Environmental Engineering Reference
In-Depth Information
�
p
�
=
0
a
a
+ ha
ƒ
p
„
mi
s
0
(6)
The micropore volume
V
mi
can be evaluated according to the formula:
0
V
=
aF
(7)
mi
mi
In latter equation, F is a conversion factor (F = 0.0015468 for nitrogen at 77 K,
F
= 0.001279 for argon at 77 K and 87 K, when the amount adsorbed is expressed in
cm
3
g
-1
and the pore volume is expressed in cm
3
g
-l
). The slope of the linear seg-
ment of the -plot () permits the evaluation of the monolayer adsorption capacity
for the mesopore surface:
a
0
0
a
=h
s
me
a
(0.4)
(8)
s
where is the monolayer capacity of the reference adsorbent, as(0.4) is the amount
adsorbed on the non-porous reference adsorbent at relative pressure p/p
o
= 0.4.
The mesopore surface area is obtained by multiplying by Avogadro's number
N
A
and the molecular area occupied by one molecule adsorbed on the mesopore
surface, that is:
0
S
a
= w
(9)
me
me
A
The total surface area, S
t
, is assessed from the slope of the low-pressure part of
the -plot:
0
a
S
=k
s
N
w
t
A
a
(0.4)
(10)
s
The difference between the total surface area and the mesopore surface area is
often used to estimate the surface area of micropores, :
S SS
=−
(11)
mi
t
me
The -plot method provides an effective and simple way for evaluation of the mi-
cropore volume
V
mi
, the total surface area S
t
and the mesopore surface area S
me
of nanoporous materials. The -plots for the active carbons studied obtained by
using nitrogen reference adsorption data for non-graphized carbon structures. The
slope of the dashed line was used to calculate the total specific surface area, S
t
,
the intercept of the dotted line was used to evaluate the micropore volume, V
mi
,
and the slope of the dotted line was used to evaluate the mesopore surface area,
S
me
[1, 2, 121, 145].
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