7.2 Evaluation of Information
137
7.2 Evaluation of Information
7.2.1 pH Equilibrium Model
This model is similar to the Osifo et al. [18] equilibrium model and is derived from two
equilibrium reactions and a balance of the nitrogen mass. Adsorption via coordination
has been suggested as the chitosan binding mechanism as given in 7.1, and the
equilibrium constant for this reaction is expressed in 7.2. The site of adsorption to
chitosan is known as –NH 2 .
M
2+
(aq) + n(−NH 2 ) + mH 2 O
M(−NH 2 ) n , (OH
−
) m
(2−m) + mH
+
(7.1)
where n is the functional group of amines, and m is the group of hydroxides.
If [M(–NH,)n, (OH
– ),](2 − m)
+ is defined as [M*], 7.2 will display the
corresponding K ads as
K ads =
M
∗
H
+
m
[−NH 2 ]
M
2+
aq
(7.2)
The base chitosan reaction can take place as follows:
−NH 2 + H
+
−NH
+
3
(7.3)
The acid–base constant for 7.3 reaction can be calculated via a titration experiment
using an experimental titration curve. The degree of protonation, α, expressed as the
ratio of the protonated amine groups to the total amine groups not complexed with
adsorbate, is defined from this experiment as
α =
−NH
+
3
[−NH 2 ] +
−NH
+
3
(7.4)
The concentration of total amine group is equal to the amount of the concentration
of unbounded amine groups [–NH 2 ], protonated amine groups [–NH 3
+ ] and adsorbed
amine groups spent (n.[M*]):
[−NH 2 ] T = [−HN 2 ] +
−NH
+
3
+ n
M
∗
(7.5)
The introduction of 7.4 and 7.5 provides
[−NH
+
3 ] = α
[−NH 2 ] T − n
M
∗
(7.6)