Description
Zeolite is a crystalline aluminosilicate with a three-dimensional cage built of corner-shared tetrahedral units 
and 
. Each tetrahedron 
gives the network a negative charge, which is compensated for by a cathion (H+, Na+, K+, Ca2+, NH+4, etc.) in most cases capable of cathion exchange.
The common empirical zeolite formula can be represented as
,
where
is the cathion charge, (
represents the silicon and aluminium molar ratio in the zeolite matrix, indicating the number positions for cathion exchange in the structure (
= 2-∞), 
is the amount of water in the system.
Tetrahedral units get connected to the secondary structural units, such as six-membered rings, five-membered rings, truncated octahedra, etc. The zeolite network contains interconnected channels and cavities, which form a porous structure with pore sizes of 0.3-1.0 nm. The average size of zeolite crystals can range from 0.5 to 30 microns. There are both natural and synthetic zeolites. The application of zeolites is based on their molecular sieve and ion exchange properties, they are used as adsorbents, catalysts, additives to detergents, etc.
and . Each tetrahedron gives the network a negative charge, which is compensated for by a cathion (H+, Na+, K+, Ca2+, NH+4, etc.) in most cases capable of cathion exchange. The common empirical zeolite formula can be represented as
, where
is the cathion charge, ( represents the silicon and aluminium molar ratio in the zeolite matrix, indicating the number positions for cathion exchange in the structure ( = 2-∞), is the amount of water in the system. Tetrahedral units get connected to the secondary structural units, such as six-membered rings, five-membered rings, truncated octahedra, etc. The zeolite network contains interconnected channels and cavities, which form a porous structure with pore sizes of 0.3-1.0 nm. The average size of zeolite crystals can range from 0.5 to 30 microns. There are both natural and synthetic zeolites. The application of zeolites is based on their molecular sieve and ion exchange properties, they are used as adsorbents, catalysts, additives to detergents, etc.
Illustrations
|
Zeolite NaA (LTA type structure, pore size 0.41 nm): а — structure; b — crystals. |
Authors
- Andrey V. Smirnov
- Nikolay N. Tolkachev
Sources
- D. Breck. Zeolite molecular sieves: structure, chemistry, and use. — Wiley, 1973. — 771 p.
- Szostak R. Molecular Sieves. — N.Y.: Van Nostrand Reinhol, 1989. — 524 p.