Desalination 351 (2014) 59–69

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Desalination

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Synthesis, characterization, permeation and antibacterial properties ofcellulose acetate/polyethylene glycol membranes modifiedwith chitosan

Sidra Waheed a,⁎, Adnan Ahmad a, Shahzad Maqsood Khan a, Sabad-e- Gul a, Tahir Jamil a,Atif Islam a, Tousif Hussain b

a Department of Polymer Engineering and Technology, University of the Punjab, Quaid-e-Azam Campus, P.O. Box 54590, Lahore, Pakistanb The Center of Advanced Studies in Physics, Government College University, Katchery Road, P.O. Box 54000, Lahore, Pakistan

H I G H L I G H T S

• 2-stage phase inversion protocol is devised for synthesis of asymmetric membranes.• A biopolymer (chitosan) is used as an additive.• Salt rejection, membrane hydraulic resistance and bacterial tolerance are improved.• Nodules and interstices spaces are observed in AFM images.• Environmentally benign membranes are fabricated successfully.

⁎ Corresponding author. Tel.: +92 3225774721 (Cell).E-mail address: sidrawaheed@gmail.com (S. Waheed)

http://dx.doi.org/10.1016/j.desal.2014.07.0190011-9164/© 2014 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 25 May 2014Received in revised form 11 July 2014Accepted 16 July 2014Available online xxxx

Keywords:Reverse osmosisPolyethylene glycolCellulose acetateChitosanPhase inversionAntibacterial

In this work, a number of cellulose acetate/polyethylene glycol-600 membranes, with different ratios wereprepared by 2-stage phase inversion protocol. The permeation propertieswere studied by subjectingmembranesin indigenously fabricated reverse osmosis plant. The flux and salt rejection ofmembraneswere determined. Themembrane with highest salt rejection was selected for modification with chitosan. The modified membraneswere characterized for their compositional analysis, surface roughness, surface morphology, permeation proper-ties, membrane hydraulic resistance and antibacterial activity. The presence of functional group was determinedby FTIR spectra. Chitosan was found to significantly enhance the salt rejection and membrane hydraulicresistance. Allmodifiedmembranes exhibited remarkable antibacterial properties. The varying nature of nodulesand interstices spaces was observed in the images obtained by the atomic forced microscopy. The asymmetricsurface morphology of membranes was elucidated from the scanning electron microscope. The synthesis ofcellulose acetate membrane, doped with polyethylene glycol and modified with chitosan, provides a convenientaccess towards the development of sustainable chemistry.

© 2014 Elsevier B.V. All rights reserved.

1. Introduction

Since the inception of life on earth, freshwater has been considered asan elixir of life [1–3]. Unfortunately, the reservoirs of freshwater are con-tinuously beetling off due to economic expansion and climatic changes.Growing globalwater scarcity proves to be the Achilles' heel for the econ-omy of a country [4–6]. Therefore, there is an urgent need to overcomethe demandof freshwater bydeveloping additionalwater sources [7]. So-lutions likewater conservation, construction of newdams orwater trans-port are insufficient to cope with increasing demand. There is no silver

.

bullet for resolving water scarcity issue, however, in order to tap thisseemingly boundless problem, desalination, has been formulated as a sig-nificant solution to overcome the shortage of freshwater [8–10]. This pro-cess enables to access the unlimitedwater resources of the oceans, whichcan be converted into drinking water [11–13].

Desalination processes can be further split into two primarycategories: (i) membrane processes and (ii) thermal processes [14].Membrane processes are gaining more fame as they are energy efficientand environment friendly [15,16]. A number of membrane based desali-nation techniques have been developed including capacitive deioniza-tion, membrane distillation, electro-dialysis, reverse osmosis andforward osmosis. Among all of these techniques, reverse osmosis (RO)is a most frequently used one and is believed to play a leading role in

60 S. Waheed et al. / Desalination 351 (2014) 59–69

the years to come [17]. The multiple advantages offered by RO plants in-volve low energy consumption, cost reduction, expedient operation, eco-friendly process and elevated recovery rate.

Polymeric membranes are used in a large scale in RO plants. Thesemembranes are synthesized by a phase inversion protocol. This ver-satile technique is used to obtain membranes with a variety of mor-phologies, ranging from enormously very porous structures to densemembranes [18]. The process of phase inversion involves severalconceptually different methods such as diffusion-induced phase sep-aration, vapor-phase precipitation, phase inversion by controlledevaporation and thermal-induced phase separation (TIPS). Thesemethods involve complex multi-component mass transfer exceptthermal-induced phase separation which primarily depends onheat transfer [19–21].

The performance of amembrane is notably influenced by its constit-uents, which affect many properties, in particular hydrophilicity, sur-face charge, permissible pH range and chlorine tolerance limit [22].Several polymers have been known for a long time to prepare mem-branes, nevertheless cellulose acetate (CA) membranes are well-likeddue to their superior transport characteristics, low protein adsorption,excellent water affinity, apt mechanical strength, excellent film-forming property, high hydrophilicity with desalting nature and easyavailability [23].

Despite all these advantages, cellulosic membranes are highlysusceptible to microbial attack and self-sterilized membrane surfaceapproach is currently seeing increasing research interest. Readily avail-able antimicrobial agents like silver oxide (AgO), zinc oxide (ZnO),titanium oxide (TiO2), fullerenes and carbon nanotubes have beenincorporated in the membranes to prevent microbial attack [24]. The ap-plication of a biocide within polymeric matrix has opened new frontiersin the development of self-sterilized surface. Recently, attempts havebeen made to render membrane surfaces as an antimicrobial by graft co-polymerization and interfacial polycondensation of amine-containingpolymers, which are considered as potentially antimicrobial agents [25,26].

In this paper, a detailed study towards the synthesis of environmen-tally benign membranes is reported. These membranes were preparedby using different ratios of cellulose acetate, polyethylene glycol andchitosan, an antimicrobial biopolymer. A 2-stage phase-inversion proto-col was devised involving thermal-induced phase inversion followed bya controlled evaporation procedure. The prepared membranes werecharacterized for their permeation activity, compositional analysis,antimicrobial properties, surface morphologies and their efficacy wasevaluated using reverse osmosis process.

2. Materials

Cellulose acetate (CA,Mw 30,000 and acetyl content 39%), polyethyl-ene glycol-600 (PEG) and acetone were supplied by BDH laboratoriessupplies Poole, England and formic acid was purchased from Merck(England). Chitosan (CS, extracted from crab shell with Mw 85,000–90,000 and the degree of deacetylation 75%) was provided by theDepartment of Metallurgy andMaterials Engineering, Pakistan Instituteof Engineering and Applied Sciences, Islamabad, Pakistan [27]. Allchemicals and solvents were used as received.

2.1. Preparation of doped solutions

10 g of CAwas dissolved in 80mL of acetonewith constant stirring at80 °C for 2 h. To this homogenous solution, 10 g of PEG was added withregular stirring at 80 °C for 6 h. The viscous and clear solution wasobtained which was termed as a blended doped Solution, CA/PEG-1[28]. Different amounts of CA (12, 14 and 16 g) and PEG (8, 6 and 4 g)were used to prepare three additional doped solutions which werelabeled as CA/PEG-2, CA/PEG-3 and CA/PEG-4 respectively. The castingsolutions were allowed to cool down to room temperature (25 °C)

and kept for 24 h in a sealed flask to remove micro bubbles formed inthe solution.

2.2. Casting of membranes

The doped solutions were spread slowly on a glass plate ensuringuniform thickness by a micrometer adjustable film applicator(Ref: 1117/300 Sheen instruments). The temperature of the castedmembranes was lowered to 0 °C to induce thermally induce phaseseparation (TIPS) which caused the formation of dense asymmetricstructure. Itwas followed by precipitation under controlled evaporationby increasing temperature up to 60 °C [29]. The skinned membraneswere obtained [30–32] which were carefully removed from the glassplates by using a sharp knife. The thickness of the resulting membraneswas measured to be in the range of 0.05–0.2 mm. These membraneswere evaluated for the permeation performance and CA/PEG-4membrane was selected for further modification by incorporatingantimicrobial biopolymer, chitosan (CS) and termed as CPC1–CPC5.

2.3. Modification of doped solutions

Chitosan (0.5–2.5%, w/v) was dissolved in formic acid (10 mL) andadded to the CA/PEG-4 blended dope solution with constant stirringfor 2 h at 80 °C. The membranes (CPC–CPC5) were casted and dried asmentioned previously (Section 2.2).

2.4. Experimental set up of reverse osmosis plant

The permeation experiments were carried out in the RO experimen-tal rig using a plate and frame membrane module. The process flowdiagram for plate and frame membrane module is shown in Fig. 1. Itconsists of feed tank of 10 L capacity. The temperature of the feedsolutionwas indicated and controlled by a thermocouple and controllersetup. The feed was circulated using a circulation pump of 1 kW withfeed flow of 2500 L/min. The effective membrane area in contact withthe feed was 0.018 m2. The permeate was collected from the samplepoints, provided after the membrane module. The feed tank was filledwith saline solution with conductance of 20 mS. The pressure duringthe processwas increased from 10,000 to 150,000 Pa. Feed temperaturewas kept at 30 °C during the process. The permeation process wascontinued till it attained a steady state.

3. Characterization

The prepared membranes were subjected to various characteriza-tion techniques which are described as below.

3.1. Fourier transform infrared spectroscopy (FTIR)

FTIR spectra of membranes were recorded by using Shimadzu IRPrestige-21 equipped with Horizontal Attenuated Total Reflectance(HATR) kit and in the transmission mode at wave number range4000–400 cm−1. The experiments were run with air as the background.For each spectrum 100 scans were accumulated with a resolution of4 cm−1.

3.2. Scanning electron microscopy (SEM)

Themorphologies and structures of themembranes were character-ized by a JSM-6480, Jeol field emission scanning electron microscope.The membranes were cut into small pieces and placed on stub andkept in a specific chamber in a vacuum. The electron beams weresputtered on sample and images of membranes on varying resolutionswere observed.

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3.3. Atomic forced microscopy (AFM)

AFM images were obtained by Shimadzu SPM-9500 J3. Surfaceroughness was observed by using contact mode with oscillating tip.The scan area was chosen as 5 × 5 μm. The values of root mean square(rms) roughness were derived from AFM images, which were obtainedfrom the average of the values measured in random areas.

The membrane surface morphology can be expressed in terms ofvarious roughness parameters, such as:

3.3.1. Mean roughness (Ra)This parameter represents the mean value of the surface relative

to the center plane, the plane for which the volumes enclosedby the image above and below this plane are equal. It is calculatedby

Ra ¼ 1Lx Ly

ZLx

0

ZLy

0

f x; yð Þj jdxdy ðiÞ

where f(x,y) is surface relative to the center of planewhile Lx and Ly rep-resent dimensions of surface in x and y directions respectively [33].

3.3.2. Average differences in height (Rz)It explains the difference between the highest and the lowest points

within the given area.

Fig. 1. Flow sheet diagram o

3.3.3. Root mean square (RMS)The root mean square average of the measured height deviations

from the mean surface taken within the evaluation area is given as[34,35]

RMS ¼ 1.

Ae

� �ZLx

0

ZLy

0

Z2 x; yð Þdxdy0@

1A

1=2

ðiiÞ

3.4. Evaluation of membrane performance

3.4.1. Permeate fluxThe permeate flux (J) represents the amount of pure water collected

per unit time andper unit area at variable pressures. Itwas calculated by[36,37].

J ¼ Q=t� A ðiiiÞ

where J is the permeate flux (mL/h.m2), Q is the amount of permeate(mL), t is the time and A is the area (m2).

3.4.2. Salt rejectionPercentage of salt rejection narrates the efficiency of membrane and

its ability to remove contaminates [38].

f reverse osmosis plant.

Fig. 2. FTIR spectra of control and modified membranes.

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Sr %ð Þ ¼ 1− Cp=Cfð Þ � 100 ðivÞ

where Sr (%) is the salt rejection, Cp and Cf are the conductance ofpermeate and feed respectively.

3.4.3. Salt passageIt describes the amount of salt passing through the membrane.

Sp %ð Þ ¼ 100−Srð Þ ðvÞ

where Sp (%) is the salt passage.The flux, salt rejection, salt passage and membrane hydraulic

resistance were measured by using Eqs. (iii), (iv), (v) and (vi)

Fig. 3. SEM images of top surface of co

Fig. 4. SEM images of

respectively; all doped and modified membranes were calculated byvarying pressure from 10,000 to 150,000 Pa after every hour.

3.5. Membrane hydraulic resistance (Rm)

Themembrane hydraulic resistance (Rm) is the resistance offered bythemembrane to the flow of the feed. To determine Rm, the flux is mea-sured at different trans membrane pressures (10,000 to 15,0000 Pa).The resistance of the membrane is evaluated from the inverse ofslope obtained by plotting permeate flux versus membrane pressuredifference (Δp), using Eq. (vi) [39].

Rm ¼ Δp= J ðviÞ

where Rm is the membrane hydraulic resistance [Pa/mL·.h−1·.m−2]and Δp is a pressure difference (Pa).

3.6. Antibacterial assay

Antibacterial test was carried out against Escherichia coli accord-ing to JIS L 1902–2002 method [40]. 20 mL of broth was preparedin six conical flasks of 250 mL capacity. All flasks were autoclavedat 121 °C with a pressure of 15 psi for 15 min. After autoclaving100 μl of DH5 alpha E. coli strain was inoculated in the flasks. Themembranes with different composition were introduced in eachflask. All flasks were incubated at 35 °C in an incubator for 18 h.After incubation, optical density (OD) at 600 nm was taken byusing spectrophotometer [41].

4. Results and discussions

4.1. FTIR analysis

Spectroscopic methods play a crucial role in polymer characteriza-tion. The use of methods such as infrared spectroscopy is essential in

ntrol (a) and its cross section (b).

CPC1 membrane.

Fig. 5. SEM images of CPC2 membrane.

Fig. 6. SEM images of CPC3 membrane.

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order to investigate molecular structure of membranes. The obtainedFTIR spectrum of the control and modified membranes are given inFig. 2.

In the case of control membrane, peak at 3469 cm−1 representedstretching of O\H, 2877 cm−1 showed stretching of C\H bond,1739 cm−1 depicted the strong peak for C_O of carbonyls,1433 cm−1 indicated bending of C\H followed by peaks at1369 cm−1 and 1224 cm−1 which described the rocking and wag-ging mode of C\H bond. The strongest peak at 1035 cm−1 specifiedC\O\C while peak at 1112 cm−1 and 904 cm−1 illustrated the pres-ence of saccharide. Similar results have been previously reported inthe literature [42–44]. In the spectra of the CPC1 membrane, there

Fig. 7. SEM images of

was a peak shift at 3616 cm−1 which indicated the interaction of\OH with \NH. It conforms an incorporation of an amine groupinto a matrix of blended CA and PEG. The emergence of a new peakat 1643 cm−1 in the spectra of all modified membranes provides astriking evidence for the substitution of N-acetylated chitosan.With an increase in the amount of chitosan, this peak became moreprominent as noticed in the case of CPC3, CPC4 and CPC5 mem-branes. All other peaks were similar to the peaks present in controlmembrane. The spectra of CPC3 membrane indicated broadening ofpeak from 3450 to 3650 cm−1. The peak shift was stronger in thespectra of the CPC4 membrane. The peak shifted from 3469 cm−1

to 3573 cm−1 with the appearance of new peak at 3743 cm−1. This

CPC4 membrane.

Fig. 8. SEM images of CPC5 membrane.

Fig. 9. (a). AFM images (2-dimensional) of control and CPC1membranes. (b). AFM images (2-dimensional) of CPC2 and CPC3membranes. (c). AFM images (2-dimensional) of CPC4 andCPC5 membranes.

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Fig. 10. (a). AFM images (3-dimensional) of control andmodifiedmembranes. (b). AFM images (3-dimensional) of CPC2 and CPC3membranes. (c). AFM images (3-dimensional) of CPC4and CPC5 membranes.

65S. Waheed et al. / Desalination 351 (2014) 59–69

shift was attributed to the strong interaction between HO\NH bond[43].

4.2. SEM analysis

The surface structure of a membrane, which acts as a skin of themembrane is the most critical part, helping to identify the role of themembrane in themechanismof permeation and rejection. SEM analysis

Table 1Effect of concentration of CA/PEG on flux, salt rejection, salt passage and membranehydraulic resistance.

Membranetype

Flux(mL/h·.m2)

Salt rejection(%)

Salt passage(%)

Rm

(Pa/mL.h−1.m−2)

CA/PEG-1 353.37 52.00 48.00 370.37CA/PEG-2 296.86 60.00 40.00 568.18CA/PEG-3 260.08 69.20 30.80 613.49CA/PEG-4 234.64 81.50 18.50 636.94

is important for the determination of the morphology of the mem-branes. To attain high performancemembranes for specific applications,it is essential to manipulate the morphological structures of themembranes. Hence, the morphological studies of the various sectionsof control and modified membranes were made by using SEM.

It is evident from Figs. 3–8, all membranes exhibited denseasymmetric composite structure, with top skinned-layer and sub-layer. The lacy structure was observed, which was interconnected

Table 2Flux, salt rejection, salt passage and membrane hydraulic resistance of modifiedmembranes.

Membranetype

Flux(mL/h·.m2)

Salt rejection(%)

Salt passage(%)

Rm

(Pa/mL.h−1.m−2)

CPC1 397.94 83.07 16.93 769.23CPC2 375.84 83.07 16.93 787.40CPC3 353.73 85.00 15.00 900.90CPC4 292.93 91.60 8.40 1934.23CPC5 287.40 92.30 7.70 3076.92

Fig. 11. Relationship between flux and salt rejection.

Table 3Average roughness (Ra), average difference in height (Rz), root mean square average(RMS), optical density and flux for control and modified membranes.

Membranetype

Ra(nm)

Rz(nm)

RMS(nm)

Optical density(OD) at 600 nm

Flux(mL/h·m2)

Control 35.47 78.48 22.08 1.280 234.64CPC1 39.57 155.77 48.5 0.036 397.94CPC2 24.29 99.95 29.43 0.019 375.84CPC3 27.105 89.29 33.81 0.039 353.73CPC4 12.24 67.77 15.53 0.078 292.93CPC5 8.96 32.98 10.74 0.045 287.40

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with few voids. This morphology can be explained on the basis ofthermal-induced phase separation. It involved phase separationthrough the formation of diluent rich and liquid polymer rich phase.The diluent rich phase formed droplet in the liquid polymer richmatrix.With the passage of time, diluent rich phase grew through coarsening.Following the solidification of matrix, spherulites were formed. Thediluents rich domains were entrapped within spherulites. The growthof spherulite was restricted in small spaces which prevented thedevelopment of spherulite and resulted in a lacy structure [45,46]. Theentrapped diluent was extracted by controlled evaporation whichform voids between spherulite resulting into dense asymmetriccomposite structures.

4.3. AFM analysis

All the surface roughness parameters were calculated from theAFM images using an AFM software program. Fig. 9(a–c) shows 2-dimensional surface view of control and modified membranes. In allmembrane views, nodule formation was a prominent feature, but thepattern variation was observed in each membrane. The bright siteswere nodules and dark sites represented interstitial domains. In control,nodular aggregates were assembled in string like structure giving wavyappearance. The roughness parameter increased with increase in nod-ules [47]. The compacted nodules resulted in the formation of supra-nodules whichwere prominent in CPC1. The supra-nodules reduced in-terstitial domains and resulted in an increase in surface roughness. In

Fig. 12. Relationship between pressure and flux.

CPC2, CPC3, CPC4 and CPC5 membranes, the few compacted noduleswith dominant interconnected interstitial realm were present. Thepresence of interstitial spaces reduced the surface roughness. In CPC4,dark interstitial regionswere quite prominent thus resulting in decreaseof average roughness of the membrane [48,49].

Fig. 10(a–c) represents 3-dimensional views of all membranes. Thecolorific intensity shows the vertical profile of the membrane, wherebright regions are the peaks and dark regions are valleys.

Table 1 represents the average roughness (Ra), average differencesin height (Rz) and root mean square average (RMS). These parameterswere calculated by using appropriate AFM software. It should beemphasized that all images were flattened in the same way and there-fore the roughness values were relative and not absolute ones.

There was an overall decreasing trend of Ra when modifiedmembraneswere comparedwith the controlmembrane. The roughnessof membrane was directly related to flux. Increase in roughnessaugmented surface area which in turn enhanced flux of membrane[35]. In CPC1 membrane, there was increase in Ra, but flux was still atthe lower side. Similarly, CPC3 membrane had higher Ra, but flux waslow which is against an accepted trend. It could be ascribed as afact that with higher surface roughness, there was a greater chance oforganic fouling which in turn reduced the flux.

4.4. Membrane performance

The pure water flux, salt rejection, salt passage and membranehydraulic resistance are represented in Table 2. CA/PEG-1 membranehad a maximum flux of 353.37 mL/h.m2 while it exhibited minimumsalt rejection capacity 52%. CA/PEG-4 membrane had 81.5% saltrejection and its flux was 234.64 mL/h.m2.

The CA/PEG-1 membrane, with the highest flux, had reduced saltrejection capacity and CA/PEG-4 membrane with the lowest flux hadan elevated salt rejection capacity as indicated in Fig. 11. The CA/PEG-2 and CA/PEG-3 membrane had 60.00% and 69.20% salt rejection, withprogressive decrease in flux. It was noticed that with the increasedcontents of cellulose acetate, the flux was slightly decreased while saltrejection capacity was increased remarkably.

The transport mechanism within membrane can be best explainedon the basis of the solution diffusion model. According to this model,transport process within the membrane involves three steps: 1)sorption at the surface of the membrane, 2) diffusion into dense mem-brane under pressure, and 3) desorption. The hydrophilic natureof PEG acts as driving force for sorption of water into membrane[50–52].

It was deduced pragmatically that salt rejection was inverselyrelated to salt passage. Cellulose acetate being desalting in nature wasresponsible for the removal of salt [53]. This is the reason CA/PEG-4had maximum salt rejection ability. When salt rejection efficiencyof membrane was at its best, at the same time flux was reduced,depending upon the varying amount of CA and PEG.

PEG is hydrophilic in nature and act as a pore former [54]. CA/PEG-1membrane, with maximum quantity of PEG, showed enhanced waterflux, but at the same time salt rejection was compromised. This mightbe attributed to the formation of macro voids [55] on membrane

Fig. 13. Comparison of flux of modified membranes with control.

67S. Waheed et al. / Desalination 351 (2014) 59–69

which allowed the passage of salt along with water. Moreover, thediffusion rate of water was accelerated by the presence of PEG due toits hydrophilic nature. PEG increased the tendency of pore formationand as a consequence flux was increased [56].

It was observed that within the pressure range of 10,000 to60,000 Pa, the flux increased linearly with increase in trans membranepressure as indicated in Fig. 12. These results were in agreement withthe literature [57]. This was due to the increase in effective drivingforce (trans membrane pressure) required for water permeation.

The decline of flux with the passage of time, even at high pressureis attributed to the compaction phenomena occurring on the mem-brane surface. The compaction of membrane under pressure involvesrearrangement of polymeric chains, which leads to a change inmembrane structure with lowered volume of porosity, consequentlylowering the flux. Similar results were obtained and reported byArthanareeswaran and colleagues [37].

On the basis of salt rejection and flux, CA/PEG-4 membrane wasselected for modification with chitosan and modified membranes,CPC1–CPC5, were prepared using 0.5, 1.0, 1.5, 2.0 and 2.5% (w/v)chitosan. Thesemodifiedmembraneswere characterized and comparedwith the control.

Fig. 14. Comparison of salt rejection of modified membranes with control.

The flux, salt rejection, salt passage and membrane hydraulicresistance of modified membranes were calculated by using Eqs. (iii),(iv), (v) and (vi) as given in Table 3.

Table 3 indicates that CPC1 membrane had a maximum fluxof 397.94 mL/h.m2 but as amount of chitosan (CS) increased, fluxgradually declines. These modified membranes had reduced flux ascompared to control membrane, without chitosan. The comparisonbetween the flux for the control and modified membranes is given inFig. 13. The modified membrane CPC5 showed a drastic decrease influx of 287.40 ml/h.m2, as compared to CPC1.

The salt rejection capacity of modified membranes was enhancedwhen compared with control, as indicated in Fig. 14. Modified mem-brane CPC5 had a highest salt rejection capacity of 92.3%. The effect onflux was due to modification of neat membrane with chitosan. Thepresence of an amine group on chitosan developed hydrogen bondingand Van der Wall's forces which caused a change in hydrophilicity ofblended membranes [43]. Due to increase electrostatic interactions,extensive cross linkage was developed which helped in the exclusionof salt ions [58].

An inverse relation between salt rejection and flux for the modifiedmembranes was observed. The same trend was noticed for neatmembranes with varying amounts of CA and PEG. Membranes CPC1and CPC2 showed an identical trend for flux and salt rejection whileCPC4 and CPC5 membranes exhibited an appreciable increase in saltrejection capacity.

4.5. Membrane hydraulic resistance (Rm)

Membrane hydraulic resistance is an intrinsic resistance of themembrane. It was determined by subjecting the membranes to variouspressures and the Rm value was calculated from the inverse of slope ofthe linear relationship between pressures versus flux as presentedin Table 2. CA/PEG-4 membrane with highest CA content, exhibitedmaximum value of 636.94 Pa/mL.h−1.m−2 due to low porosity. CA/PEG-1 with a maximum amount of PEG had the lowest value of370.37 Pa/mL.h−1.m−2. PEG has a pore forming ability which causedan increase in flux but a decrease in Rm.

The Rm values for the modified membranes are given in Table 3,showing a gradual increase with increasing amount of chitosan.Modified membrane CPC5 offered the highest hydraulic resistance.

It was found that all modifiedmembranes had exhibited an increasein hydraulic resistance as compared to control (Fig. 15). It might beattributed to the development of strong electrostatic interaction

Fig. 15. Comparison of membrane hydraulic resistance for modified membranes andcontrol.

Fig. 16. Antibacterial activities of control and surface modified membranes.

68 S. Waheed et al. / Desalination 351 (2014) 59–69

between \NH groups of chitosan and \OH groups of CA and PEG,which reduced voids and resulted in an increased Rm.

4.6. Antibacterial activity

The antibacterial activity was determined against E. coli according toJIS L 1902–2002 method. It was observed that flask containing controlmembrane was turbid which indicated the growth of bacteria whileall other modified membranes showed a clear solution as indicated inFig. 16. The optical density (OD) recorded for the control and modifiedmembranes are given in Table 1. The OD of all modified membranesindicated that there was negligible bacterial growth. The controlmembranewithODof 1.280 indicated induction of E. coli onmembrane.It was inferred that modified membranes successfully inhibited thegrowth of bacteria. Chitosan has the ability to penetrate into bacterialcell and rupture the living cell. As a result intracellular componentpenetrates out along with inhibition of RNA synthesis [59].

5. Conclusions

In this study, self-sterilized asymmetric membranes were synthe-sized through a 2-stage phase inversion method. A series of CA/PEGblended membranes showed change in flux with change in ratio ofPEG and CA. The salt rejection was improved due to the presence ofhigher concentration of CA. The blended membranes with optimumflux and salt rejection was selected for modification with CS. Themodified membranes resulted into an improved trend for the saltrejection. Modified membrane CPC5 had 92.3% salt rejection whichprovided almost 11% increase in salt rejection capacity compared withthe control membrane (81.5%). A remarkable increase in Rm was alsoobserved for the CPC5 membrane. The CS substitution was strongestin CPC4 as evident from FTIR. The microbial growth was noticed in thepresence of the control while it was inhibited completely in the caseof modified membranes. The surface roughness was decreased withincrease CS concentration. SEM images depicted the asymmetric natureof membranes with the presence of lacy structure. Moreover, all thepolymers used in our studies are biopolymer, which is promising andleads to sustainable chemistry. Additional studies in the area of biopoly-mer based membranes and their applications are currently underway.

Acknowledgments

The authors express their cordial gratitude to the team of Depart-ment of Polymer Engineering and Technology, University of the Punjab,for their cooperation during the execution of this research project. Theauthors like to acknowledge Dr. Qamar Bashir, School of BiologicalSciences, University of the Punjab, for performing biological assay.Authors also express their sincerest gratitude to Dr. Nadeem Sadiq

Sheikh, Department of Chemistry, King Faisal University Saudi Arabiafor the proofreading of this article.

References

[1] I.A. Shiklomanov, Appraisal and assessment of world water resources, Water Int. 25(2009) 11–32.

[2] M. Falkenmark, Growing water scarcity in agriculture: future challenge to globalwater security, Phil. Trans. R. Soc. A 371 (2013).

[3] P. Ball, Seeking the solution, Nature 436 (2005).[4] P.H. Gleick, Water in crisis: paths to sustainable water use, Ecol. Appl. 8 (1998)

571–579.[5] N. Johnsona, H.M. Ravnborgb, O. Westermanna, K. Probst, User participation in

watershed management and research, Water Policy 3 (2001) 507–520.[6] D. Dudgeon, A.H. Arthington, M.O. Gessner, Z. Kawabata, D.J. Knowler, C. Leveque, R.

J. Naiman, A. Richard, D. Soto, M. Stiassny, C.A. Sullivan, Freshwater biodiversity:importance, threats, status and conservation challenges, Biol. Rev. 81 (2006)163–182.

[7] S.L. Postel, Water for food production: will there be enough in 2025? Bioscience 48(1998) 629–637.

[8] T. Hoepner, S. Lattemann, Chemical impacts from seawater desalination plants— acase study of northern red sea, Desalination 152 (2002) 130–140.

[9] T. Hoepner, J. Windelberg, Elements of environmental impact studies on coastaldesalination plants, Desalination 108 (1996) 11–18.

[10] V.G. Gude, N. Nirmalakhandan, Desalination using low-grade heat sources, J. EnergyEng. 134 (2008) 95–101.

[11] I.C. Karagiannis, P.G. Soldatos, Water desalination cost literature: review andassessment, Desalination 223 (2008) 448–456.

[12] S.A. Kalogirou, Seawater desalination using renewable energy sources, Prog. EnergyCombust. 31 (2005) 242–281.

[13] A. Idris, L.K. Yet, The effect of different molecular weight PEG additives on celluloseacetate asymmetric dialysis membrane performance, J. Membr. Sci. 280 (2006)920–927.

[14] C. Charcosset, A review of membrane processes and renewable energies fordesalination, Desalination 245 (2009) 214–231.

[15] A.W. Zularisam, A.F. Ismail, R. Salim, Behaviours of natural organic matter inmembrane filtration for surface water treatment — a review, Desalination 194(2006) 211–231.

[16] W. Lang, J. Shen, Y. Zhang, Y. Yu, Y. Guo, C. Liu, Preparation and characterizationsof charged poly(vinylbutyral) hollow fiber ultrafiltration membranes withperfluorosulfonic acid as additive, J. Membr. Sci. 430 (2013) 1–10.

[17] M.G. Buonomenna, Nano-enhanced reverse osmosis membranes, Desalination 314(2013) 73–88.

[18] G.T. Caneba, D.S. Soong, Polymer membrane formation through the thermal-inversion process. 1. Experimental study of membrane structure formation,Macromolecules 18 (1985) 2538–2545.

[19] M. Muller (Ed.), Membrane preparation/phase inversion membranes, Netherlands,Academic Press, 2000.

[20] D. Li, W. Krantz, A.R. Greenberg, R.L. Sani, Membrane formation via thermallyinduced phase separation (TIPS): model development and validation, J. Membr.Sci. 276 (2006) 50–60.

[21] R.K. Arya, Drying induced phase separation in multicomponent polymeric coatings— simulation study, Int. J. Sci. Technol. Res. 1 (2012) 48–52.

[22] P. Rustemeyer, History of CA and evolution of the markets, Macromol. Symp. 208(2004) 1–6.

[23] S. Fischer, K. Thummler, B. Volkert, K. Hettrich, I. Schmidt, K. Fischer, Properties andapplications of cellulose acetate, Macromol. Symp. 262 (2008) 89–96.

[24] D. Saeki, S. Nagao, I. Sawada, Y. Ohmukai, T. Maruyama, H. Matsuyama,Development of antibacterial polyamide reverse osmosis membrane modifiedwith a covalently immobilized enzyme, J. Membr. Sci. 428 (2013) 403–409.

[25] A.M. Hassanien, M.A. El-Hashash, M.A. Mekewi, D.B. Guirguis, A.M. Ramadan,Fabrication of polyvinyl alcohol/cellulose acetate (PVA/CA/PEG) antibacterial

69S. Waheed et al. / Desalination 351 (2014) 59–69

membrane for potential water purification application, Hydrol. Curr. Res. 4(2013).

[26] M.A. Ashraf, M.J. Maah, A.K. Qureshi, M. Gharibreza, I. Yusoff, Synthetic polymercomposite membrane for the desalination of saline water, Desalin. Water Treat. 51(2013) 3650–3661.

[27] A. Islam, T. Yasin, I. Rehman, Synthesis of hybrid polymer networks of irradiatedchitosan/poly(vinylalcohol) for biomedical applications, Radiat. Phys. Chem. 96(2014) 115–119.

[28] H.K. Lonsdale, U. Merten, R.L. Riley, J. Jay, Transport properties of cellulose acetateosmotic membranes, J. Appl. Polym. Sci. 9 (1965) 1341–1362.

[29] C.A. Smolders, A.J. Smolders, Formation of membranes by means of immersionprecipitation. Part II. The mechanism of formation of membranes prepared fromthe system cellulose acetate–acetone–water, J. Membr. Sci. 34 (1987) 67–86.

[30] J. Eckelt, S. Loske, M.C. Gonçalves, B.A. Wolf, Formation of micro- and nano-sphericparticles (filter dust) during the preparation of cellulose acetate membranes,J. Membr. Sci. 212 (2003) 69–74.

[31] J. Li, K. Nagai, T. Nakacawa, S. Wang, Preparation of polyethyleneglycol (PEG) andcellulose acetate (CA) blend membranes and their gas permeabiIities, J. Appl.Polym. Sci. 58 (1995) 1455–1463.

[32] J. Li, K. Nagai, S. Wang, K. Nagai, T. Nakagawa, A. Mau, Effect of polyethyleneglycol(PEG) on gas permeabilities and permselectivities in its cellulose acetate (CA)blend membranes, J. Membr. Sci. 138 (1998) 143–152.

[33] N. Gizli, Morphological characterization of cellulose acetate based reverse osmosismembranes by atomic microscopy (AFM) effect of evaporation time, Chem. Chem.Technol. 5 (2011) 327–333.

[34] D.F. Stamatialis, C.R. Dias, M.N. Pinho, Atomic force microscopy of dense andasymmetric cellulose-based membranes, J. Membr. Sci. 160 (1999) 235–242.

[35] S. Singh, K.C. Khulbe, T. Matsuura, P. Ramamurthy, Membrane characterizationby solute transport and atomic force microscopy, J. Membr. Sci. 142 (1998)111–127.

[36] E. Saljoughi, M. Sadrzadeh, T. Mohammadi, Effect of preparation variables onmorphology and pure water permeation flux through asymmetric cellulose acetatemembranes, J. Membr. Sci. 326 (2009) 627–634.

[37] G. Arthanareeswaran, T.K.S. Devi, M. Raajenthiren, Effect of silica particles oncellulose acetate blend ultrafiltration membranes: part I, Sep. Purif. Technol. 64(2008) 38–47.

[38] S. Kwak, S. Kim, Hybrid organic/inorganic reverse osmosis (RO) membrane forbactericidal anti-fouling.1. Preparation and characterization of TiO2 nanoparticleself-assembled aromatic polyamide thin-film-composite (TFC) membrane, Environ.Sci. Technol. 35 (2001) 2388–2394.

[39] G. Arthanareeswaran, T.K.S. Devi, D. Mohan, Development, characterization andseparation performance of organic–inorganicmembranes: part II. Effect of additives,Sep. Purif. Technol. 67 (2009) 271–281.

[40] W. Chou, D. Yu, M. Yang, The preparation and characterization of silver-loadingcellulose acetate hollow fiber membrane for water treatment, Polym. Adv. Technol.16 (2005) 600–607.

[41] J.G. Cappuccino, N. Sherman, Microbiology: A Laboratory Manual, CummingsScience Publishing, California, 1998.

[42] M. Zafar, M. Ali, S.M. Khan, T. Jamil, M.T.Z. Butt, Effect of additives on the propertiesand performance of cellulose acetate derivative membranes in the separation ofisopropanol/water mixtures, Desalination 285 (2012) 359–365.

[43] C. Liu, R. Bai, Preparation of chitosan/cellulose acetate blend hollow fibers foradsorptive performance, J. Membr. Sci. 267 (2005) 68–77.

[44] M. Ali, M. Zafar, T. Jamil, M.T.Z. Butt, Influence of glycol additives on the structureand performance of cellulose acetate/zinc oxide blend membranes, Desalination270 (2011) 98–104.

[45] H. Matsuyama, K. Ohga, T. Maki, M. Tearamoto, S. Nakatsuka, Porous celluloseacetate membrane prepared by thermally induced phase separation, J. Appl.Polym. Sci. 89 (2003) 3951–3955.

[46] L. Wenjun, Y. Youxin, Cabbasso, Formation and microstructure of polyethylene mi-croporous membrane through thermaly induced phase separation, Chin. J. Polym.Sci. 13 (1995) 7–19.

[47] Y. Zeng, Z. Wang, L. Wan, Y. Shi, G. Chen, C. Bai, Surface morphology and noduleformation mechanism of cellulose acetate membranes by atomic force microscopy,J. Appl. Polym. Sci. 88 (2003) 1328–1335.

[48] K.C. Khulbe, C.Y. Feng, T. Matsuura, Synthetic Polymeric Membranes: Characterizedby Atomic Force Microscopy, Springer, 2007.

[49] E.M. Vrijenhoek, S. Hong, M. Elimelech, Influence of membrane surface propertieson initial rate of colloidal fouling of reverse osmosis and nanofiltration membranes,J. Membr. Sci. 188 (2001) 115–118.

[50] M.A. Mazid, Mechanisms of transport through reverse osmosis membranes, Sep. Sci.Technol. 19 (1984) 357–373.

[51] H.G. Burghoff, K.L. Lee, W. Pusch, Characterization of transport across celluloseacetate membranes in the presence of strong solute–membrane interactions, J.Appl. Polym. Sci. 25 (1980) 323–347.

[52] R. Malaisamy, R. Mahendran, D. Mohan, M. Rajendran, V. Mohan, Cellulose acetateand sulfonated polysulfone blend ultrafiltration membranes. I. Preparation andcharacterization, J. Appl. Polym. Sci. 86 (2002) 1749–1761.

[53] B. Chakrabarty, A.K. Ghoshal, M.K. Purkait, Effect of molecular weight of PEG onmem-brane morphology and transport propertie, J. Membr. Sci. 309 (2008) 209–221.

[54] G. Arthanareeswaran, D. Mohan, M. Raajenthiren, Preparation, characterizationand performance studies of ultrafiltration membranes with polymeric Additives,J. Membr. Sci. 350 (2010) 130–138.

[55] H. Bai, Y. Zhou, X. Wang, L. Zhang, The permeability and mechanical properties ofcellulose acetate membranes blended with polyethylene glycol 600 for treatmentof municipal sewage, Prece, Environ. Sci. 16 (2012) 346–351.

[56] G. Arthanareeswaran, P. Thanikaivelan, K. Srinivasn, D. Mohan, M. Rajendran,Synthesis, characterization and thermal studies on cellulose acetate membraneswith additive, Eur. Polym. J. 40 (2004) 2153–2159.

[57] M. Theresa, M. Pendergast, E.M.V. Hoek, A review of water treatment membranenanotechnologies, Energy Environ. Sci. 4 (2011) 1946–1971.

[58] T. Yang, R.R. Zall, Chitosan membranes for reverse osmosis application, J. Food Sci.49 (1984) 91–93.

[59] Q. Li, S. Mahendra, D.Y. Lyon, L. Brunet, M.V. Liga, D. Li, P.J.J. Alvarez, Antimicrobialnanomaterials for water disinfection and microbial control: Potential applicationsand implications, Water Res. 42 (2008) 4591–4602.