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Journal of Membrane Science 401– 402 (2012) 292– 299

Contents lists available at SciVerse ScienceDirect

Journal of Membrane Science

j ourna l ho me pag e: www.elsev ier .com/ locate /memsci

he improvement of antibiofouling efficiency of polyethersulfone membrane byunctionalization with zwitterionic monomers

achrul Razia,b, Isao Sawadaa, Yoshikage Ohmukaia, Tatsuo Maruyamaa, Hideto Matsuyamaa,∗

Center for Membrane and Film Technology, Department of Chemical Science and Engineering, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe 657-8501, JapanDepartment of Chemical Engineering, Syiah Kuala University, Banda Aceh, Indonesia

r t i c l e i n f o

rticle history:eceived 24 November 2011eceived in revised form 6 February 2012ccepted 8 February 2012vailable online 17 February 2012

a b s t r a c t

To improve the antifouling properties of a hollow fiber PES membrane it was functionalized withthe zwitterionic monomers [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide(MEDSAH) and 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) by photografting. Each modified PESmembrane (PES-g-MEDSAH and PES-g-MPC) was investigated for its antifouling properties for organicfouling and biofouling. To evaluate the organic antifouling properties, each membrane was used to filter a

eywords:urface functionalizationollow fiber polyethersulfone membranewitterionic monomerrganic fouling

solution of bovine serum albumin or lysozyme. For biofouling, the antifouling properties were evaluatedby immersion tests and filtration of a Pseudomonas putida solution. The modified PES membranes hadbetter organic antifouling properties and higher biofouling resistance than the unmodified PES mem-brane. In the immersion test, almost no bacteria were detected on the modified membrane surfaces.Thus, surface functionalization of PES membranes with zwitterionic monomers can improve antifouling

ling a

iofouling properties for organic fou

. Introduction

Biofouling of polymeric membranes is a serious problem,articularly in water reclamation, wastewater treatment, wateresalination and drinking water applications [1–4]. Generally, bio-ouling is generated by attachment of microorganisms such asacteria to membrane surfaces [4–7]. This produces a biopolymeratrix or complex structure called a biofilm at the membrane sur-

ace [8–10]. Particularly in drinking water production and waterreatment, biofilm formation can be harmful because it can causeecondary pollution of purified water [10–12]. Membrane biofoul-ng decreases membranes performance, which increases operationosts because of the need for frequent cleaning and maintenance.

Many attempts have been made to functionalize membrane sur-aces and improve their antibacterial properties. These approachesave included incorporation of silver ions or silver nanoparticlesnto the membrane surface [12–16], functionalization of the mem-rane surface with positively charged groups such as quaternarymmonium and phosphonium compounds [17–19], and additionf negatively charged groups such as sulfonated glycidyl methacry-ate and heparin [7,20,21]. Fu et al. produced a poly(ethylene

erepthalate) film with anti-adhesive and antibacterial proper-ies via layer-by-layer assembly of heparin and chitosan [22].

any papers have reported reduction of bacterial adhesion after

∗ Corresponding author. Tel.: +81 78 803 6180; fax: +81 78 803 6180.E-mail address: matuyama@kobe-u.ac.jp (H. Matsuyama).

376-7388/$ – see front matter © 2012 Elsevier B.V. All rights reserved.oi:10.1016/j.memsci.2012.02.020

nd biofouling.© 2012 Elsevier B.V. All rights reserved.

incorporation of a hydrophilic polymer or polymer segments thatcan interact with water through strong hydrogen bonds [23–25].

Extensive research has focused on membrane modification byblending, coating, and surface grafting methods. Among thesemethods, surface grafting is considered a useful method for alteringthe surface characteristics of a membrane [26,27]. UV irradiationinduced surface graft polymerization is a common technique thathas been used to enhance substrate functionality, such as adhesive-ness, wettability, biocompatibility, and antifouling. This techniqueis a simple, useful, and versatile approach to improve the surfaceproperties of base polymers [26–28]. A number of papers havereported that hemocompatible and biocompatible materials suchas phospholipids and sulfobetaine can be used to tailor membranesurface properties to resist nonspecific protein adhesion and celladhesion [29–35].

However, only a few papers have reported surface mod-ification of hollow fiber membranes to improve antifoulingproperties for organic fouling and biofouling [36,37]. In this work,we attempted to improve the antifouling properties of hollowfiber polyethersulfone (PES) membranes by functionalizing thePES membrane with zwitterionic monomers by UV irradiationinduced graft polymerization. The zwitterionic monomers used forgrafting were 2-(methacryloyloxy)ethyl-dimethyl-(3-sulfopropyl)ammonium hydroxide (MEDSAH) and 2-(methacryloyloxy)ethyl

phosphorylcholine (MPC). The MEDSAH monomer has a cationicquaternary ammonium (N+) group and an anionic sulfonate (SO3

-)group on its backbone, while the MPC monomer has a cationic qua-ternary ammonium (N+) group and an anionic phosphate (PO4

−)

F. Razi et al. / Journal of Membrane Sci

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Fig. 1. Molecular structures of the MEDSAH and MPC monomers.

roup. These cationic and anionic groups result in net electri-al neutrality. MPC monomer has the same zwitterionic group ashospholipid. It was reported that the zwitterionic group of phos-holipid was quite effective to prevent the adhesion of protein38,39]. One purpose of this work is the comparison of the effec-iveness of different zwitterionic groups of MEDSAH and MPC. Therganic antifouling properties of the modified membranes werenvestigated by filtration of a solution of bovine serum albuminBSA) or lysozyme (LYZ). The antifouling properties for biofoulingere evaluated using an immersion test and filtration of Pseu-

omonas putida as a model bacterial solution.

. Experimental

.1. Materials

Hollow fiber PES ultrafiltration (UF) membranes with molecu-ar weight cut-offs (MWCO) of 30 kDa and 150 kDa were purchasedrom Daicen Membrane Systems, Ltd., (Osaka, Japan). MEDSAHas purchased from Sigma–Aldrich, Japan (Tokyo, Japan) and MPCas purchased from TCI Co. Ltd. (Tokyo, Japan). Benzophenone,ethanol, bovine serum albumin, sodium hydrogen phosphate

NaH2PO4) and disodium hydrogen phosphate (Na2HPO4) wereurchased from Wako Pure Chemical Industries, Ltd. (Osaka, Japan).ifco nutrient broth (NB) was purchased from Becton, Dickin-

on and Company (Spark, MD 21152, USA). Water purified with Milli Q-system (Millipore, Billerica, MA, USA) was used to pre-are a phosphate buffer saline (PBS) solution. All chemicals weresed as received. The chemical structures of the MEDSAH and MPConomers are shown in Fig. 1.

.2. UV photografting of MEDSAH and MPC monomers onto theES membrane

Surface modification of the hollow fiber PES membrane wasarried out by the UV photografting method. A hollow fiber PESembrane (150 kDa MWCO) 12 cm in length was coated with ben-

ophenone by placing it in a 0.1 mol/L benzophenone solution inethanol. After the membrane was removed from the solution, sur-

ace liquid was removed gently with filter paper and the membraneas dried at room temperature for 1 h. The dried PES membraneas then immersed in a degassed solution of the MEDSAH or MPConomer. These monomer solutions were prepared by dissolvingEDSAH or MPC in deionized (DI) water. The membranes wereV irradiated by a high pressure Hg-UV lamp (UM-102; Ushio

nc., Tokyo, Japan) at 170 mW/cm2 and 350 nm. The polymeriza-ion was conducted at 35 ◦C for a designated time under a flow ofr gas. After polymerization was complete, the modified PES mem-rane was removed from the monomer solution and thoroughly

ence 401– 402 (2012) 292– 299 293

washed with DI water. The modified PES membrane was thencontinuously washed with methanol/water solution (1:20, v/v)for 2 h at 40 ◦C and immersed in DI water overnight to removenon-grafted monomer, polymer, and residual initiator. Finally, themodified PES membranes were dried under vacuum on a freezedryer overnight and their dry weight measured. Modified PES mem-branes (PES-g-MEDSAH and PES-g-MPC) with different amounts ofthe monomers grafted on the surface were obtained by varying thepolymerization time and monomer concentration. The amount ofeach monomer grafted (GA) on the PES membrane surface was cal-culated as the weight gain of the modified PES membrane per outersurface area according to the following equation:

Grafting amount (GA) (mg/cm2) = W1 − W0

A

where W0 is the initial membrane weight (mg), W1 is the dry weightof the modified membrane (mg), and A is the outer surface area ofmembrane (cm2). A microbalance (AB204; Mettler Toledo GmbH,Greifensee, Switzerland) was used to measure the weight of theoriginal and modified PES membranes.

2.3. Membrane morphology

Morphological changes of the original PES (150 kDa), PES(150 kDa)-g-MEDSAH, and PES (150 kDa)-g-MPC membranes wereobserved by a field scanning electron microscope (SEM) (JSF-7500F;JEOL Co. Ltd., Tokyo, Japan) with an accelerating voltage of 5 kV. Themembrane samples were first dried on a freeze dryer (FDU-1200EYELA; Tokyo Rikakikai Co. Ltd., Japan) overnight. The dried hollowfiber PES membranes were fractured in liquid nitrogen and treatedby Pt/Pd sputtering.

2.4. Surface analysis of the PES-g-MEDSAH and PES-g-MPCmembranes

The unmodified PES (150 kDa), PES (150 kDa)-g-MEDSAH, andPES (150 kDa)-g-MPC membranes were characterized by atten-uated total reflectance Fourier transform infrared spectroscopy(FTIR-8100A; Shimadzu Co. Ltd., Kyoto, Japan). Before analysis,the original PES (150 kDa), PES (150 kDa)-g-MEDSAH, and PES(150 kDa)-g-MPC membranes were dried overnight on a freezedryer and the IR spectra of the membrane samples were recordedfrom 600–2400 cm−1. The surface compositions of the originalPES (150 kDa), PES (150 kDa)-g-MEDSAH, and PES (150 kDa)-g-MPCmembranes were analysed by X-ray photoelectron spectroscopy(XPS) (ESCA-3400; Shimadzu Co. Ltd., Kyoto, Japan) equippedwith an X-ray gun at an acceleration voltage of 10 kV and20 mA.

2.5. Water contact angle of membranes and water absorptioninto monomers

Water contact angle measurements with a contact angle meter(CAA-Drop Master 300; Kyowa Interface Science Co. Ltd., Saitama,Japan) were used to observe the degree of membrane hydrophilic-ity. An aliquot (0.5 �L) of DI water was dropped onto the outersurface of each hollow fiber membrane and the contact angle wasmeasured automatically. Measurements were repeated ten timesfor each sample, and average values were obtained for the watercontact angle of each tested membrane.

Absorption of water into pure MEDSAH and MPC with time wasused to evaluate the compatibility between each monomer and

water. One gram of MEDSAH or MPC monomer was placed in aPetri dish and the dish was placed in a test chamber equipped with atemperature and humidity controller (SH-221; ESPEC Corp., Osaka,Japan). The temperature and relative humidity were kept constant

294 F. Razi et al. / Journal of Membrane Sc

Fig. 2. Schematic diagram of the filtration experiments using the single hollow fiberm

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medium was prepared according to Heydorn et al. [45] which con-sists of sodium citrate, (NH4)2SO4, NaCl, KH2PO4, MgCl2, CaCl2 and

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embrane.

t 40 ◦C and 80%, respectively. The weight gain of the MEDSAH orPC monomer caused by water absorption was measured at 2 h

ntervals.

.6. Organic fouling evaluation

Filtration experiments were carried out with laboratory-scalepparatus using a single hollow fiber membrane as shown in Fig. 2nd described by Hashino et al. [40,41]. This experiment was usedo test the performance of the original PES (150 kDa) membrane,nd modified PES (150 kDa)-g-MEDSAH and PES (150 kDa)-g-MPCembranes in ultrafiltration experiments with a single protein

olution. Solutions (50 ppm) of BSA (MW 67 kDa) and LYZ (MW4 kDa) were prepared by dissolving 50 mg of BSA or LYZ in 1 L of.15 mol/L PBS (pH 7.0).

In the fouling experiment, the pure water permeability, J0, withI was measured for 1 h until a steady state was obtained. BSA orYZ solution then permeated through the membrane for 4 h, andhe permeate flux, J, was measured. BSA or LYZ rejection by the

embrane was determined by measuring the BSA or LYZ concen-ration in the feed solution, Cf, and in the permeate solution, Cp,

t 280 nm with a UV spectrophotometer (U-2000; Hitachi Co. Ltd.,okyo, Japan) [42,43].

ig. 3. SEM images of the membrane outer surfaces. (a) PES (150 kDa), (b) PES (150 kDa)-ES (150 kDa)-g-MPC (GA = 0.4 mg/cm2), (e) PES (150 kDa)-g-MPC (GA = 1.2 mg/cm2), and

ience 401– 402 (2012) 292– 299

2.7. Antibiofouling evaluation

2.7.1. Static adhesion testAn immersion test was used to test the anti-adhesion proper-

ties of the modified PES membranes. The original PES (150 kDa)membrane, and the PES (150 kDa)-g-MEDSAH and PES (150 kDa)-g-MPC membranes were immersed in 40 mL of a suspensionof P. putida (107 cfu/mL) in Vogel Bonner minimum medium(VBMM) for 1 week. The major ingredients of VBMM wereconsist of MgSO4·7H2O, trisodium citrate dehydrate, K2HPO4,NaHNH4PO4·4H2O, and glucose [44]. P. putida was purchased fromthe Biological Resource Center at the National Institute of Tech-nology and Evaluation (Shibuya, Japan). The biofilm formed on themembrane surface was observed by SEM (JSF-7500F; JEOL Co. Ltd.,Tokyo, Japan). The membrane samples after the immersion testwere washed with PBS, and the bacteria on the membrane surfaceswere fixed in a 2.5% (volume fraction) glutaraldehyde solution inPBS for 4 h at 4 ◦C. The membranes were then rinsed with PBS toremove any glutaraldehyde from the surfaces. To reduce the watercontent of the membrane samples, they were dehydrated withethanol according to Zhu et al. [15]. Finally, the membrane sampleswere dried in air and stored in a desiccator. The dried membranesamples were then coated with Pt/Pd before SEM observation.

2.7.2. Filtration experiment with a bacterial solutionFiltration of a bacterial solution was used to evaluate bacte-

rial adhesion to the original PES (150 kDa) membrane, and PES(150 kDa)-g-MEDSAH and PES (150 kDa)-g-MPC membranes in theactual membrane operation. This filtration experiment was car-ried out using laboratory-scale apparatus with a single hollow fibermembrane as described above. Instead of the protein solution, abacterial solution of P. putida was used as the feed solution. P.putida was first cultured in 2 L of FAB medium overnight. The FAB

trace metal solution as major ingredients. The final concentrationof P. putida in FAB medium was about 106 cells/mL. Pure water

g-MEDSAH (GA = 0.4 mg/cm2), (c) PES (150 kDa)-g-MEDSAH (GA = 1.2 mg/cm2), (d) (f) PES (150 kDa)-g-MPC (GA = 1.67 mg/cm2).

F. Razi et al. / Journal of Membrane Science 401– 402 (2012) 292– 299 295

F Da)-g-MEDSAH (GA: 1.7 mg/cm2), and (c) PES (150 kDa)-g-MPC (GA: 1.67 mg/cm2).

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The N peak had a binding energy at 402.8 eV and was attributedto N+(CH3)3 of the QA groups of the MEDSAH monomer. On theother hand, the S peak was attributed to sulfonate (SO3

-) groupsof the MEDSAH monomer. The presence of these peak indicate the

ig. 4. SEM images of the membrane cross-section. (a) PES (150 kDa), (b) PES (150 k

ermeability, J0, was measured and then filtration of the bacte-ial solution began. The permeability of the bacterial solution (J)as measured for 3 h. After the filtration experiments, the bacteria

ttached to the membrane surfaces were observed by SEM.

. Results and discussion

.1. Membrane morphology and surface analysis

The surface morphologies of the original PES (150 kDa) mem-rane, and the modified PES (150 kDa)-g-MEDSAH and PES150 kDa)-g-MPC membranes are shown in Fig. 3.

The outer surface of the original PES (150 kDa) membrane wasuite porous (Fig. 3(a)), while by comparison, the modified PES150 kDa)-g-MEDSAH and PES 150 (kDa)-g-MPC membranes hadewer and smaller pores (Fig. 3(b)–(f)). A higher GA for the modi-ed PES membrane gave more complete coverage of the membraneuter surface pores with the monomer than a lower GA. Both theES (150 kDa)-g-MEDSAH and PES (150 kDa)-g-MPC membraneshowed similar levels of pore coverage with a GA of 0.4 mg/cm2

Fig. 3(b) and (d)).The cross-sections of PES and modified PES membranes were

hown in Fig. 4. As shown in Fig. 4(b) and (c), some of membraneores were covered by the polymer layer as pointed out by thellipsis. This might be due to polymer intrusion to the membraneores. This figure shows that the zwitterionic monomer coating wasot only occurred on the membrane surfaces but also inside theores to some extent. In addition, the grafted layers were observedn the outer membrane surfaces, as shown in arrows. The thick-esses of grafted layers of both modified PES membranes werebout 5–10 �m.

The membrane surfaces of the original PES (150 kDa), PES150 kDa)-g-MEDSAH and PES (150 kDa)-g-MPC membranes wereharacterized by attenuated total reflectance Fourier transformnfrared spectroscopy. Fig. 5 shows the IR spectra of the membraneurfaces.

The original PES membrane was characterized by strong bandst 1577 cm−1 and 1460 cm−1, which could be attributed to aro-atic vibrational modes [43]. By comparison, the IR spectrum of

he PES (150 kDa)-g-MEDSAH membrane showed a news peak at54 cm−1, 1100 cm−1, and 1730 cm−1, which could be attributedo the quaternary ammonium (QA), sulfonate (SO3

-), and carbonylC O) groups of the MEDSAH monomer [33,34]. The spectrum ofhe PES (150 kDa)-g-MPC membrane showed additional peaks forhe QA groups at 954 cm−1 and carbonyl group (C O) at 1680 cm−1.

he IR spectra confirmed that grafting of the MEDSAH and MPConomers onto the PES membrane was successful.The layers of the MEDSAH and MPC monomers on the mem-

rane surface were characterized by XPS analysis. Fig. 6 shows the

Fig. 5. FT-IR of the PES, PES-g-MEDSAH, and PES-g-MPC membranes.

XPS spectra of the original PES (150 kDa), PES (150 kDa)-g-MEDSAH,and PES (150 kDa)-g-MPC membranes. A strong sulfur (S) peak thatcould be attributed to polymer structure of polyethersulfone wasobserved in the spectrum of the original PES (150 kDa) membrane(Fig. 6(a)). By contrast, in the spectrum of the PES (150 kDa)-g-MEDSAH membrane (Fig. 6(b)), the nitrogen (N) and a sulphur (S)peak were detected.

Fig. 6. XPS spectra of the original PES and modified PES membranes. (a) PES mem-brane, (b) PES-g-MEDSAH membrane, and (c) PES-g-MPC membrane.

296 F. Razi et al. / Journal of Membrane Science 401– 402 (2012) 292– 299

Table 1Surface elemental composition of PES and modified PES membranes (in atomic percent) measured by XPS (grafting amount of modified PES membrane, GA: 1.2 mg/cm2).

Membrane C1s (%) O1s (%) N1s (%) S2p (%) P2p (%) N/S ratio N/P ratio

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PES 74.6 19.4 –

PES-g-MEDSAH 64.4 25.8 4.89

PES-g-MPC 63.8 26.9 4.76

EDSAH monomer was successfully grafted onto the PES mem-rane because N peak was not detected in the original PES (150 kDa)embrane. For the PES (150 kDa)-g-MPC membrane, the N peak

nd a phosphorus (P) peak were detected at binding energiesf 402.8 eV and 134.5 eV, respectively [35]. These peaks can bettributed to QA and phosphate (PO4) groups of the MPC monomer.

The surface elemental compositions of PES and modified PESembranes are shown in Table 1.As shown in this Table 1, the atomic percentages of unmodified

ES membrane were 74.6% for carbon, 19.4% for oxygen, and 5.96%or sulphur, respectively. This result agreed with the theoreticalalues of PES membrane which are 75% for oxygen, 18.8% for oxygennd 6.25% for sulphur, respectively. These results were also in goodgreement with the data reported by Liu et al. [46]. This table alsohowed that the ratio of N/S for the PES-g-MEDSAH membrane wasqual to 1.00 and the ratio of N/P for the PES-g-MPC was equalo 1.04. These results agreed with theoretical N/S and N/P ratiosf 1.0. Thus, the grafting of zwitterionic monomers onto the PESembrane was also confirmed by this XPS analysis.

.2. Water contact angle and water absorption

Fig. 7 shows the effect of GA on the water permeability and water

ontact angle of the modified PES (150 kDa) membranes. Waterermeabilities of the PES (150 kDa)-g-MEDSAH and PES (150 kDa)--MPC membranes decreased as GA increased. With the same GA,

ig. 7. Effect of the amount of monomer grated onto the modified PES membranesn water permeability (a) and water contact angle (b).

5.96 – – –4.91 0 1.00 –0 4.57 – 1.04

the water permeabilities of the two modified membranes werealmost similar.

As the GA increased the water contact angles of the mod-ified PES (150 kDa) membranes decreased. This indicates thatthe zwitterionic monomers substantially improved the mem-brane hydrophilicity. With the same GA, the PES (150 kDa)-g-MPCmembrane had a lower water contact angle than the PES (150 kDa)-g-MEDSAH membrane. This indicates that the MPC monomer hasa greater effect on the hydrophilicity than the MEDSAH monomer.The PES (150 kDa)-g-MPC membrane with a GA of 1.67 mg/cm2 hadthe lowest water contact angle (27◦).

Fig. 8 shows the change in water absorption into pure MPC andMEDSAH monomer against time. The water absorptions for bothmonomers increased sharply as the experiment time increased, andthen became constant after 8 h. The maximum water absorptionsinto the pure MPC and MEDSAH monomers were about 9% and 4.3%,respectively. These results show that the MPC monomer possessesthe higher affinity to water than the MEDSAH monomer, and this isthe reason for the higher hydrophilicity improvement for the MPCmonomer (Fig. 7).

3.3. Organic fouling evaluation

The results for the fouling experiments with BSA (MW 67 kDa)and LYZ (MW 14 kDa) using the original PES (MWCO 150 kDaand 30 kDa), PES (150 kDa)-g-MEDSAH, and PES (150 kDa)-g-MPCmembranes are shown in Figs. 9 and 10. The GA values of the PES(150 kDa)-g-MEDSAH and PES (150 kDa)-g-MPC membranes usedin these experiments were 1.67 mg/cm2 and 1.7 mg/cm2, respec-tively. In Figs. 9 and 10, the real water permeability, J, relativepermeability, J/J0, and protein rejection are plotted against thetotal permeated volume. The pH of the protein feed solution wasadjusted to 7.0. At this pH, BSA is negatively charged (zeta potential−22.3 mV) because its isoelectric point is 4.7, while LYZ is positivelycharged (zeta potential +3.5 mV) because its isoelectric point is 11.0

[47,48]. For the PES (150 kDa) and PES (30 kDa) membranes, thereal permeability and relative permeability decreased considerablybecause of severe BSA fouling caused by hydrophobic interactionbetween the PES membrane and BSA. The real permeability and

Fig. 8. Changes in the water absorption into pure MPC monomer and MEDSAHmonomer with time (T = 40 ◦C and relative humidity = 80%).

F. Razi et al. / Journal of Membrane Science 401– 402 (2012) 292– 299 297

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ig. 9. Membrane performance for filtration of a BSA solution (50 ppm, pH 7.0).

elative permeability were pretty consistent for the PES (150 kDa)--MEDSAH and PES (150 kDa)-g-MPC membranes because thereas still slight decrement in the water permeability for theodified membranes. This reduction in organic fouling can be

ttributed to the increase of hydrophilicity of the modified PESembranes. The PES (150 kDa)-g-MPC membrane showed slightly

igher antifouling reduction than the PES (150 kDa)-g-MEDSAHembrane because of its higher hydrophilicity (Fig. 7). Ishihara

t al. reported that a zwitterionic monomer could form a hydrationayer or hydrogel layer [29,32,35]. Hydrogel layers have a high free

ater content that can shield the membrane surface [38]. Thisill prevent protein molecules from contacting the membrane

urface, and when the protein does contact the membrane surfacet cannot release free water from the zwitterionic monomer. This

ould contribute to the high organic antifouling properties of theES membranes modified by zwitterionic monomers.

The BSA rejections of the PES (150 kDa)-g-MEDSAH and PES150 kDa)-g-MPC membranes were higher than that of the originalES (150 kDa) membrane because the pores were blocked on theodified membranes. The BSA rejections of these membranes were

etween the BSA rejection of PES (30 kDa) and that of PES (150 kDa).he original PES membranes showed severe organic fouling withYZ filtration (Fig. 10). This was because of the high hydrophobicnteraction of the PES membrane with LYZ. Electrostatic interaction

Fig. 10. Membrane performance for filtration of a LYZ solution (50 ppm, pH 7.0).

may be another reason for the fouling because LYZ is posi-tively charged [47] and the PES (150 kDa) membrane is negativelycharged according to surface zeta potential measurement (datanot shown here) [49,50]. By comparison, the PES membranesmodified with zwitterionic monomers (PES (150 kDa)-g-MEDSAHand PES (150 kDa)-g-MPC) remarkably reduced the organic foul-ing. One reason for this fouling reduction is the improvement ofthe hydrophilicity by the modification of zwitterionic monomers.Another reason is that the modified membranes had net neutralcharge and lack of electrostatic interaction with LYZ.

3.4. Antibiofouling evaluation

3.4.1. Static adhesion testTo evaluate the antibiofouling properties of the modified PES

membranes, immersion tests were carried out. The original PES(150 kDa), PES (150 kDa)-g-MEDSAH, and PES (150 kDa)-g-MPCmembranes were immersed in a suspension of P. putida for 1

week. The GA values of the PES (150 kDa)-g-MEDSAH and PES(150 kDa)-g-MPC membranes were 1.67 mg/cm2 and 1.7 mg/cm2,respectively. The membrane outer surfaces are shown in Fig. 11.Many bacteria adhered to the outer surface of the original PES

298 F. Razi et al. / Journal of Membrane Science 401– 402 (2012) 292– 299

F es were immersed in 107 cfu/mL of a P. putida suspension for 1 week, (a) PES membrane,( .67 mg/cm2).

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b(tr(fPr

Fig. 12. Fouling behaviour during filtration of a bacterial solution (2 L of 107 cfu/mL

F

ig. 11. SEM images of the membrane outer surfaces after adhesion test. Membranb) PES-g-MEDSAH membrane (GA = 1.7 mg/cm2), (c) PES-g-MPC membrane (GA = 1

150 kDa) membrane (Fig. 11(a)). By contrast, no bacteria weredhered to the PES (150 kDa)-g-MEDSAH (Fig. 11(b)) and PES150 kDa)-g-MPC membranes (Fig. 11(c)). These results confirmedhe modified membranes had high antibiofouling properties. Theacterial adhesion on the modified PES membrane was preventedy the layer of zwitterionic monomer because of its high free waterontent [29].

.4.2. Filtration of the bacterial solutionFor further clarification of bacterial adhesion, the membranes

ere used to filter the P. putida solution. The real water perme-bility, J, and relative permeability, J/J0, of original PES (150 kDa),ES (150 kDa)-g-MEDSAH, and PES (150 kDa)-g-MPC membranesre shown in Fig. 12. The water permeability of the PES mem-rane decreased sharply during the filtration experiment becausef attachment of bacteria on the membrane surface and blocking ofhe membrane pores. The attached bacteria would form a biofilmn the membrane surface. However, with the PES (150 kDa)-g-EDSAH and PES (150 kDa)-g-MPC membranes, the reduction inater permeability was much lower than that with the original

ES membrane because of the zwitterion layers. The zwitterion lay-rs on the membrane surface reduced bacterial attachment on theodified PES membrane.SEM images of the original PES (150 kDa), PES (150 kDa)-g-

EDSAH, and PES (150 kDa)-g-MPC membranes after filtration ofhe bacterial solution (Fig. 13) confirmed this.

In a similar result to the immersion test (Fig. 11(a)), manyacteria were adhered on the original PES (150 kDa) membraneFig. 13(a)). By contrast, only a few bacteria were adhered tohe PES (150 kDa)-g-MEDSAH membrane (Fig. 13 (b)). No bacte-ia were found on the PES (150 kDa)-g-MPC membrane surfaces

Fig. 13(c)). This reduced adhesion of bacteria is the reasonor the lower water permeability reductions for the modifiedES membranes compared to the original PES membrane. Theseesults clearly show that the PES membranes functionalized with

ig. 13. SEM images of the membrane outer surfaces after filtration of a P. putida solution. (

P. putida).

zwitterionic monomers have high antifouling properties in filtra-tion.

a) PES, (b) PES-g-MEDSAH (GA = 1.7 mg/cm2) and (c) PES-g-MPC (GA = 1.67 mg/cm2).

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F. Razi et al. / Journal of Membra

. Conclusion

The zwitterionic monomers MEDSAH and MPC were surfacerafted by UV photografting polymerization onto hollow fiber PESembranes. This grafting improved the hydrophilicity of the PES-g-EDSAH and the PES-g-MPC membranes compared to the original

ES membrane.Fouling experiments with a single protein solution of BSA or LYZ

evealed that the PES-g-MEDSAH and PES-g-MPC membranes hadetter organic antifouling properties than the unmodified mem-rane. Immersion of the membranes in a bacterial suspensionhowed that no bacteria adhered to the PES-g-MEDSAH or PES--MPC membranes. A filtration test with the bacterial solutionhowed that the modified membranes had higher final water per-eabilities than the unmodified membrane. These results clearly

how that modified PES membranes can suppress biofouling andrganic fouling.

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