The study of adsorption has quite a long history. The first document on adsorption is considered to be the study of adsorption behavior of charcoal by Fontana published in 1777. In 1814, N.T. Saussure did a lot of adsorption experiments onto charcoal. Now, his adsorption apparatus is exhibited in the National Historical Museum in England. Today's adsorption technology is widely used in the industrial process (e.g. gas and vapor separation) and for the characterization of fine materials.
An example of adsorption is visualized in the figure below. The figure shows the difference between chemisorption and physisorption. Generally, if the interaction between the adsorbate and adsorbent is strong (e.g. hydrogen bonding or acid-base adsorption), preventing desorption of the adsorbate by vacuuming at the given adsorption temperature or room temperature, it is called chemisorption. Physisorption, on the other hand, is the weak interaction mainly due to the van der Waals forces. The adsorbate can be easily desorbed by vacuuming. Recently, instead of using the terms "physisorption" and "chemisorption", "reversible" and "irreversible" adsorption have come into use.
Adsorption state
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