Activated carbon is a common material used for adsorption. . |
Adsorption Definition (Chemistry)
Adsorption is defined as the
adhesion of a chemical species onto the surface of particles.
German physicist Heinrich
Kayser coined the term "adsorption" in 1881.
Adsorption is a different
process from absorption, in which a substance diffuses into a liquid or
solid to form a solution.
In
adsorption, the gas or liquid particles bind to the solid or liquid surface
that is termed the adsorbent. The particles
form an atomic or molecular adsorbate film.
Isotherms
are used to describe adsorption because temperature has a significant effect on
the process.
The quantity of adsorbate
bound to the adsorbent is expressed as a function of pressure of concentration
at a constant temperature.
Several isotherm models have
been developed to describe adsorption, including the linear, Freundlich,
Langmuir, BET (after Brunauer, Emmett, and Teller), and Kisliuk theories.
IUPAC Definition of Adsorption
The IUPAC definition of adsorption is the "Increase
in the concentration of a substance at the interface of a condensed and a
liquid or gaseous layer owing to the operation of surface forces."
Examples of Adsorption
Examples of adsorbents include:
- silica gel
- alumina
- activated carbon or charcoal
- zeolites
- adsorption chillers used with
refrigerants
- biomaterials that adsorb proteins
Adsorption
is the first stage of a virus life cycle.
Some scientists consider the
video game Tetris a model for the process of adsorption of shaped molecules
onto flat surfaces.
Adsorption vs. Absorption
Adsorption is a surface phenomenon in which particles or
molecules bind to the top layer of a material.
Absorption, on the other
hand, goes deeper, involving the entire volume of the absorbent. Absorption is
the filling of pores or holes in a substance.
Terms Related To Adsorption
Sorption:
This encompasses both adsorption and absorption processes.
Desorption: The
reverse process of sorption. The reverse of adsorption or absorption.
Characteristics of Adsorbents
Typically, adsorbents have small pore diameters so that there is
a high surface area to facilitate adsorption. The pore size usually ranges
between 0.25 and 5 mm.
Industrial adsorbents have
high thermal stability and resistance to abrasion. Depending on the
application, the surface may be hydrophobic or hydrophilic.
Both polar and nonpolar
adsorbents exist.
The adsorbents come in many
shapes, including rods, pellets, and molded shapes.
There are three major classes
of industrial adsorbents:
- carbon-based compounds (e.g., graphite,
activated charcoal)
- oxygen-based compounds (e.g., zeolites,
silica)
- polymer-base compound
How Adsorption Works
Adsorption depends on surface energy. Surface atoms of the
adsorbent are partially exposed so they can attract the adsorbate molecules.
Adsorption may result from
electrostatic attraction, chemisorption, or physisorption.
Uses of Adsorption
There are many applications of the adsorption process,
including:
- Adsorption is used to cool water for air
conditioning units.
- Activated charcoal is used for aquarium
filtration and home water filtration.
- Silica gel is used to prevent moisture
from damaging electronics and clothing.
- Adsorbents are used to increase the
capacity of carbide-derived carbons.
- Adsorbents are used to produce non-stick
coatings on surfaces.
- Adsorption may be used to extend the
exposure time of specific drugs.
- Zeolites are used to remove carbon dioxide
from natural gas, remove carbon monoxide from reforming gas, for catalytic
cracking, and other processes.
- The process is used in chemistry labs
for ion-exchange and chromatography.
Anne
Marie Helmenstine, Ph.D. , is an author and consultant with a broad
scientific and medical background.
Experience
Anne has taught chemistry, biology, and physics
at the high school, college, and graduate level. In her doctoral work, Anne
developed ultra-sensitive chemical detection and medical diagnostic tests. She
has worked abstracting/indexing diverse scientific literature for the
Department of Energy. She presently works as a freelance writer and scientific
consultant. She enjoys adapting lab-based science projects so that they can be
performed safely at home.
Education
Dr. Helmenstine has bachelor of arts degrees in
physics and mathematics with a minor in chemistry from Hastings College in
Nebraska and a doctorate of philosophy in biomedical sciences from the
University of Tennessee at Knoxville.
Anne Marie Helmenstine, Ph.D.
Chemistry is part of everyone's life, from
cooking and cleaning to the latest computer chip technology and vaccine
development. It doesn't have to be intimidating and it doesn't have to be hard
to understand.
You can read more about Anne's current and past
work on her Google Profile: Anne Helmenstine. Find Anne's printable periodic tables
and science projects at Science Notes.
https://www.thoughtco.com/definition-of-adsorption-605820
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Multi-Media Filter, Highly-Activated Carbon Filter,
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