Molecular sieve, principle, function

Molecular sieves refer to a class of materials with uniform micropores whose pore sizes are comparable to those of ordinary molecules. Molecular sieves have a wide range of applications; they can be used as efficient desiccants, selective adsorbents, catalysts, ion exchangers, etc. However, the cost of synthesizing molecular sieves from chemical raw materials is very high. Commonly used molecular sieves are crystalline silicates or aluminosilicates, which consist of silicon oxide tetrahedra or aluminum oxide tetrahedra connected by oxygen bridge bonds to form a network of pores and cavities with a molecular size (usually 0.3–2 nm). Due to the different sizes and shapes of the molecules they can adsorb, they possess the ability to separate fluid molecules of various sizes. Function: It can distinguish molecules with different particle sizes, as well as unsaturated and polar molecules that are adsorbed. Working principle: Adsorption function: The adsorption of substances by molecular sieves is based on physical adsorption (Van der Waals forces). The crystal pores possess a strong polarity and Coulombic field, which enables them to exhibit a strong adsorption capacity for polar molecules (such as water) and unsaturated molecules. Screening function: The pore size distribution of molecular sieves is highly uniform; only substances with a molecular diameter smaller than that of the pores can enter the interior of the molecular sieve’s pores. Molecules of different substances are distinguished by their adsorption priority and size, which is why they are aptly called \"molecular sieves\".

Selecting molecular sieves based on molecular diameter enables selective adsorption and separation

It generally serves as an adsorbent and for filtration (sieving)