polysulfone nanocomposite membranes with improved hydrophilicity

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Electrochimica Acta

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olysulfone Nanocomposite Membranes with improvedydrophilicity

isebo Phelane, Francis N. Muya, Heidi L. Richards, Priscilla G.L. Baker ∗,mmanuel I. Iwuoha

hemistry Department, University of the Western Cape, Private Bag X17, Robert Sobukwe Drive, Bellville, 7535, South Africa

r t i c l e i n f o

rticle history:eceived 19 July 2013eceived in revised form2 November 2013ccepted 27 November 2013vailable online xxx

eywords:olysulfoneydrophilicity

a b s t r a c t

Membrane separation processes have been widely applied in the treatment of wastewater with polysul-fone (PSF) polymer membrane being the most frequently used in ultrafiltration of wastewater due to itschemical and structural stability and mechanical robustness. A disadvantage to these membranes is theirhydrophobicity which leads to membrane fouling caused predominantly by organic pollutants in water.Many studies have been conducted to increase the hydrophilic properties of the polysulfone membranesurface. This paper reports on the preparation and characterisation of polysulfone nanocomposites wheresilver, cobalt and nickel nanoparticles have been incorporated into polysulfone materials. The metallicnanoparticles and the nanocomposites were characterized using high resolution - transmission electronmicroscopy (HR-TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), cyclic

oltammetryiffusion coefficientltrafiltration

voltammetry (CV), square wave voltammetry (SWV), and contact angle techniques. The SEM, TEM andEDS confirmed the size of the metal nanoparticles to be in the nanometer range. The SEM images of themodified polysulfone thin film showed porous structures compared to unmodified polysulfone. Dropshape analysis confirmed a 50% reduction in surface contact angle. The fouling behaviour of the poly-sulfone materials was evaluated using electrochemical impedance spectroscopy. The PSF/Co and PSF/Nithin films showed an approximate 50% improvement in fouling performance.

. Introduction

Water pollution is one of the major environmental problems inhe world. The techniques used for the treatment of polluted water,re the traditional physicochemical methods such as precipitationy chemical agent, adsorption on activated carbon, ion-exchangen resins and membrane processes (ultra- and nanofiltration,everse osmosis and electro membrane processes) [1]. Membranesypically consist of two layers i.e. a selective layer which is respon-ible for providing the membrane with separation capabilities and

porous support layer which provides mechanical strength andtability. Nanofiltration may be applied for the removal of disin-ection by-product precursors such as natural organic matter andeavy metals. Ultrafiltration involves membranes with pore sizes

n the range of 0.1 to 0.001 micron and is used for the removal highf molecular-weight substances, and organic polymeric molecules.

Please cite this article in press as: L. Phelane, et al., Polysulfone Nanocom(2014), http://dx.doi.org/10.1016/j.electacta.2013.11.156

A major challenge to these operations is the membrane foul-ng by proteins and other biomolecules in the feed stream. Therere many factors contributing to fouling such as surface properties,

∗ Corresponding author.E-mail address: [email protected] (P.G.L. Baker).

013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved.ttp://dx.doi.org/10.1016/j.electacta.2013.11.156

© 2013 Elsevier Ltd. All rights reserved.

hydrodynamic conditions, ionic strength and solute concentration.The extent of adsorption depends on the types of solute macro-molecules. Fouling results in flux decline, which increases theenergy demand for filtration. Fouling can occur in two ways: viz.cake fouling which is generally reversible by water flushing orback washing and fouling due to the adsorption of foulants, whichis essentially irreversible and can only be counteracted to a cer-tain extent by aggressive chemical cleaning [2]. However, whencleaning becomes ineffective, the membrane has to be replaced[3]. Membranes that resist fouling are highly desirable, since theyprovide improved ultrafiltration capability and subsequently moreaffordable clean water [2].

Polysulfone is one of the most frequently used polymers in theproduction of ultrafiltration and microfiltration membranes dueto its properties [4]. The advantageous properties of polysulfoneare high thermal resistance, good mechanical and chemical sta-bilities and its superior film-forming properties [3–5]. Polysulfonemembranes are often used as sublayers in composite membrane forreverse osmosis, gas separation and pervaporation. However, the

posite Membranes with improved hydrophilicity, Electrochim. Acta

hydrophobic characteristic of polysulfone predisposes it to mem-brane fouling which shortens membrane life. Modification of themembrane may be done to improve its hydrophilicity. Hydrophilic-ity is the tendency of a surface to become wet or to absorb water

dx.doi.org/10.1016/j.electacta.2013.11.156


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4,5]. The technique of modification normally involves the use ofydrophilic polymers or copolymers, blending of hydrophilic orxchange polymers with hydrophobic polymers, grafting of poly-ers and the surface modification of the membrane itself [6].nother technique that may be used to improve hydrophilicity

nvolves modifying the polymer with metal oxides.Blending the hydrophobic polymer with metal oxides nanopar-

icle has attracted many research studies due to the ease ofetal oxide incorporation. A study that was done showed thatater flux through a polyethersulfone–titania (PES/TiO2) mem-

rane was enhanced [7,8]. More recent investigation for waterltration focused on polyethersulfone - alumina (Al2O3/PES) andolyethersulfone - zirconia (ZrO3/PES) membranes [9]. ZirconiaZrO3) membranes have been demonstrated to be chemically moretable than titania (TiO2) and alumina (Al2O3) membranes and thathey are more suitable for liquid phase inversion applications. The

embrane strength of PES casting suspension was enhanced by theddition of zirconia nanoparticles.

In this work we characterised the homogeneous incorporationf Co, Ni and Ag nanoparticles into polysulfone casting solution.he modified thin films were observed to have greatly enhancedydrophilic properties compared to unmodified polysulfone and

detailed electrochemical evaluation of the metal nanoparticleodified thin films of polysulfone is, reported here for the first

ime

. Experimental

All solutions were prepared with analytical grade reagentsnd purified water from a Milli-pore Mill Q system and analyt-cal grade Argon gas was used to purge the system. PolysulfoneSigma Aldrich, 182443) was purchased as beads. The Cobalt (Sigmaldrich, 255599, 98% purity) and Nickel (Sigma Aldrich, 339350,8% purity) were purchased as the chloride salts, as well as AgNO3Sigma Aldrich, 209139, 99% purity).

.1. Preparation of polysulfone thin film

Polysulfone membrane film was prepared by dissolving 4 g ofolysulfone in 50 ml N, N-dimethyl acetamide to give a final con-entration of 0.08 g.ml−1. The reaction mixture was sonicated in

waterbath until a clear homogenous casting suspension wasbtained. For thin film preparation, 2 �l aliquot of the solution wasrop coated onto a Pt electrode with a micropipette. Freestand-

ng films were cast by swirling the solution in a glass beaker in theresence of 0.5 M H2SO4 to obtain a homogenous film. The film washen rinsed thoroughly with deionised water and left to dry for ateast 24 hrs.

.2. Synthesis of Nanoparticles

For 1 M cobalt solution, cobalt salt (CoCl2.6H2O) was dissolvedn ethanol to form a dark blue solution. A mixture of 0.5 M sodiumorohydride and 0.2 M of sodium hydroxide was added to the 3 mlf the dark solution. The reaction mixture was left for 24 hrs to react.he resultant mixture was then centrifuged for 20 min at 14000elative centrifugal force (rcf) and the precipitate was thoroughlyashed with de-ionised water. After centrifuging for a further

0 min, it was rinsed with ethanol and left to dry for 24 hrs in anven [10]. After the precipitate was dry, it was ground with a pestlend mortar until a fine powder was obtained.

Nickel chloride (NiCl2) was dissolved in ethanol to make


solution of 0.1 M. The solution was stirred using a mag-etic stirrer whilst adding 0.025 g of polyvinylpyrollidone (PVP).olyvinylpyrrolidone was used as the protective agent [11]. Bothhe sodium borohydride (0.0757 g) and 0.3 M sodium hydroxide

PRESS Acta xxx (2014) xxx– xxx

were added to the reaction mixture and the reaction reached com-pletion after 2 hrs. The precipitate was collected and washed thesame as cobalt.

The synthesis of silver nanoparticles involved the reduction ofthe AgNO3 with trisodium citrate. Briefly 50 mL of 1 mM AgNO3solution was heated to boiling point in an Erlenmeyer flask. Into thissolution, 5 mL of 1% C6H5O7Na3 was added dropwise. The solutionwas stirred vigorously using a magnetic stirrer and heated until apale yellow colour was observed. The solution was removed fromthe heating surface and stirring continued until it cooled down toroom temperature [12].

Metal nanoparticles that were synthesized were analyzed with aTecnai G2F20 X-Twin MAT 200 kV Field Emission Gun TransmissionElectron microscope. Metal nanoparticle powder samples were dis-persed in ethanol and 2 �l of the well dispersed sample was dropcoated onto a Cu grid.

The scanning electron measurements were carried out usingthe LEO 1450 scanning electronmicroscope. Enhanced images wereobtained using the Zeiss Auriga, High resolution (fegsem) fieldemission gun scanning electron microscope. Samples were coatedfor viewing with carbon to enhance the conductivity of the mem-brane film.

2.3. Preparation of nanocomposite thin films

Polysulfone was dissolved in N, N-dimethyl acetamide (DMAc)and the metal nanoparticle powder was added. The polysulfone wasmodified by adding 10% the cobalt nanoparticles, to the polysulfonesolution and sonicated until a uniform homogenous casting suspen-sion was formed. The same concentration of nickel nanoparticlesolution (10%) was used when preparing a nickel nanocompos-ite solution. 10% of the Ag nanoparticle suspension was dropcoated onto 1 mL of polysulfone casting suspension to form anon-homogenous mixture. The dried polysulfone and Ag nanopar-ticle film was re-dissolved in 2 mL of N,N- dimethyl acetamide,to improve homogeneity and recast as thin film for voltammetrystudies.

The nanocomposite thin film solutions were drop coated ontoglass microscope slides for Raman analysis. The SEM analysis wasdone on the powder samples and the HRTEM, on nanoparticle sus-pensions in ethanol. Freestanding membrane films were preparedby casting the nanoparticle polysulfone solutions in the presenceof 0.5 M H2SO4 and leaving it to dry. Using the Sessile drop method,a drop of distilled water with a volume of 10 �l was drop coatedonto the membrane surface. The angle that the droplet makeswith the surface of the membrane was measured using KRÜSSDrop Shape analyser and software (Advanced Laboratory Solutions,South Africa). Four measurements were done for each materialand the mean contact angle and standard deviation results werereported.

3. Results and Discussion

3.1. Characterisation of the synthesized nanoparticles

SEM image of the Co nanoparticles showed that the nanopar-ticles were agglomerated which was interpreted as evidence ofincomplete reaction. It was reported that large Van Der Waalsforces and magnetic dipole interactions makes it hard to get iso-lated Co nanocrystals [13]. Cobalt nanoparticles can form threecyrstal structures; the face centered cubic (fcc), hexagonally closedpacked (hcp) and epsilon [14]. The hcp structure is stable at low


temperatures and the fcc structure is stable at higher temperaturesabove 450◦ C [14].

HR-TEM confirmed the Cobalt nanoparticles were predomi-nantly present in the hcp-Co formation with long sides in the


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rder of 50 nm. The Co is known to occur in three valence states0, +2 and +3). Co is more stable as Co (II) than Co (III), the Co0) is the metallic form which occurs in three allotropic forms,igh-coercivity hcp-Co, pseudo-cubic Co, and symmetric low coer-ivity fcc-Co. The intensity of the applied magnetic field required toeduce the magnetization of sample to zero is known as coercivity.oercivity measures the resistance of materials that are ferromag-etic to becoming demagnetized [16]. We expected Co to be presentt zero oxidation state with diameter in the nanometer range. TheDX spectrum of the Co shows the presence of Co and the Cl, theresence of the Cl is from the CoCl2.6H2O that was in the synthesis.he Cu present is due to the grid that was used to drop coat the Coanoparticles onto.

The UV-vis spectrum of the Co nanoparticles does not show anbsorbance which can be due to an incomplete reduction of theoCl2.6H2O salt. In literature cobalt nanoparticles usually absorbround 500 nm. In 2008 Zhang and Lan, prepared cobalt nanoparti-les using a laser beam method, the absorption of Co nanoparticlesas at 510 nm [17]. UV-vis absorption spectra of as synthesized

obalt colloids in ethanol showed no absorption peak, which con-rms the formation of pure cobalt nanoparticles in ethanol solutionnd it suggests that no oxidation occurs under the protection ofthanol solution. Therefore, ethanol is proposed to be an optimalubstitute of water for fabricating pure cobalt colloids. The UV-visbsorption spectra of cobalt colloids synthesized in double dis-illed water, there are two absorption peaks. One absorption peak at14 nm and 388 nm are due to the oxidation of cobalt nanoparticles18–20]

The SEM image of the Ni nanoparticles, shows the particles toxhibit a cubic shape, which was also confirmed by TEM of Nianoparticles.

The TEM image of the Ni nanoparticles confirms a cubic shape,avouring the face centered cubic crystalline form of Ni nanopar-icle. The dimensions of the cubic nanoparticles were observed toe approximately 5 nm on either face. The Ni(II) forms complexesith three different geometries i.e. tetrahedral, octahedral and

quare planar. Strong field ligands with Ni(II) forms square planaromplexes and the weak ligands forms tetrahedral complexes. Nianoparticles are useful in catalysis, conducting inks and magneticaterials. The EDX spectrum of the Ni nanoparticles confirms the

resence of nickel nanoparticles, with energy lines in the region of–9 keV which are the K lines and also in the region of 0.8–1 keV


hich are the L lines [21].The nickel nanoparticles showed absorbance at 210 nm in the

V-vis spectrum. Meftah, synthesized nickel nanoparticles by dis-olving NiCl2 salt in water and PVP was also added to the reaction

Fig. 2. (a) TEM image insert showing hcp structur

Fig. 1. SEM image of Co nanoparticles.

mixture. The nickel nanoparticles showed absorbance at 395 nm,the band was due to the electronic transitions from highly occupiedelectron orbital to the unoccupied electron orbital [22].

Ag nanoparticles produced were found to be well dispersed andnon-agglomerated with an average diameter of 40-70 nm. Atomiclattice fringes were observed on the nanoparticles demonstratingthe crystalline nature of the nanoparticles. The non-aggregationof the nanoparticles can be attributed to the electrostatic repul-sion of negatively charged sodium citrate molecules which wereadsorbed on the surface of the nanoparticles. The different shapedistribution ranging from spherical, cubic, hexagonal and rods isevident in the TEM. From the elemental analysis, the presence ofAg is confirmed as well as Na from the reducing agent that was usedto reduce AgNO3 to Ag nanoparticles.

Figs. 1–7The UV-VIS characterisation of Ag nanoparticle was done and a

major absorption band at 420 nm was observed. Ag nanoparticleswere synthesized and absorbed at 413 nm. The shift in absorbanceis due to the morphology of the nanoparticle and also size playsa role in the absorbance of nanoparticles [23]. Different shapes ofsilver nanocrystals possess a unique optical scattering response.Highly symmetric spherical particles exhibit single scattering peak,anisotropic shapes such as triangular, cubes and prisms exhibitmultiple scattering peaks in the visible wavelength due to highly


localized charge polarization [24]. The UV-VIS of metallic Ag0 isin the range of 250 nm to 330 nm. From (Fig. 8) three absorptionpeaks were observed at 275 nm, 346 nm and at 420 nm which are

e and (b) EDX spectrum of Co nanoparticles.


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Fig. 3. UV-VIS of Co nanoparticles.

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ig. 4. SEM image of Ni nanoparticles. The insert shows cubic Ni nanoparticles.

ndication of a mixture of shapes and sizes in the nanoparticles pro-uced. When the particle size is above 10 nm the absorption bandhifts to longer wavelength because of the high magnetic-dipoleoment appear for larger radii particles [25].Crystal lattice is a systematic arrangement of atoms that are


ound in crystals with the exception of amorphous solids andases. A unit cell is the smallest component of the crystal latticend illustrates the arrangement of atoms in a crystal. The unitell is characterized by its lattice parameters which consist of the

Fig. 5. (a) TEM image insert showing cubic Ni struct

Fig. 6. UV-VIS of Ni nanoparticles.

length of the cell edges and the angles between them. The latticeconstant and also known as lattice parameter refers to the con-stant distance between unit cells in a crystal lattice. The latticesin three dimensions generally have three lattice constants: a, b,and c. In case of cubic crystal structures, all of the constants areequal and referred only as a. However, in case of hexagonal crys-tal structures, the a and b constants are equal, and only refered toas a and c constants [26]. Ni nanoparticles are known to favour acubic close packed arrangement (or fcc) whereas Co nanoparti-cles favour a hexagonal closed packing (hcp) arrangement [11–27].However the packing efficiency of both these packing arrange-ments are high (74%) with co-ordination number of 12. In a fccunit cell the atoms touch along the face diagonals and the latticeparameter may be calculated from equation 1 as follows:

4r = a(2)½ (1)

Where r, is the radius of Ni = 0.1246 nmFor the hcp close packing arrangement, the lattice paramters

a (=b) and c may be calculated from the radius as follows usingequations 2 and 3:

a = 2r (2)

and


2a = [(a/√

3)2 + (c/2)2]

½(3)

where r is the radius of Co = 0.1253 nm [26,27]

ure and (b) EDX spectrum of Ni nanoparticles.




L. Phelane et al. / Electrochimica Acta xxx (2014) xxx– xxx 5

Fig. 7. (a) TEM image and (b) EDX s

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Fig. 8. UV-VIS of AgNPs.

The lattice parameters for Co and Ni nanoparticles werealcuated based on unit cell dimensions identified from TEM mea-urements (Table 1)

From the above table, it is clear that the metal nanoparticleize and close packing arrangement direct the shape and size ofore formation. Nickel nanoparticles with the smallest particle sizeroduced the smallest pore size in the modified polysulfone mem-rane, followed by Co nanoparticles. The irregular shape and sizeistribution observed for Ag nanoparticle formation, produced aembrane with very large pores.

.2. Scanning Electron Microscopy results of prepared


olysulfone thin films

SEM is an imaging technique that utilizes a high-energy beamf electrons to produce a raster scan pattern. The electrons interact

able 1able showing the particle size of the metal nanoparticles, pore size of the modified

embrane and also showing the lattice constant of the nanoparticle.

MetalNanoparticle

Nanoparticlesize (nm)

Membranepore size (�m)

Lattice parametera, b, c (nm)

Cobalt h= b = 50, l= 100 2–8 a= 0.2506b= 0.0832

Nickel l= 5 0.5–1.5 a= 0.2492Silver 40 - 70 10 - 16 -

pectrum of Ag nanoparticles.

with the atoms that make up the sample producing signals thatcontain information about the sample’s surface topography, com-position and the morphology. Polysulfone and metal nanoparticleswere drop coated onto a glass slide to produce a membrane thinfilm for microscopy evaluation.

SEM of polysulfone shows a highly branched network struc-tures. The elemental analysis spectrum of the unmodified PSFconfirms an abundance of sulfur associated with the sulphonegroups of the polymer. The SEM image of PSF/Co showed a uni-form distribution of pores, with size ranging from 1.75 -7.88 �m. A3D honey comb structure was observed for PSF/Co and the energydispersive spectroscopy (EDS) confirmed that the Co nanoparti-cles were incorporated to the PSF casting suspension as indicatedby the spectral band in the range of 6.8 keV to 7.6 keV. SEM ofPSF/Ni showed very small pores uniformly distributed throughoutthe cast film. The Ni nanoparticle spectral band was observed in therange of 7.4 keV to 8.2 keV from EDS measurements. SEM of PSF/Agshowed a uniform distribution of pores, with pore sizes rangingfrom 10.73–15. 88 �m.

3.3. Contact Angle measurements

Contact angle measurements evaluate the angle between awater droplet and the flat membrane surface and provide an indi-cation of the hydrophilicity (0-90◦) or hydrophobicity (> 90◦) ofthe membrane. A decrease in contact angle of the surface withwater was used as an indication of improvement in the hydrophilicproperty of the membrane. In contact angle measurement for ahydrophilic membrane the contact angle should be 0 degrees,although the value is purely theoretical [28].

The table shows PSF/Co to be the most hydrophilic membranewhen compared to PSF/Ni and PSF/Ag, whereas the unmodifiedpolysulfone membrane shows higher contact angle value. However


the introduction of Co, Ni and Ag nanoparticles were observed toreduce the contact angle significantly, compared to unmodified PSF.

Table 2

Table 2Contact angle measurements of the polysulfone membrane unmodified and themodified polysulfones and the standard deviation.

Membrane material Contact angle (degrees)

Polysulfone 87.5 ± 25.2Polysulfone/Co 31.7 ± 7.7Polysulfone/Ni 46.2 ± 8.5Polysulfone/Ag 49.5 ± 3.8


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.4. RAMAN Results

In preparing for the RAMAN measurements, the PSF casting solu-ion was drop coated on a glass slide and left to dry. All the modifiedasting suspensions were prepared the same as the unmodified PSF.

The Raman spectrum of unmodified polysulfone showed a peakt 1457 cm−1 which is an indication of the aromatic ring. The Ramanpectrum of PSF/Co exhibits a new peak that was not observed inA). The peak at 1139 cm−1 was due to the symmetric C-O-C stretch-ng mode, the peak at 1450 cm−1 indicated an aromatic ring. Theeak at 1590 cm−1 was due to the in-plane benzene ring vibration.

t was reported that CoNPs were used to coat graphitic carbon (C-oNPs). The Raman spectra of C-CoNPs, showed two major peaksentred at 1321 cm−1(D peak) and the other peak at 1586 cm−1 (Geak). The signal provided by the graphitic layers that are presentround the Co nanoparticles [29]. Cobalt nanocrystals were syn-hesized and coated onto a graphite carbon. The Raman spectraf the prepared samples before and after acid titration were illus-rated. Huang reported that there was a peak at 700 cm−1 that wasbserved in the spectrum which is due to uncoated cobalt nanopar-


icles [30]. After months of the carbon coated cobalt nanoparticlesn the acid, from the Raman a peak from 1582 cm−1 -1603 cm−1 andhe other from 1342 cm−1–1320 cm−1 were observed to be broader.he peak intensities were reversed, indicating that the carbon shell

ig. 9. SEM images of (A) unmodified polysulfone (scale 2 �m), (B) polysulfone modified wscale 2 �m) and (D) polysulfone modified with Ag nanoparticles (scale 20 �m).


surrounding cobalt nanoparticles became more disorded insteadof exhibiting the expected acid catalytic graphitization [29–32].The Raman spectrum of PSF/Ni exhibited a similar peak that wasobserved for PSF/Co at 1141 cm−1 which indicated the symmet-ric C-O-C stretching mode and the in-plane benzene ring vibrationpeak at 1453 cm−1. The PSF/Ag behaved similar to the PSF having 3peaks, the peak at 1455 cm−1 which is an indication of an aromaticring and the in-plane benzene ring vibration peak at 1524 cm−1.

3.5. Cyclic Voltammetry

Cyclic voltammetry (CV) and Square Wave voltammetry (SWV)were done to evaluate the interfacial kinetics of PSF, PSF/Co, PSF/Niand PSF/Ag thin films in aqueous medium. The polymer solutionswere drop coated onto a Pt working electrode. The drop coated Ptelectrode formed the working electrode in a three electrode cellarrangement with 3 mL 0.1 M HCl as the electrolyte. Voltammet-ric experiments were recorded with BASi Epsilon electrochemicalwork station (LG Fayette) using the conventional three-electrodesystem. A Pt wire (diameter 1.0 mm) and Ag/AgCl (3 M NaCl)) elec-


trode (Bioanalytical Systems Ltd., UK were used as counter andreference electrodes, respectively, in the electrochemical evalua-tion. Alumina micro-polish (1.0, 0.3 and 0.05 mm alumina slurries)and polishing pads (Buehler, IL, USA) were used for polishing the

ith Co nanoparticles (scale 10 �m), (C) polysulfone modified with Ni nanoparticles


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lectrode. The potential window ranged from -200 mV to 1500 mVvs Ag/AgCl).

The CV of all the membranes films were done at different scanates in 0.1 M HCl. The CV graphs did not show any new peaks otherhan the peaks that were due to the Pt bare electrode. From theyclic voltammetry at different scan rates, the diffusion coefficientas calculated for each thin film prepared, based on the Randles

evcik treatment of data, where a plot of peak current vs squareoot of scan rate produces a linear plot for diffusion controlledystems. The regression coefficient for anodic and cathodic peakurrent responses ranged from 0.8960 to 0.9991. The higher lin-ar regression coefficient observed for cathodic current responsendicates that the system favours reduction.

Figs. 9–11The square wave (Fig. 12) of the unmodified polysulfone thin

lm and the modified polysulfone with metal nanoparticles werevaluated in terms of their response current. The polysulfone mod-fied with cobalt nanoparticles showed to have higher conductivityhan the polysulfone modified with nickel nanoparticles and thenmodified polysulfone thin film. Cobalt is more conductive thanickel with silver being the most conductive metal, based on peakurrent measurement from SWV [33].

Diffusivity or diffusion coefficient is related to the molar fluxue to molecular diffusion and the gradient in the concentration


f the species (or the driving force for diffusion) as a proportionalonstant. Diffusion coefficient may be related to the efficiency ofransport of ions, electrons and small molecules (under mass trans-ort control) to and through a membrane. Diffusion in the absence

ig. 10. Raman spectrum of (A) unmodified polysulfone, (B) polysulfone modified with Coodified with Ag nanoparticles.

PRESS Acta xxx (2014) xxx– xxx 7

of an analyte molecule was used to assess the electron mobility tothe polymer surface in aqueous solution (Table 3).

PSF/Ni showed to have highest diffusion coefficient when com-pared to PSF unmodified membrane, PSF/Co and PSF/Ag. Thehighest value of diffusion coefficient observed for PSF/Ni corre-lates well with the drastically reduced contact angle indicating thatthe hydrophobic nature of the interface plays a role in diffusionprocesses at the interface.

Electrochemical impedance spectroscopy (EIS) was done at afixed frequency of 10 Hz in the presence of tannic acid and alginicacid, which were selected as model compounds for fouling analy-sis. The low frequency impedance of PSF materials in the presenceof a fixed concentration of the analyte was measured at very lowpotentials. The low frequency range was chosen to represent thearea where diffusion behaviour could be best observed and the lowpotentials were chosen to avoid electrochemical induced analyticalbehaviour. The data was modelled as a simple Randles circuit andthe capacitance behaviour over time was evaluated. In each case,an initial change in impedance was observed but after a certaintime the impedance stabilised. The slope of the capacitance changewas evaluated in terms of sensitivity to the analyte chemistry andthe stabilisation of the slope (time) was evaluated as the onset offouling (Table 4).

The measured cut off times indicated that unmodified polysul-


fone became fouled in the shortest time and that PSF/Co and PSF/Nishowed an approximate 50% improvement in fouling performancedue to the improved hydrophilicity of the metal nanoparticle mod-ification.

nanoparticles, (C) polysulfone modified with Ni nanoparticles and (D) polysulfone


Please cite this article in press as: L. Phelane, et al., Polysulfone Nanocomposite Membranes with improved hydrophilicity, Electrochim. Acta(2014), http://dx.doi.org/10.1016/j.electacta.2013.11.156



8 L. Phelane et al. / Electrochimica Acta xxx (2014) xxx– xxx

Fig. 11. Scan rate dependent CV of (a) PSF unmdofied membrane, (b) PSF/Co, (c) PSF/Ni and (d) PSF/Ag in the presence of 0.1 M HCl.

Fig. 12. Comparative SWV of unmodified polysulfone with modified polysulfone with metal nanoparticles (a) oxidation and (b) reduction..

Table 3Table of results showing the diffusion coefficient and the Formal potential of the unmodified PSF and modified PSF.

Membrane Diffusion Coefficient (cm2/s) (Oxidation) Diffusion Coefficient (cm2/s) (Reduction) Formal Potential (V)

Polysulfone 2.671 × 10−3 3.276 × 10−3 1.16Polysulfone/CoNPs 1.182 × 10−3 1.182 × 10−3 1.20Polysulfone/NiNPs 2.812 × 10−1 3.081 × 10−3 1.21Polysulfone/AgNPs 8.557 × 10−2 3.327 × 10−3 1.15




L. Phelane et al. / Electrochimica Acta xxx (2014) xxx– xxx 9

Table 4Capacitance evaluation of polysulfone membranes in the presence of analyte.

Material Slope (F/m) Standard Deviation (F/m) Cut-off time (m)

Polysulfone Alginic acid 3.25 × 10−9

Tannic acid 6.31 × 10−95.68 × 10−9

1.80 × 10−92035

Polysulfone/Co Alginic acid 1.80 × 10−9

−94.32 × 10−9

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Tannic acid 2.07 × 10Polysulfone/Ni Alginic acid 7.53 × 10−9

Tannic acid 3.49 × 10−9

. Conclusions

Three nanocomposites of polysulfone thin films were pre-ared and characterized using voltammetry, contact angle andicroscopy.The SEM, TEM and EDS confirmed the synthesis of metal

anoparticles and their size distribution. The face centred cubiclose packing arrangement was favoured by Ni nanoparticlehereas the hexagonally close packing was preferred for Coanoparticles. The particle size was most clearly determined byEM which confirmed Ni nanoparticles to have side lengths of 5 nmnd Co nanoparticles to have long sides equal to 20 nm. The TEMmage of Ag nanoparticles showed the nanoparticles to be well dis-ersed and non-agglomerated with the average size of 40–70 �m.

n comparing the SEM images of the modified polysulfone mem-rane with the metal and the unmodified polysulfone, the PSF/Aganocomposite showed largest pores than the PSF/Co and PSF/Ni,

ollowed by the PSF/Co and the PSF/Ni showed smallest pores.Cyclic voltammetry evaluation showed that PSF/Ni in aqueous

edium had the highest diffusion coefficient when compared tother polysulfone thin films prepared. The PSF/Ni was also observedo have the smallest particle size and smallest pore size comparedo other polysulfone membranes prepared. These results indicatedhat the pore size distribution influence the hydrophobic naturef the membrane as well as the diffusion behaviour at the mem-rane interface. It also proved that diffusion coefficient may be useds an indication of hydrophilicity of the membrane for aqueousystems.

Contact angle measurements confirmed that when the polysul-one was modified with metal nanoparticles the hydrophilicity ofhe unmodified polysulfone was improved. The contact angle ofhe unmodified polysulfone membrane was 87.5◦ and when theSF was modified with metal nanoparticles the contact angle wasecreased to below 50◦. PSF/Co membrane showed to be the mostydrophilic followed by PSF/Ni and PSF/Ag, and unmodified PSFeing the least hydrophilic of the prepared membranes. Howeverhe 50% reduction applied to all metal nanoparticle modified poly-ulfone materials and the variability due to individual metal usedas clearly seen in the pore shape and size distribution. Electro-

hemical impedance spectroscopy evaluated at low frequency andow potential provided evidence of reduced fouling behaviour of Nind Co nanoparticle modified polysulfone materials.

cknowledgements

We would like to acknowledge the financial assistance ofational Research Foundation (NRF), Water Research Commission

WRC) and University of the Western Cape (UWC) in South Africa.

eferences


[1] A.I. Schafer, A.G. Fane, T.D. Waite, Nanofiltration: Principle and Application.,Elsevier Ltd, Oxford, 2005.

[2] A. Asatekin, S. Kang, Me Elimelech, A.M. Mayes, Anti-fouling ultrafiltra-tion membranes containing polyacrylonitrile-graft-poly(ethylene oxide) combcopolymer additives, Journal of Membrane Science 298 (2007) 136–146.

[

[

93 × 10 452 × 10−9

55 × 10−84050

[3] M.F.A Goosen, S.S. Sablani, H. Ai-Hinai, S. Ai-Obeidani, R. Al-Belushi, D. Jackson,Fouling of reverse osmosis and ultrafiltration membranes: a critical review Sep,Sci. Technol. 39 (2004) 2261–2297.

[4] E.F. Castro Vidaurre, C.A. Achete, F. Gallo, D. Garcia, R. Simão, A.C. Habert, SurfaceModification of Polymeric Materials by Plasma Treatment, Materials Research,Materials Research 5 (2002) 37–41.

[5] G.J. Summers, M.P. Ndawuni, C.A. Summers, Chemical modification of poly-sulfone: anionic synthesis of dipyridyl functionalized polysulfone, Polymer 42(2001) 397–402.

[6] S. Chowdhury, P. Roy, P.K. Kumar, A. Bhattacharya, Kumar Separation char-acteristics of modified polysulfone ultrafiltration membranes using NOx,Separation/Purification Technology 24 (2001) 271–282.

[7] S. Vico, B. Palys, C. Buess-Herman, Hydration of a Polysulfone Membrane Stud-ied by Vibrational Spectroscopy, Langmuir 19 (2003) 3282–3287.

[8] N. Maximous, G. Nakhla, W. Wan, K. Wong, Performance of a Novel ZrO2/PESMembrane for Wastewater Filtration, Journal of Membrane Science 352 (2010)222–230.

[9] J. Kim, B. Van der Bruggen, The Use of Nanoparticles in Polymeric andCeramic Membrane Structures: Review of Manufacturing Procedures and Per-formance Improvement for Water Treatment, Environmental Pollution 158(2010) 2335–2349.

10] F. Guo, H. Zheng, Zhiping Yang, Yitai Qian, Synthesis of cobalt nanoparticlesin ethanol hydrazine alkaline system (EHAS) at room temperature, Materialsletters 56 (2002) 906–909.

11] Wu Szu-Han, Chen Dong-Hwang, Synthesis and characterization of nickelnanoparticles by hydrazine reduction in ethylene glycol, Journal of Colloid andInterface Science 259 (2003) 282–286.

12] Mailu Stephen N, Waryo Tesfaye T, Ndangili Peter M, Ngece Fanelwa R, BalegAbd A, Priscilla G. Baker and Emmanuel I. Iwuoha, Determination of Anthraceneon Ag-Au Alloy Nanoparticles/Overoxidized-Polypyrrole Composite ModifiedGlassy Carbon Electrodes, Sensors 10 (2010) 9449-9465.

13] F. Puntes Victor, A. Kannan Krishnanb, Paul Alivisatosa, Synthesis of colloidalcobalt nanoparticles with controlled size and shapes, Topics in Catalysis 19(2002) 145–148.

14] Nisha Shukla, B. Erik, Svedberg, A.J. John Ell, Roy Surfactant effects on the shapesof cobalt nanoparticles, Materials Letters 60 (2006) 1950–1955.

15] Vıctor A. de la Pena O’Shea, Pilar Ramırez de la Piscina, Narcis Homs, GuillemAromı, and Jose L, G. Fierro, Chem. Mater 2 (1) (2009) 5637–5643.

16] Salazar-AlVarez, Enhanced Coercivity in Co-Rich Near-Stoichiometric CoxFe3-xO4 + ä Nanoparticles Prepared in Large Batches, Chem. Mater 19 (2007)4957–4963.

17] J. Zhang, C.Q. Lan, Nickel and cobalt nanoparticles produced by laser ablationof solids in organic solution, Materials Letters 62 (2008) 1521–1524.

18] M. Srisudha, K. Karthik, S. Ponnuswamy, Synthesis of Nickel NanoparticlesUsing Polyol Process, Nano Vision 3 (2013) 37–43.

19] B. K. Pandey, R. Gopal, Study of Magnetic colloids in different liquid media.20] C. Petit, M.P. Pileni, J. Magn, Self-Organization of Magnetic Nanosized.Cobalt

Particles, Magn. Mater. 166 (1997) 82.21] S. Kapoor, H.G. Salunke, B.M. Pande, S.K. Kulshreshtha, J.P. Mittal, Radiolytic

preparation and catalytic properties of platinum nanoparticles Mater, Res. Bull.33 (1998) 1555.

22] Meftah Abdo Mohd, Saion Elias, Mohd Maarof B Hj Abd Moksin and Hishamud-din B Zainuddin, Absorbance of Nickel nanoparticle/Polyaniline CompositeFilms Prepared by Radiation Technique, Solid State Science and Technology17 (2009) 167-174.

23] Houjin Huang, Shihe Yang, Gang Gu, J. Phys. Chem B 102 (1998) 3420–3424.24] L. Baia, S. Simon, UV-VIS and TEM assessment of morphological features of

silver nanoparticles from phosphate glass matrices, Modern Research and Edu-cational Topics in Microscopy (2007).

25] Mudar A. Abdulsattar, Ab initio large unit cell calculations of the electronicstructure of diamond nanocrystals, Solid State Sci. 13 (2011) 843–849.

26] Yoshichiko Bandu, Takahito Terashima, Preparation and Coercivity of Cobaltultrafine particles by reduction of multilayered CoO-SiO films, Bull. Chem. Soc59 (1986) 607–612.

27] V. Matveev Vladimir, A. Baranov Dmitry, Yurkov Gleb Yu, G. Akatiev Nikita,P. Dotsenko Ivan, P. Gubin Sergey, Cobalt nanoparticles with preferential hcpstructure: A confirmation by X-ray diffraction and NMR, Chemical Physics Let-ters 422 (2006) 402–405.


28] J. Mulder, Basic Principles of Membrane Technology, 2nd Edition, Kluwer Aca-demic Publishers, Dordrecht, 1996, pp. p584.

29] R. Chemnnamsetty, Is Escobar, X. Xu, Characterization of commercial watertreatment membrane modified via ion beam irradiation, Desalinisation 188(2006) 203–212.


http://refhub.elsevier.com/S0013-4686(13)02391-8/sbref0005


































































































































































































































































































































































































































































































































































































































































ING Model

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1 imica

[

[


0 L. Phelane et al. / Electroch


30] J.Y. Huang, Y. K Wu, Q. Ye H, Phase transformation of cobalt induced by ballmilling, Appl. Phys. Lett. 66 (1995) 308.

31] Y. Zhou, X. Xing, Z. Liu, L. Cui, A. Yu, Q. Feng, H. Yang, Enhanced coagulation offerric chloride aided by tannic acid for phosphorus removal from wastewater,Chemosphere 72 (2008) 290–298.

[

[



32] Z. Lijun, L. Xiaoming, Room-temperature synthesis of air-stable cobalt nanopar-ticles and their high-efficient adsorption ability for Congo red, ElectronicSupplementary Material (ESI) for RSC Advances (2012).

33] Paul Tipler (2004). Physics for Scientists and Engineers: Electricity, Magnetism,Light, and Elementary Modern Physics (5th ed.). W. H. Freeman.





















































































polysulfone nanocomposite membranes with improved hydrophilicity

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