Adsorption

Definition - What does Adsorption mean?

Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. The most common industrial adsorbents are activated carbon, silica gel and alumina.

Adsorption is a different process from absorption, in which a substance diffuses into a liquid or solid to form a solution. Adsorption is a surface-based process, while absorption involves the whole volume of the material.

Some industrial applications for adsorption are:

  • Air conditioning
  • Adsorption chillers
  • Synthetic resin
  • Water purification

Corrosionpedia explains Adsorption

Adsorption is the adhesion of a chemical species onto the surface of particles. It is the capability of all solid substances to attract to their surfaces molecules of gases or solutions with which they are in contact. Solids that are used to adsorb gases or dissolved substances are called adsorbents; the adsorbed molecules are usually referred to collectively as the adsorbate. For example, charcoal is an excellent adsorbent used in gas masks to remove poisons or impurities from a stream of air.

Adsorption is, similar to surface tension, a consequence of surface energy. It may occur due to electrostatic attraction. In general, adsorption processes can be classified as:

  • Physical adsorption - Resembles the condensation of gases to liquids and depends on the physical, or van der Waals, force of attraction between the solid adsorbent and the adsorbate molecules. There is no chemical specificity in physical adsorption, with any gas tending to be adsorbed on any solid if the temperature is sufficiently low or the pressure of the gas sufficiently high.
  • Chemical adsorption - Gases are held to a solid surface by chemical forces that are specific for each surface and each gas. Chemical adsorption occurs, usually at higher temperatures than those at which physical adsorption occurs.

Adsorption is present in almost all systems, whether it is physical, chemical or biological, and is widely used in industrial and commercial applications. For example:

  • Carbon as adsorption filters makes drinking water taste better.
  • Activated alumina removes harmful chemicals like fluoride and arsenic from liquids.
  • Synthetic resins can clean up highly hazardous spills.
  • Adsorption of molecules onto polymer surfaces is used in various applications such as in the development of non-stick coatings and in various biomedical devices.

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