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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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