Desorption

Desorption is defined as the process of removing an adsorbed substance from the surface it was adsorbed onto -- it is, in effect, the reverse of adsorption. Where adsorption is the surface accumulating a substance from the surrounding gas, liquid or solution, desorption is that same substance leaving the surface again and returning to the surrounding phase. Because physisorption (Section 11.3.1) is held together only by weak van der Waals forces, it is easily desorbed by lowering the pressure of the surrounding gas or by raising the temperature -- both of which reduce how favourable it is for the adsorbate to stay stuck to the surface. Chemisorption (Section 11.3.2), by contrast, involves genuine chemical bonds between adsorbate and adsorbent, so it is much harder to reverse and is generally treated as irreversible under ordinary conditions. Desorption is practically important wherever an adsorbed layer needs to be removed or refreshed -- for i …