Biomedical Engineering Reference
In-Depth Information
energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) could be determined using the following
equations and are summarized in Table 10 [27,71].
Δ °=−
G
l
K
(14)
e
Δ °Δ°
HS
ln K
=−
+
(15)
e
RT
RT
Table 10. Thermodynamic parameters for adsorption of cationic dyes by
γ
-PGA
a
Temperature
K
e
(L/mg)
Δ
G
°
(kJ/mol)
Δ
H
°
(kJ/mol)
Δ
S
°
(J/mol K)
Au-O/γ-PGA
301
0.071
-7.69
-15.17
-25.13
318
0.046
-6.97
333
0.040
-6.92
Rh-B/γ-PGA
301
0.035
-7.06
-28.24
-70.85
318
0.016
-5.39
333
0.012
-4.84
Sa-O/γ-PGA
301
0.302
-11.67
-20.23
-28.46
318
0.194
-11.16
333
0.139
-10.76
BB-Y/γ-PGA
301
0.173
-10.72
-27.26
-55.45
318
0.079
-9.25
333
0.062
-9.01
Source
: Inbaraj et al. 2006a; 2008.
a
Dye conc. range: 10-200 mg/L; γ-PGA dose: 0.4 g/L for Au-O, Rh-B, Sa-O and 0.3 g/L for BB-Y.
where K
e
is the equilibrium constant (Langmuir constant), R is the universal gas constant
(8.314 J/mol K) and T is the absolute temperature (K). The negative ΔG° values indicated the
spontaneity of dye adsorption, while the negative ΔH° value confirmed the exothermic nature
of adsorption process [27,71]. Likewise, the negative ΔS° revealed the decreased randomness
at the solid/solution interface and no structural modification occurred in γ-PGA [27,71]. Thus,
the negative ΔH°, ΔS° and ΔG° values affirmed that the adsorption of cationic dyes Au-O,
Rh-B, Sa-O and BB-Y on γ-PGA was favored at lower temperatures.
4.4.
γ
-PGA Dose-activity Relationship
On increasing the γ-PGA dose from 0.04-6.00 g/L for a 200 mg/L dye solution, the
removal of Au-O, Rh-B and Sa-O dyes rose by 79.1, 81.8 and 67.9%, respectively, while the
