Environmental Engineering Reference
In-Depth Information
mesoporous materials. Incorporation of silver into
polymers has been shown to be a promising strategy
for the development of materials for water disinfec-
tion. The antibacterial eficiency of cylindrical poly-
propylene water ilters coated with a 35.0 nm layer of
nano-silver particles (nAg) has been evaluated (Figure
12.6). 41 After 7-h iltration, the nano-silver-coated il-
ters were able to remove 100% (3 log 10 reduction) of
E.  coli contamination, whereas the uncoated ilters
were not able to decrease the number of bacteria. The
silver leaching tests showed that the ilter releases nil
amounts of silver and it complies with the require-
ments of the US EPA. These results suggest the pos-
sibility of the use of the nano-silver-coated ilters/membranes in water disinfection. 41 In
another report, nAg-impregnated functionalized carbon nanotubes (multiwall carbon nano-
tubes [MWNTs]) polymerized with β cyclodextrin (CD) using hexamethylene diisocyanate
as the linker has been reported. 42 The polymeric nanocomposites (Ag-MWNT-CD) were
found to reduce bacterial cell counts in water spiked with E. coli to 94% within 30 min and
to as low as 0 CFU/mL (colony-forming units per milliliter) within 90 min. 42
Another strategic design of polymer-Ag nanocomposites for the development of envi-
ronmentally safe water disinfection processes is using the core-shell Ag nanoparticles or
nanocomposites with both antibacterial and magnetic properties. In these cases, the silver
released into the system can be easily collected using a simple magnet. Alonso et al. have
reported Ag@Co-NPs with a low-cost superparamagnetic Co 0 -core and an antibacterial
Ag-shell encapsulated on granulated cation exchange polymeric matrices for water purii-
cation applications. 43 The polymer-nanocomposites exhibited antibacterial activity and Ag
and Co release from Ag@Co-NCs after 60 min of continuous operation was determined by
inductively coupled plasma-mass spectrometry. All samples showed values <1.0 ppm for
Ag (the limit of silver release into water as per US EPA) and 0.1 ppm for Co. These released
core-shell nanoparticles can be easily collected in the treated water, and this approach has a
lot of potential in real-life water puriication systems, particularly for developing countries. 43
One of the disadvantages of the polymer-Ag composites thus far developed is that the
polymer used to support the inorganic material is not antibacterial. Sambhy and cowork-
ers have developed a dual-action antibacterial composite consisting of a cationic polymer
matrix and embedded silver bromide nanoparticles. 44 This composite having the antibac-
terial cationic polymer, poly(4-vinyl- N -hexylpyridinium bromide) along with the silver
bromide nanoparticles made by an on-site precipitation technique has shown long-lasting
antibacterial activity and inhibited the bioilm formation. 44 These dual-action polymer-Ag
composites have potential for use in water disinfection. Combined with the low cost and
effectiveness in its applications, the polymer-Ag technology has potential applications in
water disinfection and may have large implications in developing countries.
(a)
(b)
FIGURE 12.6
(a) Uncoated and (b) nAg-coated polypro-
pylene ilter. (From Heidarpour, F. et al.,
Clean Technol. Environ. Policy , 13, 499, 2011.
With permission.)
12.2.2 Organic-Silica Composites
12.2.2.1 N -Halamine Silica Composites
As mentioned earlier, N- halamine materials are promising materials for water disinfec-
tion. N -chlorohydantoinyl siloxanes are also used to functionalize the surfaces of silica
gel/sand particles to produce a biocidal material upon treatment with bleach solution
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