Types of adsorption, factors affecting adsorption

1. Introduction to Adsorption

1. Adsorption is the process where particles (atoms, ions, or molecules) from a substance accumulate on the surface of another substance.
2. The substance on which adsorption occurs is called the adsorbent.
3. The substance being adsorbed is called the adsorbate.
4. Adsorption is a surface phenomenon and differs from absorption, which involves penetration into the bulk.

2. Types of Adsorption

1. Physical Adsorption:
   • Also known as physisorption.
   • Occurs due to weak van der Waals forces.
   • Reversible in nature.
   • More pronounced at low temperatures.
2. Chemical Adsorption:
   • Also known as chemisorption.
   • Involves the formation of chemical bonds between adsorbate and adsorbent.
   • Irreversible in nature.
   • Occurs at higher temperatures compared to physisorption.

3. Factors Affecting Adsorption

1. Nature of Adsorbate: Substances with higher molecular weights or greater solubility in the adsorbent medium are adsorbed more easily.
2. Nature of Adsorbent: Porous materials with larger surface areas (e.g., activated charcoal, silica gel) show higher adsorption.
3. Pressure: Adsorption of gases increases with an increase in pressure, as described by Freundlich and Langmuir isotherms.
4. Temperature:
   • Physisorption decreases with an increase in temperature.
   • Chemisorption increases with an increase in temperature to a certain extent.
5. Surface Area of Adsorbent: Greater surface area leads to more adsorption.
6. Concentration: For liquids, higher concentration of the solute enhances adsorption.

4. Adsorption Isotherms

1. Freundlich Isotherm: Empirical relation describing adsorption as a function of pressure and concentration.
2. Langmuir Isotherm: Theoretical model assuming monolayer adsorption on a uniform surface.

5. Applications of Adsorption

1. Industrial Applications:
   • Used in catalysis to enhance reaction rates.
   • Adsorption is critical in chromatography for separation techniques.
2. Environmental Applications:
   • Removal of pollutants using activated carbon.
   • Control of humidity using silica gel.
3. Medical Applications: Adsorption of toxins in drugs and treatments.
4. Gas Masks: Activated charcoal adsorbs toxic gases for safety.
5. Water Purification: Adsorption of impurities to provide clean water.

6. Key Points

1. Adsorption is a surface phenomenon, distinct from absorption.
2. There are two main types: physisorption (weak forces) and chemisorption (strong chemical bonds).
3. Factors such as surface area, pressure, temperature, and nature of adsorbate affect adsorption.
4. Freundlich and Langmuir isotherms describe adsorption behavior.
5. Applications include catalysis, pollution control, water purification, and medical treatments.