PHYSICAL CHEMISTRY II
WEEK 3
ADSORPTION
By:
Fitria Dwi Andriani, S.T., M.Eng.
fitria_dwi.tk@upnjatim.ac.id
+62 852-3076-9449
ADSORPTION
• The attachment of particles to a surface is called adsorption. The
substance that adsorbs is the adsorbate and the underlying
material that we are concerned with in this section is the
adsorbent or substrate. The reverse of adsorption is desorption.
Adsorbate : species being
adsorbed (ex: H2, Zn2+, PO43-)
Adsorbent : material doing the
adsorbing (ex: carbon, zeolite)
Interface: is where surface
phenomena occur.
ADSORPTION
Application
Guillossou, et al (2019)
Adsorption Mechanism
Pore Structure of Adsorbent
Adsorbate
Macropore (>50 nm)
External
diffusion
Internal
diffusion
Mesopore (2-50 nm)
Micropore (<2 nm)
Adsorption
(equilibrium)
TYPES OF ADSORPTION
Physisorption: there is a van der Waals interaction (for example, a dispersion or a dipolar
interaction) between the adsorbate and the substrate. Van der Waals interactions have a
long range but are weak, and the energy released when a particle is physisorbed is of the
same order of magnitude as the enthalpy of condensation.
Chemisorption: the molecules (or atoms) stick to the surface by forming a chemical (usually
covalent) bond, and tend to find sites that maximize their coordination number with the
substrate. The enthalpy of chemisorption is very much greater than that for physisorption
PHYSISORPTION
CHEMISORPTION
Bonding
WEAK, LONG RANGE
Van der Waals interactions
(e.g. London dispersion,
dipole-dipole)..
STRONG, SHORT RANGE
Chemical bonding involving
orbital overlap and charge
transfer.
Saturation
Multi-layer
Mono-layer
Nature
Reversible
Mostly Irreversible
Molecule
Heterogen
Homogen
adsorbate
physisorption
pore wall
adsorbate
chemisorption
pore wall
ADSORPTION
ADSORPTION ISOTHERM (EQUILIBRIUM)
• How much adsorbate is adsorbed on the surface of the pore walls and how much adsorbate
is present in the fluid phase at equilibrium.
• the relationship curve between the concentration of solute molecules in two phases when
the adsorption process reaches equilibrium at the interface of two phases at a certain
temperature.
• to describe how solutes interact with adsorbents and to optimize the use of adsorbents.
Plot of the amount of
adsorbate
on
the
adsorbent as a function of
its Pressure (if gas) or
Concentration (if liquid) at
constant temperature.
ADSORPTION ISOTHERM
Adsorption site
Adsorption layers
Dynamic equilibrium
Adsorbed molecular
interactions
Adsorbent surface
Chemical forces
Basis of equation
Chemisorption
Process involved
Adsorption of gases on solid
FREUNDLICH
Heterogenous
Multilayer
LANGMUIR
Homogenous
Monolayer
Does not exist
Exist
Exist
Do not exist
Not uniform
Not involved
Empirical
No
Adsorption
Less satisfactory explanation
Uniform
Involved
Theoretical
Yes
Adsorption and desorption
Satisfactory explanation
ADSORPTION ISOTHERM
Freundlich
1
𝑛
𝐶𝜇 = 𝐾. 𝐶𝑒
1
𝑙𝑜𝑔𝐶𝜇 = 𝑙𝑜𝑔𝐶𝑒 + 𝑙𝑜𝑔 𝐾
𝑛
ADSORPTION ISOTHERM
𝐶𝑒
𝐶𝜇
Langmuir
𝑏. 𝐶𝑒 . 𝐶𝜇𝑚𝑎𝑥
𝐶𝜇 =
1 + 𝑏. 𝐶𝑒
𝐶𝑒
1
𝐶
=
+ 𝑒
𝐶𝜇
𝑏.𝐶𝜇𝑚𝑎𝑥
𝐶𝜇𝑚𝑎𝑥
Intercept =
1
𝑏.𝐶𝜇𝑚𝑎𝑥
; 𝑠𝑙𝑜𝑝𝑒 =
1
𝐶𝜇𝑚𝑎𝑥
SUMMARY
Batch Adsorption (liquid phase)
V = liquid volume (mL)
Ci = initial solute concentration (mg/L)
Ce = Solute concentration in the solution (mg/L)
ADSORPTION
• An adsorption study is set up in laboratory by adding a known amount of
activated carbon to six flasks which contain 200 mL of an industrial waste. An
additional flask containing 200 mL of waste but no carbon is run as a blank.
Freundlich
Flask Mass of C
No. (mg) = m (g)
Plot log Ce vs log 𝐶𝜇
Volume in
Final COD
flask (mL) = V (mg/L) =
Ce
𝐶𝜇 (mg solute/g adsorbent) =
(Ci – Ce) V / 1000 x m
Log Ce
Volume in
Final COD
flask (mL) = V (mg/L) =
Ce
𝐶𝜇 (mg solute/g adsorbent) =
(Ci – Ce) V / 1000 x m
Ce / 𝐶𝜇
Log 𝐶𝜇
Langmuir
Flask Mass of C
No. (mg) = m (g)
Plot Ce vs Ce/𝐶𝜇
THANK YOU
Fitria Dwi Andriani, S.T., M.Eng.
fitria_dwi.tk@upnjatim.ac.id