Environmental Engineering Reference
In-Depth Information
ZnO nanocomposite membranes are developed by dispersing different dosages of ZnO nanoparticles homogenously into the
polymer matrix, followed by phase inversion [98-100]. In treating reclaimed water, Hong and He [99] reported maximum pure
water flux, minimum surface roughness, and minimum membrane resistance at an optimum dosage of 0.005 wt% of ZnO
nanoparticles in the pVDF membranes because of enhanced hydrophilicity. enhanced membrane separation properties were
also observed by liang et al. [98] and balta et al. [100] Given the successful implantation of ZnO nanoparticles into the mem-
brane inner surface or pore wall, the membrane exhibited remarkable anti-irreversible fouling property and doubled water per-
meability at the optimum dosage of 6.7 wt% ZnO nanoparticles when the pVDF membranes modified with ZnO were used in
multicycle filtration experiments [98]. Aside from lower flux and improved permeability, balta et al. [100] observed a prominent
improvement in dye rejection potential induced by the addition of ZnO nanoparticles to peS membranes even at unusually low
concentrations. Given that ZnO nanoparticles exhibit properties similar to those of TiO
2
, but are comparatively cheaper, the
former have been predicted as an excellent alternative to TiO
2
for use as an antifouling material.
17.3.1.2 Fouling Mitigation for Ceramic Membranes
Metal oxides, such as Al
2
O
3
, TiO
2,
and Fe
2
O
3
are the most commonly
used nanoparticles for the fabrication of nanostructured ceramic membranes for applications in water treatment. The integration
of metal oxide nanoparticles with ceramic membranes provides additional functionalities to catalyze and degrade foulants
under oxidizing conditions.
17.3.1.2.1 Titanium Dioxide Nanoparticles
TiO
2
nanoparticles have drawn significant research attention in the fabrication
of ceramic membranes because of their excellent chemical resistance, high water flux, and photochemical and catalytic
properties [101]. previous studies fabricated ceramic membranes by incorporating highly hydrophilic TiO
2
nanoparticles to
create preferential passages for the transport of water. For example, Zhang et al. [102] prepared Al
2
O
3
ceramic membranes
doped with 5% TiO
2
by the solid-state sintering technique. compared with pure Al
2
O
3
membranes, the Al
2
O
3
-TiO
2
nanocomposite
membranes exhibited up to 30% improvement in permeate flux in the filtration of oily wastewater under the same operating
conditions because of their enhanced membrane hydrophilicity and antifouling properties resulting from the doping of TiO
2
.
Monash and pugazhenthi [103] prepared low-cost porous ceramic membranes with different loadings of TiO
2
nanoparticles.
The prepared nanocomposite membranes with optimum TiO
2
loading exhibited a maximum rejection of 99% for an oil
concentration of 200 ppm in the oil-water emulsion separation.
Yang and li [104] fabricated inside-out tubular TiO
2
/Al
2
O
3
composite membranes for electrofiltration of chemical-mechanical
polishing wastewater. The composite membranes were fabricated by coating the TiO
2
coating layer inside the tubular substrate
of Al
2
O
3
using sol-gel/slip-casting technique and then followed by firing process. The incorporation of 5% TiO
2
to Al
2
O
3
increased
the permeate flux up to 20%, indicating enhanced hydrophilicity of TiO
2
-Al
2
O
3
composite membranes compared with pure Al
2
O
3
membranes. Zhang et al. [105] fabricated a hierarchical TiO
2
nanowire ultrafiltration membrane made of two dimensions of TiO
2
nanowires, 20-100 nm TnW20 and 10 nm TnW10, by hydrothermal synthesis, followed by a filtration and hot-press process.
TnW20 acts as the supporting layer of the membrane, providing mechanical strength, while TnW10 serves as the functional
layer, providing outstanding permeability and separation properties. TiO
2
nanowire ultrafiltration membranes exhibited excep-
tional performance in photodegradation and antifouling tests because of the degradation and inactivation of organic and biological
pollutants under UV irradiation.
17.3.1.2.2 Aluminum-Based Nanoparticles
In addition to the application of aluminum-based nanoparticles as nanofillers in
nanocomposite membranes, Al
2
O
3
nanoparticles can also be used as ceramic precursors. Jones et al. [106] fabricated asymmetric
Al
2
O
3
ultrafiltration membranes with acetic acid surface-stabilized Al
2
O
3
nanoparticles (A-alumoxanes). A defect-free Al
2
O
3
membrane was obtained by contacting α-Al
2
O
3
supports with an aqueous solution of A-alumoxanes followed by firing. The
alumoxane-derived membranes possessed high porosity and similar or improved permeability as compared with commercially
available alumina membranes. The smooth surface of alumoxane-derived membranes was confirmed by scanning electron
microscopy (SeM), and their high hydrophilicity was verified by atomic force microscopy (AFM), indicating great potential in
fouling remediation of membranes. bailey et al. [107] also found that alumoxane-coated ceramic membranes are more
hydrophilic than uncoated membranes.
γ-Al
2
O
3
, another type of aluminum-based nanoparticles, has been extensively studied because of their unique surface charge char-
acteristics defined by the amphoteric behavior of their surface sites (hydroxyl groups). Majhi et al. [108] prepared a low-cost γ-Al
2
O
3
membrane on a macroporous clay support using the dip-coating method. The production cost was reduced by fabricating the γ-Al
2
O
3
top layer from a boehmite sol prepared via a sol-gel route employing aluminum chloride (Alcl
3
) salt as a starting material. The
maximum rejection values for Mgcl
2
and Alcl
3
were up to 72 and 88%, respectively, at a salt concentration of 3000 ppm.
Instead of employing self-generated γ-Al
2
O
3
, Madaeni et al. [109] employed a commercialized γ-Al
2
O
3
-based ceramic
microfiltration membrane to eliminate coke particles from petrochemical wastewaters prior to the introduction of coalescers.
