Surface Chemistry
2.0 Adsorption
2.0 Adsorption
The phenomenon of attracting and retaining the molecules of a substance on the surface of a liquid or a solid is known as adsorption. Adsorption is a surface phenomenon and is therefore a fairly rapid process.
The substrate (solid surface) on which adsorption takes place is called the adsorbent; while the adsorbed material (a gas or a liquid) is called adsorbate. The common surface between the two phases where the adsorbed molecules concentrate is called interface.
The term adsorption should be distinguished from absorption.
The term adsorption refers to the attraction and retention of the molecules of a substance only on the surface of the solid while the term absorption refers passing of the substance through the surface into the bulk of the solid. Since absorption involves diffusion into the interior of the mass, it is a slow process. In absorption, substance is uniformly distributed throughout the substance and occurs at a uniform rate.
Sometimes adsorption may be followed by the dissolution of the adsorbed substance (adsorbate) in the adsorbent, i.e., at first stage the material appears (is adsorbed) on the surface of the adsorbent (adsorption) and then passes into the bulk of the adsorbent (absorption). This happens when hydrogen is taken up by metallic palladium.
The two processes when considered together are known as sorption, the reverse of sorption, i.e., the release of absorbed or adsorbed substance into the surrounding medium is termed desorption. Sorption of gases by metals is known as occlusion.
