Adsorbed

Adsorbed refers to a substance that has become attached to a surface by adsorption, a process in which molecules accumulate at an interface rather than being absorbed into the bulk. The adsorbed layer forms on solid or liquid interfaces and can influence the properties of both the surface and the adsorbate.

Two main mechanisms drive adsorption: physisorption, where the adsorption is mediated by weak van der Waals forces and is typically reversible and highly dependent on temperature; and chemisorption, which involves the formation of chemical bonds to the surface, is stronger, more specific, and often less readily reversible.

The amount adsorbed is described by adsorption isotherms. On a simple homogeneous surface, monolayer adsorption may dominate and can be described by Langmuir behavior, while heterogeneous or porous materials can support multilayer adsorption described by models such as the BET isotherm. In practice, surface area and porosity strongly influence adsorption capacity, with porous materials like activated carbon and silica offering large interfaces for onto-surface binding.

Adsorbed layers are studied through adsorption-desorption measurements, temperature-programmed desorption, and surface-sensitive spectroscopy or microscopy. Desorption processes can be induced by increasing temperature, reducing pressure, or changing the surrounding medium.

Applications of adsorption span catalysis, environmental remediation (for example, pollutant removal with activated carbon), gas separation, chromatography, and sensing. The presence of adsorbed species can modify surface properties such as wettability, reactivity, and electronic characteristics, making adsorption a central concept in surface science and materials engineering.