Nanoparticles as Sorbents for Removal of Heavy Metal Ions from Aqueous Solutions - Nanotechnologies for Water Environment Applications - page 152

capacity of 0.6 meq/g of the resulting nanoparticles, plus their ease of preparation,
suggests its competitive edge over others. For instance, poly(amidoamine) (PAMAM)
dendrimers of generation 8 has a Cu(II) capacity of 0.65 mmol/g (Diallo et al . , 1999).
Through UV-vis spectroscopy, Amigoni-Gerbier et al . (2002) suggests that the ligand
accessibility is closely correlated with the particle size.

Chen et al . (2003) modified the surface-aminated polystyrene nanoparticles
with a specific dye molecule called azo-chromophore. It was found that the
adsorption efficiency of ligand-modified nanoparticles was enhanced and the
nanoparticles retained their adsorptive capacity for Pb(II) after 3 cycles of
adsorption/desorption operation. Bell et al . (2006) synthesized polymer nanoparticles
with a core/shell structure. They demonstrated that the sequestration selectivity for
heavy metals could be altered by grafting a macrocyclic ligand. The original
core/shell nanoparticles were selective towards mercury ions solely; whereas the
modified nanoparticles would only adsorb Co(II), despite the presence of thousand-
fold excess of other heavy metals ions, such as mercury. Therefore, the polymeric
nanoparticles could be conveniently engineered or tailored to display specific
remedial function such as selective sequestration of heavy metals.

We have synthesized and studied novel polymeric nanoparticles of 150 nm
with metal-chelating pyridine groups, for heavy metal remediation and recovery (see
Figure 6.2). The poly(vinylpyridine) nanoparticles have been found to be very
uniform in size and these nanoscale adsorbent selectively removed Cu(II) despite the
presence of other competing cationic species.

1.4

1.2 Cu( II)

Z n( II)
Ni( II)

1

0.8

0.6

0.4

0.2

0

0 0.5 1 1.5 2

Equilibrium f ree metal ion conc entration, mM

Figure 6.2 (a) Field-emission scanning electron microscopy (FESEM) micrograph of
poly(vinylpyridine) nanoparticles (scale bar denotes 500 nm). (b) Adsorption
isotherm of poly(vinylpyridine) nanoparticles from mix metal ions solution
([Cu 2+ ]:[Zn 2+ ]:[Ni 2+ ] = 1:1:1) at pH = 5; solid lines were for guide of eyes.

6.3.2.3 Biopolymer-Based Nanoparticles

Another research area which receives considerable attention recently is the
synthesis of biopolymer-based nanoparticles for environmental application (Qi and
Xu, 2004; Chang and Chen, 2005). Chitosan is a natural polysaccharide with rich
functionalities. Due to its non-toxicity and low cost, chitosan has been studied