Adsorbent vs Absorbent – Difference and Comparison

What is Adsorbent?

An adsorbent is any insoluble material that does not allow any solid, liquid, or gaseous substance to exude its surface. The molecules, ions, or atoms settle down on their surface and are not absorbed. The adsorbed substance is called adsorbate, and the adsorbed substance is called adsorbent. German physicist Heinrich Kayser first iterated the term ‘adsorption’ in 1881. 

There are two kinds of adsorption 1: physical adsorption or physisorption, and 2. chemisorption.  Physical Adsorption refers to the intermolecular attraction between a solid and the substance adsorbed, making it a readily reversible and multi-layered phenomenon. Chemisorption refers to the chemical reaction between the solid and the substance absorbed. This is an irreversible phenomenon and stronger than physical adsorption. It is a single-layered phenomenon primarily. 

The process of adsorption is essential for humankind, and for revolutionary processes. They are used for making air pollution masks. They are made of silica gel and activated charcoal powder, so when dust particles or smoke cannot pass through them, they are adsorbed on the material’s surface. The adsorption process is also used to purify water and remove moisture and humidity. This principle is used in many devices for the application of purification.

What is Absorbent?

An absorbent is any material that permits the molecules to permeate its surface and enter its volume of space. There are two types of absorption processes:- 1. Chemical Absorption, 2. Physical Absorption. The substance soaked up and absorbed within another substance is called absorbate. The absorbent is the surface that absorbs the absorbate, e.g., when water gets absorbed on calcium carbonate.

Chemical Absorption refers to the absorption of chemicals in one state by the chemicals in another state. It is also called reactive absorption. In this type of absorption, there is a reaction between the absorbed and the absorbing elements. An example can be the absorption of gases by liquid or solid material.

Physical Absorption refers to a process in which a reaction does not occur as part of the absorption process. If the absorbed and absorbing molecules have various elements that have contrasting tendencies, there are possibilities of a physical and chemical absorption to coincide.

There is another phenomenon where absorption and adsorption co-occur, called ‘sorption’. Sorption refers to the process when the molecules accumulate on the surface of solid or liquid substances. At the same time, the molecules are getting soaked up inside the bulk of a solid or liquid substance. An example of sorption will be the dipping of a sponge in water, where both the endothermic and exothermic processes occur at the same time.

Difference Between Adsorbent and Absorbent

1. Adsorbents are materials in which molecules and atoms are attached to the surface of it. But absorbents are molecular substances in which the liquid or gaseous molecules get sucked into it.
2. Adsorbents are surface materials which is why adsorption is called a surface phenomenon whereas absorbents are bulk substances, hence absorption is a bulk phenomenon. 
3. In the adsorbent’s behavioral pattern the concentration of adsorbate molecules is not uniform. But absorbents have the opposite behavioral pattern, the absorbates are uniformly distributed within the absorbent. 
4. The reaction rate of molecules, in contact with adsorbents, increases rapidly and reaches a state of equilibrium. But the reaction rate is consistently uniform throughout the entire process when molecular and gaseous substances submerge within absorbents. 
5. Adsorbent materials are silica gel, zeolites, and activated alumina. But the examples of absorbents are cotton wool, bath mat, and towel.

Comparison Between Adsorbent and Absorbent

References

1. https://www.sciencedirect.com/science/article/pii/S1687404813000552
2. https://www.sciencedirect.com/science/article/abs/pii/S1381514807000545