gasadsorption

Gas adsorption is the process by which gas molecules accumulate on a solid surface, driven by physical or chemical interactions at the solid–gas interface. It is commonly categorized into physisorption, governed by weak van der Waals forces and usually reversible, and chemisorption, involving stronger chemical bonds and often irreversible or with specific reaction pathways. Physisorption can yield multilayer adsorption, while chemisorption typically forms a fixed number of binding sites.

Adsorption isotherms describe how the amount of gas adsorbed depends on pressure at a fixed temperature. The Langmuir model assumes single-layer adsorption on a uniform surface, whereas the BET (Brunauer–Emmett–Teller) theory extends to multilayer adsorption and is widely used to estimate a material’s surface area from gas isotherms, typically using nitrogen at 77 K. Isotherm analysis also provides information on porosity and pore size distribution, using methods such as BJH or nonlocal density functional theory (NLDFT). Pressures are often reported as relative pressure (P/P0), and surface area is given in square meters per gram (m2/g).

Porous materials are central to gas adsorption. Micropores (<2 nm), mesopores (2–50 nm), and macropores (>50 nm) control accessibility and capacity. Common adsorbents include activated carbon, silica and zeolites, metal-organic frameworks (MOFs), and porous polymers. The adsorbed gas can be used for storage (e.g., hydrogen, methane), separation and purification (e.g., CO2 capture, gas purification), catalysis (as a reactant concentration on active sites), and sensing (adsorption-induced changes in electrical or mechanical properties).

In summary, gas adsorption is a foundational phenomenon for characterizing surface area and porosity and for enabling practical applications across energy, environment, and materials science.