152
through the thickness of the casting solution. These clusters also called as nodules
are then interconnected together by entanglement because of the shared polysulfone
chains. The pore sizes given for the composite membrane correspond to the apertures between nodules. A membrane skin consisting of a packed nodular morphology and a large number of pores at 0.05 wt% loading is responsible for the high flux,
while upon further addition of zeolite, the membrane permeability reduces, because
of the decrease in the number of pores which occurs due to the agglomeration of
particles, causing to enlarge nodule size. Nucleating and growth increases with the
amounts of zeolite leading to pore size significantly enlarged. The pore dimension
and the number of pores which are directly related to the permeability and molecular weight cutoff of a membrane can be precisely tuned by the nature of zeolite
suspension. Suspension with a well-dispersed zeolite nanoparticle produces a large
number of small nodules and pores, while zeolite aggregates form a less pore density as a consequence of large-sized nodules.
In general, water permeability is predominantly dependent on surface hydrophilicity of the membrane. Thus, hydrophilic nanoparticles located on the membrane
surface are mostly desired. On the other hand, recent observations have shown that
the hydrophilic nanoparticles with high surface free energy preferably migrate to
the polymer water interface during immersion precipitation process. Then, they
hydrolyze forming surface hydroxides. The resultant membrane contributes to the
passage of water and hence improves water flux. Deposition of TiO 2 nanoparticles
onto a membrane surface, in this case, can be given as an example providing the
binding of surface hydroxyl groups that are polar when initiated with UV light. The
final surface structure demonstrated strong interaction with water molecule through
hydrogen bonding and van der Waals forces (Qiu et al. 2009). This useful property
of surface-adsorbed water layer enables the membrane with substantially high permeability. In another study, Lakhotia et al. (2019) prepared a thin film nanocomposite membrane by dispersing FeO nanoparticles on the surface of the composite.
With the increase in surface density, the hydrophilicity (contact angle 85–50°), surface charge (−6.3 to −14.2 mC/m
2
), flux (28–37 L/m
2
.h), and salt rejection ( >90%)
of the nanocomposite membranes were significantly improved. A membrane without FeO nanoparticle, on the other hand, rejected salt lower than 65%.
Basically, nanoparticles are preferred to be located on membrane surface by
coating or beneath the selective layer by impregnation. However, the former leads
to pore narrowing or plugging on the membrane surface and release of nanoparticles
from the matrix due to superficial binding (Gholami et al. 2017; Bottino et al. 2002).
Particle aggregation and hence the formation of larger pore sizes in the selective
layer due to changes in both kinetics and thermodynamics of the phase inversion
process especially for the excessive loadings are the challenging issues for the latter
case. Those property changes adversely affect the membrane permeability and
selectivity. In addition, release of nanoparticles under operation is still valid if the
interactions between nanoparticles and matrix are weak. In literature, the use of
various sizes, concentrations, and types of nanoparticles and different surface modification strategies has been employed by the researchers for the reduction of agglomeration and improvement of homogenous dispersivity, stability, and
nanoparticle–polymer interactions (Méricq et al. 2015; Yang et al. 2007; Vatanpour
Y. Yurekli
through the thickness of the casting solution. These clusters also called as nodules
are then interconnected together by entanglement because of the shared polysulfone
chains. The pore sizes given for the composite membrane correspond to the apertures between nodules. A membrane skin consisting of a packed nodular morphology and a large number of pores at 0.05 wt% loading is responsible for the high flux,
while upon further addition of zeolite, the membrane permeability reduces, because
of the decrease in the number of pores which occurs due to the agglomeration of
particles, causing to enlarge nodule size. Nucleating and growth increases with the
amounts of zeolite leading to pore size significantly enlarged. The pore dimension
and the number of pores which are directly related to the permeability and molecular weight cutoff of a membrane can be precisely tuned by the nature of zeolite
suspension. Suspension with a well-dispersed zeolite nanoparticle produces a large
number of small nodules and pores, while zeolite aggregates form a less pore density as a consequence of large-sized nodules.
In general, water permeability is predominantly dependent on surface hydrophilicity of the membrane. Thus, hydrophilic nanoparticles located on the membrane
surface are mostly desired. On the other hand, recent observations have shown that
the hydrophilic nanoparticles with high surface free energy preferably migrate to
the polymer water interface during immersion precipitation process. Then, they
hydrolyze forming surface hydroxides. The resultant membrane contributes to the
passage of water and hence improves water flux. Deposition of TiO 2 nanoparticles
onto a membrane surface, in this case, can be given as an example providing the
binding of surface hydroxyl groups that are polar when initiated with UV light. The
final surface structure demonstrated strong interaction with water molecule through
hydrogen bonding and van der Waals forces (Qiu et al. 2009). This useful property
of surface-adsorbed water layer enables the membrane with substantially high permeability. In another study, Lakhotia et al. (2019) prepared a thin film nanocomposite membrane by dispersing FeO nanoparticles on the surface of the composite.
With the increase in surface density, the hydrophilicity (contact angle 85–50°), surface charge (−6.3 to −14.2 mC/m
2
), flux (28–37 L/m
2
.h), and salt rejection ( >90%)
of the nanocomposite membranes were significantly improved. A membrane without FeO nanoparticle, on the other hand, rejected salt lower than 65%.
Basically, nanoparticles are preferred to be located on membrane surface by
coating or beneath the selective layer by impregnation. However, the former leads
to pore narrowing or plugging on the membrane surface and release of nanoparticles
from the matrix due to superficial binding (Gholami et al. 2017; Bottino et al. 2002).
Particle aggregation and hence the formation of larger pore sizes in the selective
layer due to changes in both kinetics and thermodynamics of the phase inversion
process especially for the excessive loadings are the challenging issues for the latter
case. Those property changes adversely affect the membrane permeability and
selectivity. In addition, release of nanoparticles under operation is still valid if the
interactions between nanoparticles and matrix are weak. In literature, the use of
various sizes, concentrations, and types of nanoparticles and different surface modification strategies has been employed by the researchers for the reduction of agglomeration and improvement of homogenous dispersivity, stability, and
nanoparticle–polymer interactions (Méricq et al. 2015; Yang et al. 2007; Vatanpour
Y. Yurekli