Page 460 - Polymer-based Nanocomposites for Energy and Environmental Applications

Nanocomposite membrane for environmental remediation 417

Shayesteh et al. [110] prepared nanomembranes using γ-alumina and titania nan-
ocrystallites and were coated by sol-gel method on alumina supports, respectively.
A mesoporous structure for the coating layers of nanomembrane was obtained with
the average pore size of 5.8 nm. For permeability of demineralized water and rejection
of ions and microorganisms, the performance of the nanomembranes was examined
using a wastewater model. Results reveal that the permeability was reduced in the
range of 1–10 bar applied pressure. At higher than 10 bars, with the increase of
pressure, the permeability almost stayed constant owing to the increase of flux.
The multilayer nanomembranes revealed different rejections for ions up to 25%
but completely separation of the microorganisms.
Similarly, for environmental applications, Alem et al. [103] developed a meso-
porous TiO 2 multilayer membrane with high permeability and photocatalytic activity
via sol-gel method. The resulting TiO 2 multilayer membrane revealed homogeneity
with no cracks or pinholes, small pore size (4 nm), large specific surface area
2
(83 m /g), and small crystallite size (10.3 nm). Furthermore, the photocatalytic prop-
erties and permeability of the titania membrane were measured. Based on methyl
orange degradation, the photoactivity of the titania membrane was studied to be
41.9% after 9 h UV irradiation. This measurement designates high photocatalytic
activity per unit mass of the catalyst. The photocatalytic activity of the membrane
improved by 60% without sacrificing the membrane permeation via multilayer
coating technique.
Likewise, for oily wastewater treatment, Vatanpour et al. [111] employed
multiwalled carbon nanotubes (MWCNTs) coated using TiO 2 nanoparticles with
polyethersulfone (PES) membranes. In this study, the influence of embedding
TiO 2 -coated MWCNTs in PES matrix on membrane morphology, properties, and anti-
biofouling was presented, and the acquired results were compared with the prepared
oxidized MWCNTs and TiO 2 blended PES membranes. Contact angle measurements
revealed that coating of TiO 2 nanoparticles on the surface of oxidized MWCNTs
improved the hydrophilicity of the achieved membranes. The pure water flux of
the blend membranes improved with the content of TiO 2 -coated MWCNTs. Fouling
resistances of membranes were estimated by whey solution filtration. It is revealed
that 0.1 wt% of TiO 2 -coated MWCNT membrane portrayed the best antibiofouling
properties due to its lowest surface roughness and synergistic photocatalytic activity
induced by incorporated nanoparticles.
Synthesis and characterization of alumina membranes with ultrafine pores was
made by Leenaars et al. [108]. In first effort, microstructural studies were performed
on nonsupported membranes. The study reveals that <20 μm thick alumina films were
prepared using a process in which a boehmite sol is constantly gelled, dried, and
calcined. The resulting structure had the unique property that only ultrafine pores with
a narrow pore-size distribution were presented within large crack-free layers. It was
noticed that the acid concentration of precursor sol and sintering temperature may
affect the microstructure of membrane. The minimum 2.5 nm modal pore size was
achieved. Similarly, in second effort, the development of supported membranes
was carried out. Dipping method was employed to prepare supported γ-alumina mem-
branes. In this method, a capillary pressure drop is created by bringing a microporous
ceramic support into contact with a boehmite (γ-AlOOH) sol. This pressure drop