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ADSORPTIONADSORPTIONADSORPTION
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DEFINITION
Adsorption is the adhesion ofmolecules of gas, liquid, or dissolvedsolids to a surface
This process creates a film of theadsorbate (the molecules or atomsbeing accumulated) on the surface of
the adsorbent.
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Adsorption process
Adsorbate
Adsorbent
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Adsorption Physisorption: characteristic of weak
van der Waals interaction
Chemisorption: characteristic of ionic orcovalent bonding
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Physisorption
a. The fundamental interacting forceof physisorption is caused by vander Waals force
b. Reversible adsorption
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c. Interaction energy is very weak
d. The adsorbed species are chemicallyidentical with those in the fluid phase, sothat the chemical nature of the fluid isnot altered by adsorption and subsequentdesorption
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Chemisorption
a. The phenomenon is characterized bystrong interactions include chemical
bonds of the ionic or covalent variety,depending on chemical specificity
b. Adsorption takes place only in a
monolayer
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c.The chemical nature of theadsorptive(s) may be altered by
surface dissociation or reaction insuch a way that on desorption theoriginal species cannot berecovered; in this sense
chemisorption may not be reversible
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A self assembled monolayer (SAM) is an organizedlayer of amphiphilic molecules in which one end of
the molecule, the head group shows a specialaffinity for a substrate. SAMs also consist of a tailwith a functional group at the terminal end
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ION EXCHANGEION EXCHANGEION EXCHANGE
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Ion exchange is an exchange of ionsbetween two electrolytes or between anelectrolyte solution and a complex. In most
cases the term is used to denote theprocesses of purification, separation, anddecontamination of aqueous and other ion-containing solutions with solid polymeric ormineralic 'ion exchangers'.
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Ion exchangers can be unselective or
Ion exchangers have binding preferences forcertain ions or classes of ions (dependent on thesize of the ions, their charge, or their structure)
Ion exchange is a reversible process and the ion
exchanger can be regeneratedor loadedwithdesirable ions by washing with an excess of theseions
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Typical examples of ions that can bind to ionexchangers are:
H+
and OH
Single charged monoatomic ions (Na+, K+ or Cl-)
Double charged monoatomic ions like Ca2+ or Mg2+
Polyatomic inorganic ions like SO4
2- or PO4
3-
Organic bases, usually molecules containing the aminofunctional group NR2 H
+
Organic acids, often molecules containing COO-(carboxylic acid) functional groups
Biomolecules which can be ionized: amino acids, peptides,proteins, etc.
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Typical ion exchangers are
ion exchange resins (functionalizedporous or gel polymer),
zeolites, montmorillonites, Clays,
soil humus
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