Environmental Engineering Reference
In-Depth Information
concentration. The advance properties shown by biogenic Ag
0
was due to the role of the dead lactic acid bacterial cell wall
within the nanoparticles as microscale carrier matrix for the nanoparticles and prevent the aggregation problem.
nangmenyi et al. [19] reported that Ag nanoparticles impregnated on an inorganic fiberglass surface exhibit both bacterio-
static and bactericidal properties for disinfecting
E. coli
because of its inorganic fibrous network that offers high contact
efficiency and faster kinetics. Gangadharan et al. [18] used modified AgnO
3
methacrylic acid copolymer beads in disinfecting
Gram-negative and -positive bacteria.
E. coli
,
P. aeruginosa
, and
Staphylococcus aureus
were completely inhibited, but not for
spore-forming
Bacillus subtilis
. The inhibited bacteria had little resistance toward the Ag nanoparticle-bound copolymer beads,
with 99.9% reduction within the same time frame. In addition, no bacteria adhered to or were adsorbed onto the copolymer
beads containing Ag nanoparticles. Thus, these beads have potential applications in water disinfection. lin et al. immobilized
Ag nanoparticles on TiO
2
(TiO
2
/Ag) to form hybrid nanocomposite particles [76]. The antibacterial activity of TiO
2
/Ag hybrid
particles against
E. coli
is similar, with or without UV irradiation. However, the bactericidal behavior of hybrid particles is
significantly affected by Ag concentration in the nanocomposite, which is favorable for deactivating
E. coli
.
17.3
nanocomposite membranes in Water remediation
Membrane separation technology is of interest in water remediation because of its high separation efficiency and ease of opera-
tion. This technology uses polymeric and ceramic membranes composed of organic and inorganic materials, respectively.
polymeric membranes have become the focus of membrane research because of better control of the pore-forming mechanism,
higher flexibility, and lower costs as compared to ceramic membranes. polymeric membranes have been widely studied including
polyethersulfone (peS), poly(vinylidene) difluoride (pVDF), polyamide (pAm), polysulfone (pSf), and polyacrylonitrile (pAn).
However, polymeric membranes exhibit high hydrophobicity, fouling and biofouling, low flux, and low mechanical strength.
Meanwhile, ceramic membranes made of refractory oxides, such Al
2
O
3
, TiO
2
, and zirconium oxide (ZrO
2
), have excellent
chemical, thermal, and pH stability compared with polymeric membranes. Moreover, given their long lifetime and resistance to
high temperature, pressure, and corrosive solutions, ceramic membranes are very cost-effective for water treatment.
With the objective to improve the properties and functionalities of polymeric and ceramic membranes in water remediation,
nanoparticles have been introduced into polymeric and ceramic membranes. Generally, the main goals behind the incorporation
of nanoparticles into membranes include membrane fouling and biofouling mitigation, disinfection, and photocatalytic degra-
dation of pollutants.
17.3.1
development of membranes with antifouling properties
17.3.1.1 Fouling Mitigation in Polymeric Membranes
nanoparticles are added to membranes to minimize fouling and
enhance separation properties. Membrane fouling caused by organic solutes and biofouling are the most common types of foul-
ing. The addition of nanoparticles to the membranes increases skin layer thickness and skin surface porosity, suppresses mac-
rovoid formation, increases membrane permeability, and increases or decreases rejection [77]. TiO
2
nanoparticles are the most
widely used in remedying membrane fouling caused by organic solutes.
17.3.1.1.1 Titanium Dioxide Nanoparticles
One problem in the fabrication of TiO
2
/polymer nanocomposites is the dispersion
of TiO
2
nanoparticles into the polymer matrix because these nanoparticles weaken the performance of nanocomposites by
agglomeration. Thus, Wu et al. [78] modified the TiO
2
surface with γ-aminopropyltriethoxysilane before introducing TiO
2
to
the peS matrix to overcome agglomeration. TiO
2
content was optimal at 0.5 wt%. Antifouling properties were improved based
on the filtration of bovine serum albumin (bSA) solution. Yang et al. [79] employed sodium dodecyl sulfate to modify the
surface of TiO
2
nanoparticles before incorporating them into the pSf matrix. The membranes exhibited outstanding water
permeability, hydrophilicity, mechanical strength, and good antifouling properties at 2 wt% TiO
2
content. The membranes also
effectively treated emulsified oil wastewater.
Aside from homogeneously dispersing TiO
2
into the polymer matrix, other preparation methods, including membrane
surfaces coated with TiO
2
nanoparticles, have been explored to fabricate nanocomposite membranes. TiO
2
nanoparticle self-
assembly membranes were prepared by immersing a poly(styrene-alt-maleic anhydride) and pVDF blend membrane in a TiO
2
nanoparticle solution [80]. TiO
2
nanoparticles were assembled on the membrane surface via electrostatic interaction established
between TiO
2
nanoparticles and the -cOOH groups on the membrane surface. bae et al. [81] successfully fabricated sulfonated
poly(ether) sulfone (SpeS) membranes surface-coated with TiO
2
via the electrostatic interaction between TiO
2
nanoparticles
and anionic groups on the surface of SpeS membranes. permeability and antifouling ability were enhanced by the TiO
2
layer
