Desorbing

Desorbing is the process by which molecules that are adsorbed on a surface detach and move into the surrounding phase. Desorption is the reverse of adsorption and is a fundamental step in many surface phenomena, including catalysis, sensing, filtration, and gas sorption. Desorbing can occur at solid–gas, solid–liquid, or solid–solid interfaces, depending on the system and conditions.

Desorption can proceed through several mechanisms. Thermal desorption uses heat to supply the energy required to overcome binding between the surface and the adsorbate. Photodesorption involves photons transferring energy to promote detachment. Chemical desorption occurs when surface reactions release products that leave the surface, and electron- or ion-stimulated desorption uses energetic particles to eject adsorbates. The dominant mechanism depends on the material, temperature, and binding strength.

Kinetics and factors: The rate of desorption generally increases with temperature and decreases with stronger binding and higher surface coverage. Desorption can follow different kinetic orders (often first order for isolated species), and is typically analyzed with activation energies and Arrhenius-type expressions. Surface roughness, porosity, and co-adsorbates can alter desorption energies and rates. In steady conditions, desorption competes with adsorption and transport processes.

Applications and methods: Experimental techniques such as temperature-programmed desorption (TPD) and thermal desorption spectroscopy (TDS) quantify desorption by monitoring desorbed species as a function of temperature. Desorption studies inform catalysis design, environmental remediation, material science, and chromatography, where controlled release or recovery of adsorbates is relevant.