adsorbateille

Adsorbates are atoms, ions, or molecules that accumulate on a solid surface, forming an adsorbed layer, or adsorbate. The process is adsorption, distinguished from absorption, which involves entry into the bulk. Adsorbates interact with the surface via physisorption or chemisorption. Physisorption involves weak van der Waals forces and is typically reversible and temperature-dependent; chemisorption involves the formation of chemical bonds and can be highly selective and often irreversible at room temperature.

Adsorbates and the underlying material (adsorbent) form the surface complex. The extent of adsorption is governed by surface area, porosity, site distribution, temperature, pressure, and the chemical potential of the adsorbate. On gas-solid systems, adsorption is often described by isotherms such as Langmuir (monolayer, homogeneous sites), Freundlich (heterogeneous surfaces), and BET (multilayer adsorption). In liquid-phase adsorption, competitive adsorption and desorption play key roles.

Adsorbates are central to catalysis, environmental remediation, gas storage, and sensing. In heterogeneous catalysis, reactants adsorb on active sites, react, and desorb as products. Common adsorbates include water on oxides, CO on metal catalysts, dyes on activated carbon, and pollutants on zeolites.

Characterization methods include gravimetric measurements, calorimetry, X-ray photoelectron spectroscopy, infrared spectroscopy, and adsorption isotherm fitting, often alongside microscopy. This field informs design of adsorbents, catalysts, and sensors by describing how species interact with surfaces at molecular level.