Chromatographic method for pre-concentration
and separation of Zn(II) with microalgae and density
functional optimization of the extracted species†
Bhabatosh Mandal,
*
Monalisha Mondal, Bhavya Srivastava, Milan K. Barman,
Chandan Ghosh and Mousumi Chatterjee
A novel wild strain of microalgae, Phormidium luridum containing Gloeothece rupestris and Chlorococcum
infusionum (99 : 0.08 : 0.02), was studied for its ability to remove and retrieve Zn(II) from aqueous solutions
in the presence of some commonly occurring ions (Na
+
,K
+
, Cl
, SO
4
2
, ClO
4
, NO
3
) in their natural
contamination concentration range (50–300 mg L
1
). The algae, which were previously collected from
the river basin (Ajay), were grown on naturally occurring gravels in a glass column of nutrient enriched
raw water media. Systematic studies of the sorption of Zn(II) (0.02 mg mL
1
) over a pH range of 4.5–7.5
identified a maximum removal extent of 104 mMg
1
at neutral pH, mainly by adsorption at the surface
layer. Zn(II) was retrieved by selective elution with 5 10
3
M HNO
3
solution. Initially, [Zn(H
2
O)(OH)]
+
(h
[Zn(OH)(H
2
O)]
+ ¼ 1.25 eV) is adsorbed at the surface of the algae, which is built up of polysaccharides
(h
[glucose]
¼ 6.34 eV), before moving inside by the formation of a more stable complex with
Phycocyanobilin2, which has similar hardness (h
[Phycocyanobilin]
¼ 2.37 eV). The complex is stabilized by
52 195.48 eV mol
1
through the formation of two strong intramolecular hydrogen bonds (–OH/O ¼
163.54 pm; HOH/O ¼ 129.71 pm). Density functional theory optimization corroborates a stable
[Zn(H
2
O)(OH)]
+
–Phycocyanobilin2 tetrahedral complex.
1. Introduction
Due to several industrial activities, natural water sources have
become contaminated by metallic toxicants.
1
Owing to their
tendency to (bio) accumulate throughout the food chain,
2–4
even
at trace levels these non-biodegradable contaminants are
extremely toxic to humans, as well as to the ora and fauna of
the effluent-receiving bodies of water.
5
It goes without saying
that trace level monitoring and measurement of metallic toxi-
cants in real samples poses a challenge to analytical chemists.
However, the effect of the matrix has serious implications for
sophisticated instrumental methods of analysis.
6
Sample clean
up through preconcentration and selective separation of an
analyte is therefore usually necessary before it can be monitored
or measured. During preconcentration, ultimately the target
species is selectively gathered in a small volume from a large
volume of sample of a complex nature. The problem of
enrichment can be tackled by two consecutive processes: (1)
exploiting selective sorption, the target species is adsorbed by
the adsorbent from a large volume sample of low concentration
and (2) the analyte is collected in a more concentrated form
using a small volume of a selective eluent for its desorption.
Small amounts of metal pollutant can, therefore, be quantied
by coupling a preconcentration system to a sensitive, selective
detection/estimation technique.
7,8
In this regard, the most
widely used techniques include solvent extraction,
9
coprecipi-
tation,
10,11
ion exchange–extraction chromatography,
12,13
adsorption,
14
cloud point extraction,
15
electrochemical deposi-
tion,
16
solid phase extraction (SPE).
17–19
However, these classic
technologies are oen inefficient or too expensive when heavy
metals are present at trace level in a real sample with a large
amount of matrix.
20
Moreover, these need a signicant amount
of hazardous solvents/chemicals which may increase environ-
mental risks. It is therefore important to devise efficient bio-
sorption methods to remove those toxic elements, with a further
requirement of being environmentally-friendly. Metabolic
specicity for a given metallic toxicant can be advantageous in
bioremediation strategies using bioaccumulation.
21
Sorption of
heavy metals using cyanobacterium as biosorbents offers a
potential alternative to conventional processing methods,
mainly because of their low cost, strong metal binding capacity,
high sorption efficiency in dilute effluents, environmentally-
friendliness
22,23
and, more importantly, because of their self-
maintained adsorbent beds.
21
The analytical applicability of
Phormidium luridum (microalgae) as a biosorbent for the
recovery/removal of Zn(II) has been rationalized for two reasons.
Firstly, the extensive use of zinc in galvanization and
Analytical Laboratory, Department of Chemistry, Visva-Bharati, Santiniketan 731235,
India. E-mail: bhabatosh_mandal@yahoo.co.in
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c5ra01867f
Cite this: RSC Adv. , 2015, 5, 31205
Received 30th January 2015
Accepted 13th March 2015
DOI: 10.1039/c5ra01867f
www.rsc.org/advances
This journal is © The Royal Society of Chemistry 2015 RSC Adv., 2015, 5, 31205–31218 | 31205
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