Langmuir Adsorption Isotherm

Adsorption!Isotherm?

SurfaceConsider gas molecules striking a surfaceIn this case, molecules do not adsorb or stick to the surface

Now, consider the following scenarioIn this case, molecules do adsorb to the surfaceSurface

Isotherm- it meansConstant TemperatureThat is, adsorption at a fixed temperatureWhat about

molecules in the gas phasemolecules adsorbed at the surfaceTo describe the equilibrium between the molecules in the gas phase and the molecules bound to the surfaceThe objective of Langmuir Equation

The ExperimentWe will:Introduce molecules in this chamber2. Wait for an equilibrium to reach3. Plot number of molecules adsorbed versus the equilibrium pressure

No Gas MoleculeThe Experiment

The ExperimentNow, Lets introduce 4 Molecules

3 adsorbed1 in gas phaseThe ExperimentNow, Lets introduce 4 Molecules

The ExperimentNow, Lets introduce 8 Molecules6 adsorbed2 in gas phase

Now, Lets introduce 12 MoleculesThe Experiment8 adsorbed4 in gas phase

Now, Lets introduce 15 MoleculesThe Experiment9 adsorbed7 in gas phase

Now, Lets introduce 21 MoleculesThe Experiment10 adsorbed11 in gas phase

Finally, Lets introduce 24 MoleculesThe Experiment10 adsorbed14 in gas phase

Pressure, PFraction AdsorbedWe can plot this data as a fraction of molecules adsorbedFraction AdsorbedMaximum Available sitesNumber Adsorbed

3. Only a monolayer coverage is possibleIrving Langmuir1881 -1957In 1916, Langmuir proposed a simple modelSo, how to describe this behavior?Basic Assumptions

Adsorption sites are homogeneous and equivalent2. The adsorbed molecules are immobile and they do not interact

Irving Langmuir1881 -1957In 1916, Langmuir proposed a simple modelSo, how to describe this behavior?Based on these assumptions, Langmuir derived the following equationFraction AdsorbedEquilibrium constantEquilibrium Pressure

The Langmuir EquationBased on these assumptions, Langmuir derived the following equationPressure, PFraction AdsorbedFraction AdsorbedEquilibrium constantEquilibrium PressureThis is the Langmuir Equation describing (fitting) the DataRecall, the data we collected

The Langmuir EquationPressure, PFraction AdsorbedNoticeAnd at low concentration, adsorption is linearly proportional to Pi.e. reaches a monolayerThis is the Langmuir Equation describing (fitting) the DataRecall, the data we collected

The Langmuir EquationWhat about the Equilibrium Constant, KLarger the value of K, stronger the bindingEquilibrium constant can be used to calculate Gibbs free energy of adsorption using the following equationNow, thats an equation for another video!Stronger binding affinity

Langmuir Equation - ApplicationKinetics of Catalytic ReactionsPollution Remediationadsorption of contaminants to colloids Material Sciencee.g. adsorption on DSSCs

HistoricalWas nearly blind for the first eleven years of his lifeIrving Langmuir1881 -1957Tidbits about LangmuirGraduated from Columbias School of Mines, NYC in 1903

Post graduate work at Univ. of Gottingen in Germany in Physical Chemistry under Walther Nernst

HistoricalIrving Langmuir1881 -1957Tidbits about LangmuirGraduated from Columbias School of Mines, NYC in 1903

Post graduate work at Univ. of Gottingen in Germany in Physical Chemistry under Walther Nernst Worked at the General Electric LabsWas nearly blind for the first eleven years of his life

HistoricalIrving Langmuir1881 -1957Tidbits about LangmuirGraduated from Columbias School of Mines, NYC in 1903

Post graduate work at Univ. of Gottingen in Germany in Physical Chemistry under Walther Nernst Worked at the General Electric Labs1932 First Industrial Chemist to receive Nobel Prize in Chemistryfor his discoveries and investigations in surface chemistry

This is the same year Schrodinger won the prize in PhysicsWas nearly blind for the first eleven years of his life

http://www.britannica.com/biography/Irving-Langmuir

http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1932/langmuir-bio.html

http://www.aip.org/history/newsletter/spring2007/photos.htm

http://www.nndb.com/people/776/000079539/

Music: Mouton Swing by Robert R. Putnam https://archive.org/details/MoutonSwing

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