分子篩，一種多孔固體，通常是合成或天然沸石，用于分離分子尺寸的顆粒。沸石是水合金屬鋁硅酸鹽化合物，具有明確的晶體結構。硅酸鹽和鋁酸鹽群在空腔周圍形成三維晶格，金屬離子和水分子松散地固定在空腔中。通道貫穿整個晶體，將腔相互連接，并在晶體表面終止。加熱后，沸石失去水分，其晶體結構幾乎沒有變化。脫水沸石可以可逆地吸收水或其他小到足以通過通道或孔隙的分子。金屬離子也很容易被其他電荷和大小相似的離子單元所取代。
分子篩用于干燥氣體和液體，并根據分子的大小和形狀分離分子。當兩個分子同樣小并且可以進入孔隙時，分離是基于分子的極性（電荷分離），更極性的分子優先被吸附。比較凝膠色譜法。
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.
Molecular sieves are used for drying gases and liquids and for separating molecules on the basis of their sizes and shapes. When two molecules are equally small and can enter the pores, separation is based on the polarity (charge separation) of the molecule, the more polar molecule being preferentially adsorbed. Compare gel chromatography.