adsorb

Adsorb is a verb used in surface science to describe the accumulation of atoms, ions, or molecules (adsorbates) on the surface of a solid or liquid (adsorbent). Adsorption occurs at interfaces and is driven by intermolecular forces, contrasting with absorption, where a substance penetrates into the bulk of another.

An adsorbent is a material with surfaces that promote adsorption, such as activated carbon, silica gel, zeolites, alumina, and clays. The adsorbate is the species being adsorbed. Adsorption can be classified by mechanism: physisorption (physical adsorption), which involves weak van der Waals forces and is typically reversible and favored at lower temperatures; and chemisorption (chemical adsorption), which involves stronger chemical bonds and may be irreversible or require activation energy.

Factors influencing adsorption include the surface area and porosity of the adsorbent, the nature and concentration of the adsorbate, temperature, and pressure. Adsorption is often described by isotherms, with Langmuir isotherms modeling monolayer adsorption on a homogeneous surface with finite sites, and Freundlich isotherms describing adsorption on heterogeneous surfaces without a fixed capacity.

Kinetics and thermodynamics of adsorption depend on system conditions; physisorption is generally exothermic and decreases with rising temperature, while chemisorption can involve activation steps. Desorption or regeneration of adsorbents is common in practical use, enabling repeated cycles in processes such as drying, purification, or catalysis.

Applications span environmental cleanup (removal of pollutants from air and water), gas separation and purification, heterogeneous catalysis, chromatography, sensors, and surface characterization. Adsorption measurements and surface area determinations frequently employ techniques like BET analysis using nitrogen adsorption.