Slide 1

• Surface Chemistry - Physisorption and adsorption
• Definition: The process of adsorption onto the surface of solids, liquids, or gases.
• Types of adsorption: physisorption and chemisorption.

Slide 2

• Physisorption
• Also known as physical adsorption.
• Weak intermolecular forces (van der Waals forces) between the adsorbent and the adsorbate.
• Activated by decreasing temperature or increasing pressure.

Slide 3

• Physisorption - Characteristics
• Reversible process.
• Easily influenced by temperature and pressure.
• Forms multi-layer adsorption.
• Adsorption isotherm - usually follows Freundlich adsorption isotherm equation.

Slide 4

• Physisorption - Examples
• Physisorption of gases on activated charcoal.
• Formation of a thin layer of moisture on window glass.
• Binding of molecular oxygen by hemoglobin in our blood.

Slide 5

• Adsorption on Activated Charcoal
• Activated charcoal has a large surface area due to adsorbed gases.
• It can adsorb various substances, including gases, liquids, and impurities.
• Used in air and water purification, gas masks, and in the treatment of poisoning.

Slide 6

• Adsorption on Silica Gel
• Silica gel is a microporous, solid form of silicon dioxide.
• It has a high adsorption capacity for water molecules.
• Used as a desiccant, humidity indicator, and in chromatography.

Slide 7

• Adsorption Isotherms
• Plots that represent the relationship between the amount of adsorbate on the surface and the equilibrium pressure of the adsorbate.
• Freundlich adsorption isotherm equation:
  • x/m = k*p^(1/n)
  • x/m: amount of adsorbate adsorbed per unit mass of adsorbent
  • p: partial pressure of the adsorbate
  • k and n: constants

Slide 8

• Adsorption Isotherms - Type I
• Represents physical adsorption at low temperatures and high pressures.
• Adsorption increases rapidly at low pressures.
• Saturation is reached when no more adsorbate can be adsorbed.

Slide 9

• Adsorption Isotherms - Type II
• Represents physical adsorption at higher temperatures and lower pressures.
• Adsorption occurs over a wide range of pressures.
• Saturation can still occur but at higher pressures.

Slide 10

• Adsorption Isotherms - Type III
• Represents adsorption in microporous solids.
• Adsorption increases slowly at low pressures.
• Large surface area is required for significant adsorption.

Slide 11

• Applications of Physisorption
• Gas storage in activated carbon.
• Separation and purification of gases and liquids.
• Use of desiccants like silica gel.
• Catalysis in certain reactions.
• Drug delivery systems.

Slide 12

• Factors Affecting Physisorption
• Temperature: Decreasing temperature increases physisorption.
• Pressure: Increasing pressure increases physisorption.
• Nature of adsorbate and adsorbent: Different substances have different affinities for adsorption.
• Surface area of adsorbent: Greater surface area provides more sites for adsorption.

Slide 13

• Adsorption of Gases on Solids
• Gases like H2, O2, N2, etc., are physisorbed on solids like activated carbon.
• The adsorbed gases can be easily released by heating or decreasing pressure.
• This adsorption is used in gas storage, gas masks, etc.

Slide 14

• Langmuir Adsorption Isotherm
• Proposed by Irving Langmuir.
• Represents monolayer adsorption of gases on solid surfaces.
• Equation: θ = (KP)/(1 + KP)
  • θ: Fraction of surface covered by adsorbate
  • P: Pressure of adsorbate gas
  • K: Equilibrium constant related to adsorption-desorption rate

Slide 15

• Heterogeneous Catalysis
• A type of catalysis where reactants are adsorbed on a catalyst surface.
• Catalyst provides an active site for adsorption and reaction.
• Examples: Haber process, oxidation reactions using platinum catalyst.

Slide 16

• Shape-selective Catalysis
• Certain catalysts have pore structures that allow only specific reactant molecules to enter and get adsorbed.
• This leads to selective catalytic reactions depending on the shape and size of the reactant molecules.
• Examples: Zeolite catalysts, catalytic converters.

Slide 17

• Adsorption in Biological Systems
• Many biological processes involve adsorption of molecules on cell surfaces or enzyme surfaces.
• Examples:
  • Antibodies binding to antigens.
  • Enzymes binding to substrates.
  • Hemoglobin binding to oxygen.

Slide 18

• Surface Area Determination
• Surface area of a solid can be determined by various methods.
• BET (Brunauer, Emmett, and Teller) method is commonly used.
• Based on adsorption of a gas (usually N2) on the solid and measuring the amount adsorbed.

Slide 19

• Adsorption Chromatography
• Chromatographic technique based on differential adsorption of solutes on a stationary phase.
• Stationary phase is usually a solid adsorbent.
• Used for separation and purification of mixtures in various industries and laboratories.

Slide 20

• Summary
• Physisorption is a type of adsorption where weak forces are involved.
• It is reversible and easily influenced by temperature and pressure.
• Adsorption isotherms describe the relationship between adsorbate amount and pressure.
• Physisorption has numerous applications in gas storage, purification, catalysis, etc.
• Understanding physisorption is important in various fields of chemistry.

Slide 21

• Factors Affecting Adsorption
  • Nature of adsorbent and adsorbate
  • Surface area and porosity of adsorbent
  • Temperature and pressure
  • Presence of impurities or competitive adsorption
  • Activation of adsorbent surface

Slide 22

• Chemisorption
• Also known as chemical adsorption.
• Involves strong chemical bonds between the adsorbent and the adsorbate.
• Irreversible process, typically forms a single layer.

Slide 23

• Chemisorption - Characteristics
• Higher specificity than physisorption.
• Large energy changes due to bond formation.
• Activation energy is required for the surface reaction.
• Generally occurs on metal surfaces or surfaces with unsaturated atoms.

Slide 24

• Chemisorption - Examples
• Adsorption of hydrogen on platinum catalyst.
• Oxidation of methane to carbon dioxide and water on a metal surface.
• Adsorption of oxygen during the formation of a metal oxide.

Slide 25

• Adsorption Isotherms - Type IV
• Represents chemisorption or mixed physisorption-chemisorption.
• Shows rapid adsorption at low pressures and slow adsorption at high pressures.
• Saturation can still occur, but at higher pressures than in physisorption.

Slide 26

• Catalysis
• The process of increasing the rate of a chemical reaction by providing an alternate pathway with lower activation energy.
• Catalysts are not consumed in the reaction and can be reused.
• Heterogeneous catalysis involves adsorption of reactants on the surface of a solid catalyst.

Slide 27

• Shape-selective Catalysis - Zeolites
• Zeolites are a type of crystalline, microporous material.
• Have a well-defined pore structure with uniform size and shape.
• Used as catalysts due to their shape-selective adsorption properties.
• Example: Conversion of methanol to gasoline in petrochemical industry.

Slide 28

• Industrial Applications of Adsorption
• Gas purification: Removal of impurities, such as nitrogen from air.
• Water treatment: Removal of dissolved organic compounds and heavy metals.
• Separation and purification of fine chemicals.
• Removal of odors and volatile organic compounds.

Slide 29

• Environmental Applications of Adsorption
• Adsorption of pollutants from air and water.
• Removal of volatile organic compounds (VOCs) from industrial emissions.
• Removal of heavy metals and dyes from wastewater.
• Adsorption-based water filters and purification systems.

Slide 30

• Summary
• Adsorption is the process of attraction and accumulation of molecules on a surface.
• Physisorption involves weak van der Waals forces and is reversible.
• Chemisorption involves strong chemical bonds and is irreversible.
• Adsorption is influenced by factors like temperature, pressure, and surface characteristics.
• Adsorption is widely used in catalysis, gas purification, and environmental applications.