Biomedical Engineering Reference
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coupled with ICP-AES was successfully applied to the determination of transition and
rare-earth metals in river water samples.
Similarly, Li and his group (Li et al., 2009) synthesized a new chemically modified
chitosan hydrogel with 2,5-dimercapto-1,3,4-thiodiazole (CTS-DMTD). A range of
static sorption studies were performed on this adsorbent, which showed the selectivity
towards cations of the precious metals over other transition metal cations. They have
also found that adsorption capacities were significantly affected by the pH of solution,
with optimum pH values of 3.0 for Au(III), 2.0 for Pd(II) and Pt(IV). The saturated
adsorption capacities were 198.5, 16.2, and 13.8 mg/g for Au(III), Pd(II), and Pt(IV),
respectively. Langmuir and Freundlich isotherm adsorption models were applied to
analyze the experimental data and the results showed that adsorption isotherms of
Pd(II) and Pt(IV) could be well described by the Langmuir equation. The adsorption
kinetic investigations indicated that the kinetic data correlated well with the pseudo
second-order model. The recovery experimental data showed that CTS-DMTD had a
higher affinity toward Au(III), Pd(II), and Pt(IV) in the coexistence system contain-
ing Cu(II), Fe(III), Cd(II), Ni(II), Mg(II), and Zn(II). The studies of desorption were
carried out using various reagents and the optimum effect was obtained using thio-
urea. The sorption studies also revealed a considerable capacity for Au(III) ions, which
might be useful in the removal of gold from ores. However, the CTS-DMTD was a
little bit more difficult to reuse.
Quite recently, Guibal and his research team (Butewicz et al., 2010) have immo-
bilized thiourea onto chitosan; the new polymer was employed for the sorption and
recovery of platinum and palladium from acidic solutions (up to 1-2 M HCl concen-
trations). The kinetics of the sorption process was investigated and the pseudo-second
rate equation was used for modeling the uptake kinetics. Similarly, Chanthateyanonth
et al. (2010) reported the successful immobilization of vinyl sulfonic acid sodium salt
onto dendritic hyper branched chitosan. The new chitosan derivatives displayed im-
proved water solubility as compared to the starting material. In addition, the new ma-
terial showed better antimicrobial activity and chelating behavior with cadmium(II),
copper(II), and nickel(II) than chitosan itself.
Calix[n]arenes are cyclic oligomers composed of phenol units and are very well
known as attractive and excellent ionophores because they provide a unique three-
dimensional structure with almost unlimited derivatization possibilities (Asfari et al.,
2001; Gutsche, 1998; Vicens and Bohmer, 1991). Tabakci and Yilmaz evaluated the
sorption properties of a calix[4]arene-based chitosan polymer (C[4]BCP) toward some
heavy metal cations (Co
2+
, Ni
2+
, Cu
2+
, Cd
2+
, Hg
2+
, and Pb
2+
) and dichromate anions
(Cr
2
O
7
-2
/HCr
2
O
7
-1
) as sorbent materials. The results for heavy metal cations showed
that C[4]BCP was an excellent sorbent while chitosan exhibits poor sorption than C[4]
BCP (Tabakci and Yilmaz, 2008). In the sorption studies of dichromate anions, C[4]
BCP was a highly effective sorbent at pH 1.5. The sequence of sorption efficiency of
C[4]BCP is Hg
2+
> Pb
2+
> Cd
2+
> Cu
2+
> Ni
2+
> Co
2+
. From the previous works (Memon
et al., 2006; Tabakci et al., 2006; Yilmaz et al., 2006), it has been concluded that the
amide derivatized calixarenes are effective sorbents for these cations because NHC=O
group is preferable to complex the more polarizable transition metal ions especially
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