Chemisorptio

Chemisorptio is the adsorption of a molecule or atom onto a solid surface through the formation of chemical bonds between the adsorbate and the surface. This contrasts with physisorption, which involves weaker van der Waals interactions without new bonds and generally occurs with lower binding energies.

In chemisorption, electronic exchange or sharing occurs, leading to higher binding energies and a significant rearrangement of electronic structure at the interface. The process can be dissociative, where a molecule splits and each fragment bonds to the surface, or associative, where the intact molecule binds by sharing electrons with surface states. Because a chemical bond must form, chemisorption often has an activation barrier and is highly dependent on temperature, surface structure, and adsorbate identity.

The adsorption is typically localized to specific active sites and can approach a monolayer coverage. Corresponding isotherms are often modeled by Langmuir-type descriptions, though real surfaces may show heterogeneity and lateral interactions. Kinetics are governed by the rate of arrival at the surface and the surface reaction step, which can limit overall adsorption rates. Desorption usually requires higher temperatures or chemical change, which can make chemisorption more nearly irreversible under modest conditions.

Chemi sorption is central to heterogeneous catalysis, sensor design, corrosion science, and surface modification. Common examples include hydrogen chemisorption on metal surfaces, and carbon monoxide or oxygen chemisorption on transition metals. Analytical techniques such as temperature-programmed desorption, X-ray photoelectron spectroscopy, infrared spectroscopy, and scanning probe microscopy are used to study chemisorption.