Adsorption at Solid Interfaces

Definition of Adsorption at Solid Interfaces

• Adsorptions at solid interfaces involves the accumulation of molecules from a liquid or gas onto a solid surface.

Types of Adsorption:

1. Physical Adsorption (Physisorption)

   • Forces: Weak van der Waals forces; reversible.
   • Characteristics:
     • Occurs at low temperatures; decreases with heat.
     • Forms multilayers as molecules are loosely held.
   • Example: Adsorption of gases (e.g., nitrogen) on charcoal.

2. Chemical Adsorption (Chemisorption)

   • Forces: Strong chemical bonds; usually irreversible.
   • Characteristics:
     • Happens at higher temperatures.
     • Forms a monolayer as bonds are specific and localized.
   • Example: Hydrogen bonding on a metal surface (e.g., platinum).

Factors Affecting Adsorption

• Surface Area: Higher area increases adsorption capacity.
• Pore Size Distribution: Affects accessibility of adsorbate molecules.
• Temperature and Pressure: Physical adsorption decreases with temperature; chemisorption may increase.

Applications of Adsorption at Solid Interfaces

• Controlled Release: Adsorption onto carriers for sustained drug delivery.
• Catalysis: Surface reactions in drug synthesis and degradation.
• Chromatography: Separation techniques based on differential adsorption.

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