Introduction
In the field of materials science, two common types of adsorption include chemisorption and physisorption. Both of these processes involve the adsorption of molecules or ions onto a solid surface, resulting in the formation of an adsorbate layer. Chemisorption is a form of surface adsorption in which atoms or molecules are physically attracted to a surface and form strong covalent chemical bonds. The forces that produce the attachment are typically quite strong and the bonds are believed to be more permanent than those of physisorption. Physisorption, on the other hand, is a form of adsorption in which molecules or ions are held onto a surface due to physical forces such as London (van der Waals) forces, hydrogen bonding or electrostatic interactions. These forces are weaker than those of chemisorption and the bonds are typically more easily broken. Therefore, the adsorbate layers formed through physisorption tend to be more easily displaced or removed from a surface compared to those formed through chemisorption.
Chemisorption
Chemisorption is a special form of adsorption in which a material adsorbs molecules or ions and forms a chemical bond with them. The adsorbed molecules or ions remain on the surface of the material due to strong chemical bonding between the molecules or ions and the surface atoms. This type of adsorption is often referred to as “surface-bonding”. The adsorbent molecules are normally covalently bonded to the surface and the adsorbed species remain bound to the surface until the bond is broken by the application of energy. The bonds formed in chemisorption are relatively strong and may be either ionic or covalent, depending on the type of atoms or molecules involved.
In general, chemisorption is considered to be more permanent than physisorption. This is because the binding forces between the adsorbent molecules and the substrate are stronger, and thus, it is harder to disrupt the adsorbed layer. Chemisorption occurs at relatively high temperatures, often between 300 and 600°C, and involves the dissociation of molecules (e.g. water molecules) and the diffusion and attachment of species (e.g. hydrogen and oxygen) to the surface of the material.
Physisorption
Physisorption is a type of adsorption in which molecules or ions are held onto a surface due to physical forces such as London (van der Waals) forces, hydrogen bonding or electrostatic interactions. This type of adsorption is much weaker than chemisorption and the adsorbed layer is usually less permanent. The molecules or ions adsorbed will typically remain on the surface for a much shorter period of time than those that are chemisorbed to the material. Additionally, physisorption can occur at relatively low temperatures (e.g. room temperatures or lower) and does not involve the dissociation of molecules or the diffusion of species onto the surface.
The forces of physisorption are typically induced by the interaction between two molecules or ions. These forces are weaker than those of chemisorption and the bond that is formed is easily broken by the application of energy. The adsorbate layer formed is much less rigid and less permanent than that formed through chemisorption. Additionally, the adsorption that occurs is not bound to a specific type of compound; instead, it can occur to almost any type of compound, regardless of its chemical nature.
Conclusion
In summary, chemisorption and physisorption are two common forms of adsorption that involve the attachment of molecules or ions to a solid surface. Chemisorption involves the formation of strong covalent bonds between the adsorbed species and the surface atoms, while physisorption involves the weaker physical forces that occur between two molecules or ions. The forces that produce chemisorption are typically much stronger than those of physisorption, resulting in a more permanent adsorbate layer. However, physisorption is generally quicker and easier to achieve than chemisorption, as it does not involve the transfer or dissociation of molecules and can occur at relatively low temperatures.
