Difference Between Adsorbent and Absorbent (With Table)

Adsorbent and absorbent are key elements of the physical process of adsorption and absorption respectively. Both sorption processes play a vital role in many natural as well as artificial processes. Adsorbent refers to any substance or material that can efficiently hold a liquid within its molecular fabric and boundaries. They are capable of soaking up liquids within themselves either partially or entirely. Adsorbent refers to any insoluble material capable of holding a definite amount of liquid in small chambers. 

Adsorbent vs Absorbent

The main difference between Adsorbent and Absorbent is that adsorbent is the process of accumulation of some amount of liquid or gas on the surface of a solid material, in contrast absorbent is the absorption of some amount of liquids and gas into an absorbent material. 

Adsorption is the ‘adherence of molecules, ions, and atoms’ stemming from a dissolved solid, liquid, or gas settling on a solid surface. One prime example of an adsorbent can be silica gel. Adsorption is a purely surface phenomenon because the gas or liquid is not absorbed within the solid material.

Absorption is called as permeation process of a gas or liquid into a porous and absorbent material. Examples of absorbents can be cotton wool, bath mat, towels, paper towels. Absorption is not a pure surface process as the liquid or gas is evenly dissolved into the absorbent material.

Comparison Table Between Adsorbent and Absorbent

Parameters of ComparisonAdsorbentAbsorbent
DefinitionAn adsorbent is the deposition of molecular species, ions, and atoms onto a surface. An absorbent is any solid material that allows liquid or gas to be uniformly assimilated or absorbed within it.
Nature It is endothermic.It is exothermic
Process of WorkingIn the process of adsorption, a substance forms a layer on the surface of the object.In the process of absorption, a liquid or gaseous substance moves inside the solid surface.
UsesAdsorbents are used for industrial purposes, for example, activated charcoal, water purification, and synthetic resins.
Absorbents are widely used for household purposes, for example, sponges to clean utensils, etc.
Inclusion of Scientific ProcessAdsorption involves the operation of adhesion.Absorption includes the process of dissolution and diffusion.

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.

Main Differences 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.

Conclusion

In a nutshell, absorbents and adsorbents are essential to carrying out day-to-day tasks and industrial applications. It is very confusing to understand and recall the difference between the two because of similar spellings, the only difference being the alphabets ‘b’ and ‘d’. But both are complete opposites. 

The absorbents allow the molecules to penetrate their surface, restricting them and settling them onto their surface. The absorption process is related to the volume, while the adsorption process is related to the surface. The former is unaffected by the temperature, and low temperatures favor the latter.

References

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