Page 459 - Polymer-based Nanocomposites for Energy and Environmental Applications

416 Polymer-based Nanocomposites for Energy and Environmental Applications

categories: nanoadsorbents, nanocatalysts, and nanomembranes. Among the three,
nanomembrane is the third class of the nanomaterials employed in the wastewater
treatment processes. Nanomembranes are widely employed for wastewater treatment
in industries because of small pore sizes, low cost, high efficiency, and eco-
friendliness [24]. Generally, nanomembranes can be synthesized using nanomaterials
such as metals, nonmetal nanoparticles, and CNTs [19]. Nanomembranes are com-
monly classified into two main groups named polymeric and inorganic ceramic.
Recently, advantages of ceramic nanomembranes and disadvantages of polymeric
nanomembranes have drawn much attention toward the novel application of conclud-
ing ones. Inorganic ceramic nanomembranes prepared using metal oxides such as alu-
mina, zirconia (ZrO 2 ), SiO 2 , and titania, and nonoxides such as silicon carbide and
silicon nitride have been introduced as a novel approach substituting the conventional
polymeric nanomembranes [101,102]. Ceramic nanomembranes are generally made
as a monolayer and multilayered structure. A monolayer membrane has the advantage
over multilayered owing to its low cost and simple preparation method. However,
monolayer membranes cannot perform NF processes. Consequently, a membrane hav-
ing a multilayer configuration should be acquired with high-performance parameters
such as low cutoff values or high water fluxes [103]. Various skills have been adopted
for manufacturing of support including slip casting, extrusion, or powder pressing,
followed by coating of several micron layers of several types of ceramics on it. For
thin films, various methods of coating including chemical vapor deposition, sputtering
[104], laser ablation, and sol-gel processing are employed as preparation methods.
Regarding sol-gel method, several coating techniques have been used including slurry
coating, dip coating, and spray coating [105,106]. In order to acquire thin films of
better homogeneity, sol-gel method is highly acknowledged as low-temperature pre-
paration, high purity, and controlled chemical composition [107]. Nanocrystalline
alumina and titania films have been widely used in area such as UF and NF owing
to their resistances against high temperature withstanding capacity, different solvents,
easy availability, and wider processing possibility [108]. In developing high-efficient
wastewater treatment and reuse systems, TiO 2 photocatalytic membrane has a great
potential because of its multifunctional capability such as decomposition of organic
pollutants and physical separation of contaminants [103]. In other way, fouling is one
of the major concerns in almost all membrane processes. To reduce fouling, great
efforts have been made by the scientist.
Madaeni and Ghaemi [109] in creating self-cleaning membrane studied the effects
of coating of membrane surface with TiO 2 particles and UV radiation. Membrane
hydrophilicity and photocatalytic property can be improved by coating the membrane
surface with TiO 2 particles. Surface coating was employed on the membrane surface
by self-assembly of TiO 2 particles via coordinate bonds with OH functional groups of
polymer. The flux of the coated membrane with TiO 2 particles after being radiated by
UV light was amplified significantly in comparison with a virgin membrane. This
reveals that the self-cleaning property has been shaped by TiO 2 particles on the sur-
face of membrane. To study the influence of various research parameters in increasing
the self-cleaning property of the membrane, the concentration of TiO 2 particles, dura-
tion of UV radiation, and duration of being kept in water, the membrane roughness and
the presence of SiO 2 particles have been studied worldwide.