molecular sieve

noun Chemistry.
a compound with molecule-size pores, as some sodium aluminum silicates, that chemically locks molecules in them: used in purification and separation processes.

Origin:
1925–30

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molecular sieve
 
n
chem a material that can absorb large amounts of certain compounds while not absorbing others and is thus suitable for use in separating mixtures

Collins English Dictionary - Complete & Unabridged 10th Edition
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molecular sieve

a porous solid, usually a synthetic or a natural zeolite, that separates particles of molecular dimension. Zeolites are hydrated metal aluminosilicate compounds with well-defined crystalline structures. The silicate and aluminate groupings form three-dimensional crystal lattices surrounding cavities in which the metal ions and the water molecules are loosely held. Channels run through the entire crystal, interconnecting the cavities and terminating at the crystal surface. Upon heating, the zeolites lose their water content with little or no change in their crystal structure. The dehydrated zeolite can reversibly absorb water or other molecules that are small enough to pass through the channels or pores. The metal ions are also readily replaceable by other ionic units of similar charge and size

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
Recently, a molecular sieve, desiccant-based heat wheel technology has been developed that actually improves indoor air quality.
To remove water from the desulfurized naphtha, the hydrocarbon feed is typically dried using molecular sieve.
The dilute acid was routinely used to leach alumina and molecular sieve beads.
Activated charcoal canister located in the molecular sieve unit.
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