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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. 170 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 172 S.M. Hosseini et al. / Journal of the Taiwan Institute of Chemical Engineers 82 (2018) 169–178 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%. 174 S.M. Hosseini et al. / Journal of the Taiwan Institute of Chemical Engineers 82 (2018) 169–178 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. 176 S.M. Hosseini et al. / Journal of the Taiwan Institute of Chemical Engineers 82 (2018) 169–178 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 178 S.M. Hosseini et al. / Journal of the Taiwan Institute of Chemical Engineers 82 (2018) 169–178 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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