of improved hydrothermal stability, and as seeds for zeolite syntheses are illustrated. The emerging applications of nanozeolites in sensing, optoelectronics, and medicine constitute another topic in this review. Finally, some future trends in the area are envisaged.

Synthesis of hierarchical porous materials with ZSM-5 structures via template-free sol–gel method

“…The first step consists of the preparation of ZSM-5 precursor sol. In a typical synthesis, 25.4 g of 20% aqueous solution of TPAOH was added to the mixture of 20.8 g of TEOS and 0.4 g of Al(i-OPr) 3 under vigorous stirring at 273 K to obtain a turbid solution with molar composition of 1.0TEOS: 0.02Al(i-OPr) 3 : 0.25TPAOH: 11.3H 2 O. Clear ZSM-5 precursor sol containing a little floccule was obtained by stirring the turbid solution at 323 K for 48 h. In the second step, the ZSM-5 precursor sol filtrated floccule was dried at 303 K in a vacuum box retaining the vacuum value of 6.65 kPa until it became xerogel.…”

“…However, their small pore size brings diffusion and mass transfer limitations, which can be solved by using zeolite nanocrystals [2]. Unfortunately, nanozeolites cannot be used directly due to the much higher pressure drops in packed-bed reactors and difficulty of separation [3]. Currently, interests are focused on preparation of hierarchical porous materials with zeolite structures.…”

Potential uses of natural zeolites for the development of new materials: short review

“…Nanozeolites are a type of zeolites, which have narrow particle size distribution with sizes of less than 200 nm [36]. Compared to "ordinary" zeolites of which the particle diameters are of micrometer order, nanozeolites represent very small particle size, and especially, the fact that they are composed of discrete particles (single crystals) rather than aggregates.…”

Mesostructured Zeolites: Bridging the Gap Between Zeolites and MCM-41

“…One method involves the preparation of nano-sized zeolite particles to increase the external surface area and shorten the diffusion path lengths. [17][18][19][20][21] Nevertheless, zeolite nano-particles with crystal size below 100 nm not only may cause filtration problems due to their colloidal nature, but also a decrease of micropore volume and a reduction of thermal/hydrothermal stability corresponding to the poor crystalline structures. 6 Another procedure usually applied to improve the diffusion of large-sized molecules into the host porous materials is the synthesis of extra-large pore zeolites with channel windows circumvented by more than 12 T atoms.…”