Preparation and characterization of emulsion poly(vinyl chloride)(EPVC)/TiO2 nanocomposite ultrafiltration membrane

Hesamoddin Rabiee, Mohammad Hossein Davood Abadi Farahani, Vahid Vatanpour n

Faculty of Chemistry, Kharazmi University, 15719-14911 Tehran, Iran

a r t i c l e i n f o

Article history:Received 30 June 2014Received in revised form21 August 2014Accepted 26 August 2014Available online 6 September 2014

Keywords:Mixed matrix membranePoly(vinyl chloride)TiO2

UltrafiltrationAntifouling

a b s t r a c t

Emulsion poly(vinyl chloride)/titanium dioxide (EPVC/TiO2) nanocomposite ultrafiltration membraneswere prepared using the phase inversion method with different TiO2 contents. Pure water flux throughthe membranes was investigated at a operating pressure of 2 bar and its antifouling properties werestudied using bovine serum albumin (BSA) as a foulant. The results showed an increment in pure waterflux with increasing content of TiO2 up to 2 wt%, and then it slightly decreased by addition of 4 wt% TiO2

due to agglomeration of the nanoparticles at this content. The static water contact angle test showedimprovement in membrane hydrophilicity, due to hydrophilic behavior of the nanoparticles, which ledto higher water flux. SEM and EDAX analyses were applied to investigate membrane morphologicalchanges. EDAX analysis indicated that the nanoparticles are homogeneously dispersed in membranestructure at low concentrations. However, at high loading, the nanoparticles have a propensity toaggregate. SEM images showed that with TiO2 addition, initially finger-like structures change to macro-voids and after 1 wt% TiO2 loading, they return to finger-like construction with elongated finger-likepores. TiO2 addition also enhanced BSA rejection properties. BSA ultrafiltration experiments showed thatthe antifouling ability of nano-TiO2 embedded membranes was better than the unfilled EPVC membrane.

& 2014 Elsevier B.V. All rights reserved.

1. Introduction

Membrane separation processes have been taken into account dueto their interesting features like separation efficiency and low operat-ing costs, for the last two decades. Porous membranes, fabricated bydifferent phase inversion methods such as nonsolvent induced phaseseparation (NIPS) and thermally introduced phase separation (TIPS),are widely being used for waste water treatment. Various polymerslike poly(ethersulfone) (PES) [1], poly(sulfone) (PSf) [2], Poly(vinyli-dene fluoride) (PVDF) [3], cellulose acetate (CA) [4], poly(acrylonitrilePAN) [5,6] or their blends [7,8] have been considered to preparemembranes with desired structure.

Poly(vinyl chloride) (PVC) is a promising membrane material for itssuitable mechanical and chemical resistance, low cost and excellentthermal stability. This polymer could be easily dissolved in differentorganic solvents such as N-methyl-pyrrolidinone (NMP), N, Ndimethylacetamide (DMAc), dimethylformamide (DMF) and tetrahy-drofuran (THF), which makes it appropriate for industrial membraneseparation application. In the recent years several studies haveconcentrated on preparation of ultrafiltration and microfiltration

membranes with PVC and different solvents. Liu et al. [9] investigatedthe effect of Pluronic F127, as a polymeric additive, onmorphology andperformance of PVC membrane. Their results showed reduction inpore size, pore density and flux of the membranes. However,antifouling properties of the membranes enhanced remarkably. Meiet al. [10] studied the effect of different additives (PVP, PEG andsucrose) on phase diagram of PVC/DMAc in the presence of water asthe nonsolvent. They found that the velocity of gelation in the systemwith PVP is more than two others, and a small amount of sucroseaddition can cause membrane structure causing it to turn into sponge-like. However, in the case of PVP addition, finger-like extended intomembrane body. Peng et al. [11] enhanced hydrophilicity properties ofPVC membrane by the addition of poly(vinyl butyral) (PVB) whichcaused a reduction in the contact angle of PVCmembranes from 781 to42.31, along with increment in water flux. Zhang et al. evaluated usingPVC ultrafiltration membrane as a pretreatment for a reverse osmosis(RO) system and obtained 131% and 129% enhancement for permeateflux and recovery of the RO system respectively [12]. Xu et al. prepareda hollow fiber ultrafiltration membrane with PVC/DMAc system in thepresence of PVP and PEG as polymeric pore former additives [13]. Theyobserved lower mechanical properties and rejection for protein, alongwith higher porosity and permeation flux as a result of PVP/PEGaddition. It is noteworthy to mention that among different grades ofPVC, emulsion polyvinyl chloride (EPVC) is desirable for membrane

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Journal of Membrane Science

http://dx.doi.org/10.1016/j.memsci.2014.08.0510376-7388/& 2014 Elsevier B.V. All rights reserved.

n Corresponding author. Tel./fax: þ98 26 34551023.E-mail address: vahidvatanpoor@yahoo.com (V. Vatanpour).

Journal of Membrane Science 472 (2014) 185–193

preparation due to its low temperature of processing, good thermalstability, low cost and high chemical resistance, which makes it a greatoption for membrane preparation.

Recently, incorporation of different types of nanoparticles formodification of filtration membranes has attracted a great deal ofattention. Various types of nanoparticles such as titanium oxide (TiO2)[14–16], zinc oxide (ZnO) [17–19], alumina (Al2O3) [20], ZrO2 [21], silica(SiO2) [22] and carbon nanotube [23,24] have been utilized in order toimprove antifouling properties of fabricated membranes and preparemembranes with desired performance. Wu et al. showed that additionof TiO2 nanoparticles into PES, led to lower fouling ratio and conse-quently, water flux went up as TiO2 content increased [16]. They alsofound that hydrophilicity, thermal stability and mechanical strength ofthe membranes were enhanced with TiO2 addition. Shen et al. [17]fabricated PES/ZnO hybrid membrane and observed improvement inmembrane porosity with ZnO addition. They also reported betterantifouling ability, lower contact angle and higher porosity of themodified membranes. Maximous et al. investigated the separationproperty and morphology of Al2O3 entrapped-PES UF membranes.Their results showed higher porosity and better antifouling in com-parison with unfilled PES UF membrane [20]. They also studied theinfluence of nano-ZrO2 on PES membrane and observed lower foulingresistance compared to neat PES membrane [21]. Shen et al. reportedhigher pure water flux, hydrophilicity and flux recovery with additionof SiO2 for the case of PES/SiO2 composite membranes [25].

Among all these nanoparticles, various types of TiO2 have beenused bymany researches to improve membrane performance, becauseof its suitable properties like desirable hydrophilicity and fine disper-sion in polymeric solution [26]. In addition, nano-TiO2 has a tendencyto absorb OH-groups and become hydrophilic. In previous work, weinvestigate the effect of different sizes and types of nano-TiO2 onantifouling and performance of PES membrane [27]. Results showedan increment in hydrophilicity and pure water flux with increasingTiO2 content. In addition, P25 type of TiO2 showed lower tendency toaggregate, resulting in more active membrane pores and higher purewater flux and water flux recovery ratio. Cao et al. also observed thatsmaller nano-TiO2 could more remarkably improve antifouling prop-erty of the PVDF membrane [28].

To the best of our knowledge, preparation of ultrafiltrationmembranes with EPVC and TiO2 has not been worked on. Thereby,the current study focuses on the effect of TiO2 nanoparticle concen-tration on performance of EPVC membrane, fabricated by the non-solvent induced phase inversion. The membranes were synthesizedwith addition of TiO2 in five different loadings. Pure water flux andBSA flux were measured to calculate flux recovery of the membranes.The membranes were characterized by SEM to evaluate theirmorphology. Contact angle of the neat and nanocomposite mem-branes was measured to detect the change in their hydrophilicity.

2. Experimental

2.1. Materials

Emulsion polyvinyl chloride (EPVC) was supplied from ArvandPetrochemical Co., Iran. TiO2 Degussa P25 nanoparticles wereobtained from Degussa Co., Germany. 1-Methyl 2-pyrrolidone(NMP) and polyethylene glycol (PEG) with molecular weight of6 kDa were purchased from Merck, Germany. Bovine serumalbumin (BSA) was bought from Sigma.

2.2. Preparation of (EPVC)/TiO2 nanocomposite ultrafiltrationmembranes

The immersion precipitation phase inversion method was usedto prepare flat sheet asymmetric membranes. First of all, the

precise amounts of TiO2 were dispersed into NMP as a polymersolvent and sonicated for one hour to obtain homogeneous TiO2

suspensions. Based on literaure, TiO2 contents were selected as 0.2,0.5, 1, 2 and 4 wt% of polymeric solution [17,27–30]. Subsequently,PEG (4 wt%) and then EPVC (15 wt%) were added to suspensionsand stirred to achieve homogeneous solutions. The final polymer/TiO2 casting solutions were again sonicated for 30 min to removeair bubbles. Following that, the membranes were casted with a200 μm casting knife onto a glass plate at room temperature.Immediately after that, the glass plates were immersed in adeionized water coagulation bath at 25 1C. After 10 min, thefabricated films were put in the second bath with fresh distilledwater for 24 h to ensure that the solvent is leached and phaseinversion is completely done. Finally, the prepared membraneswere dried by placing them between two filter papers. Table 1shows the compositions of the prepared membranes.

2.3. Membrane characterization

2.3.1. SEM and EDAXScanning electron microscopy (SEM) was applied to investigate

the surface and cross-sectional morphology of the preparedmembranes using VEGA\\TESCAN SEM, Czech Republic. Forcross-sectional images, the membranes were fractured in liquidnitrogen. The samples were coated with gold before SEM analysis.In addition, since SEM device was equipped with dispersive X-rayanalysis (EDAX) detector, this analysis was used to inspect disper-sion of nano-TiO2 particles in the cross section of the fabricatedmembranes.

2.3.2. Contact angleThe hydrophilicity of the membranes was examined by static

water contact angle measurement, using OCA20, DataphysicsInstruments, Germany. Deionized water droplets were placed onthe surface of membranes, and then the contact angle between thewater and membrane was measured until no change wasobserved. At least, five measurements were taken at differentlocations on the membrane surface to ensure about the repeat-ability of the results of contact angle value. The tests were done at25 1C.

2.3.3. Pore size and porosityThe overall porosity (ε) of the nanocomposite membranes was

calculated by the gravimetric method, as follows [15]:

ε¼ ω1�ω2

A� l� dwð1Þ

where ω1 and ω2 are the weights of the wet and dry membranes,respectively, l is the membrane thickness (m), A is the membranearea (m2) and dw is the water density (0.998 g/cm3). In order tomeasure porosity, first a piece of the membranes with known areais immersed in distillated water at least for 12 h to make sure thatall the pores of the membranes are filled. Immediately after that,the sample should be weighted only after the water on the surfaceof the samples is cleaned cautiously. Subsequently, the samples are

Table 1Compositions of the prepared membranes.

Membrane EPVC (wt%) PEG 6 kDa (wt%) TiO2 (wt%) NMP (wt%)

Neat EPVC 15 4 0 810.2 wt% TiO2/EPVC 15 4 0.2 80.80.5 wt% TiO2/EPVC 15 4 0.5 80.51 wt% TiO2/EPVC 15 4 1 802 wt% TiO2/EPVC 15 4 2 794 wt% TiO2/EPVC 15 4 4 77

H. Rabiee et al. / Journal of Membrane Science 472 (2014) 185–193186

placed in an oven for 2 h at 60 1C to evaporate water frommembrane pores and weighted again.

Mean pore radius (rm) of the membranes was also measured bythe Guerout–Elford–Ferry equation, as follows [15]:

rm ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffið2:9�1:75εÞ � 8ηlQ

ε� A�ΔP

rð2Þ

where Q is the water flux (m3/s), η is the water viscosity(8.9�10�4 Pa s) and ΔP is the operation pressure (0.2 MPa).

2.4. Permeation experiments

2.4.1. Ultrafiltration test apparatusPermeation apparatus used in this study is schematically

shown in Fig. 1. The membrane is located in the dead-end cellwith effective area of 19.6 cm2. The feed (pure water or BSA) ispoured into the feed tank and N2 pressure provides the neededdriving force for the feed to pass the membrane. The liquid in thecell is magnetically stirred. The weight of permeation is measuredby a scale, which is linked to a computer that records the weight ofpermeation in the given period of time.

2.4.2. Performance calculationsPermeation experiments were carried out at pressure of 2 bar

for pure water and BSA with concentration of 500 ppm to evaluatewater flux, flux recovery and rejection. Prior to the main tests, themembranes were compacted by applying 3 bar pressure forapproximately 30 min. First, pure water flux was passed for90 min and calculated as follows:

J ¼ MAΔt

ð3Þ

where J, M, A and Δt are the flux, mass of permeated water,membrane effective area and permeation time, respectively.

After water permeation, the feed tank is filled with 500 ppmBSA solution to measure its permeation for analyzing the mem-branes rejection and fouling resistance. BSA flux test was carriedout for 90 min. Next, the membranes were brought out of the celland were placed in fresh water for 1 h and the feed tank wascleaned with distilled water. Finally, second water flux was

measured to investigate the flux recovery ratio (FRR) of themembranes as follows:

FRR ð%Þ ¼ Jwater;2

Jwater;1

� �� 100 ð4Þ

where Jwater,2 and Jwater,1 are the flux of pure water after and beforeBSA flux, respectively.

The percentage of BSA rejection (R) was calculated by

R ð%Þ ¼ 1�Cp

CF

� �� 100 ð5Þ

where Cp and Cf are the BSA concentrations in permeate and feed,respectively.

3. Results and discussion

3.1. Morphological properties of membranes

The cross-sectional and surface morphology of the neat and thenanocomposite membranes were investigated by SEM, as shownin Figs. 2 and 3 at different magnifications. All the images indicatetypically porous and asymmetric structure of the membranes,which have a dense top layer and a porous sub-layer. Addition ofTiO2 as a hydrophilic additive affects thermodynamic and kineticsof the phase inversion process which leads to obtain differentmorphologies [31,32]. As it is obvious from Fig. 2, the neatmembrane has large finger-like structure that is due to highaffinity between solvent (NMP) and non-solvent (water) andinstantaneous demixing during phase separation. However, withincreasing the content of TiO2, first, the finger-like structureschange to the macro-voids and next, return to finger-like con-struction with elongated finger-like pores extended throughoutthe membrane cross-section. Also, the top-layer pore size of theprepared membranes increases and then, diminishes with highTiO2 contents. Compared to the neat PVC dope solution, thepresence of hydrophilic titanium dioxide nanoparticles in thedope solution strongly facilitates diffusion of water from coagula-tion bath to the cast polymer film (the faster exchange ratebetween solvent and non-solvent), causing the development oflarge finger-like or macro-voids and the improvement in overallporosity and mean pore size (Table 2) [33,34].

However, high concentration of TiO2 nanoparticles in the poly-meric solution leads to increment in viscosity (can be visually seen).The kinetic of the phase inversion is influenced by viscosity, whichdecreases the exchange velocity in membrane formation. Thevelocity of phase inversion and solvent/non-solvent instantaneousdemixing act as the main deterrent for macro-void formation andthe membrane morphology turns to narrow finger-like [35]. In spiteof changes in membrane structure with addition of TiO2, cross-sectional morphology did not turn to sponge-like. This behavior hasbeen seen by some researches for other polymers like PSf [36]. Theobserved results are fairly consistent with other studies aboutnanocomposite membranes [25,27,30,37].

The surface of the membranes was also visualized by SEM andresults are presented in Fig. 3. The amount of the TiO2 nanoparticleson the surface of the prepared membranes has been increased byenlarging the nanoparticle concentration in the casting solution.However, it is apparent that increasing TiO2 content leads to moreaggregation of the nanoparticles. It is well-known that the TiO2

nanoparticles exhibit a tendency to aggregate (formation of largersize TiO2 clusters) due to their high specific surface area and thehydroxyl groups on the TiO2 surface [38].

EDAX analysis was applied to observe nano-TiO2 dispersion inthe membrane structures. Titanium (Ti) was selected for elementmapping. As shown in Fig. 4, the amount of TiO2 in the membraneFig. 1. Schematic diagram of dead-end UF setup.

H. Rabiee et al. / Journal of Membrane Science 472 (2014) 185–193 187

matrix increases with increment in the weight of the nanoparti-cles. Also, at low concentrations, the nanofiller is homogeneouslydispersed throughout the membrane with low aggregation.In spite of asymmetric structure of the membranes with differentmorphologies from top to bottom of the membranes, the nano-particle distribution is completely uniform and in accordance withincreasing weight of TiO2 in the nanocomposite membranes.Nevertheless, at higher loadings (particularly at 4 wt% TiO2), thenanoparticles show tendency to aggregate slightly that is commonin other nanoparticle-modified membranes [17].

In addition, leach out of the nanoparticle from the preparedmembranes was negligible. EDAX analysis showed the percentagesof TiO2 nanoparticles in dried membranes were 0.2170.03,

0.4970.05, 0.9470.11, 1.8570.2 and 3.8970.4 for 0.2, 0.5, 1, 2,and 4 wt% TiO2/EPVC membranes, respectively.

3.2. Permeation and rejection results

The effect of TiO2 content on pure water flux was investigatedfor 90 min at operating pressure of 2 barg. As shown in Fig. 5, theflux of water increases as the TiO2 content increases up to 2 wt%and next, it decreases. TiO2 addition can be two dissimilar effectson water permeation: one is improving of flux due to increase ofthe porosity and hydrophilicity and another is decreasing of fluxdue to pore blocking.

The existence of TiO2 leads to more porous structure (Table 2)and also, more connectivity between top layer and bottom layer ofthe membrane, which reduce the resistance of water permeationthrough the membranes, as observed from the SEM images. On theother hand, based on the results of contact angle (Fig. 6), hydro-philicity of the membranes is improved, which is more favorableto the water flux. Thereby, the nanocomposite membranes tend toattract water molecules and facilitate water penetration more thanthat of the neat membrane, owing to higher hydrophilicity andenhanced structure, which means higher water flux [39].

However, at high TiO2 content, nanoparticles may cause poreblockage of the membranes, which leads to lower water flux. Thus,pore blockage can neutralize the positive effect of morphology andhydrophilicity on water permeation. In addition, as mentionedearlier, TiO2 addition at high values leads to increment in dopeviscosity and formation of membranes with thicker skin layer,which acts as a resistance for water flux [37,39]. In this study, eventhough sonication of polymeric/nano-TiO2 solution was applied todisperse the nanoparticles, at high TiO2 content, the agglomera-tion took place, and at 4 wt% TiO2 the pure water flux reduced.However, the flux reduction is not very considerable and permea-tion of 4 wt% TiO2/EPVC membrane is much higher than the neatmembrane and only slightly lower than 2 wt% TiO2/EPVC. Thisbehavior shows that higher TiO2 content after 4 wt% will lead toserious pore blockage and permeation reduction. In the case ofagglomeration of the nanoparticle in the polymer matrix and poreblockage, EDAX analysis presented in Fig. 4 obviously shows thatthe white dots at high TiO2 content membranes are accumulatedand joined together specially in 4 wt% embedded membrane,showing aggregation of the nanoparticles. Similar results for othernanocomposite membranes have been reported in literature[25,27,37].

In order to investigate the hydrophilicity of the membranes,static water contact angle test was applied and the results areshown in Fig. 6. The contact angle of the prepared mixed matrixmembranes decreased continuously as the content of TiO2 nano-particles increased. For the unmodified EPVC, the contact anglewas around 66.81 and it reduced to 55.41 for 4 wt% TiO2/EPVCmembrane. It shows that the surface of the membranes becomesmore hydrophilic by TiO2 addition. The reason for this observationis that during membrane preparation, it is possible for thenanoparticles to move towards the surface of the membrane.Therefore, as the nanoparticles are hydrophilic, the hydrophilicityof the membranes increases. This phenomena lead to higher wateradsorption and consequently, higher water permeability. Thissurface migration of nanoparticles could be due to reduction ininterface energy or the gravitational force [18,40].

Table 2 represents mean pore size and porosity of the preparednanocomposite membranes. All the fabricated membranes haveporosity between 68% and 79%, due to low polymer concentrationand existence of polyethylene glycol additive in polymeric dopewhich acts as a pore former and leach out the membrane duringdemixing process in the coagulation bath [35]. However, as anoverall trend, the porosity enhances because of faster precipitation

Fig. 2. Cross-sectional SEM images of the neat and TiO2/EPVC nanocompositemembranes.

H. Rabiee et al. / Journal of Membrane Science 472 (2014) 185–193188

and exchange of solvent/non-solvent with addition of TiO2 nano-particles [23]. Pore size of the membranes is also influenced by thenanoparticles which on the one hand lead to faster demixing dueto its hydrophilic behavior, thus larger pores are formed. However,

as presented in Table 2, mean pore size again decreases at highloading. This could be due to slight nanoparticle aggregation.

The BSA rejection properties, of the modified and unmodifiedmembranes, are shown in Fig. 7. As can be seen, BSA rejection for

Fig. 3. Surface SEM images of the neat and TiO2/EPVC nanocomposite membranes.

H. Rabiee et al. / Journal of Membrane Science 472 (2014) 185–193 189

all the membranes is more than 90%. The rejection enhances toalmost 98% for 2 wt% TiO2/EPVC membrane. The incorporation ofhydrophilic TiO2 nanoparticle with surface hydroxyl group causedto increase the interaction between BSA and membrane surfaceand improve BSA rejection. TiO2 addition increases surface hydro-philicity of the membranes, which results in lower affinity andinteraction between BSA and membrane surface and higherrejection [41]. In addition, the thicker skin layer can be anotherreason for increment in BSA rejection for TiO2-modified mem-branes and that is why TiO2 addition causes higher BSA retention.However, similar to water flux order, BSA rejection for 4 wt% TiO2/EPVC membrane decreased slightly, which can be attributed to thenanoparticles agglomeration at high content and formation oflarge pores that diminish the rejection [37,41].

3.3. Antifouling properties of the membranes

The membranes, fabricated by hydrophobic materials like PESand PVC, suffer from fouling during the processes, in whichcomponents such as natural organic matter (NOM), whey ormicro-organism exist as foulants. They lead to lower permeationdue to fouling of membrane surface. Thereby, modified mem-branes should be able to reduce fouling as much as possible andmake it reversible with water washing to recover the pure waterflux after foulant permeation, sufficiently. Thus, the flux of BSAsolution was performed to evaluate antifouling properties of themixed matrix membranes. Fig. 8 shows the permeation results ofthe neat and the nanocomposite membranes at three differentperiods of time. First, pure water is passed through the membrane,then BSA is filtered and finally, second water flux is performed tocompare water flux before and after BSA.

As can be seen in Fig. 8, all the permeations in the three stepsfollow the same trends, and 2 wt% TiO2/EPVC membrane showsthe highest permeation for water and BSA solution. The fluxes ofall the fabricated membranes decreased till they almost reached tostable plateau. BSA molecules can interact with the surface ofmembrane, resulting in the formation of a layer which leads to theformation of gel layer, increase membrane resistance and reducewater flux. However, the presence of TiO2 on the surface ofmembrane and inner surface of membrane pores could reducethe interaction between BSA and membrane surface and preventBSA adsorption and consequently, decrease the membrane fouling[27,39].

Fig. 9 presents flux recovery ratio (FRR) of the preparedmembranes. The flux recovery ratio of the membranes increasedwith addition of TiO2 content and reduced slightly for 4 wt% TiO2.The FRR promoted from 69% for the unmodified membrane to 89%for 2 wt% TiO2/EPVC, which showed the highest antifoulingproperties of the nanocomposite membranes. This means thatprotein fouling becomes more reversible with increment in TiO2

addition. The observations are in good accordance with other

Table 2Porosity and mean pore size of the nanocomposite membranes.

Membrane Porosity (%) Mean pore radius, r (nm)

Neat EPVC 68.5 (73.2) 9.1 (70.6)0.2 wt% TiO2/EPVC 72.6 (73.8) 9.6 (70.7)0.5 wt% TiO2/EPVC 76.4 (73.9) 10.0 (70.7)1 wt% TiO2/EPVC 79.1 (74.2) 10.3 (70.6)2 wt% TiO2/EPVC 78.7 (73.1) 12.5 (70.8)4 wt% TiO2/EPVC 75.2 (73.2) 12.1 (70.9)

Fig. 4. EDAX of the cross-section of TiO2/EPVC nanocomposite membranes:(a) 0.2 wt%, (b) 0.5 wt%, (c) 1 wt%, (d) 2 wt% and (e) 4 wt%.

H. Rabiee et al. / Journal of Membrane Science 472 (2014) 185–193190

membranes modified by nanoparticles for water treatment[27,37,42].

However, for the case of 4 wt% TiO2 content, the FRR decreasesslightly that could be attributed to the nanoparticle agglomeration.Excessive loading of TiO2 nanoparticles leads to significantagglomeration on the substrate surface, reducing the contact areaof hydroxyl groups carried by TiO2 nanoparticles and possiblydecreases repulsion between protein and membrane surface [33].

The water flux and FRR of 4 wt% TiO2 membrane are very closeto that of 2 wt% TiO2/EPVC and still more than that of 1 wt% TiO2,which confirms that agglomeration is not very remarkable. Byincorporation of hydrophilic nanoparticles on the membrane sur-face, a hydrated layer is formed, which can effectively prevent theattachment of foulants [43].

In order to investigate the performance reproducibility of theprepared membranes, three-cycle water and BSA flux were per-formed for unmodified EPVC and 2 wt% TiO2/EPVC membranes,which showed the best result for flux recovery ratio. The fluxes areshown in Fig. 10 and as it can be seen, water and BSA fluxes decreasefor both the membranes; therefore FRR reduces after the second andthird BSA flux, compared to the first one. However, this reduction inFRR is not very significant, particularly for 2 wt% TiO2/EPVC mem-brane; its FRR are 89%, 85% and 81% related to the first water flux.First, second and third FRR for neat EPVCmembrane are 69%, 65% and61%, respectively. This observation indicates high efficiency of theTiO2-modified membranes in hydraulic cleaning. Accordingly, it canbe said that the addition of TiO2 to emulsion polyvinyl chloridematrix for preparation of ultrafiltration membrane develops theantifouling characteristic of the prepared mixed matrix membranes.

4. Conclusion

EPVC/TiO2 nanocomposite ultrafiltration membranes were fab-ricated via induced immersion precipitation technique with NMP

213 221

284

323

435403

0

50

100

150

200

250

300

350

400

450

500

Neat E

PVC

0.2 w

t.% TiO

2/EPVC

0.5 w

t.% TiO

2/EPVC

1 wt.%

TiO2/E

PVC

2 wt.%

TiO2/E

PVC

4 wt.%

TiO2/E

PVC

Pure

Wat

er F

lux

(kg/

m2 .

h)

Fig. 5. Pure water flux of EPVC/TiO2 nanocomposite membranes (results areaverage of three replicates).

66.864.6

61.03 59.157.2

55.4

0

10

20

30

40

50

60

70

80

Neat E

PVC

0.2 w

t% TiO

2/EPVC

0.5 w

t% TiO

2/EPVC

1 wt%

TiO2/E

PVC

2 wt%

TiO2/E

PVC

4 wt%

TiO2/E

PVC

Stat

ic W

ater

con

tact

ang

le (°

)

Fig. 6. Static water contact angle of the TiO2/EPVC membranes (average contactangle of five replicates is reported).

50

60

70

80

90

100

Unmodified EPVC

0.2 wt.% TiO2/EPVC

0.5 wt.% TiO2/EPVC

1 wt.% TiO2/EPVC

2 wt.% TiO2/EPVC

4 wt.% TiO2/EPVC

Rej

ectio

n of

BSA

(%)

Fig. 7. BSA rejection of unmodified and TiO2-modified membranes.

0

50

100

150

200

250

300

350

400

450

500

550

0 30 60 90 120 150 180 210 240 270 300

Flux

(kg/

m2h)

Time (min)

4 wt.% TiO2/EPVC

2 wt.% TiO2/EPVC

1 wt.% TiO2/EPVC

0.5 wt.% TiO2/EPVC

0.2 wt.% TiO2/EPVC

Neat EPVC

Fig. 8. Flux of water and BSA versus time for the modified and unmodifiedmembranes as follows: the first 90 min for pure water flux, the second for BSAflux and the third for water flux after membrane washing with pure water for30 min.

6975

7984

8986

0

10

20

30

40

50

60

70

80

90

100

Neat EPVC 0.2 wt.% TiO2/EPVC

0.5 wt.% TiO2/EPVC

1 wt.% TiO2/EPVC

2 wt.% TiO2/EPVC

4 wt.% TiO2/EPVC

Flux

reco

very

ratio

(%)

Fig. 9. Flux recovery ratio (FRR) of the modified and unmodified membranes.

H. Rabiee et al. / Journal of Membrane Science 472 (2014) 185–193 191

as the solvent and water as the non-solvent. The SEM imagesshowed finger-like pores in membrane structure with moreconnectivity between top and bottom of the membranes, afterTiO2 addition. EDAX analysis showed fine and homogeneousdispersion of TiO2 nanoparticles in membrane matrix at lowconcentrations. The prepared mixed matrix membranes showedan increment in hydrophilicity, pure water flux and flux recoveryratio with increasing TiO2 content. At 4 wt% TiO2, a slight reduc-tion in pure water flux and FRR was observed, which could be dueto nanoparticles tendency to aggregate at this loading. TiO2

addition also led to more BSA rejection and antifouling propertiesof the prepared membranes. Flux recovery ratio of the nanocom-posite membranes increased from 69% for the neat membrane to89% for 2 wt% TiO2 nanocomposite membrane. This study showedthat the incorporated TiO2 nanoparticle could improve antifoulingproperties of the emulsion poly (vinyl chloride) membrane to beused as an ultrafiltration membrane for treatment of high foulingwastewaters.

Acknowledgment

The authors gratefully acknowledge the financial support ofthis project by Novel Technology Research Group, PetrochemicalResearch and Technology Co. of Iran (Grant no. 0870289208).

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