5.4 Adsorption Capacity
103
adsorption isotherms (Fig. 5.5a) indicates a fast initial rise in adsorption potential,
owing to chitosan’s great selectivity for the Zn(II)-cations.
The isotherm adsorption models, Langmuir and Freundlich, were utilized to
design Zn(II) adsorption onto the chitosan membranes. The Langmuir model is the
model that is widely utilized explaining the adsorption of metal ions on chitosan [2,
16, 24]. The Langmuir model suggests equal adsorption energies on the layer and
no sorbent transmigration on the top layer level. This model is true for single-layer
sorption on a layer consisting a limited number of sites [2] and is defined by the
linearization form:
C e
q e
=
C e
Q m
+
1
Q m b
(5.3)
In (5.3), q e and Q m are the equilibrium and maximum monolayer adsorption potential accordingly, and C e is the equilibrium concentration of metal ion in mmol L
−1 , b
is the criterion of affinity in L mmol
−1 . The regression plot of C e /q e versus concentration at equilibrium, C e , could be used to evaluate criterion b of affinity and optimum
adsorbent power, Q m . The essential features of the Langmuir model can be interpreted in terms of a non-dimensional factor identified as the separation factor (R L )
applied only to assess whether or not an adsorption mechanism is desirable [2], as
indicated in 5.4. The conditions of R L > 1, R L = 1 and R L between 0 and 1 signify
unfavourable, linear and favourable correspondingly [19].
R L =
1
1 + bC o
(5.4)
The Freundlich model is the next most commonly utilized isotherm model and
reflects a semi-analytical correlation between the concentration of adsorbents and the
concentration of adsorbents [7]. The Freundlich model’s linearized form is calculated
by using (5.5), for the determination of adsorption efficiency and adsorption rate. The
value of parameter n is in the range of 1–10 under standard adsorption requirements
[19].
log q e = log K F +
1
n
log C e
(5.5)
where K F and n (non-dimensional coefficients) separately indicate the adsorption
power and the adsorption strength [19].
The tests of the Langmuir and Freundlich models linearized plots using (5.3)
and (5.5) are shown in Fig. 5.5b, c accordingly, and the criteria for the model are
presented in Table 5.1. From the R
2 -values of 0.966–0.985 for predictable fitting to
the Langmuir model (Fig. 5.2a), and the R
2 -values of 0.774–0.911 for predictable
fitting to the Freundlich model (Fig. 5.2b), it was established that the Langmuir model
offered the more precise explanation of performance.
103
adsorption isotherms (Fig. 5.5a) indicates a fast initial rise in adsorption potential,
owing to chitosan’s great selectivity for the Zn(II)-cations.
The isotherm adsorption models, Langmuir and Freundlich, were utilized to
design Zn(II) adsorption onto the chitosan membranes. The Langmuir model is the
model that is widely utilized explaining the adsorption of metal ions on chitosan [2,
16, 24]. The Langmuir model suggests equal adsorption energies on the layer and
no sorbent transmigration on the top layer level. This model is true for single-layer
sorption on a layer consisting a limited number of sites [2] and is defined by the
linearization form:
C e
q e
=
C e
Q m
+
1
Q m b
(5.3)
In (5.3), q e and Q m are the equilibrium and maximum monolayer adsorption potential accordingly, and C e is the equilibrium concentration of metal ion in mmol L
−1 , b
is the criterion of affinity in L mmol
−1 . The regression plot of C e /q e versus concentration at equilibrium, C e , could be used to evaluate criterion b of affinity and optimum
adsorbent power, Q m . The essential features of the Langmuir model can be interpreted in terms of a non-dimensional factor identified as the separation factor (R L )
applied only to assess whether or not an adsorption mechanism is desirable [2], as
indicated in 5.4. The conditions of R L > 1, R L = 1 and R L between 0 and 1 signify
unfavourable, linear and favourable correspondingly [19].
R L =
1
1 + bC o
(5.4)
The Freundlich model is the next most commonly utilized isotherm model and
reflects a semi-analytical correlation between the concentration of adsorbents and the
concentration of adsorbents [7]. The Freundlich model’s linearized form is calculated
by using (5.5), for the determination of adsorption efficiency and adsorption rate. The
value of parameter n is in the range of 1–10 under standard adsorption requirements
[19].
log q e = log K F +
1
n
log C e
(5.5)
where K F and n (non-dimensional coefficients) separately indicate the adsorption
power and the adsorption strength [19].
The tests of the Langmuir and Freundlich models linearized plots using (5.3)
and (5.5) are shown in Fig. 5.5b, c accordingly, and the criteria for the model are
presented in Table 5.1. From the R
2 -values of 0.966–0.985 for predictable fitting to
the Langmuir model (Fig. 5.2a), and the R
2 -values of 0.774–0.911 for predictable
fitting to the Freundlich model (Fig. 5.2b), it was established that the Langmuir model
offered the more precise explanation of performance.