Adsorption

Adsorption is the accumulation of atoms, ions, or molecules at a material’s surface, forming a layer at the boundary with another phase.

Adsorption isotherm: A relationship between the amount adsorbed and the pressure or concentration of a surrounding phase at fixed temperature. It describes the equilibrium loading of a surface as gas pressure or solution concentration changes.
Adsorbate: The substance whose atoms, ions, or molecules accumulate on a surface through adsorption. Its identity and concentration determine what can populate the surface layer.
Activated carbon: A porous carbon material processed to create a large internal surface area for adsorption. Its extensive pores capture dissolved contaminants and gases from fluids.
Desorption: The release of atoms, ions, or molecules from a surface into a surrounding phase. It reverses adsorption and governs regeneration of many adsorbents.
Adsorption hysteresis: A difference between adsorption and desorption paths at the same pressure or concentration. It signals that pore geometry or metastable states affect measured uptake.
Langmuir adsorption model: A model of adsorption onto identical sites that each bind at most one adsorbate, forming a single layer. Its finite-site assumption captures monolayer adsorption on idealized surfaces.
Adsorbent: A solid or liquid material whose surface takes up an adsorbate. Its surface chemistry and area provide the sites where adsorption occurs.
Pressure swing adsorption: A gas-separation process that alternates pressure to adsorb and release selected gas components. It exploits pressure-dependent adsorption to separate gases without a liquid solvent.
Ion exchange: A reversible exchange of ions between a solution and an insoluble material bearing charged sites. It can accompany adsorption but relies specifically on exchanging ions at charged sites.
Pore size distribution: A description of how pore volume or surface area varies across pore sizes in a material. Different pore sizes change access, confinement, and the shape of adsorption measurements.

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