Environmental Engineering Reference
In-Depth Information
For instance, the Dubinin-Stoeckli (DS) and Stoeckli models which have been
proposed based on the Dubinin theory of volume filling of micropores (TVFM)
implement Gaussian and gamma type of mathematical function, respectively [1,
2, 133].
1.2.1. BASIC MODELS FOR ADSORPTION PARAMETERS CALCULATING
IN CARBON NANO ADSORBENTS
1.2.1.1 CALCULATE OF S
BET
, V
MICRO
AND S
MESO
IN POROUS CARBONS
First stage in characterization of adsorption properties of active carbons is usually
determination of their surface area and pore volume. The surface area is normally
determined from equilibrium adsorption isotherm of a gas or vapor measured in a
range of relative pressures from 0.01 to 0.3. Currently, there are two major meth-
ods used to evaluate specific surface area from gas adsorption data: the Brunauer-
Emmett-Teller (BET) method and the comparative plot analysis.
The evaluation of the specific area by the BET method is based on the deter-
mination of the monolayer capacity (i.e., the number of adsorbed molecules in
the monolayer on the surface of a material) by fitting experimental gas adsorption
data to the BET equation:
p
aC
p
m
a
=
�
0
p
�
p
(
)
1
− +−
1
C
1
-
€
‚
(2)
p
p
ƒ
„
0
0
where is the total amount adsorbed, is the monolayer capacity, p/p
o
is the relative
pressure and is the constant related to the heat of first-layer adsorption:
qq
−
�
�
C
=
exp
1
L
€
‚
ƒ
„
(3)
RT
where is the difference between the heat of adsorption in the first layer and heat
ofcondensation, T is the absolute temperature and R is the universal gas constant.
The above equation (Eq. (3)) was derived for an infinite number of adsorbed lay-
ers. This equation is usually expressed in the following linear form:
p
p
1
Cp
−
1
0
=
+
(4)
aC
aC p
�
p
�
m
m
0
a
1
−
€
‚
p
ƒ
„
0
Eq. (4) is used to evaluation the monolayer capacity, am, which is necessary for
the evaluation of the surface area, . If the crosssectional area for a single molecule
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