Nanoparticles as Sorbents for Removal of Heavy Metal Ions from Aqueous Solutions - Nanotechnologies for Water Environment Applications - page 149

The simplest form of polymeric nanoparticles, in the form of latexes (also
known as emulsion polymer or polymeric dispersion), has been manufactured in high
tonnage around the globe and constitutes a major volume of polymer manufacturing
nowadays. The major applications of latexes or polymeric nanoparticles include paint
and coating, paper and paperboard, packaging and adhesives. Antonietti and Tauer
(2003) estimated that about 25% of the total amount of synthetic polymer produced
worldwide (approximately 2 x 10 8 metric tons per annum at that time) is prepared via
various heterophase polymerization routes. This rough estimation implies that a
minimum financial value of 47 billion USD was generated annually. In fact, the
environmental applications of these polymers are not uncommon. For instance, water
soluble polymers are used in the coagulation/flocculation unit of every
water/wastewater treatment process.
Other emerging application areas for polymer nanoparticles are in biomedical
and pharmaceutical fields, for protein bioseparation and drug-delivery, etc.
(Kawaguchi, 2000). The concept of immobilizing reagents or probes on a polymer
support for use in chemistry and biology has received a great deal of attention. Since
the activity of supported reagents depends on the accessibility of the active sites and
is often limited by intraparticle-diffusion (Guyot, 1988), considerable efforts have
been made to develop new polymer supports with improved capacity, accessibility
and selectivity (Okay, 2000; Sherrington, 2001). This issue has tremendous
implication on the environmental applications of such polymer supports. For instance,
it is well known that the chelating resin (diameters of 0.31.2 mm) has slow kinetics
despite their high affinity towards heavy metals cations (Sengupta and SenGupta,
2002). A variety of polymeric nanoparticles with different surface functional groups,
for instance amine groups or epoxy groups, could be synthesized from scratch (Ma,
1999) or surface-functionalized (Kawaguchi, 1999; Wang et al . , 2003). Besides
surface chemistry, morphology of polymeric nanoparticles could be varied as well
(see Figure 6.1). Hence, the polymeric nanoparticles could serve as nanoscale
polymer supports, for instance, nanocarriers for precious metal catalysts (Biffis,
2001). Larpent et al . (2004) demonstrated that the polymeric nanoparticles could be
dendronized at ease, and the resulting nanoparticles could be an inexpensive
substitute for applications involving dendrimers.
In other words, the synthetic processes whereby these polymeric nanoparticles
are manufactured are highly well-established and scalable. These synthetic versatility
and availability should not thwart the efforts in utilizing them as remedial agents for
either in-situ or ex-situ treatment. Despite the various advances in synthesis and
functionalization of polymeric nanoparticles in recent decades, relevant
environmental application remains rare. This could be due to the misconceptions,
including difficulties in recovery and reuse of nanoparticles and the associated high
synthesis/manufacturing cost. The manufacturing industry of polymer-emulsions is
highly established world-wide, so is the associated downstream separation process.
Filtration processes such as microfiltration and ultrafiltration have already been
accepted by industry as major operation for separation of latex emulsions (Cheryan,