Isotherm differences

Question 1

Define differences between the isotherms

Answer 1

• Both Langmuir and BET assume all surface sites are equal (homogeneous adsorbent surface) and derived theoretically
• Other adsorption isotherms used if adsorption sites not equivalent (adsorption enthalpy changes as function of coverage)
• Temkin and freundlich assume there may be interactions between neighbours
• Heat of adsorption decreases with increasing theta => most favourable sites occupied first
• Temkin and Freundlich - both empirical in derivation, depends on data

Question 2

Which graphs are suitable for the isotherms?

Answer 2

• Isotherm 1 is most suited to Langmuir - straight line
• Isotherm 2 is most suited to Temkin
• Isotherm 3 is most suited to Freundlich

Question 3

Give an example of an anomalous isotherm

Answer 3

Type VI = layers due to formation of complete monolayer before each subsequent layer forms

Question 4

Give examples of different porous materials

Answer 4

• Carbonaceous materials - ability to adsorb large amounts of gas/vapour => applications e.g. insole, feminine hygiene products, water filters
• Zeolites - used for gas purification, catalytic properties and sorption capabilities, e.g. catalysis, gas separation
Metal organic frameworks - new generation of novel materials also exhibit porous structures, flexible