The adsorption type of activated carbon is different according to the adsorption force of the solid surface. The adsorption can be divided into three types: physical adsorption, chemical adsorption and ion exchange adsorption:
Physical adsorption
The adsorption of the adsorbent and the adsorbate (solute) through the molecular force is called physical adsorption. This is the most common type of adsorption phenomenon. It is characterized in that the molecules of the adsorbate are not attached to the fixed point of the adsorbent, but can be moved freely on the interface. Since the adsorption is caused by molecular forces, the adsorption heat is small, and the physical adsorption does not require activation energy, and can be carried out under low temperature conditions. This adsorption is reversible, and the adsorbed molecules in the adsorption are also separated from the solid appearance by the sub-thermal motion, and this phenomenon is called desorption. Physical adsorption may constitute a single molecule adsorption layer or a multi-molecular adsorption layer. Because intermolecular forces are ubiquitous, an adsorbent can adsorb a variety of substances, but because the nature of the adsorbate (solute) is different, the amount of adsorption is also different. This adsorption appearance is closely related to the appearance of the adsorbent and the pore dispersion.
Chemical adsorption
The chemical bond between the adsorbent and the adsorbate (solute) causes a chemical reaction to bind the adsorbent to the adsorbate (solute). Because the chemical reaction requires a lot of activation energy, it is usually required to be carried out at a higher temperature, and the adsorption heat is large. Chemical adsorption is a selective adsorption, that is, an adsorbent only has an adsorption effect on certain or specific substances. Because chemisorption is carried out by the direct chemical bond between the adsorbent and the adsorbate, chemisorption can only form a single layer, and the adsorption is relatively stable and difficult to desorb. This adsorption is directly related to the external chemical properties of the adsorbent. It is related to the chemical nature of the adsorbate.
AC adsorption
The ions of a substance are concentrated on the charged point on the surface of the adsorbent due to electrostatic attraction. During the adsorption process, the ions of the same amount of ions are exchanged, that is, ions adsorbing one adsorbate (solute). The adsorbents together emit an equal amount of ions, ie ion exchange. The charge of ions is a determining factor in AC adsorption. If the concentration of the adsorbate (solute) is the same, the more charge the ion carries, the stronger its adsorption on the anti-charge point on the surface of the adsorbent. With regard to ions with the same charge, the smaller the hydration radius, the closer it is to the adsorption point, which is advantageous for adsorption. Physical adsorption and chemical adsorption agree that ion exchange adsorption often exists together. In the activated carbon adsorption process, three kinds of adsorption induction effects are used to reach the intention of removing the pollutants. Regarding different adsorbed substances, the effects of the three kinds of adsorption are different.