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FUNDAMENTALS
Adsorption–aphenomenologicaldescription
Adsorptionisacomple[phenomenonbecauseatthecontactsurfaceoftwo
phasesthereareforceswhicharerelatedtovariousinteractionsfrom
thesolidphaseandtheliquidphasecontactingitandwhichcompensate
foreachotherinsidethephase.Inadditiontotheforcesresultingfrom
dierencesintheVanderWaalsforce-typeinteractions9functionalgroups
ofmoleculescanappearonthesurfaceofasolid.Thefunctionalgroupscan
formhydrogenbondsorreactwiththemoleculescontainedinthebound-
aryphase.Asaresultoftheseforces9thesubstancesremaininginthesolid
phaseandthosedissolvedinthesolutionmaybeselectivelycollectednear
theinterfaceorrepelledfromthisspace.Inaddition9adsorbedmolecules
showresidualattractiveforcesthatcanadsorbfurthermoleculesandcause
theformationofmultiparticulatelayersontheadsorbedsubstance[1].
Foramonomolecularlayeroftheadsorbedsubstance9thedependence
oftheamountofadsorbedsubstanceontheparametersdescribingthesys-
tem(temperature9substanceconcentration9typeofadsorbent9adsorbate9
etc.)arerelativelysimpleandeasytointerpret.
Formultilayeradsorption9theserelationshipsarequalitativelysimi-
lar9buttheinterpretationoftheresultsismuchmorecomple[.Tochar-
acterizetheprocesses9adsorptionisothermsaremostoftengiven.Assum-
inganidealizedmodelassumingthatthereisacertainnumberofsites
capableofattachingtheadsorbatemoleculeonthesurfaceoftheadsor-
bent9theadsorptionprocesscanbedescribedbyappropriateequations
(Freundlich9Langmuir9BET).Underconstanttemperatureconditions9
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