Definition
Adsorption at solid interfaces involves the accumulation of molecules from a liquid or gas onto a solid surface.
Types of Adsorptions
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.
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
Controlled Release: Adsorption onto carriers for sustained drug delivery.
Catalysis: Surface reactions in drug synthesis and degradation.
Chromatography: Separation techniques based on differential adsorption.