adsorbs

Adsorption is the process by which atoms, ions, or molecules from a gas, liquid, or dissolved phase accumulate on a solid surface, forming a film at the interface. The material accumulated on the surface is the adsorbate, and the surface that holds it is the adsorbent. Adsorption is distinct from absorption, where substances diffuse into a bulk phase.

There are two main types: physical adsorption (physisorption), driven by weak van der Waals forces, and chemical adsorption (chemisorption), involving stronger chemical bonds.

Factors influencing adsorption include surface area and porosity of the adsorbent, the chemical nature of the adsorbate, temperature, pressure, and the solvent or medium. Higher surface area and suitable pore structure generally increase capacity.

Common adsorbents include activated carbon, silica gel, alumina, zeolites, clays, ion-exchange resins, and newer materials such as metal-organic frameworks.

Isotherms describe equilibrium. The Langmuir model assumes monolayer adsorption on a homogeneous surface, while the Freundlich model applies to heterogeneous surfaces. Other models address multilayer adsorption and interactions.

Kinetics describe how fast adsorption occurs and may involve external mass transfer, intraparticle diffusion, and surface reaction steps; models include pseudo-first-order and pseudo-second-order equations.

Applications span water treatment (removal of dyes, pesticides, and heavy metals), air purification, solvent recovery, catalysis as a support for active species, and separation technologies such as chromatography.

Regeneration of spent adsorbents by heating, solvent washing, or pressure swing adsorption enables reuse, while spent materials require proper handling to manage hazardous contaminants.

Quantitative metrics include adsorption capacity (often mg of adsorbate per g of adsorbent) and surface area measurements by the BET method, used to compare materials.