Journal of the Taiwan Institute of Chemical Engineers 82 (2018) 169–178
Contents lists available at ScienceDirect
Journal of the Taiwan Institute of Chemical Engineers
journal homepage: www.elsevier.com/locate/jtice
Activated carbon nanoparticles entrapped mixed matrix
polyethersulfone based nanofiltration membrane for sulfate and
copper removal from water
S.M. Hosseini a, S.H. Amini a, A.R. Khodabakhshi b, E. Bagheripour a, B. Van der Bruggen c,d,∗
a
Department of Chemical Engineering, Faculty of Engineering, Arak University, Arak 38156-8-8349, Iran
Department of Chemistry, Faculty of Sciences, Arak University, Arak 38156-8-8349, Iran
Process Engineering for Sustainable Systems Section, Department of Chemical Engineering, University of Leuven, Celestijnenlaan 200F, 3001 Leuven,
Belgium
d
Faculty of Engineering and the Built Environment, Tshwane University of Technology, Private Bag X680, Pretoria 0001, South Africa
b
c
a r t i c l e
i n f o
Article history:
Received 14 August 2017
Revised 7 November 2017
Accepted 11 November 2017
Available online 28 November 2017
Keywords:
Mixed matrix membranes
Nanofiltration
Activated carbon nanoparticles
Physico-chemical characterization
Sulfate/copper ion removal
a b s t r a c t
Mixed matrix activated carbon nanoparticles (ACNPs) embedded polyethersulfone based nanofiltration
membranes were prepared by solution casting technique. SEM images show that utilization of nanoparticles in the membrane matrix causes a decrease of the size of the channels in both top and sub layers.
SOM images show a uniform nanoparticle distribution for the prepared membranes. SOM images also
show agglomeration of nanoparticles at high additive concentrations. The surface images show a reduction of roughness for membranes filled with ACNPs. The flux decreases at 0.05 wt% nanoparticles loading
rate and then increases again by an increase of the nanoparticles dosage from 0.05 to 0.1 wt%. The flux
then decreases again at a nanoparticles ratio from 0.1 to 1 wt%. According to the performance test, the
membrane with 0.5 wt% nanoparticles indicated the highest sulfate (95%) and Cu (97%) ions removal. The
water contact angle was found to decrease from 54° to 43° by increasing the ACNPs concentration. This
is assigned to a decrease of the membrane surface roughness due to migration of nanoparticles to the
membrane surface during the fabrication process. The water content in the membrane and the porosity
were also improved by increasing the nanoparticles ratio up to 0.1 wt%, but decreased for higher additive
concentrations. The tensile strength of the membranes was enhanced by utilizing a nanoparticles ratio
up to 0.05 wt%, but showed a decreasing trend for higher nanoparticles concentrations. The decrease of
the flux ratio (J/Jo ) was measured to be 5% for the modified membrane containing 0.5 wt% ACNPs and
63% for the pristine membrane.
© 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction
Nanofiltration (NF) is attractive and effective for the treatment
of effluents, especially the removal of heavy metal ions from water, compared to treatment techniques such as adsorption, electrochemical oxidation, ion-exchange and coagulation-flocculation. NF
is also useful for concentration/purification in the pharmaceutical
and chemical products industries [1–3]. This technique offers several advantages compared with other separation methods such as a
relatively low investment cost, low energy consumption, high per∗
Corresponding author at: Process Engineering for Sustainable Systems Section,
Department of Chemical Engineering, University of Leuven, Celestijnenlaan 200F,
3001 Leuven, Belgium.
E-mail addresses:
[email protected],
[email protected] (B. Van der Bruggen).
meation flux and removal efficiency and singular separation capability for ions of different valences [4–6]. Sulfate and copper ions,
harmful contaminants of potable water resources, should be removed because of their risks for humans, plants growth and scaling problems in industrial applications [1,4,5].
Nowadays, various methods have been used for modification
of NF membranes with special characteristics in chemical and
waste treatment applications such as polymers blending, polymers
photo-grafting, plasma treatment, chemical modification, use of
different filler additives and many more [7–14].
Elimination of sulfate and copper ions by nanofiltration membrane has been reported. Adsorptive membranes prepared by
blending adsorptive polymers such as chitosan and incorporating
nanoparticles such as metal oxides and magnetic nanoparticles in
the membrane matrix can improve the membrane performance in
sulfate and copper ions removal from water [1,4,15–18].
https://doi.org/10.1016/j.jtice.2017.11.017
1876-1070/© 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
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S.M. Hosseini et al. / Journal of the Taiwan Institute of Chemical Engineers 82 (2018) 169–178
Utilizing inorganic particles or fillers, especially nanomaterials,
into polymeric NF matrices has been examined in many applications to enhance their stability in demanding conditions and the
separation properties of membranes, based on a synergism between the organic and inorganic components. An increase of thermal, chemical and mechanical stabilities and an improvement of
hydrophilicity, water permeability and rejection and antifouling
properties of NF nanocomposite membranes has been observed
[2,7,8].
Currently only few studies considered incorporating activated
carbon nanoparticles (ACNPs) into NF membranes and the literature is silent on the characteristics of mixed matrix PES based
nanofiltration membranes prepared by using ACNPs for sulfate and
copper ions removal from water. In this study, activated carbon
nanoparticles embedded mixed matrix asymmetric polyethersulfone based nanofiltration membranes were prepared by solution
casting to increase the removal efficiency of sulfate and copper
ions from water.
Activated carbon nanoparticles are a new class of advanced materials with good chemical stability, high surface area, and good activation/adsorption characteristics due to its unique structure and
functionality. These make it to an attractive additive in water treatment [19].
Polyethersulfone (PES) is one of the most used polymers in
the preparation of commercial and laboratory nanofiltration membranes. Its thermal stability and outstanding mechanical strength
have made this polymer an interesting material in membrane fabrication [20,21].
The use of hybrid systems making use of a membrane with
nanoparticles can create additional properties to increase the efficiency of the system based on the synergism between the properties of the different components.
The influence of the concentration of activated carbon nanoparticles in the casting solution on physico/chemical properties,
separation characteristics and antifouling ability of PES based
nanofiltration membranes was investigated.
2. Materials and methods
2.1. Materials
Polyethersulfone (PES) provided by (BASF) (Ultrason E6020P,
MW = 58,0 0 0 g/mol), New Jersey, USA, polyvinylpyrrolidone
(PVP, MW = 25,0 0 0 g/mol) and N, N Dimethyl acetamide (DMAc,
Mw = 87.12 g/mol) provided by Merck Inc., Darmstadt, Germany
and deionized water were used as membrane base polymer, pore
former, solvent and non-solvent, respectively. Activated carbon
nanoparticles (ACNPs), (Bamboo, black powder, spherical, specific
surface area (SSA) >10 0 0 m2 /g, iodine adsorption >10 0 0 mg/g,
methylene blue number >240 mg/g, negative-ions concentration: 7150/cm³, decoloration rate >99%, electrical conductivity:
0.4 Ω cm, high activation/adsorption capability, average particle
size <100 nm) were obtained from US Research Nanomaterials,
Inc., Houston, USA., and used as inorganic filler additive. All other
chemicals were supplied by Merck Inc., Darmstadt, Germany.
Table 1
Composition of casting solutions used in fabrication of membranes.
Samples (No)
PES (wt%)
PVP (wt%)
DMAc (wt%)
ACNPs (wt%)
1
2
3
4
5
18
18
18
18
18
1
1
1
1
1
81
80.95
80.9
80.5
80
0
0.05
0.1
0.5
1
1 h in an ultrasonic cleaner bath (Parsonic 11S model, S/N PN88159, Iran) for breaking up any aggregates between the nanoparticles. The prepared solutions were kept for about 4 h at room temperature without stirring in order to completely remove the air
bubbles and then they were cast onto clean glass plates with a
film applicator with constant thickness of 150 μm. Subsequently,
the glass plates were immersed into distilled water parallel to horizontal plane at ambient temperature. After primary phase separation and membrane solidification, the membranes were kept in
fresh distilled water for 24 h to ensure the complete solvent extraction. Then, the membranes were placed between two filter paper
sheets for 24 h at room temperature for drying. The composition of
the polymeric solutions is shown in Table 1.
2.3. Characterization of membranes
2.3.1. Scanning electron microscopy (SEM)
The cross-sectional morphology of membranes was observed
using a SEM (Seron Technology Inc. Korea) instrument. Before taking SEM images, the membranes were dipped in liquid nitrogen for
5 min and then all the samples were gold sputtered and carefully
handled to avoid contaminations. In this way, the membranes were
prepared for SEM images and images were taken at 15 kV in high
vacuum conditions.
2.3.2. Scanning optical microscopy (SOM)
Scanning optical image analyzing was used for surface characterization and investigation of the distribution of nanoparticles
in the prepared membranes. The instrument used for this aim
was Olympus; model IX 70, transmission mode with light going
through the sample. For taking SOM images, small squares of prepared membranes (1 cm × 1 cm) were cut and placed between
two glassy blades.
2.3.3. Three dimensional (3D) surface images
In order to study the surface morphology of the fabricated
membranes and the effect of roughness on the separation efficiency, 3D surface images were prepared using optical microscopy
and SPIP software (version 6.4) in the area of 8 μm × 10 μm.
2.2. Preparation of ACNPs entrapped mixed matrix PES based NF
membrane
2.3.4. Water contact angle
In order to observe the membrane surface hydrophilicity, water contact angles were measured statically by using a contact angle measuring instrument. De-ionized water was the probe liquid
in this test. Measurements were done shortly after drop formation
on the membrane surface. To minimize the experimental errors,
the contact angle was measured in three different locations for all
membranes; the average was reported.
Asymmetric flat sheet PES base membranes were fabricated by
phase inversion induced by the immersion precipitation technique.
To this aim, certain amounts of PES (18 wt%) and PVP (1 wt%) were
dissolved in DMAc by mechanical stirring for 4 h with a mechanical stirrer (Velp Scientifica Multi 6 stirrer). Afterwards, activated
carbon nanoparticles were dispersed in various concentrations into
the polymeric solutions. Dispersing was followed by sonication for
2.3.5. Water content
The water content was measured as the weight difference between dried and wet membranes. For the purpose, prepared membrane were cut in square pieces (4 cm × 4 cm) and immersed in
distilled water for 72 h. After discharging the samples, their surface were wiped by filter paper and weighed (OHAUS, PioneerTM ,
readability: 10−4 g, OHAUS Corp., USA). The wet membranes were
S.M. Hosseini et al. / Journal of the Taiwan Institute of Chemical Engineers 82 (2018) 169–178
171
The antifouling properties of the lab-made membranes were
also measured as the flux decrease in a continuous filtration experiment. The flux decrease was calculated according to:
M% =
J − J
0
1
J0
.100
(4)
where J0 is the original flux, J1 is the flux after continuously filtrating during t min.
2.3.8. Porosity and pore size
The following equation was utilized for determining the average
porosity of a membrane (ε ) [26,27]:
ε=
Wwet − Wdry
A × l × dw
(5)
where A is the membrane effective area (m2 ), dw is the water density (10 0 0 kg/m3 ) and l is the membrane thickness (m). Additionally, the Guerout–Elford–Ferry equation was used for calculation of
the mean pore radius of the membrane (rm ). This equation is based
on the pure water flux [26,27].
Fig. 1. Schematic diagram of dead end experimental cell set up.
rm =
dried in an oven (Behdad Co., Model: O5, Iran) at a fixed temperature (60 °C) for 12 h until a constant weight was achieved. The
following equation was used for calculation of the water content
[22]:
Water content =
ww − wd
× 100
ww
2.3.7. Water permeability and salt rejection
The performance of the prepared membranes was analyzed
through a dead-end stirred cell setup (Fig. 1) with an effective
membrane area of 11.94 cm2 . The experiment was performed at
fixed pressure (4 bar). The permeation flux was calculated by the
following equation [23–25]:
(2)
where Jv (L/m2/h), Q (L), A (m2 ), t (h) are the permeation flux,
content of permeated water, membrane area and permeation time,
respectively. Na2 SO4 (10 0 0 mg/L) and Cu(NO3 )2 (20 mg/L) aqueous
solutions, were used to investigate the membranes’ potential in
sulfate and copper ions removal. Distilled water (electrical conductivity < 5 μS/cm) was utilized in preparation of aqueous solutions.
Measurements were done at the original pH. The following equation was employed for the calculation of the rejection [20,21,23]:
Cp
Cf
∗100
where η is the water viscosity (8.9 × 10 − 4 Pa.s), Q is the volume
of permeated pure water per unit time (m3 /s), and P is the operational pressure (0.5 MPa). In order to minimize the experimental
errors, measurements were done three times for each sample and
their average was reported.
3. Results and discussion
2.3.6. Mechanical properties
The mechanical tensile strength of the fabricated NF membranes was measured by applying ASTM 1922-03 standard. For this
aim, the membranes were cut into standard shapes and the maximum tolerable load of the membrane was measured [23]. For each
test, three samples were used and the average values were reported.
Rejection % = 1 −
(6)
(1)
where Ww and Wd are the weight of wet and dried membranes,
respectively. Measurements were carried out three times for each
sample and then their average was reported.
Jv = Q/A.t
(2.9 − 1.75ε )8ηlQ
ε × A × P
(3)
where Cp and Cf are the ionic solution concentration in permeate
and feed, respectively.
3.1. Membrane morphology
SEM cross sectional images of prepared NF membranes with
different concentration of ACNPs is shown in Fig. 2. Images show
typical asymmetric membranes containing a finger-like porous
sublayer and a dense skin top-layer in all prepared membranes.
According to SEM images, an increase of nanoparticle concentration in the casting solution causes a dense structure with smaller
channel size for the prepared membranes compared to pristine
PES ones. This is in agreement with hydrophobic characteristic of
nanoparticles and their effect on phase inversion kinetics which
changes the exchange rate between solvent (DMAc) and nonsolvent (water) during the phase inversion process. The migration
of hydrophobic ACNPs and their accommodation on the membrane
surface during the precipitation process, as a result of ACNPs’ low
density, declines the diffusion rate of water into the polymeric
film. This decreases the exchange rate between solvent and nonsolvent and leads to formation of a membrane with thick top layer,
dense structure and less channel size in their matrix [1,4,8,28]. The
images of the top and bottom surface of composite membranes are
shown in Fig. 3. The difference between their colors confirms the
movement of ACNPs to the membrane surface. Moreover, an increase of polymeric solution viscosity by utilizing of nanoparticles
reduces the driving force for the film precipitation by decreasing
the exchange rate between solvent and non-solvent [8,28].
To investigate the distribution of nanoparticles in membrane
matrix, SOM and SEM images were provided (Figs. 4 and 5). It
was found that ACNPs were uniformly distributed on the surface
of the membranes. However, images indicate that agglomeration
of nanoparticles occurs at high additive concentrations. Increase
of casting solution viscosity at high additive concentration slows
down the phase inversion process and let the nanoparticles to
gather near each other due to delayed demixing [1,4].
The 3D surface images (Fig. 6) and calculated roughness parameters obtained from the images (Table 2), reveal that the
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Fig. 2. Cross-sectional SEM images of prepared membranes with various ratios of activated carbon nanoparticles: (a) 0.0 wt%; (b) 0.05 wt%; (c) 0.1 wt%; (d) 0.5 wt%; (e) 1 wt%.
membrane roughness was decreased initially by utilizing ACNPs
up to 0.5 wt% in the membrane matrix from 56.9 to 27.6 nm. This
might be related to dispersion of nanoparticles on the membrane
surface, which reduces the surface pore size [1]. Moreover, migration of nanoparticles to the surface of the membrane due to
their low density during the fabrication process causes the forma-
tion of a uniform and tight surface for the prepared membranes,
which decreases the membrane surface roughness. Difference between the colors of top and bottom of prepared membranes confirm the nanoparticles’ movement to membrane surface (Fig. 3).
The surface roughness was enhanced again from 26.7 to 41.3 nm by
more increase of additive concentration up to 1 wt% in the casting
S.M. Hosseini et al. / Journal of the Taiwan Institute of Chemical Engineers 82 (2018) 169–178
173
solution. This is assigned to more accumulation and less dispersion
of activated carbon nanoparticles at high nanoparticles concentration which produces more hunks (Fig. 5-(b)). All modified membranes containing ACNPs showed a lower roughness compared to
the pristine membrane.
3.2. Membrane water content and porosity
Fig. 3. Digital photograph of top and bottom surface of PES-ACNs nanofiltration
membrane.
The results (Table 3) reveal that increase of the nanoparticles
concentration up to 0.1 wt% in the casting solution initially led
to an improvement in membrane water content and porosity. This
may be due to an increase in membrane heterogeneity by utilizing
ACNPs, which enhances the amount of voids and cavities throughout the membrane matrix and improves the accommodation of
Fig. 4. SOM images of mixed matrix membranes with various ratios of activated carbon nanoparticles: (a) 0.0 wt%; (b) 0.05 wt%; (c) 0.1 wt%; (d) 0.5 wt%; (e) 1 wt%.
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Table 2
Effect of activated carbon nanoparticles concentration on membrane roughness.
Ra (nm) (roughness
average)
Rq (nm) (root mean
square roughness)
Rt (nm) (maximum height
of the roughness)
Rv (nm) (maximum
roughness valley height)
Rp (nm) (maximum
roughness peak height)
56.9
48.1
42.1
27.6
41.3
77.3
61.6
61.2
35.6
51.3
415.5
371
436
229.7
252.4
202.8
153.7
194.4
141.6
124.3
212.6
217.3
241.5
88
128.1
Table 3
Membrane water content, membrane porosity (ε ) and mean pore radius (rm ).
Membrane sample (ACNPs wt%)
Water content (%)
Porosity (%)
Pure water flux (L/m2 /h)
Mean pore size (nm)
1
2
3
4
5
77.1
79.1
79.0
77.9
74.1
78.1
79.5
79.3
76.4
75.5
8.5
3.8
9
5.5
4.4
5.7 ×10 − 9
3.3 ×10 − 9
5.3 ×10 − 9
4.7 × 10 − 9
3.7 ×10 − 9
(0.0 wt%)
(0.05 wt%)
(0.1 wt%)
(0.5 wt%)
(1.0 wt%)
bic characteristic of the nanoparticles, and enhances the membrane
surface hydrophilicity by providing more spatial region for the water molecules. Moreover, the carboxyl and hydroxyl groups of NPs
affect the membrane water contact angle.
3.4. The effect of ACNPs concentration on water permeability and salt
rejection
Fig. 5. Surface SEM images of mixed matrix membrane: (a) nanoparticles dispersion in membrane matrix; (b) nanoparticle agglomeration at high additive concentration.
water molecules and the membrane porosity. The membrane water
content and porosity were decreased again by a further increase of
the additives content from 0.1 to 1 wt%. This may be attributed
to pore filling [7,20] by the nanoparticles at high additive loading
ratio. Moreover, hydrophobic characteristic of ACNPs declines the
membrane water content.
3.3. Membrane surface hydrophilicity
Water contact angle measurements were carried out to study
the effect of ACNPs in the casting solution on the hydrophilicity
of the membrane surface. The obtained results (Fig. 7) show that
an increase of ACNPs percentage in the membrane matrix causes a
decrease of the water contact angle from 54° to 43° (inner angle).
This can be explained by the decrease of the membrane surface
roughness by utilizing ACNPs, which prevailed upon the hydropho-
The effect of the concentration of ACNPs in the casting solution
on the water permeability (flux) is shown in Fig. 8. Results show
that the water flux was decreased initially by utilizing ACNPs up
to 0.05 wt% as additive in the membrane matrix while the membrane water content and porosity were enhanced by using NPs
(Table 3). This can be described with respect to the mutual effect
of activated carbon nanoparticles on membrane porosity increment
against reduction of mean pore size (Table 3) which decreases the
membrane flux. Moreover, the formation of disconnected channels [29] in the membrane matrix as shown in SEM images
(Fig. 2-(b)), restricts the water passage through the membrane
matrix.
The water flux was enhanced again by a further increase of the
nanoparticles concentration from 0.05 to 0.1 wt%, due to an increase of membrane porosity and mean pore size related to an
increase of the membrane heterogeneity at increased nanoparticle concentration. The permeability/flux decreased again by an increase of the nanoparticles content from 0.1 to 1 wt% which is due
to the decrease of the membrane water content, membrane porosity and mean pore size at higher additive concentration. Moreover,
the migration of ACNPs to the top of the membrane during the fabrication process and their accumulation on the membrane surface
at high concentration causes the formation of a tighter surface for
the membrane and its pore blockage [1] which reduce the water
flux.
The results indicate that the sulfate and copper ions rejection (Fig. 9) was improved by an increase of the concentration of
activated carbon nanoparticles in the casting solution. This may be
attributed to increase of membrane charge density which is assigned to carboxyl and hydroxyl groups of ACNPs. Moreover, the
adsorption characteristics of ACNPs improve the surface and depth
filtration mechanism during filtration. In this condition, the solutes
present in the feed solution adsorb on the membrane surface
leading to an improved rejection. Furthermore, the pore blockage phenomenon caused by the nanoparticles in membrane matrix
restricts the transport of salt through the membrane. Thus, more
S.M. Hosseini et al. / Journal of the Taiwan Institute of Chemical Engineers 82 (2018) 169–178
175
Fig. 6. 3D images of PES-ACNs nanofiltration membrane (top surfaces); (a) 0.0 wt%; (b) 0.05 wt%; (c) 0.1 wt%; (d) 0.5 wt%; (e) 1 wt%.
solutes are trapped in the pores; they cannot pass through the
membrane so that the rejection improves. Furthermore, an increase
of the membrane surface hydrophilicity and a decrease of the surface roughness by increasing the ACNPs loading ratio reduce the
formation of a polarized layer on membrane surface which declines the salt percolation through the membrane and improves
the salt rejection. Additionally, membranes with smoother surface
and lower agglomerated ACNPs provide more accessible active sites
for ions to be adsorbed. The slight decrease of the rejection at high
additive concentrations (1 wt%) may be due to the agglomeration
of ACNPs in the membrane matrix, which reduces the membrane
charge density and effective adsorption sites of the nanoparticles.
Additionally, accumulation of nanoparticles provides more defects
and heterogeneity in the membrane [1,4].
3.5. Membrane mechanical strength
An increase of the ACNPs concentration up to 0.05 wt%
in the membrane matrix initially caused an increase of the
membrane tensile strength from 2.79 to 3.65 MPas. This may be
due to the presence of favorable/strong interfacial bonding between the polymers and activated carbon nanoparticles, which
causes an improvement of the mechanical properties [30]. The
membrane tensile strength decreased from 3.65 to 2.88 MPas again
by further increasing the nanoparticles content from 0.05 to 1 wt%
in the membrane matrix. This may be attributed to agglomeration
of nanoparticles and the discontinuity of polymer chain binders at
higher concentrations of nanoparticles, which decline the mechanical strength of the membrane.
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60
58
Contact angle ( )
56
54
52
50
48
46
44
42
40
1
2
3
4
5
Samples' number
Fig. 7. Contact angle of prepared membranes with various ratios of ACNs: (a) 0.0 wt%; (b) 0.05 wt%; (c) 0.1 wt%; (d) 0.5 wt%; (e) 1 wt% (inner angle).
10
(0.1 %wt)
9
(0.0 %wt)
8
Flux (L/m 2/h)
7
6
(0.5 %wt)
5
(1.0 %wt)
(0.05 %wt)
4
3
2
1
0
0
1
2
3
4
5
6
Sample's number
Fig. 8. Effect of activated carbon nanoparticle dosage on membrane flux.
3.6. The effect of nanoparticles concentration on antifouling ability of
membranes
Fouling reduces the membrane performance, the permeation
quality, energy consumption and cost and limits the useful lifetime
of the membrane. The decrease of the flux can be used to assess
the antifouling performance of a membrane [31]. Na2 SO4 aqueous
solution with concentration of 10 0 0 mg/L was used as feed. The
operating pressure was 4 bar. The membrane flux as a function of
permeation time (during 60 min) is shown in Fig. 10. As can be
seen, the flux of all prepared membranes decreased with time. The
decrease of the flux ratio (J/Jo ) is given in Table 4. The mixed matrix membranes showed better antifouling ability compared to the
pristine membrane. The amount of decreasing in flux ratio for a
mixed matrix membrane containing 0.5 wt% nanoparticles is about
5% after 60 min of filtration, whereas it is 64% for the unmodified PES membrane. In order to study the reproducibility of the
Table 4
Effect of activated carbon nanoparticles on the decrease of the flux
ratio (J/Jo ).
Membrane sample (ACNPs wt%)
Decrease of flux ratio (J/Jo ) (%)
1
2
3
4
5
63.89
39.99
11.11
5.0
28.57
(Unmodified membrane)
(0.05 wt%)
(0.1 wt%)
(0.5 wt%)
(1.0 wt%)
performance of mixed matrix membranes, the used membranes
were removed from the cell and washed/kept in distilled water for
5 h. Consequently, their performance was estimated to evaluate the
membrane reusability. Obtained results showed a slight decrease of
the average performance for the modified membranes (less than
5%).
S.M. Hosseini et al. / Journal of the Taiwan Institute of Chemical Engineers 82 (2018) 169–178
Sulfate rejection
Copper ion rejection (%)
100
100
(0.5 %wt)
(1.0 %wt)
95
95
(0.1 %wt)
90
90
(0.0 %wt)
85
85
(0.05 %wt)
80
80
75
75
70
0
1
2
3
4
5
6
Sulfate ion rejection (%)
Copper rejection
177
70
Sample's number
Fig. 9. Sulfate and copper ions removal: the effect of activated carbon nanoparticles dosage on membrane rejection.
0
0.05
0.1
0.5
1
14
12
Flux (L/m2/h)
10
8
6
4
2
0
0
10
20
30
40
50
60
70
Time (min)
Fig. 10. Effect of separation time on the decrease of membrane flux (antifouling ability).
4. Conclusion
PES-co-ACNPs mixed matrix nanofiltration membranes were
prepared by phase inversion. The effect of the concentration of
nanoparticles in the casting solution on the membrane morphology was studied. SEM images showed that increasing the concentration of nanoparticles in the casting solution caused a decrease
of the channel size in both the top layer and the sub layer of the
membrane matrix. SOM images showed a uniform distribution of
nanoparticles for the prepared membranes. Agglomeration at high
additive concentrations was observed. The membrane roughness
was decreased initially by utilizing of ACNPs up to 0.5 wt% in the
membrane matrix and then enhanced again by a further increase
of the additive concentration. Moreover, results showed that the
flux decreased initially by utilizing nanoparticles up to 0.05 wt%
in the membrane matrix and then increased again for a nanoparticles concentration from 0.05 to 0.1 wt%. The flux decreased again
for a nanoparticle content from 0.1 to 1 wt%. The rejection of sulfate and copper ions was also improved by adding super activated
carbon nanoparticles in the casting solution. The water contact angle was found decreased from 54° to 43° by increasing the ACNPs concentration. The increase of the ACNPs concentration up to
0.1 wt% in the casting solution led to a higher water content in the
membrane and porosity. The membrane water content and porosity decreased again by further increasing the concentration of the
additive. The membrane tensile strength was also improved from
2.798 to 3.653 MPas by utilizing nanoparticles up to 0.05 wt%
in the casting solution and then showed decreasing trend by a
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further increase of the nanoparticles content. The decrease of
the flux ratio for a mixed matrix membrane containing 0.5 wt%
nanoparticles is about 5% after 60 min of filtration whereas the flux
decrease of the unmodified PES membrane is 64%.
Acknowledgment
The authors gratefully acknowledge Arak University for the financial support during this research.
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