Adsorpce

Adsorpce, commonly translated as adsorption, is the process by which atoms, ions, or molecules (the adsorbate) accumulate on a solid surface (the adsorbent) from a surrounding gas or liquid. It is a surface phenomenon, in contrast to absorption, where substances penetrate into a bulk phase. Adsorption can be reversible or irreversible and is governed by intermolecular forces at the interface.

Two main mechanisms underlie adsorption: physisorption, where van der Waals forces hold the adsorbate to the surface; and chemisorption, involving chemical bonds that are typically stronger and more specific. Physisorption is usually reversible and favored at lower temperatures, while chemisorption often requires activation energy and can be more selective.

Factors influencing adsorption include the surface area and porosity of the adsorbent, the distribution of adsorption sites, and the properties of the adsorbate (such as size, polarity, and functionality). Conditions such as temperature, pressure (in the gas phase), and pH (in aqueous systems) strongly affect capacity. Common adsorbents include activated carbon, silica gel, alumina, zeolites, and metal-organic frameworks; targeted adsorbates include water, gases like CO2, and various organic pollutants.

Adsorption is described by isotherms, models that relate the amount adsorbed to conditions at a constant temperature. The Langmuir isotherm assumes monolayer adsorption on a uniform surface. The Freundlich isotherm describes adsorption on heterogeneous surfaces and multilayer formation. The Brunauer–Emmett–Talz (BET) model extends these concepts to multilayers for surface area determination.

Applications span environmental remediation (air and water purification), catalysis and catalyst support, gas separation and carbon capture, adsorption-based sensors, and analytical separation techniques such as chromatography. Adsorbents can often be regenerated by desorption through heating, reducing pressure, or changing the solvent, enabling reuse.