Adsorption, which should not be confused with absorption, is a surface phenomenon in which gas or liquid molecules attach themselves to the solid surfaces of adsorbents. The adsorbed molecules are the adsorbate. If the energy or kinetic conditions allow the molecule to penetrate into the adsorbing phase, adsorption occurs.
Adsorption depends on the property of solid surfaces to fix certain molecules reversibly by weak Van der Waals type bonds. This property is related to the structure of the solid where, on the surface, there are still unbalanced forces resulting from dissymmetry in atom distribution: the formation of a layer of adsorbed molecules partially compensates this imbalance.
The main adsorbent materials on the market are:
Active charcoal, an adsorbent material. © wikipedia-creative commons