BIOSORPTION OF Pb2+, Cd2+, & Ni2+ FROM WATERS BY ...

3.1.2. FTIR Results
FTIR spectroscopy gives valuable information about the nature of the bonds
present and allows identification of functional sites such as carboxyl, sulfonate,
hydroxyl, and amino groups on the cell surface. These groups have been proposed to
be responsible for the biosorption of metals by algae. Their relative importance in the
biosorption of metals might rely on the parameters such as the quantity and
availability of the binding sites, chemical site, and affinity between the metal and the
functional site.
FTIR technique has been widely utilized to detect vibrational frequency
changes in seaweeds (Park, et al. 2004; Sheng, et al. 2004; Figuera, et al. 1999). The
organic functional groups and the corresponding IR frequencies observed in seaweeds
(literature values) and in the biomasses used in this study are tabulated in Table 3.1.
Almost all of the frequencies obtained from Dunaliella salina, Oocystis sp.,
Porphyridium cruentum, and Scenedesmus protuberans are in accordance with each
other and with the literature values. Strong similarities among the FTIR spectra can
also be seen in Figure 3.2. The region between 3200-3500 cm -1 exhibits the stretching
vibration of O-H and N-H which also confirms the presence of hydroxyl and amine
functional groups in the algal structure. The region between 3000-2800 cm -1 shows
the C-H stretching vibrations of sp 3 hybridized C in CH3 and ˃CH2 functional groups.
The peaks at 1652 cm -1 (for Dunaliella salina), 1642 cm -1 (for Oocystis sp.), 1638
cm -1 (for Porphyridium cruentum), and 1647 cm -1 (for Scenedesmus protuberans)
reveal the presence of carbonyl group. The presence of amide in the structure of each
alga is confirmed by the peak at 1545 cm -1 (for Dunaliella salina), 1544 cm -1 (for
Oocystis sp.), 1542 cm -1 (for Porphyridium cruentum), and 1542 cm -1 (for
Scenedesmus protuberans). The absorption peaks around 1240 cm -1 and 1150 cm -1
indicate the phosphate esters in Dunaliella salina, Oocystis sp., and Scenedesmus
protuberans. The phosphate esters are the source of phosholipids. The absorption
peaks at the respective frequencies of 1075 cm -1 and 1076 cm -1 confirm the presence
of sulfoxides in Dunaliella salina and Porphyridium cruentum. The observed
frequencies in FTIR spectra of the algae used indicate the presence of amine (R–NH2),
amide (R1(CO)NR2R3) (aminoacids, proteins, glycoproteins, etc.), carboxylic acids
(fatty acids, lipopolysaccharides, etc.), sulfoxides and phosphates.
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