Environmental Engineering Reference
In-Depth Information
100 nm
Zeolite
Polysulfone
Polyamide
FIGURE 16.2
TEM cross section of a TFN membrane.
found to exhibit lux similar to TFC control membranes (made without silver nanopar-
ticles), but were found to resist development of
Pseudomonas
bacteria on the surface.
An alternate approach aimed at reducing fouling was presented by Hyun Soo Lee et al.
in 2008 [13]. TiO
2
nanoparticles were incorporated into an interfacially prepared RO mem-
brane by addition to the organic solvent phase. Changes in performance were attributed
to increased hydrophilicity, and the potential for these membranes to be photoactivated
to degrade organic compounds was mentioned. To improve incorporation, later work by
Babak Rajaeian et al. amino-silanized TiO
2
nanoparticles to allow covalent incorporation
of the nanoparticles into the membrane and gave good lux and rejection [14].
Puyam Singh explored an alternate nanoparticle composition, silica (Ludox
®
HS-40), and
used small-angle neutron scattering to explore the effect of nanoparticles on the polymer
structure to help correlate performance with structure [15]. Up to about 4.5 wt% silica in the
polyamide, good incorporation was observed with an alteration to the polyamide packing
adjacent to the nanoparticle. Above 4.5 wt%, less effective dispersion of the nanoparticle
was observed. Jadav and Singh continued the exploration of silica-based additives [16] and
found the aggregate pore size of the membrane was tunable from 0.34 to 0.73 nm by adjust-
ing the amount of Ludox HS-40 or laboratory-made silica used. Mengru Bao et al. describe
the use of monodispersed spherical mesoporous nanosilica in TFN membranes and found
increased hydrophilicity and permeability [17].
Mary Laura Lind and Eric Hoek, in a follow-up to the original TFN article presented in
May of 2009, reported on the ability to modify the zeolite used by changing the nature of
the mobile cation [18]. In this article, both Na
+
and Ag
+
were evaluated. Silver-exchanged
zeolites were found to give improved performance, and were also able to resist adhesion
of bacteria cells on the membrane, although antimicrobial activity was reduced relative
to nonpolyamide-bound silver-containing zeolites. An article later that year also demon-
strated the importance of nanoparticle zeolite size [19] with smaller zeolites that have the
greatest impact on lux and rejection, while larger zeolites had the largest effect on surface
properties such as charge, hydrophilicity, and roughness. In 2010, the effect of process
conditions was explored [20] by investigating the effect of curing, rinsing, and posttreat-
ments on TFN performance. This optimization work was found to give membranes having
performance better than commercially available samples.
A new potential application for nanocomposites was presented by Junwoo Park et al.
The subject membranes used a typical polyamide composition but used carbon nanotubes
as the additive and found the resulting nanocomposite had improved resistance to chlo-
r i n e [21].
