Adsorption
Adsorption is a fundamental surface phenomenon where atoms, ions, or molecules from a gas, liquid, or dissolved solid adhere to the surface of an adsorbent. Unlike absorption, which involves a substance permeating the entire bulk of a material, adsorption is strictly a boundary-layer process.
The Mechanism of Surface Adhesion
Adsorption occurs due to the imbalance of attractive forces on the surface of a solid. When a "solute" (the adsorbate) comes into contact with a high-surface-area solid (the adsorbent), it is captured through two primary pathways:
- Physisorption (Physical Adsorption): Driven by weak van der Waals forces. This process is generally reversible and occurs at low temperatures.
- Chemisorption (Chemical Adsorption): Involves the formation of strong chemical bonds between the surface and the adsorbate. This is typically irreversible and requires activation energy.
Engineering Significance
From an industrial perspective, adsorption is the bedrock of separation science. It is the core technology behind water purification, gas mask filtration, and desiccant air drying. We quantify this process using Adsorption Isotherms (such as the Langmuir or Freundlich models), which describe the relationship between the amount of substance adsorbed and the pressure or concentration at a constant temperature.
In the context of modern manufacturing, mastering adsorption kinetics is essential for reducing carbon footprints and reclaiming high-value solvents from industrial exhaust streams.