Adsorptio

Adsorptio is the process by which atoms, ions, or molecules from a gas, liquid, or dissolved phase accumulate on a solid or liquid surface, forming an adsorbed layer. It is distinct from absorption, where substances penetrate into the bulk of the material. Adsorptio can occur through physical forces (physisorption) or chemical bonding (chemisorption). Physisorption involves weak van der Waals interactions and is typically reversible; chemisorption involves stronger chemical bonds and can be more specific and less easily reversed at ambient conditions.

The extent and rate of adsorptio depend on temperature, pressure, surface area and porosity of the adsorbent, and the chemical nature of the adsorbate. Common adsorbents include activated carbon, silica gel, zeolites, metal-organic frameworks, clays, and porous polymers. Adsorption isotherms describe how much is adsorbed at a given pressure or concentration at constant temperature; examples include Langmuir (monolayer adsorption) and Freundlich (heterogeneous surfaces). The Brunauer–Emmett–Teller method provides estimates of surface area from gas adsorption data, often using nitrogen.

Applications span environmental and industrial contexts: air and water purification, gas separation, catalyst supports, chromatography, sensors, and energy storage. Adsorptio is often reversible, and adsorbents are regenerated by heating, vacuum, or solvent washing, enabling repeated use.

Kinetics and selectivity depend on diffusion within pores and on surface chemistry. Governing concepts include surface area, pore size distribution, and interactions between adsorbate and adsorbent. The study of adsorptio draws on foundational models developed in the early 20th century by Langmuir and BET, among others.