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cSMM blend UF membranes
Accepted Manuscript Title: Separation of macromolecular proteins and rejection of toxic heavy metal ions by PEI/cSMM blend UF membranes Author: P. Kanagaraj A. Nagendran D. Rana T. Matsuura S. Neelakandan PII: DOI: Reference:
S0141-8130(14)00551-0 http://dx.doi.org/doi:10.1016/j.ijbiomac.2014.08.018 BIOMAC 4542
To appear in:
International Journal of Biological Macromolecules
Received date: Revised date: Accepted date:
26-6-2014 28-7-2014 7-8-2014
Please cite this article as: P. Kanagaraj, A. Nagendran, D. Rana, T. Matsuura, S. Neelakandan, Separation of macromolecular proteins and rejection of toxic heavy metal ions by PEI/cSMM blend UF membranes, International Journal of Biological Macromolecules (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.08.018 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Separation of macromolecular proteins and rejection of toxic heavy
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metal ions by PEI/cSMM blend UF membranes
P. Kanagaraja, A. Nagendrana, *, D. Ranab, T. Matsuurab, S. Neelakandana
PG & Research Department of Chemistry, Polymeric Materials Research Lab,
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Alagappa Government Arts College, Karaikudi - 630 003, India
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a
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Department of Chemical and Biological Engineering, Industrial Membrane Research Institute,
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University of Ottawa, 161 Louis Pasteur St., Ottawa, ON, K1N 6N5, Canada
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RESEARCH HIGHLIGHTS
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First time we are using PEI/cSMM blend UF membranes for macromolecular protein and toxic metal ion removal.
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cSMM is blended with PEI to improve separation performance, MWCO, pore size and porosity.
Modified UF membranes possessed higher protein and metal ion permeate flux. Rejection performance of toxic metal ions found to be great in higher PETIM ligand concentration.
Stability complexation of PETIM with metal ion also plays significant role in metal ion rejection.
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*Corresponding author: Email: [email protected] (Dr. A. Nagendran),
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Phone: 91-4565-224283 Fax. No: 91-4565-227497
Abstract
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The charged surface modifying macromolecule (cSMM) was blended into the casting solution of
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poly(ether imide) (PEI) to prepare surface modified ultrafiltration membranes by phase inversion
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technique. The separation of proteins including bovine serum albumin, egg albumin, pepsin and trypsin was investigated by the fabricated membranes. On increasing cSMM content, solute rejection decreases whereas membrane flux increases. The pore size and surface porosity of the 5 wt % cSMM blend PEI membranes increases to 41.4 Å and 14.8 %, respectively. Similarly, the molecular weight cut-off of the membranes ranged from 20 to 45 kDa, depending on the various compositions of the prepared membranes. The toxic heavy metal ions Cu(II), Cr(III), Zn(II) and Pb(II) from aqueous solutions were subjected to rejection by the prepared blended membrane with various concentration of polyethyleneimine (PETIM) as water soluble polymeric ligand. It was found that the rejection behavior of metal ion depends on the PETIM concentration and the stability complexation of metal ion with ligand. 2 Page 2 of 32
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Keywords: Ultrafiltration membrane; Proteins separation; Toxic metal ions rejection
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1. Introduction
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Membrane based separations are now used in a wide range of water purification as well as other industrial applications. In recent years, membrane separation processes have evolved from
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simple applications in the laboratory to utilization in important industrial operations with significant technical and commercial impact [1]. In various industrial fields, such as metals, food and medical industries, it is becoming increasingly important to separate solution constituents such as proteins, enzymes, antibodies, hormones, blood proteins and toxic heavy metal ions. There are several different methods to separate proteins from their mixtures including liquid chromatography, electrophoretic and membrane based techniques [2]. Among the aforesaid separation processes, ultrafiltration (UF) has been widely used for product recovery and pollution control in the chemical, electro-coating, metal refining as well as food, pharmaceutical and biotechnological industries. This process is more efficient and easy to handle than the other
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processes and can be scaled up at low cost. Separation of colloidal suspensions by UF can be achieved by perm-selective membranes, which allow the passage of solvent and small solute molecules but retain macromolecules [3]. Intensive research has been carried out by several
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researchers on the rejection of proteins using cellulose acetate (CA) and polysulfone (PS) membranes, and it has been concluded that the UF membrane is a reliable process for
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macromolecular separation [4].
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To further improve separation performance, researchers have made considerable efforts to fabricate low fouling UF membranes with higher selectivity by anchoring anionic or cationic
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groups in the barrier layer of the membranes. This has been achieved via membrane surface modification, or by blending a hydrophilic functionalized polymer with a hydrophobic
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membrane forming polymer [5]. For instance, Liu et al. have prepared hydrophilic negatively
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charged UF membranes using sulfonated poly(phenyl sulfone) random copolymer. The
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hydrophilicity and antifouling ability of the membranes were enhanced with an increasing fraction of sulfonated copolymer [6]. Li et al. have also developed negatively and positively
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charged hollow fiber UF membranes by dual-layer hollow fiber technology, using sulfonated poly(ether sulfone) (PES) and quaternized PES. These membranes were used in the separation of bovine serum albumin (BSA) and hemoglobin (Hb) from the model solution mixture [7]. Attempts were then made to prepare charged UF membranes which were found to yield good salt rejection. The charged membranes were found to be effective in prevented plugging by ovalbumin that bears the same charge [8]. According to Nagendran et al. CA/PEI blend UF membranes showed better results for the separation of proteins and toxic metal ions [9]. Pore statistics, molecular weight cut-off (MWCO) and morphology are the structural properties of membranes that are essential for the application of the membranes processes for the
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desired permeate qualities [10]. Only solute molecules smaller than membrane pore diameter are allowed to transport through the membrane [11]. Most of the commercially available membranes are specified by their pore size or MWCO [12], which are important parameters affecting the
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separation characteristics of the UF membranes [13].
Removal of toxic heavy metals such as Cu, Zn, Hg, Cd, Pb and Ni from industrial wastewaters
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is required for meeting discharge limits or for water reuse. Many industrial wastewaters
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produced by metal plating, metal finishing, mining, automotive, aerospace, battery and other chemical processes industries, often are often highly concentrated with heavy metals. These toxic
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metals in air, water and soil are major problems as a threat to the environment. Zinc is an essential heavy metal for biological functions; however, it becomes hazardous beyond certain
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concentrations [14]. Copper is a metal commonly found in industrial wastewaters both in particulate form and as organic complexes. In aqueous environments, the function of the metal is
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dependent both on ligand concentration and pH [15]. While the cupric ion (Cu2+) is the metallic form most toxic to flora and fauna it is also a nutrient necessary for algal growth [16]. If allowed
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to enter the environment it can cause serious potential health issues. Even at low concentrations copper may be harmful to humans. It has been found that absorption of excess copper results in ‘‘Wilson’s disease’’ where copper is deposited in the brain, skin, liver, pancreas and myocardium. The presence of lead in drinking water is known to cause various types of serious health problems leading to death in extreme exposure cases [17]. One of the major technical requirements of the leather and other industries employing large quantities of chromium salts in wet processing is the need to minimize the concentration of the metal in the effluents and its removal [18]. These inorganic micro-pollutants are of considerable concern because they are non-biodegradable, highly toxic and in some cases have a probable carcinogenic effect. If
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directly discharged into the sewage system they may seriously affect the operation of biological treatment systems and render the activated sludge unsuitable for application to agricultural land [19].
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Therefore, the removal and separation of toxic and environmentally hazardous heavy metal ions are technological challenge. For separating species with ionic dimensions, reverse osmosis
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membranes are often required but they will result in high operative costs and low permeate flow
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rate. A promising process for the removal of heavy metal ions from aqueous solution involves the UF – complexation, also named the polymer enhanced UF, which is based on complexation
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of heavy metals by water soluble macromolecule polymers such as polyethyleneimine (PETIM), poly(acrylic acid) (PAA), poly(vinyl alcohol) (PVA), etc. The heavy metal ions, by
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complexation with macromolecules, become larger molecular weight than the MWCO of the
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membranes, are retained by UF membrane, producing permeate free of heavy metals. The
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advantage of this method is the low energy requirements of UF and the high removal efficiency [20]. A wide variety of water soluble polymers have been utilized in UF processes for the
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recovery of heavy metals. Amongst those, PETIM is one of the most extensively used mainly because of its high water solubility, its high capacity to bind metal ions and its physical and chemical stability [21-24].
There are several research efforts that have been made to study the applicability of polymer enhanced ultrafiltration (PE-UF) in metal removal from water of various origins. CA has been blended with PS and applied for the separation of chromium using PVA as the macromolecular chelating agent [25]. Labanda et al. made a feasibility study on the recovery of chromium (III) by PE-UF [26]. Trivunac et al. have studied the removal of heavy metal ions from water by complexation-assisted UF. According to their results obtained that, the removal of Cd2+ and Zn2+
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was more than 95 % and 99 %, respectively, at best operating conditions when diethylaminoethyl cellulose was added to the solution [27]. Petrov et al. used carboxy methyl cellulose (CMC) as a water soluble metal binding polymer in combination with UF for selective removal and recovery
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of copper from water [28]. Zamariotto et al. studied the retention of Cu(II) – and Ni(II) – nitrilotriacetic acid and ethylenediaminetetraacetic acid formation of polyaminocarboxylate
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complexes by UF assisted with polyamines. Metal retentions higher than 98 % were observed
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when PETIM in the pH range of 4–9 [29]. Canizares et al. have studied selective separation of Pb from hard water by a semi-continuous PE-UF process using PAA as a complexation agent
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[30]. The obtained results show that when Pb:Ca molar ratio is 1:1, the concentration stage of the semi-continuous process reaches very high rejection coefficients, which means a permeate
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stream with less than 0.05 ppm of Pb and 1.5 ppm of Ca. Bayer et al. studied the PETIM as a
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complexing agent for separation of heavy metals ion using membrane filtration [31]. It was
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found that the PETIM has been an effective complexing agent and suitable for retention and separation of metals in aqueous dilute solutions.
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The objective of this study is to improve the separation efficiency of proteins and metal ions by the addition of cSMM into the casting dope to modify the surface of PEI UF membrane. Average pore size, surface porosity and MWCO of surface modified PEI membranes were determined. Further, the effect of cSMM additive concentration on the rejection and permeate flux was investigated when proteins of different molecular weight such as trypsin, pepsin, egg albumin (EA), and BSA were filtrated.
The rejection and permeate flux for the aqueous
solutions of toxic heavy metal ions such as Cu(II), Cr(III), Zn(II) and Pb(II) were also investigated when PETIM of different concentrations were added to the feed solution.
2. Methodology 7 Page 7 of 32
2.1. Materials Poly(ether imide) (PEI, Ultem® 1000) was supplied by GE Plastics, India as a gift sample. It was dried at 150°C for 4 h before being used. Diethylene glycol (DEG), 4,4’-methylene
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bis(phenyl isocyanate) (MDI), hydroxyl benzene sulfonate (HBS), glycerol, N,N- dimethyl
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acetamide (DMAc), N-methyl-2-pyrrolidone (NMP), bovine serum albumin (BSA,69kDa), egg albumin (EA, 45kDa), pepsin (35kDa), trypsin (20kDa) and sodium lauryl sulfate (SLS) of AR
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grade were procured from Sigma Aldrich Inc., St. Louis, MO, USA. Anhydrous sodium monobasic phosphate and sodium dibasic phosphate heptahydrate were also procured from
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Sigma Aldrich Inc., St. Louis, MO, USA and used for the preparation of phosphate buffer
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solutions in the protein analysis. Zinc (II) sulfate, copper (II) sulfate and lead (II) nitrate of AR grade were procured from Loba Chemie Ltd., Mumbai, India and used for the preparation of
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aqueous metal ion solutions. Chromium (III) sulfate of AR grade and polyethyleneimine
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(PETIM) (MW 5x104to 1x105 Da) 50 % aqueous solution were procured from Himedia Lab. Pvt. Ltd., Mumbai, India. All chemicals were used as such without further purification. De-ionized
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water was employed for the preparation of membranes and UF experiments. 2.2. Synthesis of charged surface modifying macromolecule The cSMM synthesis was done according to the procedure reported by Mohd Norddin et al. [32,33]. The cSMM, endcapped with hydroxy benzene sulfonate (HBS), was synthesized using a two-step solution polymerization method. The first step involved the reaction of MDI with DEG in a common solvent of DMAc. This mixture formed a urethane prepolymer solution. The prepolymer
is
a
segment
blocked
urethane
oligomer,
poly
(4,4׳
diphenylenemethylenemethoxymethylene urethane) having both endcapped with isocyanate. The reaction was then terminated by the addition of HBS resulting in a solution of charged or 8 Page 8 of 32
sulfonated SMM. Detailed procedure: The effect of moisture was removed by drying all glassware overnight at 110 °C and the polymerization reaction was performed in a controlled condition. A solution of 0.03 mol MDI (7.5 g) in 50 ml of degassed DMAc was loaded in a 1-L
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Pyrex round bottom flask. Then, a solution of 0.02 mol degassed DEG (2.122 g) in 100 ml of degassed DMAc was added drop-wise with stirring to react with MDI for 3 h. Then 0.02 mol of
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HBS (4.644 g) dissolved in 50 ml of degassed DMAc was added drop-wise and the solution was
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left under stirring for 24 h at 48-50 °C, resulting in a solution of cSMM. The chemical structure of cSMM is presented in Fig. 1. Distilled water was added to cSMM solution in DMAC under
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vigorous stirring to precipitate the cSMM. Prepared cSMM was kept immersed in distilled water for 24 h under stirring to leach out residual solvent. cSMM was then dried in an air circulation
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oven at 120 °C for 5 days and stored in a glass bottle.
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2.3. Preparation of membrane
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Fig. 1 – Insert here
The blend solutions based on PEI (17.5 wt %) and cSMM additive (1, 3, 5 wt %) were
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prepared in a solvent, NMP (77.5 – 82.5 %) under constant mechanical stirring at 200 rpm of rotation in a round-bottomed flask for 4 h at 40 ⁰C. The casting and gelation conditions were maintained constant throughout, because the thermodynamic conditions would largely affect the morphology and performance of the resulting membranes [34]. The membrane-casting chamber was maintained at a temperature of 24 ± 1 ⁰C and a relative humidity of 50 ± 2 ⁰C. Before casting, a 2-L gelation bath, consisting of 2.5 % NMP solvent and 0.2 wt % surfactant, SLS in distilled water (non solvent) was prepared and kept at 20 ± 1 ⁰C. The membranes were cast over a glass plate using a doctor blade. After casting, the solvent was allowed to evaporate for 30 s and then, the cast film along with the glass plate was gently immersed in the gelation bath for 1 9 Page 9 of 32
h. The membrane formed was peeled off from the glass plate slowly. The membrane was removed from gelation bath and washed thoroughly with distilled water to remove solvent and surfactant from the membranes. The thickness of the cast membranes was maintained throughout
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the studies at 0.22 ± 0.02 mm. Finally, the membranes were stored in distilled water containing 0.1 % formalin solution to prevent microbial growth.
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2.4. Experimental setup
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The prepared membranes were cut into the required size for use in the UF dead end cell (Amicon 8400-Model, Millipore, USA) fitted with a Teflon-coated magnetic paddle. The
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effective membrane area available for UF was 38.5 cm2. The solution filled in the cell was stirred at 300 rpm using a magnetic stirrer. All the experiments were carried out at 30 ± 2°C and
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345 kPa trans-membrane pressures. The membranes were initially pressurized with distilled
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experiments at 345 kPa.
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water at 414 kPa for 5 h. These pre-pressurized membranes were used in subsequent UF
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2.4.1. Measurement of average pore size and porosity Average pore size of the membrane surface area was determined by the UF of protein solutions of different molecular weights. The molecular weight of the solute which has solute rejection (SR) above 80 % was used to evaluate the average pore size of the membranes by the following equation:
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Where
is the average pore size (radius) of the membrane (m), and α is the average solute
radius (m). The average solute radii, also known as the Stoke radii, were obtained from the plot of solute molecular weight versus solute radius in aqueous solution, which was developed by
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Sarbolouki [35].
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The porosity of membrane was determined by gravimetric method [36]. A membrane was soaked in glycerol and sheared. The glycerol on the surface of membrane was wiped away to
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obtain the wet membrane with a weight, Ww. Then the wet membrane was dried in a vacuum oven until a constant weight of dried membrane, Wd, was achieved. The porosity of membrane,
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Pr, was calculated by the equation:
Where, d is the average thickness of membrane,
is the density of glycerol and S is filtering
area, respectively.
2.4.2. Molecular weight cut-off and protein rejection study MWCO is an attribute of pore size of the membranes and is related to the rejection of a spherical solute of a given molecular weight. The MWCO has a linear relationship with the pore size of the membrane [37]. In general, the MWCO of the membrane is determined by identifying an inert solute of lowest molecular weight that has a solute rejection of 80–100 % in steady state UF experiments [38]. Thus, the proteins of different molecular weights such as, BSA (69 kDa); 11 Page 11 of 32
EA (45 kDa); pepsin (35 kDa); and trypsin (20 kDa) were chosen for rejection studies of the PEI/cSMM blended membranes. The UF cell was filled with protein solution and pressurized at a constant pressure of 345 kPa. During UF, the permeate solutions were collected over a period
spectrophotometer (Shimadzu, Model UV-160A) at 280 nm.
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of time in a graduated cylinder and were analyzed for the protein concentration by UV–VIS From the feed and permeate
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concentrations, the percentage solute rejection of the protein was calculated using the equation:
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2.4.3. Metal ion rejection study
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Where Cp and Cf are the concentrations of the permeation and feed solution, respectively.
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To find the influence of PETIM on metal ion rejection, preliminary experiments were carried out to separate metal salt solutions in the absence of PETIM using the neat PEI membrane. Aqueous solutions containing Cu(II), Zn(II), Pb(II) and Cr(III) salts of 1000 ppm in 0.5, 1, 1.5 and 2 wt % solution of PETIM in de-ionized water were prepared individually. The pH of these solutions was adjusted to 6.25 using 0.1N HCl and 0.1N NaOH. Solutions containing both PETIM and metal salt solutions were thoroughly mixed and left for 5 days at 25 ⁰C to allow complete binding before being subjected to an UF study at TMP of 345 kPa. For each run, the first few ml of permeate was discarded. The metal ion concentrations in the feed and permeate solutions were determined by atomic absorption spectrophotometer (Shimadzu, Model-AA 6300,
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Japan) according to the standard method. The percentage metal ion rejection (% SR) was calculated with the same formula as that for protein rejection.
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3. Results and discussion 3.1. Protein rejection study
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The rejection of BSA, EA, pepsin and trypsin were attempted individually with the prepared membranes. The sequence of UF experiments was from low to high molecular weight protein to
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prevent pore blocking by high molecular weight protein that would affect membrane
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performance in subsequent UF experiments. The percentage rejection of the proteins is shown in Fig. 2, for different cSMM contents in the PEI blended membranes. From the figure, rejection of
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BSA deceases from 94.6 to 87.1 % as cSMM content increases from 0 to 5 wt %. Other proteins also exhibited the same trend. This may be due to the fact that the higher cSMM content made
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the mixed casting solution uneven and inhomogeneous, resulting in the formation of larger pores
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within the membranes. Therefore, the rejection percentage decreased as cSMM content increased
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in the blended PEI membranes. Furthermore, it is observed from Fig. 2, that the protein rejection follows the sequence of the protein molecular size as expected.
Fig. 2 – Insert here
3.2. Permeate flux study
The permeate flux is the measure of product rate of the membrane for the given protein solution. Fig.3, illustrates the permeate flux for various feed protein solutions as a function of the cSMM content. Pure PEI membrane shows the lowest permeate flux of 2.1 Lm-2h-1 for BSA in the absence of additive. The other proteins such as EA, pepsin, and trypsin show comparatively higher fluxes with pure PEI membranes. The figure shows that the flux increases as the SMM 13 Page 13 of 32
content increases. For example, the flux increases from 6.3 to 47.6 Lm-2h-1 with an increase in cSMM content from 0 to 5 wt %, when trypsin solution was the feed. A similar trend was
Table 1 & Fig. 3 – Insert here
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observed for all the other proteins.
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As well, the flux increased as the protein molecular size decreases, thus the order of permeate
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flux was BSA < EA < pepsin < trypsin. The reason for this trend may be due to the fact that the large BSA protein plugs the membrane pores more readily, resulting in lower permeate flux.
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Furthermore, since the MWCO of the blended membranes is quite high, the lower molecular weight solute such as trypsin passes through the membrane faster than BSA [39].
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3.3. Molecular weight cut-off study
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Molecules having a molecular weight larger than the MWCO of a membrane will not pass
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through the membrane. The MWCO of the membranes was determined using different standard solutions. The solutes generally used are proteins which are considered to be spherical; however
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it is no longer spherical at the membrane surface. For each membrane, a protein that shows nearly 80 % rejection was chosen (see Table 1), and MWCO was calculated by equation (1) using the radius of that particular protein and the rejection data [35]. From Table 1, MWCO increases progressively from 20 to 45 kDa as the cSMM content increases from 0 to 5 wt %. 3.4. Pore size and surface porosity study The addition of cSMM to the PEI membrane has changed the pore statistics substantially. The effect of cSMM content on porosity and pore size of the membranes is shown in Table 1. From the table, the pore size increases from 28.00 to 41.41 Å and the porosity increases from 5.4 to 14.8 % as cSMM content increases from 0 to 5 wt %. The increase in pore size by the addition of 14 Page 14 of 32
cSMM is likely due to the formation of clusters of sulfonate ions, into which water droplets are entrapped. This would lead to the increase in the permeation rate of the membrane [40]. These results are in good agreement with those obtained in the earlier study [41,42]. It is also noted that
3.5. Metal ion permeation at various PETIM concentrations
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wt % of PES dopes with and without 7 wt % poly(vinyl pyrrolidone) [43].
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pore size of the membrane has increased by adding 1.5 wt % hydrophobic SMM into 15 and 17
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The permeate flux studies are important to predict the economics of the membrane process. Thus, the permeation fluxes of all prepared membranes were measured and the results shown in
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Figures 4,5,6 and 7 for the PETIM concentrations of 0.5, 1.0, 1.5 and 2.0 wt %, respectively.
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From Fig. 4, the increasing order of permeate flux is Cu(II) (3.6 Lm-2h-1) < Cr(III) (4.1 Lm-2h-1) < Zn(II) (5.2 Lm-2h-1) < Pb(II) (6.3 Lm-2h-1). As well, the flux increased with an increase in
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cSMM content. The same trends were observed in Figs. 5-7. Interestingly, no considerable
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decrease in flux was observed as PETIM concentration in the feed increased from 0.5 (Fig. 4) to 2.0 wt % (Fig. 7). The increase in flux with increasing cSMM content is due to the increase in
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pore size.
Table 2 & Fig. 4 – 7 Insert here
3.6. The effect of PETIM concentration on metal ions rejection Polymeric ligand concentration (PLC) plays a major role in the rejection behavior of metal ions. In general, the increase in the concentration of water- soluble polymeric ligands in aqueous stream makes the process of complexation - UF more efficient. Probably, it leads to an increment in the concentration polarization phenomenon close to the surface of the membrane, which can be related to a higher metal removal [44]. In order to study the effect of PETIM on rejection, 15 Page 15 of 32
experiments were carried out in the absence of PETIM and it was observed that all metal ions were completely passing through membranes over the entire range of acidic pH. Further, at pH beyond 7.0, all metal ions precipitated as insoluble hydroxides. Hence, the pH of feed was kept
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exactly at 6.25 and rejections were carried out in the presence of PETIM due to the fact that at this pH, strong protonation of metal chelates along with relatively larger extent of stretching of
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complex takes place [45]. The effect of PETIM on the rejection of the pure PEI and PEI/cSMM
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blended membranes are shown in Table 2 and 3. From, Table 2 copper rejections are almost constant at all polymer ligand concentrations except for 0.5 wt % PETIM, showing the strong
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binding capacity of PETIM even at low concentration.
The rejection of Pb(II) keeps increasing as the PETIM concentration increases.. For the neat
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PEI membrane, with 0.5 wt % PETIM the Pb(II) rejection increased from 60.1 to 69.4 % as the
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PETIM concentration increased from 0.5 to 2 wt %. A similar trend was observed for all the
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complexation of Pb(II).
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other blended membranes. The rejection of Pb(II) was much lower than Cu(II) due to weaker
Table 3 – Insert here
In case of Cr(III) and Zn(II), the rejection increase progressively as PETIM concentration is increased. For example, for the neat PEI membrane, the rejection of Cr(III) increases from 86.8 to 94.4 % and Zn(II) rejection increases from 76.3 to 82.4 % as the PETIM is increased from 0.5 to 2 wt %. The same trend was observed for the other blended membranes (Table 3). This behavior is possibly attributed to the more complexation of metal ions at the higher PETIM concentration [46]. Thus the order of rejection was found to be Cu(II) > Cr(III) > Zn(II) >
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Pb(II). The rejection order seems to reflect the order in complexation capacity of the studied heavy metal ions with the PLC. It was indeed confirmed that interaction with Cu(II) are normally more intense than with other
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divalent metal ions [47]. Furthermore, the metal ions and ligand binding efficiency depends on the number of functional groups in the macromolecular complex and the atomic size of the metal
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[44].
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4. Conclusions
PEI/cSMM blended UF membranes with various polymer blend compositions were subjected
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to the separation of proteins and toxic heavy metal ions. The addition of cSMM enhanced the
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pore size, porosity, and MWCO compared to the neat PEI membranes. With an increasing content of cSMM in the casting solution, the rejection of proteins decreased, whereas protein
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permeation had an increasing trend. The protein separation study revealed that the MWCO of the
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prepared membranes was in the range of 20 kDa to 45 kDa. Regarding the UF experiments with feed solutions with heavy metal ions and PLC (PETIM), the rejection of metal ions was
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marginally decreased, whereas the permeate flux was radically improved by the addition of cSMM on PEI membranes. The rejection of the metal ions increased significantly with an increasing PETIM concentration from 0.5 to 2 wt %. The order in the heavy metal ion rejection was Cu(II) > Cr(III) > Zn(II) > Pb(II), possibly reflecting the order in the binding capacity of PLC with the heavy metal cations.
Acknowledgements This work was supported by the Science and Engineering Research Board (SERB), Department of Science and Technology, Government of India under the project number SR/FT/CS-22-2011. This support is gratefully acknowledged. The authors also gratefully 17 Page 17 of 32
acknowledge the financial support from Natural Sciences and Engineering Research Council of Canada for the partial support of this work.
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[18] P. Thanikaivelan, V. Geetha, J. R. Rao, K. J. Sreeram, B.U. Nair, A novel chromiumiron tanning agent: Cross-fertilisation in solo tannage, J. Soc. Leather Technol. Chem. 84 (2000) 82–87. [19] L. Gzara, A. Hafiane, M. Dhahbi, Removal of divalent lead cation from aqueous streams using micellar-enhanced ultrafiltration, Rev. Sci. Eau. 13 (2000) 289–304. [20] R. S. Juang, R. C. Shiau, Metal removal from aqueous solutions using chitosanenhanced membrane filtration, J. Membr. Sci. 165 (2000) 159–167. [21] J. Muslehiddinoglu, J. Uludag, H. O. Ozbelge, L. Yilmaz, Effect of operating parameters on selective separation of heavy metals from binary mixtures via polymer enhanced ultrafiltration, J. Membr. Sci. 140 (1998) 251–266. [22] A. Nagendran, S. Vidya, D. Mohan, Preparation and characterization of cellulose acetate-sulfonated poly (ether imide) blend ultrafiltration membranes and their applications, Soft Mater. 6 (2008) 45–64. [23] B.L. Rivas, S.A. Pooley, E.D. Pereira, R. Cid, M. Luna, M.A. Jara, K.E. Geckeler, Water-soluble amine and imine polymers with the ability to bind metal ions in conjunction with membrane filtration, J. Appl. Polym. Sci. 96 (2005) 222–231. [24] A. Nagendran, D. L. Arockiasamy, D. Mohan, Effect of poly (ethylene glycol) on separations by cellulose aceate/poly (ether imide) blend membranes, Int. J. Polym. Mater. 57 (2007) 138–153. [25] M. Sivakumar, D. Mohan, V. Mohan, C. M. Lakshmanan, Modification of polysulphone with cellulose acetate and application as membranes : Recent advances in membranebased separation science and technology Indian J. Chem. Tech. 3 (1996) 184–186. [26] J. Labanda, M. S. Khaidar, J. Llorens, Feasibility study on the recovery of chromium (III) by polymer enhanced ultrafiltration, Desalination. 249 (2009) 577–581. [27] K. Trivunac, S. Stevanovic, Removal of heavy metal ions from water by complexationassisted ultrafiltration, Chemosphere. 64 (2006) 486–491. [28] S. Petrov, V. Nenov, Removal and recovery of copper from wastewater by a complexation-ultrafiltration process, Desalination. 162 (2004) 201–209. [29] D. Zamariotto, B. Lakard, P. Fievet, N. Fatin-Rouge, Retention of Cu(II)– and Ni(II)– polyaminocarboxylate complexes by ultrafiltration assisted with polyamine, Desalination. 258 (2010) 87–92. [30] P. Canizares, A. Perez, R. Camarillo, J. Llanos, M. L. Lopez, Selective separation of Pb from hard water by a semi-continuous polymer-enhanced ultrafiltration process (PEUF), Desalination. 206 (2007) 602–613. [31] E. Bayer, B.Ya. Spivakov, K. Geckeler, Poly(ethyleneimine) as complexing agent for separation of metal ions using membrane filtration, Polym. Bull. 13 (1985) 307–311. [32] M. N. A. Mohd Norddin, A. F. Ismail, D. Rana, T. Matsuura, A. Mustafa, A. Tabe – Mohammadi, Characterization and performance of proton exchange membranes for direct methanol fuel cell: Blending of sulfonated poly(ether ether ketone) with charged surface modifying macromolecule, J. Membr. Sci. 323 (2008) 404–413. [33] M. N. A. Mohd Norddin, D. Rana, A. F. Ismail, T. Matsuura, R. Sudirman, J. Jaffar, J. Ind. Eng. Chem. 18 (2012) 2016–2023. [34] C. Barth, M. C. Gonclaves, A. T. N. Pires, J. Roeder, B. A. Wolf, Asymmetric polysulfone and polyethersulfone membranes: Effects of thermodynamic conditions during formation on their performance, J. Membr. Sci. 169 (2000) 287–299.
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[35] M. N. Sarbolouki, A general diagram for estimating pore size of ultrafiltration and reverse osmosis membranes, Sep. Sci. Technol. 17 (1982) 381–386. [36] Y. X. Gao, L. B. Ye, Fundamental of membrane separation technology: Chinese Science Press, Beijing, 1989. [37] S. Vidya, A. Vijayalakshmi, A. Nagendran, D. Mohan, Effect of additive concentration on cellulose acetate blend membranes-Preparation, characterization and application studies, Sep. Sci. Technol. 43 (2008) 1933–1954. [38] R. Malaisamy, R. Mahendran, D. Mohan, Cellulose acetate and sulfonated polysulfone blend ultrafiltration membranes. II. Pore statistics, molecular weight cut-off, and morphological studies, J. Appl. Polym. Sci. 84 (2002) 430–444. [39] S. I. Nakao, S. Yamota, S. Kimura, Analysis of rejection characteristics of macromolecular gel layer for low molecular weight solutes in ultrafiltration, Chem. Eng. Jpn. 15 (1982) 463–468. [40] Y. Kim, D. Rana, T. Matsuura, W. J. Chung, Influence of surface modifying macromolecules on the surface properties of poly (ether sulfone) ultrafiltration membranes, J. Membr. Sci. 338 (2009) 84–91. [41] P. Kanagaraj, S. Neelakandan, A. Nagendran, Poly(ether imide) membranes modified with charged surface-modifying macromolecule—Its performance characteristics as ultrafiltration membranes, J. Appl. Polym. Sci. 131(2014) 40320 (8pp). [42] P. Kanagaraj, S. Neelakandan, A. Nagendran, Preparation, characterization and performance of cellulose acetate ultrafiltration membranes modified by charged surface modifying macromolecule, Korean. J. Chem. Eng. 31 (2014) 1057-1064. [43] D. E. Suk, T. Matsuura, H. B. Park, Y. M. Lee, Development of novel surface modified phase inversion membranes having hydrophobic surface-modifying macromolecule (nSMM) for vacuum membrane distillation, Desalination. 261 (2010) 111–116. [44] J. Korus, M. Bodzek, K. Loska, Removal of zinc and nickel ions from aqueous solutions by means of the hybrid complexation–ultrafiltration process Sep. Purif. Technol. 17 (1999) 111–116. [45] D. L. Arockiasamy, A. Nagendran, K. H. Shobana, D. Mohan, Preparation and characterization of cellulose acetate/aminated polysulfone blend ultrafiltration membranes and their application studies, Sep. Sci. Technol. 44 (2009) 398–421. [46] A. Nagendran, A. Vijayalakshmi, D. L. Arockiasamy, K. H. Shobana, D. Mohan, Toxic metal ion separation by cellulose acetate/sulfonated poly (ether imide) blend membranes: Effect of polymer composition and additive. J. Hazard. Mater. 155 (2008) 477–485. [47] B. L. Rivas, E. D. Pereira, I. M. Villoslada, Water - soluble polymer-metal ion interactions, Prog. Polym. Sci. 28 (2003) 173–208.
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Fig. 3. Effect of the cSMM additive content on the permeate flux of feed solutions of protein for the PEI/cSMM blended membranes.
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Fig. 4. Effect of 0.5 wt% PETIM concentration on the permeate flux of feed solutions of metal ion for the PEI/cSMM blended membranes.
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Fig. 5. Effect of 1 wt% PETIM concentration on the permeate flux of feed solutions of metal ion
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for the PEI/cSMM blended membranes.
Fig. 6. Effect of 1.5 wt% PETIM concentration on the permeate flux of feed solutions of metal
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ion for the PEI/cSMM blended membranes.
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for the PEI/cSMM blended membranes.
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Fig. 7. Effect of 2 wt% PETIM concentration on the permeate flux of feed solutions of metal ion
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Table(s)
Blend composition (wt %)
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Table 1 Blend composition, pore radius, porosity and molecular weight cut-off of PEI/cSMM blended membranes
Pore radius,
Porosity,
(Lm-2h-1)
R (Å)
ε (%)
SR (%)
(kDa)
M an
PWF
MWCO
cSMM
NMP
17.5
0
82.5
6.4 0.4
28.0
5.4
83.4 0.2
20
17.5
1
81.5
6.1
79.7 0.3
20
17.5
3
17.5
5
ed
PEI
28.2
79.5
26.7 0.5
34.3
9.7
79.6 0.1
35
77.5
60.4 0.4
41.4
14.8
82.1 0.5
45
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10.6 0.2
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Table 2 Effect of PETIM concentration on rejection of Cu(II) and Pb(II) ions of pure PEI and PEI/cSMM blended membranes
Metal ions rejection, %
Blend composition
PWF
PETIM concentration (wt %)
(Lm-2h-1) cSMM
NMP
ed
PEI
Pb(II)
M an
Cu(II)
(wt %)
PETIM concentration (wt %)
0.5
1.0
1.5
2.0
0.5
1.0
1.5
2.0
0
82.5
6.4 0.4
88.4 0.6
95.4 0.8
95.1 1.6
96.1 0.8
60.1 1.5
64.3 2.2
66.6 2.6
69.4 0.4
17.5
1
81.5
10.6 0.2
87.1 0.5
94.6 0.9
94.0 0.5
94.7 0.4
59.2 2.1
60.4 0.4
63.9 1.2
64.2 1.5
17.5
3
17.5
5
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17.5
79.5
26.7 0.5
84.2 0.7
92.8 0.8
91.8 2.6
92.0 0.9
55.6 0.6
57.1 0.4
59.7 0.6
62.4 2.3
77.5
60.4 0.4
81.6 1.3
90.3 0.6
90.5 0.7
91.7 1.5
50.2 1.9
52.4 1.4
53.6 0.9
57.4 0.6
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Table 3 Effect of PETIM concentration on rejection of Cr(III) and Zn(II) ions of pure PEI and PEI/cSMM blended membranes
Metal ions rejection, %
M an
Blend composition
Cr(III)
Zn(II)
PETIM concentration (wt %)
PETIM concentration (wt %)
(wt %) PWF (Lm-2h-1)
cSMM
NMP
ed
PEI
0
82.5
17.5
1
81.5
17.5
3
17.5
5
1.5
2.0
0.5
1.0
1.5
2.0
6.4 0.4
86.8 0.9 90.8 1.5 92.6 0.2 94.4 1.4 76.3 0.7 78.4 2.3 80.4 1.6 82.4 1.3
10.6 0.2
85.1 0.6 89.2 0.9 91.2 0.5 92.5 0.5 74.5 0.5 76.6 0.4 79.2 0.7 83.8 1.8
Ac
17.5
1.0
ce pt
0.5
79.5
26.7 0.5
82.6 0.6 87.4 0.8 90.1 0.6 91.2 0.7 66.5 0.3 71.2 0.6 75.2 0.6 78.4 0.6
77.5
60.4 0.4
80.2 1.2 85.6 1.3 87.8 2.1 89.6 0.8 60.4 0.6 64.6 0.8 71.6 0.9 75.6 0.8
Page 24 of 32
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Figure captions
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Fig. 1. Chemical structure of charged surface modifying macromolecule (cSMM).
Fig. 2. Effect of the cSMM additive content on the rejection of proteins for the PEI/cSMM blended membranes. Fig. 3. Effect of the cSMM additive content on the permeate flux of feed solutions of protein for the PEI/cSMM blended membranes.
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Fig. 4. Effect of 0.5 wt% PETIM concentration on the permeate flux of feed solutions of metal ion for the PEI/cSMM blended membranes.
membranes.
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Fig. 5. Effect of 1 wt% PETIM concentration on the permeate flux of feed solutions of metal ion for the PEI/cSMM blended
membranes.
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Fig. 6. Effect of 1.5 wt% PETIM concentration on the permeate flux of feed solutions of metal ion for the PEI/cSMM blended
Fig. 7. Effect of 2 wt% PETIM concentration on the permeate flux of feed solutions of metal ion for the PEI/cSMM blended membranes.
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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Figure 5
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Figure 6
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Figure 7
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S0141-8130(14)00551-0 http://dx.doi.org/doi:10.1016/j.ijbiomac.2014.08.018 BIOMAC 4542
To appear in:
International Journal of Biological Macromolecules
Received date: Revised date: Accepted date:
26-6-2014 28-7-2014 7-8-2014
Please cite this article as: P. Kanagaraj, A. Nagendran, D. Rana, T. Matsuura, S. Neelakandan, Separation of macromolecular proteins and rejection of toxic heavy metal ions by PEI/cSMM blend UF membranes, International Journal of Biological Macromolecules (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.08.018 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Separation of macromolecular proteins and rejection of toxic heavy
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metal ions by PEI/cSMM blend UF membranes
P. Kanagaraja, A. Nagendrana, *, D. Ranab, T. Matsuurab, S. Neelakandana
PG & Research Department of Chemistry, Polymeric Materials Research Lab,
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Alagappa Government Arts College, Karaikudi - 630 003, India
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a
b
Department of Chemical and Biological Engineering, Industrial Membrane Research Institute,
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University of Ottawa, 161 Louis Pasteur St., Ottawa, ON, K1N 6N5, Canada
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RESEARCH HIGHLIGHTS
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First time we are using PEI/cSMM blend UF membranes for macromolecular protein and toxic metal ion removal.
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cSMM is blended with PEI to improve separation performance, MWCO, pore size and porosity.
Modified UF membranes possessed higher protein and metal ion permeate flux. Rejection performance of toxic metal ions found to be great in higher PETIM ligand concentration.
Stability complexation of PETIM with metal ion also plays significant role in metal ion rejection.
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*Corresponding author: Email: [email protected] (Dr. A. Nagendran),
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Phone: 91-4565-224283 Fax. No: 91-4565-227497
Abstract
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The charged surface modifying macromolecule (cSMM) was blended into the casting solution of
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poly(ether imide) (PEI) to prepare surface modified ultrafiltration membranes by phase inversion
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technique. The separation of proteins including bovine serum albumin, egg albumin, pepsin and trypsin was investigated by the fabricated membranes. On increasing cSMM content, solute rejection decreases whereas membrane flux increases. The pore size and surface porosity of the 5 wt % cSMM blend PEI membranes increases to 41.4 Å and 14.8 %, respectively. Similarly, the molecular weight cut-off of the membranes ranged from 20 to 45 kDa, depending on the various compositions of the prepared membranes. The toxic heavy metal ions Cu(II), Cr(III), Zn(II) and Pb(II) from aqueous solutions were subjected to rejection by the prepared blended membrane with various concentration of polyethyleneimine (PETIM) as water soluble polymeric ligand. It was found that the rejection behavior of metal ion depends on the PETIM concentration and the stability complexation of metal ion with ligand. 2 Page 2 of 32
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Keywords: Ultrafiltration membrane; Proteins separation; Toxic metal ions rejection
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1. Introduction
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Membrane based separations are now used in a wide range of water purification as well as other industrial applications. In recent years, membrane separation processes have evolved from
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simple applications in the laboratory to utilization in important industrial operations with significant technical and commercial impact [1]. In various industrial fields, such as metals, food and medical industries, it is becoming increasingly important to separate solution constituents such as proteins, enzymes, antibodies, hormones, blood proteins and toxic heavy metal ions. There are several different methods to separate proteins from their mixtures including liquid chromatography, electrophoretic and membrane based techniques [2]. Among the aforesaid separation processes, ultrafiltration (UF) has been widely used for product recovery and pollution control in the chemical, electro-coating, metal refining as well as food, pharmaceutical and biotechnological industries. This process is more efficient and easy to handle than the other
3 Page 3 of 32
processes and can be scaled up at low cost. Separation of colloidal suspensions by UF can be achieved by perm-selective membranes, which allow the passage of solvent and small solute molecules but retain macromolecules [3]. Intensive research has been carried out by several
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researchers on the rejection of proteins using cellulose acetate (CA) and polysulfone (PS) membranes, and it has been concluded that the UF membrane is a reliable process for
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macromolecular separation [4].
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To further improve separation performance, researchers have made considerable efforts to fabricate low fouling UF membranes with higher selectivity by anchoring anionic or cationic
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groups in the barrier layer of the membranes. This has been achieved via membrane surface modification, or by blending a hydrophilic functionalized polymer with a hydrophobic
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membrane forming polymer [5]. For instance, Liu et al. have prepared hydrophilic negatively
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charged UF membranes using sulfonated poly(phenyl sulfone) random copolymer. The
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hydrophilicity and antifouling ability of the membranes were enhanced with an increasing fraction of sulfonated copolymer [6]. Li et al. have also developed negatively and positively
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charged hollow fiber UF membranes by dual-layer hollow fiber technology, using sulfonated poly(ether sulfone) (PES) and quaternized PES. These membranes were used in the separation of bovine serum albumin (BSA) and hemoglobin (Hb) from the model solution mixture [7]. Attempts were then made to prepare charged UF membranes which were found to yield good salt rejection. The charged membranes were found to be effective in prevented plugging by ovalbumin that bears the same charge [8]. According to Nagendran et al. CA/PEI blend UF membranes showed better results for the separation of proteins and toxic metal ions [9]. Pore statistics, molecular weight cut-off (MWCO) and morphology are the structural properties of membranes that are essential for the application of the membranes processes for the
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desired permeate qualities [10]. Only solute molecules smaller than membrane pore diameter are allowed to transport through the membrane [11]. Most of the commercially available membranes are specified by their pore size or MWCO [12], which are important parameters affecting the
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separation characteristics of the UF membranes [13].
Removal of toxic heavy metals such as Cu, Zn, Hg, Cd, Pb and Ni from industrial wastewaters
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is required for meeting discharge limits or for water reuse. Many industrial wastewaters
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produced by metal plating, metal finishing, mining, automotive, aerospace, battery and other chemical processes industries, often are often highly concentrated with heavy metals. These toxic
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metals in air, water and soil are major problems as a threat to the environment. Zinc is an essential heavy metal for biological functions; however, it becomes hazardous beyond certain
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concentrations [14]. Copper is a metal commonly found in industrial wastewaters both in particulate form and as organic complexes. In aqueous environments, the function of the metal is
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dependent both on ligand concentration and pH [15]. While the cupric ion (Cu2+) is the metallic form most toxic to flora and fauna it is also a nutrient necessary for algal growth [16]. If allowed
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to enter the environment it can cause serious potential health issues. Even at low concentrations copper may be harmful to humans. It has been found that absorption of excess copper results in ‘‘Wilson’s disease’’ where copper is deposited in the brain, skin, liver, pancreas and myocardium. The presence of lead in drinking water is known to cause various types of serious health problems leading to death in extreme exposure cases [17]. One of the major technical requirements of the leather and other industries employing large quantities of chromium salts in wet processing is the need to minimize the concentration of the metal in the effluents and its removal [18]. These inorganic micro-pollutants are of considerable concern because they are non-biodegradable, highly toxic and in some cases have a probable carcinogenic effect. If
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directly discharged into the sewage system they may seriously affect the operation of biological treatment systems and render the activated sludge unsuitable for application to agricultural land [19].
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Therefore, the removal and separation of toxic and environmentally hazardous heavy metal ions are technological challenge. For separating species with ionic dimensions, reverse osmosis
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membranes are often required but they will result in high operative costs and low permeate flow
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rate. A promising process for the removal of heavy metal ions from aqueous solution involves the UF – complexation, also named the polymer enhanced UF, which is based on complexation
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of heavy metals by water soluble macromolecule polymers such as polyethyleneimine (PETIM), poly(acrylic acid) (PAA), poly(vinyl alcohol) (PVA), etc. The heavy metal ions, by
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complexation with macromolecules, become larger molecular weight than the MWCO of the
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membranes, are retained by UF membrane, producing permeate free of heavy metals. The
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advantage of this method is the low energy requirements of UF and the high removal efficiency [20]. A wide variety of water soluble polymers have been utilized in UF processes for the
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recovery of heavy metals. Amongst those, PETIM is one of the most extensively used mainly because of its high water solubility, its high capacity to bind metal ions and its physical and chemical stability [21-24].
There are several research efforts that have been made to study the applicability of polymer enhanced ultrafiltration (PE-UF) in metal removal from water of various origins. CA has been blended with PS and applied for the separation of chromium using PVA as the macromolecular chelating agent [25]. Labanda et al. made a feasibility study on the recovery of chromium (III) by PE-UF [26]. Trivunac et al. have studied the removal of heavy metal ions from water by complexation-assisted UF. According to their results obtained that, the removal of Cd2+ and Zn2+
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was more than 95 % and 99 %, respectively, at best operating conditions when diethylaminoethyl cellulose was added to the solution [27]. Petrov et al. used carboxy methyl cellulose (CMC) as a water soluble metal binding polymer in combination with UF for selective removal and recovery
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of copper from water [28]. Zamariotto et al. studied the retention of Cu(II) – and Ni(II) – nitrilotriacetic acid and ethylenediaminetetraacetic acid formation of polyaminocarboxylate
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complexes by UF assisted with polyamines. Metal retentions higher than 98 % were observed
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when PETIM in the pH range of 4–9 [29]. Canizares et al. have studied selective separation of Pb from hard water by a semi-continuous PE-UF process using PAA as a complexation agent
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[30]. The obtained results show that when Pb:Ca molar ratio is 1:1, the concentration stage of the semi-continuous process reaches very high rejection coefficients, which means a permeate
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stream with less than 0.05 ppm of Pb and 1.5 ppm of Ca. Bayer et al. studied the PETIM as a
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complexing agent for separation of heavy metals ion using membrane filtration [31]. It was
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found that the PETIM has been an effective complexing agent and suitable for retention and separation of metals in aqueous dilute solutions.
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The objective of this study is to improve the separation efficiency of proteins and metal ions by the addition of cSMM into the casting dope to modify the surface of PEI UF membrane. Average pore size, surface porosity and MWCO of surface modified PEI membranes were determined. Further, the effect of cSMM additive concentration on the rejection and permeate flux was investigated when proteins of different molecular weight such as trypsin, pepsin, egg albumin (EA), and BSA were filtrated.
The rejection and permeate flux for the aqueous
solutions of toxic heavy metal ions such as Cu(II), Cr(III), Zn(II) and Pb(II) were also investigated when PETIM of different concentrations were added to the feed solution.
2. Methodology 7 Page 7 of 32
2.1. Materials Poly(ether imide) (PEI, Ultem® 1000) was supplied by GE Plastics, India as a gift sample. It was dried at 150°C for 4 h before being used. Diethylene glycol (DEG), 4,4’-methylene
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bis(phenyl isocyanate) (MDI), hydroxyl benzene sulfonate (HBS), glycerol, N,N- dimethyl
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acetamide (DMAc), N-methyl-2-pyrrolidone (NMP), bovine serum albumin (BSA,69kDa), egg albumin (EA, 45kDa), pepsin (35kDa), trypsin (20kDa) and sodium lauryl sulfate (SLS) of AR
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grade were procured from Sigma Aldrich Inc., St. Louis, MO, USA. Anhydrous sodium monobasic phosphate and sodium dibasic phosphate heptahydrate were also procured from
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Sigma Aldrich Inc., St. Louis, MO, USA and used for the preparation of phosphate buffer
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solutions in the protein analysis. Zinc (II) sulfate, copper (II) sulfate and lead (II) nitrate of AR grade were procured from Loba Chemie Ltd., Mumbai, India and used for the preparation of
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aqueous metal ion solutions. Chromium (III) sulfate of AR grade and polyethyleneimine
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(PETIM) (MW 5x104to 1x105 Da) 50 % aqueous solution were procured from Himedia Lab. Pvt. Ltd., Mumbai, India. All chemicals were used as such without further purification. De-ionized
Ac ce p
water was employed for the preparation of membranes and UF experiments. 2.2. Synthesis of charged surface modifying macromolecule The cSMM synthesis was done according to the procedure reported by Mohd Norddin et al. [32,33]. The cSMM, endcapped with hydroxy benzene sulfonate (HBS), was synthesized using a two-step solution polymerization method. The first step involved the reaction of MDI with DEG in a common solvent of DMAc. This mixture formed a urethane prepolymer solution. The prepolymer
is
a
segment
blocked
urethane
oligomer,
poly
(4,4׳
diphenylenemethylenemethoxymethylene urethane) having both endcapped with isocyanate. The reaction was then terminated by the addition of HBS resulting in a solution of charged or 8 Page 8 of 32
sulfonated SMM. Detailed procedure: The effect of moisture was removed by drying all glassware overnight at 110 °C and the polymerization reaction was performed in a controlled condition. A solution of 0.03 mol MDI (7.5 g) in 50 ml of degassed DMAc was loaded in a 1-L
ip t
Pyrex round bottom flask. Then, a solution of 0.02 mol degassed DEG (2.122 g) in 100 ml of degassed DMAc was added drop-wise with stirring to react with MDI for 3 h. Then 0.02 mol of
cr
HBS (4.644 g) dissolved in 50 ml of degassed DMAc was added drop-wise and the solution was
us
left under stirring for 24 h at 48-50 °C, resulting in a solution of cSMM. The chemical structure of cSMM is presented in Fig. 1. Distilled water was added to cSMM solution in DMAC under
an
vigorous stirring to precipitate the cSMM. Prepared cSMM was kept immersed in distilled water for 24 h under stirring to leach out residual solvent. cSMM was then dried in an air circulation
M
oven at 120 °C for 5 days and stored in a glass bottle.
te
2.3. Preparation of membrane
d
Fig. 1 – Insert here
The blend solutions based on PEI (17.5 wt %) and cSMM additive (1, 3, 5 wt %) were
Ac ce p
prepared in a solvent, NMP (77.5 – 82.5 %) under constant mechanical stirring at 200 rpm of rotation in a round-bottomed flask for 4 h at 40 ⁰C. The casting and gelation conditions were maintained constant throughout, because the thermodynamic conditions would largely affect the morphology and performance of the resulting membranes [34]. The membrane-casting chamber was maintained at a temperature of 24 ± 1 ⁰C and a relative humidity of 50 ± 2 ⁰C. Before casting, a 2-L gelation bath, consisting of 2.5 % NMP solvent and 0.2 wt % surfactant, SLS in distilled water (non solvent) was prepared and kept at 20 ± 1 ⁰C. The membranes were cast over a glass plate using a doctor blade. After casting, the solvent was allowed to evaporate for 30 s and then, the cast film along with the glass plate was gently immersed in the gelation bath for 1 9 Page 9 of 32
h. The membrane formed was peeled off from the glass plate slowly. The membrane was removed from gelation bath and washed thoroughly with distilled water to remove solvent and surfactant from the membranes. The thickness of the cast membranes was maintained throughout
ip t
the studies at 0.22 ± 0.02 mm. Finally, the membranes were stored in distilled water containing 0.1 % formalin solution to prevent microbial growth.
cr
2.4. Experimental setup
us
The prepared membranes were cut into the required size for use in the UF dead end cell (Amicon 8400-Model, Millipore, USA) fitted with a Teflon-coated magnetic paddle. The
an
effective membrane area available for UF was 38.5 cm2. The solution filled in the cell was stirred at 300 rpm using a magnetic stirrer. All the experiments were carried out at 30 ± 2°C and
M
345 kPa trans-membrane pressures. The membranes were initially pressurized with distilled
te
experiments at 345 kPa.
d
water at 414 kPa for 5 h. These pre-pressurized membranes were used in subsequent UF
Ac ce p
2.4.1. Measurement of average pore size and porosity Average pore size of the membrane surface area was determined by the UF of protein solutions of different molecular weights. The molecular weight of the solute which has solute rejection (SR) above 80 % was used to evaluate the average pore size of the membranes by the following equation:
10 Page 10 of 32
Where
is the average pore size (radius) of the membrane (m), and α is the average solute
radius (m). The average solute radii, also known as the Stoke radii, were obtained from the plot of solute molecular weight versus solute radius in aqueous solution, which was developed by
ip t
Sarbolouki [35].
cr
The porosity of membrane was determined by gravimetric method [36]. A membrane was soaked in glycerol and sheared. The glycerol on the surface of membrane was wiped away to
us
obtain the wet membrane with a weight, Ww. Then the wet membrane was dried in a vacuum oven until a constant weight of dried membrane, Wd, was achieved. The porosity of membrane,
Ac ce p
te
d
M
an
Pr, was calculated by the equation:
Where, d is the average thickness of membrane,
is the density of glycerol and S is filtering
area, respectively.
2.4.2. Molecular weight cut-off and protein rejection study MWCO is an attribute of pore size of the membranes and is related to the rejection of a spherical solute of a given molecular weight. The MWCO has a linear relationship with the pore size of the membrane [37]. In general, the MWCO of the membrane is determined by identifying an inert solute of lowest molecular weight that has a solute rejection of 80–100 % in steady state UF experiments [38]. Thus, the proteins of different molecular weights such as, BSA (69 kDa); 11 Page 11 of 32
EA (45 kDa); pepsin (35 kDa); and trypsin (20 kDa) were chosen for rejection studies of the PEI/cSMM blended membranes. The UF cell was filled with protein solution and pressurized at a constant pressure of 345 kPa. During UF, the permeate solutions were collected over a period
spectrophotometer (Shimadzu, Model UV-160A) at 280 nm.
ip t
of time in a graduated cylinder and were analyzed for the protein concentration by UV–VIS From the feed and permeate
M
an
us
cr
concentrations, the percentage solute rejection of the protein was calculated using the equation:
te
2.4.3. Metal ion rejection study
d
Where Cp and Cf are the concentrations of the permeation and feed solution, respectively.
Ac ce p
To find the influence of PETIM on metal ion rejection, preliminary experiments were carried out to separate metal salt solutions in the absence of PETIM using the neat PEI membrane. Aqueous solutions containing Cu(II), Zn(II), Pb(II) and Cr(III) salts of 1000 ppm in 0.5, 1, 1.5 and 2 wt % solution of PETIM in de-ionized water were prepared individually. The pH of these solutions was adjusted to 6.25 using 0.1N HCl and 0.1N NaOH. Solutions containing both PETIM and metal salt solutions were thoroughly mixed and left for 5 days at 25 ⁰C to allow complete binding before being subjected to an UF study at TMP of 345 kPa. For each run, the first few ml of permeate was discarded. The metal ion concentrations in the feed and permeate solutions were determined by atomic absorption spectrophotometer (Shimadzu, Model-AA 6300,
12 Page 12 of 32
Japan) according to the standard method. The percentage metal ion rejection (% SR) was calculated with the same formula as that for protein rejection.
ip t
3. Results and discussion 3.1. Protein rejection study
cr
The rejection of BSA, EA, pepsin and trypsin were attempted individually with the prepared membranes. The sequence of UF experiments was from low to high molecular weight protein to
us
prevent pore blocking by high molecular weight protein that would affect membrane
an
performance in subsequent UF experiments. The percentage rejection of the proteins is shown in Fig. 2, for different cSMM contents in the PEI blended membranes. From the figure, rejection of
M
BSA deceases from 94.6 to 87.1 % as cSMM content increases from 0 to 5 wt %. Other proteins also exhibited the same trend. This may be due to the fact that the higher cSMM content made
d
the mixed casting solution uneven and inhomogeneous, resulting in the formation of larger pores
te
within the membranes. Therefore, the rejection percentage decreased as cSMM content increased
Ac ce p
in the blended PEI membranes. Furthermore, it is observed from Fig. 2, that the protein rejection follows the sequence of the protein molecular size as expected.
Fig. 2 – Insert here
3.2. Permeate flux study
The permeate flux is the measure of product rate of the membrane for the given protein solution. Fig.3, illustrates the permeate flux for various feed protein solutions as a function of the cSMM content. Pure PEI membrane shows the lowest permeate flux of 2.1 Lm-2h-1 for BSA in the absence of additive. The other proteins such as EA, pepsin, and trypsin show comparatively higher fluxes with pure PEI membranes. The figure shows that the flux increases as the SMM 13 Page 13 of 32
content increases. For example, the flux increases from 6.3 to 47.6 Lm-2h-1 with an increase in cSMM content from 0 to 5 wt %, when trypsin solution was the feed. A similar trend was
Table 1 & Fig. 3 – Insert here
ip t
observed for all the other proteins.
cr
As well, the flux increased as the protein molecular size decreases, thus the order of permeate
us
flux was BSA < EA < pepsin < trypsin. The reason for this trend may be due to the fact that the large BSA protein plugs the membrane pores more readily, resulting in lower permeate flux.
an
Furthermore, since the MWCO of the blended membranes is quite high, the lower molecular weight solute such as trypsin passes through the membrane faster than BSA [39].
M
3.3. Molecular weight cut-off study
d
Molecules having a molecular weight larger than the MWCO of a membrane will not pass
te
through the membrane. The MWCO of the membranes was determined using different standard solutions. The solutes generally used are proteins which are considered to be spherical; however
Ac ce p
it is no longer spherical at the membrane surface. For each membrane, a protein that shows nearly 80 % rejection was chosen (see Table 1), and MWCO was calculated by equation (1) using the radius of that particular protein and the rejection data [35]. From Table 1, MWCO increases progressively from 20 to 45 kDa as the cSMM content increases from 0 to 5 wt %. 3.4. Pore size and surface porosity study The addition of cSMM to the PEI membrane has changed the pore statistics substantially. The effect of cSMM content on porosity and pore size of the membranes is shown in Table 1. From the table, the pore size increases from 28.00 to 41.41 Å and the porosity increases from 5.4 to 14.8 % as cSMM content increases from 0 to 5 wt %. The increase in pore size by the addition of 14 Page 14 of 32
cSMM is likely due to the formation of clusters of sulfonate ions, into which water droplets are entrapped. This would lead to the increase in the permeation rate of the membrane [40]. These results are in good agreement with those obtained in the earlier study [41,42]. It is also noted that
3.5. Metal ion permeation at various PETIM concentrations
cr
wt % of PES dopes with and without 7 wt % poly(vinyl pyrrolidone) [43].
ip t
pore size of the membrane has increased by adding 1.5 wt % hydrophobic SMM into 15 and 17
us
The permeate flux studies are important to predict the economics of the membrane process. Thus, the permeation fluxes of all prepared membranes were measured and the results shown in
an
Figures 4,5,6 and 7 for the PETIM concentrations of 0.5, 1.0, 1.5 and 2.0 wt %, respectively.
M
From Fig. 4, the increasing order of permeate flux is Cu(II) (3.6 Lm-2h-1) < Cr(III) (4.1 Lm-2h-1) < Zn(II) (5.2 Lm-2h-1) < Pb(II) (6.3 Lm-2h-1). As well, the flux increased with an increase in
d
cSMM content. The same trends were observed in Figs. 5-7. Interestingly, no considerable
te
decrease in flux was observed as PETIM concentration in the feed increased from 0.5 (Fig. 4) to 2.0 wt % (Fig. 7). The increase in flux with increasing cSMM content is due to the increase in
Ac ce p
pore size.
Table 2 & Fig. 4 – 7 Insert here
3.6. The effect of PETIM concentration on metal ions rejection Polymeric ligand concentration (PLC) plays a major role in the rejection behavior of metal ions. In general, the increase in the concentration of water- soluble polymeric ligands in aqueous stream makes the process of complexation - UF more efficient. Probably, it leads to an increment in the concentration polarization phenomenon close to the surface of the membrane, which can be related to a higher metal removal [44]. In order to study the effect of PETIM on rejection, 15 Page 15 of 32
experiments were carried out in the absence of PETIM and it was observed that all metal ions were completely passing through membranes over the entire range of acidic pH. Further, at pH beyond 7.0, all metal ions precipitated as insoluble hydroxides. Hence, the pH of feed was kept
ip t
exactly at 6.25 and rejections were carried out in the presence of PETIM due to the fact that at this pH, strong protonation of metal chelates along with relatively larger extent of stretching of
cr
complex takes place [45]. The effect of PETIM on the rejection of the pure PEI and PEI/cSMM
us
blended membranes are shown in Table 2 and 3. From, Table 2 copper rejections are almost constant at all polymer ligand concentrations except for 0.5 wt % PETIM, showing the strong
an
binding capacity of PETIM even at low concentration.
The rejection of Pb(II) keeps increasing as the PETIM concentration increases.. For the neat
M
PEI membrane, with 0.5 wt % PETIM the Pb(II) rejection increased from 60.1 to 69.4 % as the
d
PETIM concentration increased from 0.5 to 2 wt %. A similar trend was observed for all the
Ac ce p
complexation of Pb(II).
te
other blended membranes. The rejection of Pb(II) was much lower than Cu(II) due to weaker
Table 3 – Insert here
In case of Cr(III) and Zn(II), the rejection increase progressively as PETIM concentration is increased. For example, for the neat PEI membrane, the rejection of Cr(III) increases from 86.8 to 94.4 % and Zn(II) rejection increases from 76.3 to 82.4 % as the PETIM is increased from 0.5 to 2 wt %. The same trend was observed for the other blended membranes (Table 3). This behavior is possibly attributed to the more complexation of metal ions at the higher PETIM concentration [46]. Thus the order of rejection was found to be Cu(II) > Cr(III) > Zn(II) >
16 Page 16 of 32
Pb(II). The rejection order seems to reflect the order in complexation capacity of the studied heavy metal ions with the PLC. It was indeed confirmed that interaction with Cu(II) are normally more intense than with other
ip t
divalent metal ions [47]. Furthermore, the metal ions and ligand binding efficiency depends on the number of functional groups in the macromolecular complex and the atomic size of the metal
cr
[44].
us
4. Conclusions
PEI/cSMM blended UF membranes with various polymer blend compositions were subjected
an
to the separation of proteins and toxic heavy metal ions. The addition of cSMM enhanced the
M
pore size, porosity, and MWCO compared to the neat PEI membranes. With an increasing content of cSMM in the casting solution, the rejection of proteins decreased, whereas protein
d
permeation had an increasing trend. The protein separation study revealed that the MWCO of the
te
prepared membranes was in the range of 20 kDa to 45 kDa. Regarding the UF experiments with feed solutions with heavy metal ions and PLC (PETIM), the rejection of metal ions was
Ac ce p
marginally decreased, whereas the permeate flux was radically improved by the addition of cSMM on PEI membranes. The rejection of the metal ions increased significantly with an increasing PETIM concentration from 0.5 to 2 wt %. The order in the heavy metal ion rejection was Cu(II) > Cr(III) > Zn(II) > Pb(II), possibly reflecting the order in the binding capacity of PLC with the heavy metal cations.
Acknowledgements This work was supported by the Science and Engineering Research Board (SERB), Department of Science and Technology, Government of India under the project number SR/FT/CS-22-2011. This support is gratefully acknowledged. The authors also gratefully 17 Page 17 of 32
acknowledge the financial support from Natural Sciences and Engineering Research Council of Canada for the partial support of this work.
References
Ac ce p
te
d
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ip t
[1] H. Strathmann, Membrane separation processes, J. Membr. Sci. 9 (1981) 121–189. [2] P. D. Peeva, T. Knoche, T. Pieper, M. Ulbricht, Cross-flow ultrafiltration of protein solutions through unmodified and surface functionalized polyethersulfone membranes – Effect of process conditions on separation performance, Sep. Purif. Technol. 92 (2012) 83-92. [3] R. W. Baker, H. Strathmann, Ultrafiltration of macromolecular solutions with high-flux membranes, J. Appl. Polym. Sci. 14 (1970) 1197–1214. [4] S. Nakatsuka, A. S. Michaels, Transport and separation of proteins by ultrafiltration through sorptive and non-sorptive membranes, J. Membr. Sci. 69 (1992) 189–211. [5] M. Ulbricht, Advanced functional polymer membranes, Polymer. 47 (2006) 2217–2262. [6] Y. Liu, X. Yue, S. Zhang, J. Ren, L. Yang, Q. Wang, G. Wang, Synthesis of sulfonated polyphenylsulfone as candidates for antifouling ultrafiltration membrane, Sep. Purif. Technol. 98 (2012) 298–307. [7] Y. Li, S. C. Soh, T. S. Chung, S.Y. Chan, Exploration of ionic modification in dual- layer hollow fiber membranes for long-term high-performance protein separation, AIChE J. 55 (2009) 321–330. [8] I. Jitsuhara, S. J. Kimura, Structure and properties of charged ultrafiitration membranes made of sulfonated polysulfone, Chem. Eng. Jpn. 16 (1983) 389–393. [9] A. Nagendran, D. Mohan, Protein separation by cellulose acetate/sulfonated poly(etherimide) blend ultrafiltration membranes, Polym. Adv. Technol. 19 (2008) 24– 35. [10] L. Zeman, M. Wales, Steric rejection of polymeric solutes by membranes with uniform pore size distribution, Sep. Sci. Technol. 16 (1981) 275–290. [11] B. J. McCoy, Membrane sieving of a continuous poly disperse mixture through distributed pores, Sep. Sci. Technol. 30 (1995) 487–507. [12] A. Hernandez, J. I. Calve, P. Pradanos, F. Tejrina, Pore size distributions in microporous membranes. A critical analysis of the bubble point extended method, J. Membr. Sci. 112 (1996) 1–12. [13] R. Snir, L. Wicker, P. E. Koehler, K. A. Sims, Membrane fouling and molecular weight cut off effects on the partitioning of pectin esterase, J. Agric. Food Chem. 44 (1996) 2091–2095. [14] A. Corami, S. Mignardi, V. Ferrini, Copper and zinc decontamination from single- and binary - metal solutions using hydroxyl apatite, J. Hazard. Mater. 146 (2007) 164–170. [15] J. F. Elder, A. J. Horne, Copper cycles and CuSO4 algicidal capacity in two California lakes, Environ. Manage. 2 (1978) 17–30. [16] B. Volesky, Z. R. Holan, Biosorption of Heavy Metals, Biotechnol. Prog. 11 (1995) 235–250. [17] B. Volesky, Biosorption and biosorbents. In: Biosorption of heavy metals, CRC Press, Boca Raton, 1990.
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[18] P. Thanikaivelan, V. Geetha, J. R. Rao, K. J. Sreeram, B.U. Nair, A novel chromiumiron tanning agent: Cross-fertilisation in solo tannage, J. Soc. Leather Technol. Chem. 84 (2000) 82–87. [19] L. Gzara, A. Hafiane, M. Dhahbi, Removal of divalent lead cation from aqueous streams using micellar-enhanced ultrafiltration, Rev. Sci. Eau. 13 (2000) 289–304. [20] R. S. Juang, R. C. Shiau, Metal removal from aqueous solutions using chitosanenhanced membrane filtration, J. Membr. Sci. 165 (2000) 159–167. [21] J. Muslehiddinoglu, J. Uludag, H. O. Ozbelge, L. Yilmaz, Effect of operating parameters on selective separation of heavy metals from binary mixtures via polymer enhanced ultrafiltration, J. Membr. Sci. 140 (1998) 251–266. [22] A. Nagendran, S. Vidya, D. Mohan, Preparation and characterization of cellulose acetate-sulfonated poly (ether imide) blend ultrafiltration membranes and their applications, Soft Mater. 6 (2008) 45–64. [23] B.L. Rivas, S.A. Pooley, E.D. Pereira, R. Cid, M. Luna, M.A. Jara, K.E. Geckeler, Water-soluble amine and imine polymers with the ability to bind metal ions in conjunction with membrane filtration, J. Appl. Polym. Sci. 96 (2005) 222–231. [24] A. Nagendran, D. L. Arockiasamy, D. Mohan, Effect of poly (ethylene glycol) on separations by cellulose aceate/poly (ether imide) blend membranes, Int. J. Polym. Mater. 57 (2007) 138–153. [25] M. Sivakumar, D. Mohan, V. Mohan, C. M. Lakshmanan, Modification of polysulphone with cellulose acetate and application as membranes : Recent advances in membranebased separation science and technology Indian J. Chem. Tech. 3 (1996) 184–186. [26] J. Labanda, M. S. Khaidar, J. Llorens, Feasibility study on the recovery of chromium (III) by polymer enhanced ultrafiltration, Desalination. 249 (2009) 577–581. [27] K. Trivunac, S. Stevanovic, Removal of heavy metal ions from water by complexationassisted ultrafiltration, Chemosphere. 64 (2006) 486–491. [28] S. Petrov, V. Nenov, Removal and recovery of copper from wastewater by a complexation-ultrafiltration process, Desalination. 162 (2004) 201–209. [29] D. Zamariotto, B. Lakard, P. Fievet, N. Fatin-Rouge, Retention of Cu(II)– and Ni(II)– polyaminocarboxylate complexes by ultrafiltration assisted with polyamine, Desalination. 258 (2010) 87–92. [30] P. Canizares, A. Perez, R. Camarillo, J. Llanos, M. L. Lopez, Selective separation of Pb from hard water by a semi-continuous polymer-enhanced ultrafiltration process (PEUF), Desalination. 206 (2007) 602–613. [31] E. Bayer, B.Ya. Spivakov, K. Geckeler, Poly(ethyleneimine) as complexing agent for separation of metal ions using membrane filtration, Polym. Bull. 13 (1985) 307–311. [32] M. N. A. Mohd Norddin, A. F. Ismail, D. Rana, T. Matsuura, A. Mustafa, A. Tabe – Mohammadi, Characterization and performance of proton exchange membranes for direct methanol fuel cell: Blending of sulfonated poly(ether ether ketone) with charged surface modifying macromolecule, J. Membr. Sci. 323 (2008) 404–413. [33] M. N. A. Mohd Norddin, D. Rana, A. F. Ismail, T. Matsuura, R. Sudirman, J. Jaffar, J. Ind. Eng. Chem. 18 (2012) 2016–2023. [34] C. Barth, M. C. Gonclaves, A. T. N. Pires, J. Roeder, B. A. Wolf, Asymmetric polysulfone and polyethersulfone membranes: Effects of thermodynamic conditions during formation on their performance, J. Membr. Sci. 169 (2000) 287–299.
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cr
ip t
[35] M. N. Sarbolouki, A general diagram for estimating pore size of ultrafiltration and reverse osmosis membranes, Sep. Sci. Technol. 17 (1982) 381–386. [36] Y. X. Gao, L. B. Ye, Fundamental of membrane separation technology: Chinese Science Press, Beijing, 1989. [37] S. Vidya, A. Vijayalakshmi, A. Nagendran, D. Mohan, Effect of additive concentration on cellulose acetate blend membranes-Preparation, characterization and application studies, Sep. Sci. Technol. 43 (2008) 1933–1954. [38] R. Malaisamy, R. Mahendran, D. Mohan, Cellulose acetate and sulfonated polysulfone blend ultrafiltration membranes. II. Pore statistics, molecular weight cut-off, and morphological studies, J. Appl. Polym. Sci. 84 (2002) 430–444. [39] S. I. Nakao, S. Yamota, S. Kimura, Analysis of rejection characteristics of macromolecular gel layer for low molecular weight solutes in ultrafiltration, Chem. Eng. Jpn. 15 (1982) 463–468. [40] Y. Kim, D. Rana, T. Matsuura, W. J. Chung, Influence of surface modifying macromolecules on the surface properties of poly (ether sulfone) ultrafiltration membranes, J. Membr. Sci. 338 (2009) 84–91. [41] P. Kanagaraj, S. Neelakandan, A. Nagendran, Poly(ether imide) membranes modified with charged surface-modifying macromolecule—Its performance characteristics as ultrafiltration membranes, J. Appl. Polym. Sci. 131(2014) 40320 (8pp). [42] P. Kanagaraj, S. Neelakandan, A. Nagendran, Preparation, characterization and performance of cellulose acetate ultrafiltration membranes modified by charged surface modifying macromolecule, Korean. J. Chem. Eng. 31 (2014) 1057-1064. [43] D. E. Suk, T. Matsuura, H. B. Park, Y. M. Lee, Development of novel surface modified phase inversion membranes having hydrophobic surface-modifying macromolecule (nSMM) for vacuum membrane distillation, Desalination. 261 (2010) 111–116. [44] J. Korus, M. Bodzek, K. Loska, Removal of zinc and nickel ions from aqueous solutions by means of the hybrid complexation–ultrafiltration process Sep. Purif. Technol. 17 (1999) 111–116. [45] D. L. Arockiasamy, A. Nagendran, K. H. Shobana, D. Mohan, Preparation and characterization of cellulose acetate/aminated polysulfone blend ultrafiltration membranes and their application studies, Sep. Sci. Technol. 44 (2009) 398–421. [46] A. Nagendran, A. Vijayalakshmi, D. L. Arockiasamy, K. H. Shobana, D. Mohan, Toxic metal ion separation by cellulose acetate/sulfonated poly (ether imide) blend membranes: Effect of polymer composition and additive. J. Hazard. Mater. 155 (2008) 477–485. [47] B. L. Rivas, E. D. Pereira, I. M. Villoslada, Water - soluble polymer-metal ion interactions, Prog. Polym. Sci. 28 (2003) 173–208.
20 Page 20 of 32
Fig. 3. Effect of the cSMM additive content on the permeate flux of feed solutions of protein for the PEI/cSMM blended membranes.
ip t
Fig. 4. Effect of 0.5 wt% PETIM concentration on the permeate flux of feed solutions of metal ion for the PEI/cSMM blended membranes.
cr
Fig. 5. Effect of 1 wt% PETIM concentration on the permeate flux of feed solutions of metal ion
us
for the PEI/cSMM blended membranes.
Fig. 6. Effect of 1.5 wt% PETIM concentration on the permeate flux of feed solutions of metal
an
ion for the PEI/cSMM blended membranes.
Ac ce p
te
d
for the PEI/cSMM blended membranes.
M
Fig. 7. Effect of 2 wt% PETIM concentration on the permeate flux of feed solutions of metal ion
23 Page 21 of 32
ip t
Table(s)
Blend composition (wt %)
us
cr
Table 1 Blend composition, pore radius, porosity and molecular weight cut-off of PEI/cSMM blended membranes
Pore radius,
Porosity,
(Lm-2h-1)
R (Å)
ε (%)
SR (%)
(kDa)
M an
PWF
MWCO
cSMM
NMP
17.5
0
82.5
6.4 0.4
28.0
5.4
83.4 0.2
20
17.5
1
81.5
6.1
79.7 0.3
20
17.5
3
17.5
5
ed
PEI
28.2
79.5
26.7 0.5
34.3
9.7
79.6 0.1
35
77.5
60.4 0.4
41.4
14.8
82.1 0.5
45
Ac
ce pt
10.6 0.2
Page 22 of 32
ip t
us
cr
Table 2 Effect of PETIM concentration on rejection of Cu(II) and Pb(II) ions of pure PEI and PEI/cSMM blended membranes
Metal ions rejection, %
Blend composition
PWF
PETIM concentration (wt %)
(Lm-2h-1) cSMM
NMP
ed
PEI
Pb(II)
M an
Cu(II)
(wt %)
PETIM concentration (wt %)
0.5
1.0
1.5
2.0
0.5
1.0
1.5
2.0
0
82.5
6.4 0.4
88.4 0.6
95.4 0.8
95.1 1.6
96.1 0.8
60.1 1.5
64.3 2.2
66.6 2.6
69.4 0.4
17.5
1
81.5
10.6 0.2
87.1 0.5
94.6 0.9
94.0 0.5
94.7 0.4
59.2 2.1
60.4 0.4
63.9 1.2
64.2 1.5
17.5
3
17.5
5
Ac
ce pt
17.5
79.5
26.7 0.5
84.2 0.7
92.8 0.8
91.8 2.6
92.0 0.9
55.6 0.6
57.1 0.4
59.7 0.6
62.4 2.3
77.5
60.4 0.4
81.6 1.3
90.3 0.6
90.5 0.7
91.7 1.5
50.2 1.9
52.4 1.4
53.6 0.9
57.4 0.6
Page 23 of 32
ip t
us
cr
Table 3 Effect of PETIM concentration on rejection of Cr(III) and Zn(II) ions of pure PEI and PEI/cSMM blended membranes
Metal ions rejection, %
M an
Blend composition
Cr(III)
Zn(II)
PETIM concentration (wt %)
PETIM concentration (wt %)
(wt %) PWF (Lm-2h-1)
cSMM
NMP
ed
PEI
0
82.5
17.5
1
81.5
17.5
3
17.5
5
1.5
2.0
0.5
1.0
1.5
2.0
6.4 0.4
86.8 0.9 90.8 1.5 92.6 0.2 94.4 1.4 76.3 0.7 78.4 2.3 80.4 1.6 82.4 1.3
10.6 0.2
85.1 0.6 89.2 0.9 91.2 0.5 92.5 0.5 74.5 0.5 76.6 0.4 79.2 0.7 83.8 1.8
Ac
17.5
1.0
ce pt
0.5
79.5
26.7 0.5
82.6 0.6 87.4 0.8 90.1 0.6 91.2 0.7 66.5 0.3 71.2 0.6 75.2 0.6 78.4 0.6
77.5
60.4 0.4
80.2 1.2 85.6 1.3 87.8 2.1 89.6 0.8 60.4 0.6 64.6 0.8 71.6 0.9 75.6 0.8
Page 24 of 32
ip t cr us
Figure captions
M an
Fig. 1. Chemical structure of charged surface modifying macromolecule (cSMM).
Fig. 2. Effect of the cSMM additive content on the rejection of proteins for the PEI/cSMM blended membranes. Fig. 3. Effect of the cSMM additive content on the permeate flux of feed solutions of protein for the PEI/cSMM blended membranes.
ed
Fig. 4. Effect of 0.5 wt% PETIM concentration on the permeate flux of feed solutions of metal ion for the PEI/cSMM blended membranes.
membranes.
ce pt
Fig. 5. Effect of 1 wt% PETIM concentration on the permeate flux of feed solutions of metal ion for the PEI/cSMM blended
membranes.
Ac
Fig. 6. Effect of 1.5 wt% PETIM concentration on the permeate flux of feed solutions of metal ion for the PEI/cSMM blended
Fig. 7. Effect of 2 wt% PETIM concentration on the permeate flux of feed solutions of metal ion for the PEI/cSMM blended membranes.
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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Figure 5
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Figure 6
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Figure 7
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