OIA1008 ADSORPTION

Adsorption

The process where molecules adhere to a surface without penetrating into it.

Absorption

The process where molecules penetrate and distribute throughout a substance.

Adsorbate

The substance being adsorbed onto a surface.

Adsorbent

The surface onto which adsorption occurs (e.g., charcoal, silica).

Physisorption (Physical Adsorption)

Weak Van der Waals forces, low heat of adsorption (20-40 kJ/mol), reversible.

Chemisorption (Chemical Adsorption)

Strong chemical bonds, high heat of adsorption (40-400 kJ/mol), irreversible.

Multimolecular Adsorption

Occurs in physisorption, forming multiple layers.

Monomolecular Adsorption

Occurs in chemisorption, forming a single layer.

Surface Area of Adsorbent

Larger surface area increases adsorption (e.g., activated charcoal).

Temperature

Physisorption decreases with increasing temperature.

Chemisorption increases with increasing temperature.

Pressure (for gas adsorption)

Higher pressure increases adsorption due to increased gas collisions.

Nature of Adsorbate

Gases with higher polarity adsorb better (e.g., NH₃ > O₂).

effect of pH

Ionizable adsorbates show variable adsorption depending on pH.

Adsorption Isotherm

A curve showing the relationship between the amount adsorbed and equilibrium pressure or concentration at constant temperature.

Freundlich Adsorption Isotherm

Empirical model describing multilayer adsorption.

Equation: x/m = kP^(1/n)

Log form: log(x/m) = log k + (1/n) log P (Straight-line graph).

Limitations of Freundlich Isotherm

Does not explain monolayer adsorption.

Breaks down at high pressures.

Langmuir Adsorption Isotherm

Assumes monolayer adsorption on fixed sites.

Equation: θ = (bP) / (1 + bP)

Linear form: P/y = 1/bym + P/ym.

Limitations of Langmuir Isotherm

Only valid for monolayers, not multilayers.

Does not work at high pressures.

BET (Brunauer-Emmett-Teller) Isotherm

Extends Langmuir’s model to multilayer adsorption.

Used for surface area determination.

Types of Adsorption Isotherms

Type I: Monolayer adsorption (Langmuir).

Type II & III: Multilayer adsorption.

Type IV & V: Capillary condensation.

Activated Charcoal

Adsorbs gases due to high surface area.

Gas Mask Adsorption

Uses activated carbon to trap toxic gases.

Catalyst Surface Adsorption

Essential in heterogeneous catalysis.

Industrial Adsorption

Zeolites used for gas separation.

Decolorization of Solutions

Activated charcoal removes dyes and impurities.

Protein Adsorption in Drug Delivery

Proteins adsorb onto polymeric surfaces in drug formulations.

Ion Exchange Adsorption

Resins remove unwanted ions from solutions.

Adsorption in Chromatography

Silica gel or alumina used in adsorption chromatography.

Adsorption of Toxins

Activated charcoal treats poisoning by adsorbing toxic substances.

Drug Adsorption on Excipients

Affects drug release and stability.

Gastrointestinal Adsorption

Kaolin adsorbs bacteria and toxins in diarrhea treatment.

Antacid Adsorption

Aluminum hydroxide adsorbs gastric acid.

Controlled Drug Release

Adsorbents help regulate drug release.

Microparticle Adsorption

Used for extended-release formulations.

Nanoparticle Drug Carriers

Surface-modified nanoparticles improve drug delivery.

Water Purification

Activated carbon removes pollutants.

Adsorption in Detergency

Surfactants enhance dirt adsorption.

Adsorption in Food Preservation

Silica gel adsorbs moisture in packaged foods.

Gas Adsorption in Catalysis

Metal catalysts adsorb reactant gases.

Pharmaceutical Packaging

Desiccants (silica gel) adsorb moisture to protect drugs.