Environmental Engineering Reference
In-Depth Information
on the membrane surface [80, 81]. rahimpour et al. [82] discovered that the performance and antifouling properties of TiO
2
-
coated membranes are better than those of TiO
2
-entrapped membranes.
The effect of UV irradiation on the performance of TiO
2
nanocomposites has also been examined [82-84]. Membrane performance
and antifouling properties significantly improved with the increased hydrophilicity of the membrane and the photocatalysis reaction
initiated by the UV irradiation, thereby decomposing and removing the foulants, especially organic compounds.
The size of TiO
2
nanoparticles also significantly affects the performance of TiO
2
nanocomposite membranes. Vatanpour et
al. [85] and cao et al. [86] studied the effect of TiO
2
nanoparticle size on the performance of peS and pVDF membranes,
respectively. The antifouling property of the TiO
2
nanocomposite membrane improved with decreasing TiO
2
nanoparticle size
because of the large surface area and high adsorption of water.
17.3.1.1.2 Silicon Dioxide Nanoparticles
Aside from TiO
2
, SiO
2
is used to mitigate fouling in polymeric membranes. SiO
2
has been widely used in fabricating thin-film nanocomposites for various applications because of its availability and low price
compared with TiO
2
. Jadav and Singh [87] incorporated self-synthesized SiO
2
nanoparticles via the hydrolysis of tetraethyl
orthosilicate in an acidic medium into pAm films coated over a porous pSf support through interfacial polymerization to produce
a thin-film nanocomposite membrane. The flux increased as a function of SiO
2
loading because of increasing pore size. excellent
separation efficiency and productivity flux are obtainable with nanocomposite membranes containing about 1-2 wt% SiO
2
.
Similarly, commercialized SiO
2
nanoparticles incorporated into thin-film nanocomposite membranes were synthesized by adopt-
ing poly(amidoamine) dendrimers as aqueous monomers, trimesoyl chloride as organic monomer, and pSf as substrate [88]. The
addition of 1.0 wt% SiO
2
nanoparticles increased the permeation performance of the pAm-SiO
2
membrane by nearly 50%, without
a decrease in the salt rejection rate. When subjected to one cycle of filtration with oily wastewater, the pAm-SiO
2
membrane demon-
strated higher stable flux and nearly 50% salt removal. Jin et al. [89] reported that using pAm-SiO
2
thin-film nanocomposite mem-
branes prepared by a similar method in treating raw surface water enhanced membrane separation and antifouling properties.
Yin et al. [90] synthesized McM-41 (~100 nm) and nonporous spherical silica nanoparticles (~100 nm) as nanofillers to
study the influence of the internal pore structures of SiO
2
nanoparticles on the performance of thin-film nanocomposite mem-
branes. The McM-41 nanoparticles incorporated in the membrane showed significant improvement in permeating water flux,
while maintaining high rejection of salts. This result suggests that the internal pores of McM-41 nanoparticles significantly
improved water permeability compared with those of nonporous silica nanoparticles.
Apart from the incorporation of SiO
2
nanoparticles into thin-film nanocomposite membranes by in situ polymerization, the
hydrophilicity of pSf ultrafiltration membranes functionalized with SiO
2
nanoparticles via solution blending was also enhanced
[91]. The functionalized pSf membrane exhibited good antifouling properties and an increased permeability that is 16 times
higher than that of the neat pSf membrane in the filtration of oil-in-water emulsion, which is attributed to the larger pore size
and higher hydrophilicity.
17.3.1.1.3 Aluminum Oxide Nanoparticles
like other metal oxide nanoparticles, aluminum-based nanoparticles possess
properties that improve the performance of nanocomposite membranes. Yan et al. [92] dispersed commercialized Al
2
O
3
nanoparticles
(10 nm) into pVDF membranes homogeneously via ultrasonication for the treatment of oily wastewater. Antifouling ability was
enhanced as a result of decreased contact angle at constant surface porosity. The antifouling ability of the membranes was also
proven by filtration of α-amylase solutions [93] and oil field wastewater [94]. Yang et al. [95] also found that the integration of
nanosized Al
2
O
3
into the pVDF membrane structure significantly enhanced the antifouling ability of the pVDF membrane.
Aside from homogeneously dispersing the nanoparticles into a polymer matrix, as discussed previously, Saleh and Gupta
[96] fabricated pAm nanocomposite membranes containing Al
2
O
3
nanoparticles by in situ interfacial polymerization. They used
Al
2
O
3
nanoparticles with an average size of 14 nm, self-generated by an aqueous sol-gel method using precursors of aluminum
nitrate and citric acid mixed solution. The permeate flux was enhanced, while maintaining the salt rejection with the introduc-
tion of nanoparticles to the pAm membranes.
Apart from Al
2
O
3
nanoparticles, boehmite, an aluminum oxide hydroxide (γ-AlOOH) particle containing extra hydroxyl
groups on its surface, was used by Vatanpour et al. [97] in preparing peS-blended membranes. Incorporating boehmite nanopar-
ticles improved the hydrophilicity and pure water flux of the membranes. boehmite nanoparticle-embedded membranes also
exhibited superior characteristics and antifouling ability compared with γ-Al
2
O
3
/peS membranes. nevertheless, pure water flux
decreased at high nanoparticle concentrations because of agglomeration.
17.3.1.1.4 Zinc Oxide Nanoparticles
ZnO nanoparticles, one of the multifunctional inorganic nanoparticles, have gained increasing
attention because of their remarkable physical and chemical properties, including high catalytic activity and effective antibacterial and
bactericidal abilities. In addition, ZnO nanoparticles are economically more practical than TiO
2
and Al
2
O
3
nanoparticles [98].
Furthermore, incorporating ZnO nanoparticles enhanced the hydrophilicity and mechanical properties of the polymer matrix.
