153
et al. 2012; Fu et al. 2008). In the study of Ayyaru and Ahn (2018), polyethersulfone
nanocomposite membranes blended with surface-modified TiO 2 nanoparticles (anatase, 20–25 nm in size) have been fabricated via phase inversion method for the
improvement of the hydrophilicity and surface charge and reduction of agglomeration at the same time. The TiO 2 nanoparticles were sulfonated by replacing the surface hydroxyl groups with –SO 3 H group, and the loading effect was investigated.
The modified membranes were reported as exhibiting notable enhancement in surface roughness, porosity, and pore size compared to the polyethersulfone membrane. The addition of 1 wt% sulfonated or nonsulfonated TiO 2 nanoparticles into
polyethersulfone membrane showed remarkable increase in water flux (102% and
63%, respectively). The same group has also investigated sulfonated graphene oxide
nanoparticles blended with polyvinylidene difluoride membranes (Ayyaru and Ahn
2017). Nanocomposite membranes via nonsolvent-induced phase separation process have been prepared by distributing sulfonated graphene oxide nanoparticles in
different concentrations (0.4–1.2 wt%). It was reported that improvement of polyvinylidene difluoride membrane properties including pore dimensions, surface roughnesses, and porosities was attributed to the addition of sulfonated graphene oxide.
Maximum water permeability attained at 0.8 wt% of sulfonated graphene oxide
addition was reported as 146% higher than the neat polyvinylidene difluoride. The
enhancement of the water flux has been explained by the improved charge density
due to the availability of extra sulfonic groups on sulfonated graphene oxide supports that can attract more water layer. In addition, the attached –SO 3 H group in
sulfonated graphene oxide provides stronger hydrogen bonding with respect to –
OH/-COOH groups available in native graphene oxide.
6.4 Effect of Nanoparticles on Antifouling
Membrane fouling caused by pore blocking, physical adsorption, and cake formation decreases flux greatly, affects the quality and quantity of products, and shortens
the membrane lifetime. Concentration polarization explained by the formation of a
relatively high concentration layer at the membrane interface due to retention of
solutes is also another phenomenon. All the resistances in series reduce driving
force (ΔP–Δπ) at the membrane interface by exerting an osmotic pressure difference, Δπ, which increases progressively. Further, foulant concentration on the
membrane surface increases as time proceeds and eventually turns into gel. Fouling
can be categorized as reversible (directly occurring phenomena) or irreversible
(long-term phenomena), and they can be analyzed by flux recovery tests.
Accordingly, pure water flux of the virgin membrane (J wv ) under constant pressure
for a certain time is measured. Then, the foulant solution (e.g., 0.5 g/L and pH 7) is
filtered at the same condition. Next, the fouled membrane is washed several times
with water, and the water flux of the cleaned membrane is remeasured (J wc ). This
cycle is repeated many times to observe the operational stability of the membrane.
Generally, bovine serum albumin or humic acid is used as a model foulant. Figure 6.4
schematically illustrates the aforementioned scenario. From the filtration results,
6 Recovery of Heavy Metals by Membrane Adsorbers
et al. 2012; Fu et al. 2008). In the study of Ayyaru and Ahn (2018), polyethersulfone
nanocomposite membranes blended with surface-modified TiO 2 nanoparticles (anatase, 20–25 nm in size) have been fabricated via phase inversion method for the
improvement of the hydrophilicity and surface charge and reduction of agglomeration at the same time. The TiO 2 nanoparticles were sulfonated by replacing the surface hydroxyl groups with –SO 3 H group, and the loading effect was investigated.
The modified membranes were reported as exhibiting notable enhancement in surface roughness, porosity, and pore size compared to the polyethersulfone membrane. The addition of 1 wt% sulfonated or nonsulfonated TiO 2 nanoparticles into
polyethersulfone membrane showed remarkable increase in water flux (102% and
63%, respectively). The same group has also investigated sulfonated graphene oxide
nanoparticles blended with polyvinylidene difluoride membranes (Ayyaru and Ahn
2017). Nanocomposite membranes via nonsolvent-induced phase separation process have been prepared by distributing sulfonated graphene oxide nanoparticles in
different concentrations (0.4–1.2 wt%). It was reported that improvement of polyvinylidene difluoride membrane properties including pore dimensions, surface roughnesses, and porosities was attributed to the addition of sulfonated graphene oxide.
Maximum water permeability attained at 0.8 wt% of sulfonated graphene oxide
addition was reported as 146% higher than the neat polyvinylidene difluoride. The
enhancement of the water flux has been explained by the improved charge density
due to the availability of extra sulfonic groups on sulfonated graphene oxide supports that can attract more water layer. In addition, the attached –SO 3 H group in
sulfonated graphene oxide provides stronger hydrogen bonding with respect to –
OH/-COOH groups available in native graphene oxide.
6.4 Effect of Nanoparticles on Antifouling
Membrane fouling caused by pore blocking, physical adsorption, and cake formation decreases flux greatly, affects the quality and quantity of products, and shortens
the membrane lifetime. Concentration polarization explained by the formation of a
relatively high concentration layer at the membrane interface due to retention of
solutes is also another phenomenon. All the resistances in series reduce driving
force (ΔP–Δπ) at the membrane interface by exerting an osmotic pressure difference, Δπ, which increases progressively. Further, foulant concentration on the
membrane surface increases as time proceeds and eventually turns into gel. Fouling
can be categorized as reversible (directly occurring phenomena) or irreversible
(long-term phenomena), and they can be analyzed by flux recovery tests.
Accordingly, pure water flux of the virgin membrane (J wv ) under constant pressure
for a certain time is measured. Then, the foulant solution (e.g., 0.5 g/L and pH 7) is
filtered at the same condition. Next, the fouled membrane is washed several times
with water, and the water flux of the cleaned membrane is remeasured (J wc ). This
cycle is repeated many times to observe the operational stability of the membrane.
Generally, bovine serum albumin or humic acid is used as a model foulant. Figure 6.4
schematically illustrates the aforementioned scenario. From the filtration results,
6 Recovery of Heavy Metals by Membrane Adsorbers