Environmental Engineering Reference
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compete with the adsorbate molecules to reach the adsorption sites on the
surface of the adsorbent. The steam activation of date pits carried out by
Ashour involved the carbonization of the precursor at 600 C followed by
an activation stage at 950 C under partial steam environment to gain two
activated carbons with 20% and 50% burn-off, DS2 and DS5, respec-
tively [87]. The nitrogen adsorption-desorption graph indicated the exis-
tence of a hysteresis loop at DS5 indicative of the formation of mesopores
in contrast to DS2 which was predominantly microporous. As tabulated in
Table 5.11, the surface areas were calculated to be 705 and 1040
m
2
.g
-1
for
DS2 and DS5, respectively. Since the surface pH values of the obtained
carbons were considerably higher than 7, their surfaces were mainly basic.
Both of these activated carbons revealed high efficiency for the adsorption
of methylene blue (MB) and remazol yellow (RY). It is interesting to note
that contrary to the previously-discussed literature, the adsorption capac-
ity of the activated carbon for the dye molecules decreases as the pH level
increases (see Table 5.12). This is related to the basic nature of the steam-
activated carbon surfaces, where at lower pH values, the activated carbon
takes positive charge by adsorbing
H
+
ion and can uptake the anionic dye
owing to the strong electrostatic attraction between the adsorbent and
adsorbate. Reddy
et al.
[88] employed two activation methods to increase
Table 5.11
Textural properties of date pit-based activated
carbons [87].
Carbon
BET SA
(
m
2
g
-1
)
Pore vol.
(
cc.g
-1
)
Mean Pore
Radius
(nm)
Micropore
vol. (
cc.g
-1
)
Mesopore
vol.
(
cc.g
-1
)
Surface
pH
DS2
705
0.361
1.03
0.228
0.133
8.3
DS5
1040
0.884
1.70
0.365
0.519
9.5
Table 5.12
Adsorption capacities of date pit-based activated carbons for
MB and RY [87].
Carbon
Solution
pH
q
e
(
mg
.
g
-1
),
MB / 27 C
q
e
(
mg.g
-1
),
MB / 37 C
q
e
(
mg.g
-1
),
RY / 27 C
q
e
(
mg.g
-1
),
RY / 37 C
DS2
3
84.6
97.6
42.1
55.0
5
68.1
88.8
37.4
50.4
7
64.0
76.9
33.6
44.0
DS5
3
220.0
200.0
164.0
152.2
5
194.6
168.5
147.6
136.3
7
174.1
148.6
129.9
123.1
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