Accepted Manuscript

Title: Separation of macromolecular proteins and rejection oftoxic heavy metal ions by PEI/cSMM blend UF membranes

Author: P. Kanagaraj A. Nagendran D. Rana T. Matsuura S.Neelakandan

PII: S0141-8130(14)00551-0DOI: http://dx.doi.org/doi:10.1016/j.ijbiomac.2014.08.018Reference: BIOMAC 4542

To appear in: International Journal of Biological Macromolecules

Received date: 26-6-2014Revised date: 28-7-2014Accepted date: 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 heavymetal ions by PEI/cSMM blend UF membranes, International Journal of BiologicalMacromolecules (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 proofbefore it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers thatapply to the journal pertain.

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Separation of macromolecular proteins and rejection of toxic heavy

metal ions by PEI/cSMM blend UF membranes

P. Kanagaraja, A. Nagendrana, *, D. Ranab, T. Matsuurab, S. Neelakandana

aPG & Research Department of Chemistry, Polymeric Materials Research Lab,

Alagappa Government Arts College, Karaikudi - 630 003, India

bDepartment of Chemical and Biological Engineering, Industrial Membrane Research Institute,

University of Ottawa, 161 Louis Pasteur St., Ottawa, ON, K1N 6N5, Canada

RESEARCH HIGHLIGHTS

First time we are using PEI/cSMM blend UF membranes for macromolecular protein and

toxic metal ion removal.

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: nagimmm@yahoo.com (Dr. A. Nagendran),

Phone: 91-4565-224283 Fax. No: 91-4565-227497

Abstract

The charged surface modifying macromolecule (cSMM) was blended into the casting solution of

poly(ether imide) (PEI) to prepare surface modified ultrafiltration membranes by phase inversion

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.

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Keywords: Ultrafiltration membrane; Proteins separation; Toxic metal ions rejection

1. Introduction

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

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

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

macromolecular separation [4].

To further improve separation performance, researchers have made considerable efforts to

fabricate low fouling UF membranes with higher selectivity by anchoring anionic or cationic

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

membrane forming polymer [5]. For instance, Liu et al. have prepared hydrophilic negatively

charged UF membranes using sulfonated poly(phenyl sulfone) random copolymer. The

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

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

separation characteristics of the UF membranes [13].

Removal of toxic heavy metals such as Cu, Zn, Hg, Cd, Pb and Ni from industrial wastewaters

is required for meeting discharge limits or for water reuse. Many industrial wastewaters

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

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

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

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

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].

Therefore, the removal and separation of toxic and environmentally hazardous heavy metal

ions are technological challenge. For separating species with ionic dimensions, reverse osmosis

membranes are often required but they will result in high operative costs and low permeate flow

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

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

complexation with macromolecules, become larger molecular weight than the MWCO of the

membranes, are retained by UF membrane, producing permeate free of heavy metals. The

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

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

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

complexes by UF assisted with polyamines. Metal retentions higher than 98 % were observed

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

[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

stream with less than 0.05 ppm of Pb and 1.5 ppm of Ca. Bayer et al. studied the PETIM as a

complexing agent for separation of heavy metals ion using membrane filtration [31]. It was

found that the PETIM has been an effective complexing agent and suitable for retention and

separation of metals in aqueous dilute solutions.

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

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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

bis(phenyl isocyanate) (MDI), hydroxyl benzene sulfonate (HBS), glycerol, N,N- dimethyl

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

grade were procured from Sigma Aldrich Inc., St. Louis, MO, USA. Anhydrous sodium

monobasic phosphate and sodium dibasic phosphate heptahydrate were also procured from

Sigma Aldrich Inc., St. Louis, MO, USA and used for the preparation of phosphate buffer

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

aqueous metal ion solutions. Chromium (III) sulfate of AR grade and polyethyleneimine

(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

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

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Fig. 1 – Insert here

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

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

HBS (4.644 g) dissolved in 50 ml of degassed DMAc was added drop-wise and the solution was

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

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

oven at 120 °C for 5 days and stored in a glass bottle.

2.3. Preparation of membrane

The blend solutions based on PEI (17.5 wt %) and cSMM additive (1, 3, 5 wt %) were

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

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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

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.

2.4. Experimental setup

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

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

345 kPa trans-membrane pressures. The membranes were initially pressurized with distilled

water at 414 kPa for 5 h. These pre-pressurized membranes were used in subsequent UF

experiments at 345 kPa.

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

Sarbolouki [35].

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

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,

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);

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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

of time in a graduated cylinder and were analyzed for the protein concentration by UV–VIS

spectrophotometer (Shimadzu, Model UV-160A) at 280 nm. From the feed and permeate

concentrations, the percentage solute rejection of the protein was calculated using the equation:

Where Cp and Cf are the concentrations of the permeation and feed solution, respectively.

2.4.3. Metal ion rejection study

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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Fig. 2 – Insert here

Japan) according to the standard method. The percentage metal ion rejection (% SR) was

calculated with the same formula as that for protein rejection.

3. Results and discussion

3.1. Protein rejection study

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

prevent pore blocking by high molecular weight protein that would affect membrane

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

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

the mixed casting solution uneven and inhomogeneous, resulting in the formation of larger pores

within the membranes. Therefore, the rejection percentage decreased as cSMM content increased

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.

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

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Table 1 & Fig. 3 – Insert here

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

observed for all the other proteins.

As well, the flux increased as the protein molecular size decreases, thus the order of permeate

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.

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].

3.3. Molecular weight cut-off study

Molecules having a molecular weight larger than the MWCO of a membrane will not pass

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

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

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Table 2 & Fig. 4 – 7 Insert here

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

pore size of the membrane has increased by adding 1.5 wt % hydrophobic SMM into 15 and 17

wt % of PES dopes with and without 7 wt % poly(vinyl pyrrolidone) [43].

3.5. Metal ion permeation at various PETIM concentrations

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

Figures 4,5,6 and 7 for the PETIM concentrations of 0.5, 1.0, 1.5 and 2.0 wt %, respectively.

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

cSMM content. The same trends were observed in Figs. 5-7. Interestingly, no considerable

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

pore size.

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,

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Table 3 – Insert here

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

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

complex takes place [45]. The effect of PETIM on the rejection of the pure PEI and PEI/cSMM

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

binding capacity of PETIM even at low concentration.

The rejection of Pb(II) keeps increasing as the PETIM concentration increases.. For the neat

PEI membrane, with 0.5 wt % PETIM the Pb(II) rejection increased from 60.1 to 69.4 % as the

PETIM concentration increased from 0.5 to 2 wt %. A similar trend was observed for all the

other blended membranes. The rejection of Pb(II) was much lower than Cu(II) due to weaker

complexation of Pb(II).

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

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

[44].

4. Conclusions

PEI/cSMM blended UF membranes with various polymer blend compositions were subjected

to the separation of proteins and toxic heavy metal ions. The addition of cSMM enhanced the

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

permeation had an increasing trend. The protein separation study revealed that the MWCO of the

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

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

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acknowledge the financial support from Natural Sciences and Engineering Research Council of

Canada for the partial support of this work.

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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.

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.

Fig. 5. Effect of 1 wt% PETIM concentration on the permeate flux of feed solutions of metal ion

for the PEI/cSMM blended membranes.

Fig. 6. Effect of 1.5 wt% PETIM concentration on the permeate flux of feed solutions of metal

ion for the PEI/cSMM blended membranes.

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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Table 1 Blend composition, pore radius, porosity and molecular weight cut-off of PEI/cSMM blended membranes

Blend composition (wt %)

PWF

(Lm-2

h-1

)

Pore radius,

R (Å)

Porosity,

ε (%)

SR

(%)

MWCO

(kDa)

PEI

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

10.6 0.2

28.2

6.1

79.7 0.3

20

17.5

3

79.5

26.7 0.5

34.3

9.7

79.6 0.1

35

17.5

5

77.5

60.4 0.4

41.4

14.8

82.1 0.5

45

Table(s)

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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

Blend composition

(wt %)

PWF

(Lm-2

h-1

)

Metal ions rejection, %

Cu(II) Pb(II)

PETIM concentration (wt %) PETIM concentration (wt %)

PEI cSMM NMP

0.5

1.0

1.5

2.0

0.5

1.0

1.5

2.0

17.5 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 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

17.5 5 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

Blend composition

(wt %)

PWF

(Lm-2

h-1

)

Metal ions rejection, %

Cr(III)

Zn(II)

PETIM concentration (wt %) PETIM concentration (wt %)

PEI cSMM NMP

0.5

1.0

1.5

2.0

0.5

1.0

1.5

2.0

17.5 0 82.5 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

17.5 1 81.5 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

17.5 3 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

17.5 5 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

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Figure captions

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.

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.

Fig. 5. Effect of 1 wt% PETIM concentration on the permeate flux of feed solutions of metal ion for the PEI/cSMM blended

membranes.

Fig. 6. Effect of 1.5 wt% PETIM concentration on the permeate flux of feed solutions of metal ion for the PEI/cSMM blended

membranes.

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