Chemistry Reference
In-Depth Information
CH
3
CO
H
H
H
CH
2
OH
HN
O
4
O
HO
1
O
H
H
H
H
HO
1
O
4
HN
O
CH
2
OH
H
CO
H
H
CH
3
N-acetyl-D-glycosamine
n
Chitin
i.e.
poly[
β
-(1
→
4)-2-acetamido-2-deoxy-D-glucopyranose]
H
H
H
CH
2
OH
NH
2
O
4
O
HO
1
O
H
H
H
H
HO
1
O
4
NH
2
O
CH
2
OH
H
H
H
n
Chitosan
i.e.
poly[
β
-(1
→
4)-2-amino-2-deoxy-D-glucopyranose]
Scheme 3.1
Structures of chitin and chitosan.
cellulose and chitosan, a heteropolymer constituted by glucosamine and a fraction of acetylglucosamine
residues (Scheme 3.1), is a well-known biopolymer characterized by its high sorption capacity. Amine groups
of chitosan are responsible for the high sorption of metal ions through the chelation mechanism or by ion
exchange depending on the nature of metal ions and the pH conditions. Chitosan soaked in carbon tetrachloride
when irradiated with
rays leads to a cross-linked product with > CCl
2
group as a spacer and the resulting
polymer (CRC) and its hydrolyzed product (CRCH) are found to have good chemical stability [14]. Chitosan
and its derivatives have wide range of applications for example, biosensors for removal of heavy metal ions
including uranium.
γ
Green laboratory proposal
[15]
Commercially available medium viscosity grade chitosan was used for
preparing CRC and CRCH and the irradiation was carried out in a Co-60
chamber of radiation dose of 5
kGy/h. 1.0571 g CRCH or 1.05 g CRC were immersed in Millipore water and allowed to swell. The glass
column (120 mm × 8 mm) was than packed with the swollen polymer. After the column was conditioned at
pH 6 with nitric acid, 100 ppm uranium (VI) solution at pH 6 spiked with U-233 tracer was allowed to pass
through the column at a flow rate of 1 ml min
-1
. The effluent was collected in fractions and the uranium
concentration was determined either by radiometry using a scintillation detector (measuring
γ
activity of
U-233) or by spectrophotometry where Arsenazo III was used as the chromogenic agent. More than 97
α
%
elution of uranium was possible from the CRCH column using Na
2
CO
3
(1M) eluent which is known to form
strong carbonato complex. The distribution coefficient (Kd) values of uranium with CRCH and CRC were
found to be 384
−
(
Co
C
) /
W
[
Kd
=
where C
0
=
initial concentration of metal ion, C
=
total concentration of metal ion
CV
/
after equilibration, W
volume of the aqueous phase in ml] and 125, respectively.
On the other hand, the exchange capacities for uranium with those polymers were found to be respectively
0.050 and 0.034 mmol g
-1
.
=
weight of biopolymer, V
=
