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polyethylene glycol 300 membrane for reverse osmosis using MgSO4 solution
Accepted Manuscript Title: Conjugation of silica nano particles with cellulose acetate/polyethylene glycol 300 membrane for reverse osmosis using MgSO4 solution Author: Aneela Sabir Muhammad Shafiq Atif Islam Faiza Jabeen Amir Shafeeq Adnan Ahmad Muhammad Taqi Zahid Butt Karl. I. Jacob Tahir Jamil PII: DOI: Reference:
S0144-8617(15)00898-X http://dx.doi.org/doi:10.1016/j.carbpol.2015.09.042 CARP 10344
To appear in: Received date: Revised date: Accepted date:
19-6-2015 11-9-2015 12-9-2015
Please cite this article as: Sabir, A., Shafiq, M., Islam, A., Jabeen, F., Shafeeq, A., Ahmad, A., Butt, M. T. Z., Jacob, Kl. I., and Jamil, T.,Conjugation of silica nano particles with cellulose acetate/polyethylene glycol 300 membrane for reverse osmosis using MgSO4 solution, Carbohydrate Polymers (2015), http://dx.doi.org/10.1016/j.carbpol.2015.09.042 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
Conjugation of silicanano particles with cellulose acetate/polyethylene glycol
2
300 membrane for reverse osmosisusing MgSO4solution 2∗
Aneela Sabir1,
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Ahmad2, Muhammad Taqi Zahid Butt4, Karl. I. Jacob1,Tahir Jamil2
30332, USA. 2
Pakistan. 3
54590 Pakistan. 4
Faculty of Engineering and Technology, University of the Punjab, Lahore, 54590 Pakistan.
M
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Institute of Chemical Engineering and Technology (ICET), University of the Punjab, Lahore,
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Highlights
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Department of Polymer Engineering and Technology, University of the Punjab, Lahore, 54590
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School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA
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, Muhammad Shafiq2, Atif Islam2, Faiza Jabeen2, Amir Shafeeq3, Adnan
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Conjugation of Silica nanoparticle(SNPs) with polymer matrix (PM)madeby dissolution casting
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SEM micrographs of PM-SNPs showed uniform dispersed dense structured membranes
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PM-SNPs composite membranes improved MgSO4salt rejection properties up to 95%
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Thermal properties augmented PM-SNPs composite membrane compared to PM membrane
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Abstract
∗
Corresponding author: Aneela Sabir; Email: [email protected], Phone: +1 (404) 933-9732
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Thermally-induced phase separation (TIPS) method was usedto synthesize polymer matrix (PM)
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membranesfor
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conjugated with silica nanoparticles(SNPs).Experimental data showed that the conjugation of
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SNPs changed the surface properties as dense and asymmetric composite structure.The results
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were explicitly determined by the permeability flux and salt rejection efficiency of the PM-SNPs
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membranes.The effect of SNPs conjugation on MgSO4salt rejection wasmore significant in
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magnitude than on permeation flux i.e. 2.38L/m2.h.FTIR verified that SNPswere successfully
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conjugated on the surface of PM membrane.DSC of PM-SNPsshows an improved Tgfrom 76.2 to
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101.8 ̊ C for PM and PM-S4 respectively. Thermal stability of the PM-SNPs membranes was
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observed by TGA which wassignificantly enhanced with the conjugation of SNPs.The
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micrographs of SEM and AFM showed the morphological changesand increase in the valley and
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ridges on membrane surface. Experimental data showed that the PM-S4(0.4wt%SNPs)membrane
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has maximum salt rejection capacity and was selected as an optimal membrane.
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Keyword: Polymer Matrix, Silica nanoparticles, Reverse osmosis, MgSO4 salt solution
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1. Introduction:
osmosis
fromcellulose
acetate/polyethylene
glycol(CA/PEG300)
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Purification of MgSO4salt from water usingreverse osmosis (RO) membranes has become
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a progressively essential process to address the reduction of worldwide fresh water resources
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(Greenlee, Lawler et al. 2009; Drioli and Giorno 2010). Despite the fact that other minor
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monovalent ions like NaCl are present in the seawater, MgSO4 is the second most abundant
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element and the one that has the second highest concentration in sea water(Lee, Arnot et al.
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2011). For salt rejection membrane process is widely applied in many areas of the manufacturing
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industries including water desalination, oil–water separation, production of beverages, ultra-pure
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water production, electro-coat paint recovery etc. Membrane based separation hasgained more
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significance than the other separation processes owing to its low energy demand in addition to
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the absence (or highly reduced)ofhazardous chemicals(Cheryan 1998; Arthanareeswaran,
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Sriyamuna Devi et al. 2008).
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CA is generally very imperative and relatively inexpensive polymer used for RO
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membranes compared with other desalination techniques such as membrane distillation and
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hybrid membrane technology(Wu, Kong et al. 1992; Su, Yang et al. 2010; Zhang, Wang et al.
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2010; Sabir, Shafiq et al. 2015). Generally, CA is one of the best membrane constituents of RO,
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ultrafiltration (UF) and gas permeation(Kutowy and Sourirajan 1975; Kunst, Škevin et al.
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1976).Itis generally inaptfor RO application owing to its properties such asdiminished chlorine
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resistance, temperaturesensitivity and has poor mechanical strength(Jean-Pierre, Christian et al.).
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In order to overcome these deficiencies, CA is blended with other polymers like PEG,
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polyamide, polyvinyl alcohol to improve the performance of themembranes(Sajitha, Mahendran
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et al. 2002; Shashidhara, Guruprasad et al. 2002; Arthanareeswaran, Srinivasan et al. 2004;
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Chen, Deng et al. 2004; Mahendran, Malaisamy et al. 2004). The membranes produced from the
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blended polymers exhibited improved properties by assortment of organic polymer with
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inorganic materials like alumina, silica, zirconia, titania than with sole polymer (Wara, Francis et
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al. 1995; Castro, Monbouquette et al. 2000; Bottino, Capannelli et al. 2001; Liu, Li et al. 2003;
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Yan, Li et al. 2005; Yang, Zhang et al. 2007). Incorporation of inorganic nanoparticles in the
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membrane are employed to resistfouling, ascribed to enhance hydrophilicity andimproved
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membrane performance in terms of flux ormodification in membrane morphology(Lin, Chang et
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al. 2003; Ma, Wang et al. 2009; Chen, Su et al. 2010; Zavastin, Cretescu et al. 2010; Razmjou,
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Mansouri et al. 2011). It is also predicted that the dispersion and the compatibility of the
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nanoparticles modified the surface of the polymer matrix membrane (Wu, Mansouri et al.
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2013).In this respect, polymer–silica hybrid nanocomposite materials demonstrated outstanding
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mechanical properties, high chemical and thermal stability and large surface area(Boom, Wienk
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et al. 1992; Takahashi, Li et al. 2000; Sabir, Islam et al. 2015).Similarly, the use of a hydrophilic
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polymerlikePEG along with inorganic particlesisused to get desirable properties for membranes.
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The objective of thepresentarticleis to study the performance of newly synthesized
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environmentally benign polymer matrix (CA/PEG300) RO membranes conjugated with SNPs for
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filtering out MgSO4. These novel membranes are studied on a RO pilot plantfabricated in
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Pakistan to achieveimproved performance of themembranes such as permeation flux, percent
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water content and salt (MgSO4) rejection. It is an initiative towards the fabrication and
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development of membranes in Pakistan for filtration plants, as necessity of drinkable water is
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becoming difficult in many area of the country. An initial assessment of the membranes and the
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effect of conjugated SNPs on the structural chemistry, thermal stability and membrane
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morphology aredetermined using standard characterization techniques; FTIR, DSC/TGA, SEM
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and AFM.
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2. Experimental procedure
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2.1. Materials
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Analytical grade cellulose acetate was obtained from Fluka (USA) and silica
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nanoparticles,having 200 nm particle size,were obtained from Sigma Aldrich. Magnesium
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Sulphate (MgSO4)was obtained from BDH,polyethylene glycol 300 and N, N-dimethyl
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formamide (99%) were obtained from Fluka & Riedel-de Ha n, respectively.All the chemicals
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were used without further purification.
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2.2 Membrane Preparation
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2.2.1 Preparation of CA/PEG300 polymer matrix membrane Six polymer matrix solutions of CA/PEG300 were synthesized usingthermally-induced
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phase separation (TIPS) methodology. Different weight % of CA (Table 1) was dissolved in 100
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mL of DMF solvent with continuous stirring of each solution for 8 h at 80 ̊ C.PEG300 (wt.%
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are given in Table 1) was added to this homogenous solution.The clear and viscous polymer
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matrix solutions obtained were labeled as PM, PM1, PM2and PM3. The solutions were cooled at
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room temperature (25 ̊ C) for an hour.
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Table 1
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Effect of concentration CA/PEG300, SNPs, water content and AFM roughness values of the
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membranes at 6.0 bar(osmotic pressure 0.7095 bar).
Conjugated PM-SNPs
AFM- Roughness values
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Polymer Matrix Membranes
Membrane
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Membrane Type
CA/PEG 300
Water Content (%)
Membrane Type
SNP load
Water Content
(wt.%)
(%)
Membrane Type
Avg. Rough ness Ra (nm)
64.2
PM-S1
0.1
80.8
PM
PM1
75/25
68.7
PM-S2
0.2
83.2
PM-S1
PM2
65/35
75.2
PM-S3
0.3
88.4
PM-S2
PM3
55/45
77.1
PM-S4
0.4
92.1
PM-S5
0.5
46.18 67.3
46.72
56.75
PM-S4
106.14
128.7
PM-S5
131.89
153.04
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PM-S3
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90.2
47.54
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85/15
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PM
Root mean square roughn ess Rms (nm)
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The polymer matrix solutions were spread slowly on glass sheet by maintaining uniform
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thickness with micrometer adjustable film applicator (Ref: 1117/300 sheen instrument). The
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newly casted polymer matrix membranes were promptly cooled to 0̊ C for half an hour to
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induce TIPS, in order to get dense and asymmetric membrane structure. The polymer matrix
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membranes were placed inan oven at 65 ̊ Cfor controlled evaporation and carefully removed
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from glass sheet by using sharp blades after drying(Reuvers and Smolders 1987,Li, Nagai et al.
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1995). The polymer matrix membranes were tested formaximum salt rejection (MgSO4) and PM
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(85/15) was selected for further treatment with SNPsas it hasthe highest MgSO4 rejection rate.
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2.2.3Conjugation of SNPs in Polymer matrix membrane
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Different concentrations of SNPs (0.1-0.5wt.%) asshown in Table 1, were conjugated
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with polymer matrix (CA/PEG300) solution having 85/15 (w/w) and magnetically stirred for 12
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h at 80 ̊ C until homogeneous PM-SNPssolutions were formed. The solutions were casted on a
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clean dried glass plate following the same procedure mentioned in Section 2.2.2. Finally, the
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dried polymer matrix based conjugated membranes were removed from the glass plates and the
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membrane thickness (25-35 µm) was measured by screw gauge. Scheme below shows possible
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interaction between CA/PEG300 and SNPs to form PM-SNPs membranes.
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3. Membrane Characterization
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3.1 Fourier Transform Infrared Spectroscopy FTIR spectra of composite membranes were scanned by IR Prestige-21 (Shimadzu)
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using attenuated total reflectance (ATR) accessory equipped with zinc selenide (ZnSe) crystal.
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The air background of the instrument was run before each sample.The frequency range was from
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4000-600 cm-1 at 120 scans per spectrum.
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3.2 Differential scanning calorimetry / Thermo gravimetric analysis
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DSC/TGA measurement of the membranes was carried out using TA instrument (SDT-
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Q600 thermogravimetric analyzer) at heating rate of 20 ̊ C/min under nitrogen atmosphere (15
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mL/min). Thermal analysis was performed at a temperature program from 30 to 800 ̊ C.
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3.3 Scanning electron microscopy
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The PM and PM-SNPs micrographs of the conjugated membranes were taken on SU-
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1500 Hitachi. The instrument was operated under low vacuum mode to analyze sample without
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any special preparation.
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3.4 Atomic Force Microscope
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The topographical images were obtained using scanningprobe microscope (SPM 9500J3,
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Shimadzu) with tapping mode at room temperature. The scanning area was 5 µm2. The values of
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root mean square (RMS) roughness were derived from AFM images, which were obtained from
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the average of the values measured in random areas. The membrane surface morphology
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expressed in terms of various roughness parameters like mean roughness (Ra) which represents
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the mean value of the surface relative to the center plane. The volumes enclosed by the image
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above and below this plane wereequal and calculated by Equation 1: 9
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(1)
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Where,
is surface relative to the center of plane while Lx and Ly represent dimensions of
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surface in x and y directions, respectively.
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The root mean square average (RMS) of the measured height deviations from the mean surface
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taken within the evaluation area iscalculated by Equation 2:
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3.5 Water Content
(2)
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The membranes samples were dried in an oven for 48 h under vacuum at 75̊ C and then
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weighed. Dried PM and conjugated PM-SNPs membranes (1 g) were placed separately in
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vialsfilled with distilled water (100 mL)at room temperature. The weighed water content (%) of
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the membranes attained after 24 hwascalculatedusing Equation 3:
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(3)
3.6 Reverse Osmosis
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The experimental setup for reverse osmosis used in this study is given in Fig 1. The plate
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and frame module of the membrane was made of stainless steel in a circular chamber. The inlet
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stream of feed water was 0.328 wt% MgSO4(3.28 g MgSO4/L water) at 40 ̊ C. Effective
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membrane area in contact with inlet stream was 154 cm2. Permeate was collectedwithcontinuous
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operation of 8 h. The separation process was measured by the permeation flux “J” (L/m2.h),
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whereas,MgSO4salt rejection (SR %) was done by solving Equations 4 and 5. Permeate and
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retentate was collected from the sampling points after 8 h. System operating pressure was 10
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maintained at 6.0 bar (osmotic pressure 0.7095 bar) during the test using backpressure valve. The
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conductance of permeate was analyzed by using Cyber Scan Waterproof PC 300 Series
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(EUTECH).
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(5)
Where,
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Q= Amount of permeate(L), A= Membrane effective area (m2), t= Time,Cp= Permeate
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conductance (mS/cm) andCf=Feed water conductance (mS/cm).
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4. Results and Discussion
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4.1 Fourier transform infrared spectroscopy
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Spectroscopic
analysis plays an
essential
role in
the
polymeric membrane
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characterization inorder to investigate the incorporated components of the membranes. FTIR
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spectrumsof PM and PM-SNPs membranes are given in Fig. 2. In case of PM membrane, the
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bands at 3414(O-H stretching), 2881and 1435(stretchingand bending of C-H bonds,
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respectively), 1742(-C=O), 1236 (C-O) and902 cm-1(saccharide)bands were observed. Earlier
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likewise results had been reported in the literature(Liu and Bai 2005; AlTaee and Sharif 2011;
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Zafar, Ali et al. 2012). The emergence of new band at 797 cm-1 (symmetric Si-O) in the spectra of all PM-SNPs
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membranes provided a striking evidence for the substitution of SNPs(Semsarzadeh, M.A. and B.
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Ghalei 2013). The characteristic stretching vibrationbandof Si-O- at 1037 cm-1 became wider
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with the conjugation of SNPs. The band broadening canbe explained by the conjugation of SNPs
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and improved interaction between SNPs and PM. With an increase in the amount of SNPs, this
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band became more prominent as noticed in the case of PM-SNP membranes.The carbonyl band
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intensity (1742 cm-1)was shifted slightly towards 1739 cm-1 with SNPs conjugation in the
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polymer matrix, confirmed the H-bonding between -OH and -C=O group (shown in scheme)and
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proposes interactions between –OH groups of silica and -C=O groups of CA. The observed
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feature at 3414 cm-1was due to -OH stretching vibrations from the inter-molecular hydrogen
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bonds shown in schemethat have affinity to decline the force constant and shifting the
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absorbance to lower energy i.e. lower wave number (Costa-Júnior, E. S., E. F. Barbosa-Stancioli,
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et al. 2009). A broad band in the 3650–3200 cm-1 region owed to hydrogen bonded Si-OH
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(silanol) in chains that have H-bonded-OH groups (Innocenzi 2003; Dietrich O. Hummel
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2002).The presenceof new band (797 cm-1) and hydrogen bonded Si-OH band in the spectra of
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SNP conjugated PM membranes confirmed the impregnation of SNP within the PM-SNPs
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membranes.
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4.2 Differential scanning calorimetry/Thermo gravimetric analysis
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4.2.1 Differential scanning calorimetry
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The glass transition temperature (Tg) analyzed by DSC is an indicative of the structure
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and packing of the polymer chain in the membrane. A lower glass transition temperature (Tg)
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indicates that the membrane possessed more free volume having a loose structure(Zou, Wu et al.
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2008). The DSC thermograms of PM-SNPs (PM to PM-S5) with and without differentamount of
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SNPs (0–0.5 wt. %) are shown in Fig. 3(a). Nature of polymeric membrane was interpreted by
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employing Tg as higher Tgreflectedthemore stable structure of the membrane(Fritzsche, A., et al.,
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1990).It was observedthat PM without conjugated SNP exhibited Tg at 76.2 ̊ C while with the
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conjugation of SNPs in PM-S1–PM-S5; it was increased up to 89.6, 92.5, 96.1, 98.9, and 101.8
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̊ C, respectively. This showed that SNP has developed strong interactions with CA/PEG300 as
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the chains become regimented and more packed in nature.
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4.2. Thermogravimetric analysis
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Thermogravimetric analyzer was used to analyzethethermal decomposition properties of
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CA/PEG300 and SNP conjugated PM-SNPs synthesized membranesas shown in Fig.3 (b). Three
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main decomposition steps areshown by each curve of TGA. Thermograms of PM showed that
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the first step took place between 30-250 ̊ C and the decomposition was akin to the volatile
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matter volatilization and/or the evaporation of residual absorbed water. The second step showed
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that deacetylation and major degradation of CA/PEG300 polymer matrix chainsoccurred
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from250-395 ̊ C (Shieh and Chung 1998; Lucena, V. de Alencar et al. 2003). The third
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stepoccurred from395to 800 ̊ C which implied to the carbonization of degraded products to
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residue. Similarly, for all conjugated PM-SNPs membranes, the TGA curve of PM-S5 was
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thermally more stable as compared to the other PM and PM-SNPs; 20 and 70 wt.% loss of PM
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membrane was at 274.72and 363.04 ̊ C which increased up to309.76and 398.4 ̊ C in PM-S5,
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respectively. The results showed that the thermal stability of the SNP conjugated PM-SNPs
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membranes were higher than that of PM membrane exhibiting the improvement in thermal
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properties.
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4.3 Scanning electron microscopy
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The scanning electron micrographs of PM membrane andconjugated PM-SNPs
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membranes with different SNP loadings are shown in Fig.4(a,b).It reflected the dense
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asymmetric morphology of the membranes, with top layer and cross sectional layer revealed that
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the surface morphologies of the membranes were transmuted significantly with the addition of
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SNP. The top surface morphologies (Fig. 4(a))showedthatthemesoporous, nano-size silica
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particles were distributed in the PM-SNPs membranes. The interaction of SNP with polymer
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matrix disrupted the polymeric chains mobility ensuing in the formation of macroscopic
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defects(Arthanareeswaran, Sriyamuna Devi et al. 2008). As the concentration wasincreased, the
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defects of mottled surface were filled with agglomerates of SNPs.
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4.4 Atomic force microscope
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Surface topography of the PM and PM-SNPs membranes were calculated from AFM as
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shown inthe 2-dimensional surface images (Fig. 5). The consistent valley and ridge like structure
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is shown in CA/PEG300 polymer matrix membrane.Morphological improvement in membrane
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structure were generated by the reactive functionalities of polyethylene glycol (-OH group). The
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roughness parameter was increased with increase in valleys and ridges(Yin, Kim et al. 2012).
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The membrane with more roughness and elevated regions provided greater membrane surface
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area and also more active sites were available for adsorption on the membranes(Khulbe, Feng et
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al. 2007).
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The conjugation of different amounts of SNP ensured the roughness in the valleys and
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ridges of the RO membrane. The increase in conjugation of SNP increased the average and root
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mean square roughness (Ra and Rms) of the surface except for PM-S3 as given in Table1. Membrane fouling and the surface roughness were strongly interlinked. It was observed
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that hydrophilic RO membranes with smooth surfaces were less prone to fouling as compared to
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the rougher membranes that accumulated in the “valleys”. In PM-S1 to PM-S4 membranes, there
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was increase in Ra, as compared to PM and showed increased permeation flux. However, the
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particles preferentially of PM-S5rough membranes resulted in “valley clogging” which caused
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decline in permeation flux than in smooth membranes(Elimelech, Xiaohua et al. 1997;
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Vrijenhoek, Hong et al. 2001). The reason acclaimed was a decrease in the electrostatic repulsion
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between SNP and the surface of themembrane, resulting in the experience of greater adhesion
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force in the valley regions(Richard Bowen and Doneva 2000).
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Water content (WC)analysis is the studyof hydrophilicity of the PM-SNPs membranes
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that exhibited a rapid increase in absorbed water content due to the hydrophilic nature of the
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membranes. The WC % of the membrane exhibited the hydrophilic nature of the membrane. WC
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analysis of the membranes attributed to the absorption mechanism caused by the diffusion
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process controlled by the affinity between the polymer chains and water molecules(external
271
media). The hydrophilic nature of PEG300 in the membranes acted as a driving force for
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sorption of water into the polymer membrane matrix. These absorption properties of the
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membranes played an important role in RO performance processes, which affected the
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membranes permeation flux. Equation 3 was used to calculate the water content (%) ofPM
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membrane (without SNPs) i.e. 64.2 % as shown in Table 1. In case of 0.1 wt% of SNPs, the
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water content (%) showed the value of 80.8 %. When SNP contents was0.4 wt%, WC further
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increased to 92.1 %. Whereas, for SNPs with 0.5 wt%,WC wasdeclined to 90.2%.Similar
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increase in WC wasreportedin literature (Lv, C.S., et. al 2007).
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4.6 Reverse osmosis membrane performance test for flux and MgSO4 rejection The permeation flux of PM and all conjugated PM-SNPs membranes were considered at
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a pressure of 6.0 bar(osmotic pressure of feed solution is0.7095 bar)for 8 h. The permeation flux
283
and MgSO4rejectionof polymer matrix PM membranes were measured using Equations 4 and5,
284
respectively and are shown in Fig 6(c) and (d). In these membranes,PM3 showed a determined
285
flux of 2.06L/m2.h, whereas,it exhibited minimum MgSO4 rejection ability of 56%.On the
286
contrary, PM membrane had 72% MgSO4 rejection and has the flux of 1.74L/m2.h.
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The PM3 membrane, with the highest flux, showed reduced salt rejection (%) though PM
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membrane with the lowest permeation flux had a prominent MgSO4 rejection capacity as shown
289
in Fig 6 (c). The solution diffusion model can better elucidate the transport mechanismof the
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membranes. It pragmatically involved three steps: surface sorption, under pressure diffusion into
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dense membrane structure and lastly the desorption phenomenon. PEG300 hydrophilic nature
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acted as driving force for water sorption into the membrane(Burghoff, Lee et al. 1980; Mazid
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1984). Desaltingnature ofCA was a reason that PM had maximum abilityof MgSO4 rejection
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(Chakrabarty, Ghoshal et al. 2008). When membrane pertained to the highest MgSO4 rejection
295
efficiency,the flux at the same time was reduced, limiting to the varying amount of CA and
296
PEG300.
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membranes(Arthanareeswaran, Mohan et al. 2010).PM3 membrane, with highest quantity of
298
PEG300, showed increase in flux, but at the same time detrimental to MgSO4 rejection. This
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might be accredited to the voidformation inmembrane, which permitted the passage of salt with
300
water(Bai, Zhou et al. 2012; Safarpour, Khataee et al. 2015). Moreover, the diffusion rate of
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water molecules was accelerated by the existence of hydrophilic nature of PEG300. The
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tendency of pore formation was increased withincrease in PEG300 content and consequently
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The
hydrophilic
nature
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PEG300
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as
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former
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the
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theenhancement in the permeation flux. It was observed that with increase in transmembrane
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pressure (3.0 - 6.0 bar),the flux was decreased linearly as indicated in Fig. 6(a). Similar results
305
have been shownin the reported data(Pendergast and Hoek 2011). The decrease of permeation
306
flux with time,for PM even at high range pressure was ascribed to the compaction phenomena
307
occurring onthe surface of the membrane as shown in Fig. 6(b). The rearrangement of polymeric
308
chains occurred under pressure because of the compaction phenomena of the membranes
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thatchangesthe membrane structure and decreases the permeation flux.
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PM membrane was further selected for conjugation with SNPon the basis of
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MgSO4rejection. The permeation flux andMgSO4 rejection of conjugated PM-SNPs membranes
312
are depicted in Fig. 6(c) and 6(d).The permeability of PM-SNP membrane was increased with
313
increase in the conjugation of SNP. The permeation flux of conjugated membranes was
314
increasedforPM-S4,but it was decreased in PM-S5. The reason might acclaimed to the
315
agglomeration of SNP in the membrane.PM-S4 membrane has highest flux of 2.38L/m2.h.
316
Similar results have been reported by Yin et al. for silica incorporation in polyamide membranes,
317
which showed that the addition of silica nanoparticles have increased the flux(Yin, Kim et al.
318
2012).The conjugation of silica particles in CA/PEG300 polymer matrix membrane disrupted the
319
packing of polymer chains by forming microporous defects between polymer interface and
320
inorganic particles. The MgSO4 rejection increased from 72 to 95% for PM to PM-S4
321
membranes as a result of incorporation of mesoporous silica nanoparticles(Zou, Vidalis et al.
322
2011).However, a slight decrease in the permeation flux was observed at highest SNPs loading
323
(0.5 wt%). This slight decrease of flux with highest loadingattributed to the agglomeration of
324
SNPs in certain locations which affected the MgSO4 rejection and permeation flux.
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Conclusion FTIR spectra of SNPs conjugated PM membranes confirmed the impregnation of SNPs
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within the PM-SNPs membranes. The thermal stabilityof the SNPs conjugated PM-SNPs
334
membranes were higher than PM membrane.
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The observed trendin water flux and MgSO4 rejectionwasrationalized by viewing the
336
polymer matrix (PM)as a medium for conjugation with SNPs. The crucial common features of
337
PM-S4 membrane showingthe highestMgSO4 rejection could bedue tosurface roughness in the
338
membranes that helped preventing formation of non-selective nanochannels or nanopores, and
339
the presence of hydrogen-bonding affinitythat facilitated transport of water.It was observed that
340
0.1–0.5 wt% conjugation of SNPs into CA/PEG300 PM-SNPs manifestly increased the MgSO4
341
rejection at operating pressure of 6.0 bar (osmotic pressureof feed solution is 0.7095 bar) and at
342
40 ̊ C. Therefore, these resultssuggestedthat the PM-S4 among conjugated PM-SNPs
343
membranes is a promising candidate fornanoscale molecule transport device and water
344
desalination.
345
Acknowledgements
346
The authors express their cordial gratitude to the team of Department of Polymer Engineering
347
and Technology, University of the Punjab, for their co-operation during the execution of this
348
research project.
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References
354 355
AlTaee, A. and A. O. Sharif (2011). "Alternative design to dual stage NF seawater desalination using high rejection brackish water membranes." Desalination273(2–3): 391-397.
ip t
353
356
Arthanareeswaran, G., D. Mohan, et al. (2010). "Preparation, characterization and performance studies of ultrafiltration membranes with polymeric additive." Journal of Membrane Science350(1): 130-138.
360 361 362 363
Arthanareeswaran, G., K. Srinivasan, et al. (2004). "Studies on cellulose acetate and sulfonated poly (ether ether ketone) blend ultrafiltration membranes." European polymer journal40(4): 751762.
364 365 366 367
Arthanareeswaran, G., T. K. Sriyamuna Devi, et al. (2008). "Effect of silica particles on cellulose acetate blend ultrafiltration membranes: Part I." Separation and Purification Technology64(1): 38-47.
368 369 370 371
Bai, H., Y. Zhou, et al. (2012). "The permeability and mechanical properties of cellulose acetate membranes blended with polyethylene glycol 600 for treatment of municipal sewage." Procedia Environmental Sciences16: 346-351.
372 373 374
Boom, R., I. Wienk, et al. (1992). "Microstructures in phase inversion membranes. Part 2. The role of a polymeric additive." Journal of Membrane Science73(2): 277-292.
375 376 377
Bottino, A., G. Capannelli, et al. (2001). "Preparation and properties of novel organic–inorganic porous membranes." Separation and Purification Technology22: 269-275.
378 379 380 381
Burghoff, H. G., K. Lee, et al. (1980). "Characterization of transport across cellulose acetate membranes in the presence of strong solute–membrane interactions." Journal of applied polymer science25(3): 323-347.
382 383 384
Castro, R. P., H. G. Monbouquette, et al. (2000). "Shear-induced permeability changes in a polymer grafted silica membrane." Journal of Membrane Science179(1): 207-220.
385 386 387
Chakrabarty, B., A. Ghoshal, et al. (2008). "Effect of molecular weight of PEG on membrane morphology and transport properties." Journal of Membrane Science309(1): 209-221.
Ac ce pt e
d
M
an
us
cr
357 358 359
388 24
Page 24 of 38
Chen, W., Y. Su, et al. (2010). "In situ generated silica nanoparticles as pore-forming agent for enhanced permeability of cellulose acetate membranes." Journal of Membrane Science348(1): 75-83.
392 393 394 395
Chen, Z., M. Deng, et al. (2004). "Preparation and performance of cellulose acetate/polyethyleneimine blend microfiltration membranes and their applications." Journal of Membrane Science235(1): 73-86.
396 397
Cheryan, M. (1998). Ultrafiltration and microfiltration handbook, CRC press.
398 399
Dietrich O. Hummel (2002). Analysis of Spectrometric Methods, Atlas of Plastic Additives, Springer, Page 46.
cr
ip t
389 390 391
us
400
Drioli, E. and L. Giorno (2010). Comprehensive membrane science and engineering, Newnes.
402 403 404 405
Elimelech, M., Z. Xiaohua, et al. (1997). "Role of membrane surface morphology in colloidal fouling of cellulose acetate and composite aromatic polyamide reverse osmosis membranes." Journal of Membrane Science127(1): 101-109.
406 407 408
Greenlee, L. F., D. F. Lawler, et al. (2009). "Reverse osmosis desalination: Water sources, technology, and today's challenges." Water Research43(9): 2317-2348.
409 410 411
Innocenzi, P. (2003). "Infrared spectroscopy of sol–gel derived silica-based films: a spectramicrostructure overview." Journal of Non-Crystalline Solids316(2–3): 309-319.
412 413
Jean-Pierre, J., G. Christian, et al. "SYNTHETIC POLYMERIC MEMBRANES."
414 415 416
Khulbe, K. C., C. Feng, et al. (2007). Synthetic polymeric membranes: characterization by atomic force microscopy, Springer.
M
d
Ac ce pt e
417
an
401
418
Kunst, B., Đ. Škevin, et al. (1976). "A light‐scattering and membrane formation study on
419
concentrated cellulose acetate solutions." Journal of applied polymer science20(5): 1339-1353.
420 421 422
Kutowy, O. and S. Sourirajan (1975). "Cellulose acetate ultrafiltration membranes." Journal of applied polymer science19(5): 1449-1460.
423 25
Page 25 of 38
Lee, K. P., T. C. Arnot, et al. (2011). "A review of reverse osmosis membrane materials for desalination—Development to date and future potential." Journal of Membrane Science370(1– 2): 1-22.
427 428 429 430
Li, J., K. Nagai, et al. (1995). "Preparation of polyethyleneglycol (PEG) and cellulose acetate (CA) blend membranes and their gas permeabilities." Journal of applied polymer science58(9): 1455-1463.
431 432 433 434
Lin, D.-J., C.-L. Chang, et al. (2003). "Effect of salt additive on the formation of microporous poly (vinylidene fluoride) membranes by phase inversion from LiClO< sub> 4/Water/DMF/PVDF system." Polymer44(2): 413-422.
435 436 437
Liu, C. and R. Bai (2005). "Preparation of chitosan/cellulose acetate blend hollow fibers for adsorptive performance." Journal of Membrane Science267(1–2): 68-77.
438 439 440 441
Liu, S., K. Li, et al. (2003). "Preparation of porous aluminium oxide (Al2O3) hollow fibre membranes by a combined phase-inversion and sintering method." Ceramics International29(8): 875-881.
442 443 444
Lucena, M. d. C. C., A. E. V. de Alencar, et al. (2003). "The effect of additives on the thermal degradation of cellulose acetate." Polymer Degradation and Stability80(1): 149-155.
M
an
us
cr
ip t
424 425 426
Lv, C.S., Yanlei Wang, et al. (2007). “Enhanced permeation performance of cellulose acetate ultrafiltration membrane by incorporation of Pluronic F127”.Journal of Membrane Science,. 294(1): 68-74.
449 450 451
Ma, J., Z. Wang, et al. (2009). "A study on the multifunction of ferrous chloride in the formation of poly (vinylidene fluoride) ultrafiltration membranes." Journal of Membrane Science341(1): 214-224.
452 453 454 455
Mahendran, R., R. Malaisamy, et al. (2004). "Preparation, characterization and effect of annealing on performance of cellulose acetate/sulfonated polysulfone and cellulose acetate/epoxy resin blend ultrafiltration membranes." European polymer journal40(3): 623-633.
456 457 458
Mazid, M. (1984). "Mechanisms of transport through reverse osmosis membranes." Separation Science and Technology19(6-7): 357-373.
459 460 461 462
Österberg, E., K. Bergström, et al. (1993). "Comparison of polysaccharide and poly (ethylene glycol) coatings for reduction of protein adsorption on polystyrene surfaces." Colloids and Surfaces A: Physicochemical and Engineering Aspects77(2): 159-169.
Ac ce pt e
d
445 446 447 448
463 26
Page 26 of 38
Pendergast, M. M. and E. M. Hoek (2011). "A review of water treatment membrane nanotechnologies." Energy & Environmental Science4(6): 1946-1971.
466 467 468 469
Razmjou, A., J. Mansouri, et al. (2011). "The effects of mechanical and chemical modification of TiO< sub> 2 nanoparticles on the surface chemistry, structure and fouling performance of PES ultrafiltration membranes." Journal of Membrane Science378(1): 73-84.
470 471 472 473
Reuvers, A. J. and C. A. Smolders (1987). "Formation of membranes by means of immersion precipitation : Part II. the mechanism of formation of membranes prepared from the system cellulose acetate-acetone-water." Journal of Membrane Science34(1): 67-86.
474 475 476 477
Richard Bowen, W. and T. A. Doneva (2000). "Atomic force microscopy studies of membranes: effect of surface roughness on double-layer interactions and particle adhesion." Journal of colloid and interface science229(2): 544-549.
us
cr
ip t
464 465
Sabir, A., A. Islam, et al. (2015). "Novel polymer matrix composite membrane doped with fumed silica particles for reverse osmosis desalination." Desalination368: 159-170.
484 485 486
Safarpour, M., A. Khataee, et al. (2015). "Thin film nanocomposite reverse osmosis membrane modified by reduced graphene oxide/TiO2 with improved desalination performance." Journal of Membrane Science489: 43-54.
487 488 489
Sajitha, C., R. Mahendran, et al. (2002). "Studies on cellulose acetate–carboxylated polysulfone blend ultrafiltration membranes––Part I." European polymer journal38(12): 2507-2511.
490 491 492
Shashidhara, G., K. Guruprasad, et al. (2002). "Miscibility studies on blends of cellulose acetate and nylon 6." European polymer journal38(3): 611-614.
493 494 495 496
Shieh, J.-J. and T. S. Chung (1998). "Effect of liquid-liquid demixing on the membrane morphology, gas permeation, thermal and mechanical properties of cellulose acetate hollow fibers." Journal of Membrane Science140(1): 67-79.
497 498 499
Su, J., Q. Yang, et al. (2010). "Cellulose acetate nanofiltration hollow fiber membranes for forward osmosis processes." Journal of Membrane Science355(1): 36-44.
500 501 502 503
Takahashi, H., B. Li, et al. (2000). "Catalytic activity in organic solvents and stability of immobilized enzymes depend on the pore size and surface characteristics of mesoporous silica." Chemistry of Materials12(11): 3301-3305.
an
478 479 480 481 482 483
Ac ce pt e
d
M
Sabir, A., M. Shafiq, et al. (2015). "Fabrication of tethered carbon nanotubes in cellulose acetate/polyethylene glycol-400 composite membranes for reverse osmosis." Carbohydrate Polymers132: 589-597.
27
Page 27 of 38
Vrijenhoek, E. M., S. Hong, et al. (2001). "Influence of membrane surface properties on initial rate of colloidal fouling of reverse osmosis and nanofiltration membranes." Journal of Membrane Science188(1): 115-128.
508 509 510
Wara, N. M., L. F. Francis, et al. (1995). "Addition of alumina to cellulose acetate membranes." Journal of Membrane Science104(1): 43-49.
511 512 513
Wu, H., J. Mansouri, et al. (2013). "Silica nanoparticles as carriers of antifouling ligands for PVDF ultrafiltration membranes." Journal of Membrane Science433: 135-151.
514 515 516
Wu, Y., Y. Kong, et al. (1992). "Surface-modified hydrophilic membranes in membrane distillation." Journal of Membrane Science72(2): 189-196.
517 518 519 520
Yan, L., Y. S. Li, et al. (2005). "Preparation of poly (vinylidene fluoride)(pvdf) ultrafiltration membrane modified by nano-sized alumina (Al< sub> 2 O< sub> 3) and its antifouling research." Polymer46(18): 7701-7706.
521 522 523 524
Yang, Y., H. Zhang, et al. (2007). "The influence of nano-sized TiO< sub> 2 fillers on the morphologies and properties of PSF UF membrane." Journal of Membrane Science288(1): 231238.
525 526 527 528
Yin, J., E.-S. Kim, et al. (2012). "Fabrication of a novel thin-film nanocomposite (TFN) membrane containing MCM-41 silica nanoparticles (NPs) for water purification." Journal of Membrane Science423–424(0): 238-246.
529 530 531 532
Zafar, M., M. Ali, et al. (2012). "Effect of additives on the properties and performance of cellulose acetate derivative membranes in the separation of isopropanol/water mixtures." Desalination285(0): 359-365.
533 534 535 536
Zavastin, D., I. Cretescu, et al. (2010). "Preparation, characterization and applicability of cellulose acetate–polyurethane blend membrane in separation techniques." Colloids and Surfaces A: Physicochemical and Engineering Aspects370(1–3): 120-128.
537 538 539 540
Zhang, S., K. Y. Wang, et al. (2010). "Well-constructed cellulose acetate membranes for forward osmosis: Minimized internal concentration polarization with an ultra-thin selective layer." Journal of Membrane Science360(1–2): 522-535.
541 542 543
Zou, H., S. Wu, et al. (2008). "Polymer/silica nanocomposites: preparation, characterization, properties, and applications." Chem. Rev108(9): 3893-3957.
Ac ce pt e
d
M
an
us
cr
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504 505 506 507
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Zou, L., I. Vidalis, et al. (2011). "Surface hydrophilic modification of RO membranes by plasma polymerization for low organic fouling." Journal of Membrane Science369(1–2): 420-428.
547
Figure and Scheme Captions
549
Scheme: Intermolecular hydrogen acetate/polyethylene glycol 300.
552
Fig.1. Flow sheet diagram of reverse osmosis/pervaporation rig.
553
Fig.2. FTIR spectra of PM and conjugated PM-SNPs membranes
554
Fig.3(a).DSC curves of PM and conjugated PM-SNPs membranes
555
Fig.3(b).TGA curves of PM and conjugated PM-SNPs membranes
556 557
Fig.4. SEM micrographs of PM and conjugated PM-SNPs membranes (a) top surface and (b) cross-section.
558
Fig.5. AFM images (3-dimensional) of PM and conjugated PM-SNPs membranes.
559
Fig.6(a).Relationship between pressure and permeation flux of PM, PM(1-3) membranes.
560
Fig.6(b).Permeation flux of PM and conjugated PM-SNPs membrane with time
561 562
Fig.6(c).Effect of CA/PEG300 concentration on permeation flux and salt rejection of the membrane.
563 564
Fig.6(d).Effect of SNPs(0.1-0.5wt%) conjugation on PM-SNPs for permeation flux and salt rejections.
567
conjugated
SNP
and
cellulose
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d
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566
between
cr
550 551
565
bonding
ip t
548
568
Table 1
569
Effect of concentration CA/PEG300, SNPs, water contentand AFM roughness values of the
570
membranes at 6.0 bar(osmotic pressure 0.7095 bar) Polymer Matrix Membranes
Conjugated PM-SNPs
AFM- Roughness values
Membrane
29
Page 29 of 38
Membrane CA/PEG300 Water Membrane SNP Water Membrane Average Root Type Content Sample loading Content mean Type Roughness (%) square (wt.%) (%) Ra (nm) roughness Rms (nm)
85/15
64.2
PM-S1
0.1
80.8
PM
47.54
61.38
PM1
75/25
68.7
PM-S2
0.2
83.2
PM-S1
38.84
46.18
PM2
65/35
75.2
PM-S3
0.3
88.4
PM-S2
53.01
67.3
PM3
55/45
77.1
PM-S4
0.4
92.1
PM-S3
46.72
56.75
PM-S5
0.5
90.2
PM-S4
106.14
128.7
PM-S5
131.89
153.04
cr
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571
ip t
PM
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572
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S0144-8617(15)00898-X http://dx.doi.org/doi:10.1016/j.carbpol.2015.09.042 CARP 10344
To appear in: Received date: Revised date: Accepted date:
19-6-2015 11-9-2015 12-9-2015
Please cite this article as: Sabir, A., Shafiq, M., Islam, A., Jabeen, F., Shafeeq, A., Ahmad, A., Butt, M. T. Z., Jacob, Kl. I., and Jamil, T.,Conjugation of silica nano particles with cellulose acetate/polyethylene glycol 300 membrane for reverse osmosis using MgSO4 solution, Carbohydrate Polymers (2015), http://dx.doi.org/10.1016/j.carbpol.2015.09.042 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
Conjugation of silicanano particles with cellulose acetate/polyethylene glycol
2
300 membrane for reverse osmosisusing MgSO4solution 2∗
Aneela Sabir1,
4
Ahmad2, Muhammad Taqi Zahid Butt4, Karl. I. Jacob1,Tahir Jamil2
30332, USA. 2
Pakistan. 3
54590 Pakistan. 4
Faculty of Engineering and Technology, University of the Punjab, Lahore, 54590 Pakistan.
M
10 11
Institute of Chemical Engineering and Technology (ICET), University of the Punjab, Lahore,
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Highlights
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an
8 9
Department of Polymer Engineering and Technology, University of the Punjab, Lahore, 54590
us
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School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA
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1*
d
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, Muhammad Shafiq2, Atif Islam2, Faiza Jabeen2, Amir Shafeeq3, Adnan
ip t
3
14 15
•
Conjugation of Silica nanoparticle(SNPs) with polymer matrix (PM)madeby dissolution casting
16
•
SEM micrographs of PM-SNPs showed uniform dispersed dense structured membranes
17
•
PM-SNPs composite membranes improved MgSO4salt rejection properties up to 95%
18 19
•
Thermal properties augmented PM-SNPs composite membrane compared to PM membrane
20 21 22
Abstract
∗
Corresponding author: Aneela Sabir; Email: [email protected], Phone: +1 (404) 933-9732
1
Page 1 of 38
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Thermally-induced phase separation (TIPS) method was usedto synthesize polymer matrix (PM)
24
membranesfor
25
conjugated with silica nanoparticles(SNPs).Experimental data showed that the conjugation of
26
SNPs changed the surface properties as dense and asymmetric composite structure.The results
27
were explicitly determined by the permeability flux and salt rejection efficiency of the PM-SNPs
28
membranes.The effect of SNPs conjugation on MgSO4salt rejection wasmore significant in
29
magnitude than on permeation flux i.e. 2.38L/m2.h.FTIR verified that SNPswere successfully
30
conjugated on the surface of PM membrane.DSC of PM-SNPsshows an improved Tgfrom 76.2 to
31
101.8 ̊ C for PM and PM-S4 respectively. Thermal stability of the PM-SNPs membranes was
32
observed by TGA which wassignificantly enhanced with the conjugation of SNPs.The
33
micrographs of SEM and AFM showed the morphological changesand increase in the valley and
34
ridges on membrane surface. Experimental data showed that the PM-S4(0.4wt%SNPs)membrane
35
has maximum salt rejection capacity and was selected as an optimal membrane.
36
Keyword: Polymer Matrix, Silica nanoparticles, Reverse osmosis, MgSO4 salt solution
37
1. Introduction:
osmosis
fromcellulose
acetate/polyethylene
glycol(CA/PEG300)
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reverse
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Purification of MgSO4salt from water usingreverse osmosis (RO) membranes has become
39
a progressively essential process to address the reduction of worldwide fresh water resources
40
(Greenlee, Lawler et al. 2009; Drioli and Giorno 2010). Despite the fact that other minor
41
monovalent ions like NaCl are present in the seawater, MgSO4 is the second most abundant
42
element and the one that has the second highest concentration in sea water(Lee, Arnot et al.
43
2011). For salt rejection membrane process is widely applied in many areas of the manufacturing
44
industries including water desalination, oil–water separation, production of beverages, ultra-pure
2
Page 2 of 38
water production, electro-coat paint recovery etc. Membrane based separation hasgained more
46
significance than the other separation processes owing to its low energy demand in addition to
47
the absence (or highly reduced)ofhazardous chemicals(Cheryan 1998; Arthanareeswaran,
48
Sriyamuna Devi et al. 2008).
ip t
45
CA is generally very imperative and relatively inexpensive polymer used for RO
50
membranes compared with other desalination techniques such as membrane distillation and
51
hybrid membrane technology(Wu, Kong et al. 1992; Su, Yang et al. 2010; Zhang, Wang et al.
52
2010; Sabir, Shafiq et al. 2015). Generally, CA is one of the best membrane constituents of RO,
53
ultrafiltration (UF) and gas permeation(Kutowy and Sourirajan 1975; Kunst, Škevin et al.
54
1976).Itis generally inaptfor RO application owing to its properties such asdiminished chlorine
55
resistance, temperaturesensitivity and has poor mechanical strength(Jean-Pierre, Christian et al.).
56
In order to overcome these deficiencies, CA is blended with other polymers like PEG,
57
polyamide, polyvinyl alcohol to improve the performance of themembranes(Sajitha, Mahendran
58
et al. 2002; Shashidhara, Guruprasad et al. 2002; Arthanareeswaran, Srinivasan et al. 2004;
59
Chen, Deng et al. 2004; Mahendran, Malaisamy et al. 2004). The membranes produced from the
60
blended polymers exhibited improved properties by assortment of organic polymer with
61
inorganic materials like alumina, silica, zirconia, titania than with sole polymer (Wara, Francis et
62
al. 1995; Castro, Monbouquette et al. 2000; Bottino, Capannelli et al. 2001; Liu, Li et al. 2003;
63
Yan, Li et al. 2005; Yang, Zhang et al. 2007). Incorporation of inorganic nanoparticles in the
64
membrane are employed to resistfouling, ascribed to enhance hydrophilicity andimproved
65
membrane performance in terms of flux ormodification in membrane morphology(Lin, Chang et
66
al. 2003; Ma, Wang et al. 2009; Chen, Su et al. 2010; Zavastin, Cretescu et al. 2010; Razmjou,
67
Mansouri et al. 2011). It is also predicted that the dispersion and the compatibility of the
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nanoparticles modified the surface of the polymer matrix membrane (Wu, Mansouri et al.
69
2013).In this respect, polymer–silica hybrid nanocomposite materials demonstrated outstanding
70
mechanical properties, high chemical and thermal stability and large surface area(Boom, Wienk
71
et al. 1992; Takahashi, Li et al. 2000; Sabir, Islam et al. 2015).Similarly, the use of a hydrophilic
72
polymerlikePEG along with inorganic particlesisused to get desirable properties for membranes.
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The objective of thepresentarticleis to study the performance of newly synthesized
74
environmentally benign polymer matrix (CA/PEG300) RO membranes conjugated with SNPs for
75
filtering out MgSO4. These novel membranes are studied on a RO pilot plantfabricated in
76
Pakistan to achieveimproved performance of themembranes such as permeation flux, percent
77
water content and salt (MgSO4) rejection. It is an initiative towards the fabrication and
78
development of membranes in Pakistan for filtration plants, as necessity of drinkable water is
79
becoming difficult in many area of the country. An initial assessment of the membranes and the
80
effect of conjugated SNPs on the structural chemistry, thermal stability and membrane
81
morphology aredetermined using standard characterization techniques; FTIR, DSC/TGA, SEM
82
and AFM.
83
2. Experimental procedure
84
2.1. Materials
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Analytical grade cellulose acetate was obtained from Fluka (USA) and silica
86
nanoparticles,having 200 nm particle size,were obtained from Sigma Aldrich. Magnesium
87
Sulphate (MgSO4)was obtained from BDH,polyethylene glycol 300 and N, N-dimethyl
88
formamide (99%) were obtained from Fluka & Riedel-de Ha n, respectively.All the chemicals
89
were used without further purification.
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90
2.2 Membrane Preparation
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2.2.1 Preparation of CA/PEG300 polymer matrix membrane Six polymer matrix solutions of CA/PEG300 were synthesized usingthermally-induced
93
phase separation (TIPS) methodology. Different weight % of CA (Table 1) was dissolved in 100
94
mL of DMF solvent with continuous stirring of each solution for 8 h at 80 ̊ C.PEG300 (wt.%
95
are given in Table 1) was added to this homogenous solution.The clear and viscous polymer
96
matrix solutions obtained were labeled as PM, PM1, PM2and PM3. The solutions were cooled at
97
room temperature (25 ̊ C) for an hour.
98
Table 1
99
Effect of concentration CA/PEG300, SNPs, water content and AFM roughness values of the
cr
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membranes at 6.0 bar(osmotic pressure 0.7095 bar).
Conjugated PM-SNPs
AFM- Roughness values
d
Polymer Matrix Membranes
Membrane
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Membrane Type
CA/PEG 300
Water Content (%)
Membrane Type
SNP load
Water Content
(wt.%)
(%)
Membrane Type
Avg. Rough ness Ra (nm)
64.2
PM-S1
0.1
80.8
PM
PM1
75/25
68.7
PM-S2
0.2
83.2
PM-S1
PM2
65/35
75.2
PM-S3
0.3
88.4
PM-S2
PM3
55/45
77.1
PM-S4
0.4
92.1
PM-S5
0.5
46.18 67.3
46.72
56.75
PM-S4
106.14
128.7
PM-S5
131.89
153.04
us
53.01
PM-S3
an
M 2.2.2 Membrane Casting
38.84
Ac ce pt e
102
61.38
d
101
90.2
47.54
ip t
85/15
cr
PM
Root mean square roughn ess Rms (nm)
103
The polymer matrix solutions were spread slowly on glass sheet by maintaining uniform
104
thickness with micrometer adjustable film applicator (Ref: 1117/300 sheen instrument). The
105
newly casted polymer matrix membranes were promptly cooled to 0̊ C for half an hour to
106
induce TIPS, in order to get dense and asymmetric membrane structure. The polymer matrix
107
membranes were placed inan oven at 65 ̊ Cfor controlled evaporation and carefully removed
108
from glass sheet by using sharp blades after drying(Reuvers and Smolders 1987,Li, Nagai et al.
109
1995). The polymer matrix membranes were tested formaximum salt rejection (MgSO4) and PM
110
(85/15) was selected for further treatment with SNPsas it hasthe highest MgSO4 rejection rate.
111
2.2.3Conjugation of SNPs in Polymer matrix membrane
6
Page 6 of 38
Different concentrations of SNPs (0.1-0.5wt.%) asshown in Table 1, were conjugated
113
with polymer matrix (CA/PEG300) solution having 85/15 (w/w) and magnetically stirred for 12
114
h at 80 ̊ C until homogeneous PM-SNPssolutions were formed. The solutions were casted on a
115
clean dried glass plate following the same procedure mentioned in Section 2.2.2. Finally, the
116
dried polymer matrix based conjugated membranes were removed from the glass plates and the
117
membrane thickness (25-35 µm) was measured by screw gauge. Scheme below shows possible
118
interaction between CA/PEG300 and SNPs to form PM-SNPs membranes.
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7
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120
8
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120
3. Membrane Characterization
121
3.1 Fourier Transform Infrared Spectroscopy FTIR spectra of composite membranes were scanned by IR Prestige-21 (Shimadzu)
123
using attenuated total reflectance (ATR) accessory equipped with zinc selenide (ZnSe) crystal.
124
The air background of the instrument was run before each sample.The frequency range was from
125
4000-600 cm-1 at 120 scans per spectrum.
126
3.2 Differential scanning calorimetry / Thermo gravimetric analysis
us
cr
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122
DSC/TGA measurement of the membranes was carried out using TA instrument (SDT-
128
Q600 thermogravimetric analyzer) at heating rate of 20 ̊ C/min under nitrogen atmosphere (15
129
mL/min). Thermal analysis was performed at a temperature program from 30 to 800 ̊ C.
130
3.3 Scanning electron microscopy
d
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an
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The PM and PM-SNPs micrographs of the conjugated membranes were taken on SU-
132
1500 Hitachi. The instrument was operated under low vacuum mode to analyze sample without
133
any special preparation.
134
3.4 Atomic Force Microscope
Ac ce pt e
131
135
The topographical images were obtained using scanningprobe microscope (SPM 9500J3,
136
Shimadzu) with tapping mode at room temperature. The scanning area was 5 µm2. The values of
137
root mean square (RMS) roughness were derived from AFM images, which were obtained from
138
the average of the values measured in random areas. The membrane surface morphology
139
expressed in terms of various roughness parameters like mean roughness (Ra) which represents
140
the mean value of the surface relative to the center plane. The volumes enclosed by the image
141
above and below this plane wereequal and calculated by Equation 1: 9
Page 9 of 38
(1)
142
Where,
is surface relative to the center of plane while Lx and Ly represent dimensions of
144
surface in x and y directions, respectively.
145
The root mean square average (RMS) of the measured height deviations from the mean surface
146
taken within the evaluation area iscalculated by Equation 2:
cr
1/2
us
147
3.5 Water Content
(2)
an
148
ip t
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The membranes samples were dried in an oven for 48 h under vacuum at 75̊ C and then
150
weighed. Dried PM and conjugated PM-SNPs membranes (1 g) were placed separately in
151
vialsfilled with distilled water (100 mL)at room temperature. The weighed water content (%) of
152
the membranes attained after 24 hwascalculatedusing Equation 3:
154
d
Ac ce pt e
153
M
149
(3)
3.6 Reverse Osmosis
155
The experimental setup for reverse osmosis used in this study is given in Fig 1. The plate
156
and frame module of the membrane was made of stainless steel in a circular chamber. The inlet
157
stream of feed water was 0.328 wt% MgSO4(3.28 g MgSO4/L water) at 40 ̊ C. Effective
158
membrane area in contact with inlet stream was 154 cm2. Permeate was collectedwithcontinuous
159
operation of 8 h. The separation process was measured by the permeation flux “J” (L/m2.h),
160
whereas,MgSO4salt rejection (SR %) was done by solving Equations 4 and 5. Permeate and
161
retentate was collected from the sampling points after 8 h. System operating pressure was 10
Page 10 of 38
maintained at 6.0 bar (osmotic pressure 0.7095 bar) during the test using backpressure valve. The
163
conductance of permeate was analyzed by using Cyber Scan Waterproof PC 300 Series
164
(EUTECH).
us
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162
(5)
Where,
170
Q= Amount of permeate(L), A= Membrane effective area (m2), t= Time,Cp= Permeate
171
conductance (mS/cm) andCf=Feed water conductance (mS/cm).
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Page 11 of 38
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172 173
4. Results and Discussion
174
4.1 Fourier transform infrared spectroscopy
175
Spectroscopic
analysis plays an
essential
role in
the
polymeric membrane
176
characterization inorder to investigate the incorporated components of the membranes. FTIR
177
spectrumsof PM and PM-SNPs membranes are given in Fig. 2. In case of PM membrane, the
178
bands at 3414(O-H stretching), 2881and 1435(stretchingand bending of C-H bonds,
12
Page 12 of 38
179
respectively), 1742(-C=O), 1236 (C-O) and902 cm-1(saccharide)bands were observed. Earlier
180
likewise results had been reported in the literature(Liu and Bai 2005; AlTaee and Sharif 2011;
181
Zafar, Ali et al. 2012). The emergence of new band at 797 cm-1 (symmetric Si-O) in the spectra of all PM-SNPs
183
membranes provided a striking evidence for the substitution of SNPs(Semsarzadeh, M.A. and B.
184
Ghalei 2013). The characteristic stretching vibrationbandof Si-O- at 1037 cm-1 became wider
185
with the conjugation of SNPs. The band broadening canbe explained by the conjugation of SNPs
186
and improved interaction between SNPs and PM. With an increase in the amount of SNPs, this
187
band became more prominent as noticed in the case of PM-SNP membranes.The carbonyl band
188
intensity (1742 cm-1)was shifted slightly towards 1739 cm-1 with SNPs conjugation in the
189
polymer matrix, confirmed the H-bonding between -OH and -C=O group (shown in scheme)and
190
proposes interactions between –OH groups of silica and -C=O groups of CA. The observed
191
feature at 3414 cm-1was due to -OH stretching vibrations from the inter-molecular hydrogen
192
bonds shown in schemethat have affinity to decline the force constant and shifting the
193
absorbance to lower energy i.e. lower wave number (Costa-Júnior, E. S., E. F. Barbosa-Stancioli,
194
et al. 2009). A broad band in the 3650–3200 cm-1 region owed to hydrogen bonded Si-OH
195
(silanol) in chains that have H-bonded-OH groups (Innocenzi 2003; Dietrich O. Hummel
196
2002).The presenceof new band (797 cm-1) and hydrogen bonded Si-OH band in the spectra of
197
SNP conjugated PM membranes confirmed the impregnation of SNP within the PM-SNPs
198
membranes.
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182
199
200
13
Page 13 of 38
ip t cr us an M d Ac ce pt e
201 202
4.2 Differential scanning calorimetry/Thermo gravimetric analysis
203
4.2.1 Differential scanning calorimetry
204
The glass transition temperature (Tg) analyzed by DSC is an indicative of the structure
205
and packing of the polymer chain in the membrane. A lower glass transition temperature (Tg)
206
indicates that the membrane possessed more free volume having a loose structure(Zou, Wu et al.
207
2008). The DSC thermograms of PM-SNPs (PM to PM-S5) with and without differentamount of
208
SNPs (0–0.5 wt. %) are shown in Fig. 3(a). Nature of polymeric membrane was interpreted by
209
employing Tg as higher Tgreflectedthemore stable structure of the membrane(Fritzsche, A., et al.,
14
Page 14 of 38
1990).It was observedthat PM without conjugated SNP exhibited Tg at 76.2 ̊ C while with the
211
conjugation of SNPs in PM-S1–PM-S5; it was increased up to 89.6, 92.5, 96.1, 98.9, and 101.8
212
̊ C, respectively. This showed that SNP has developed strong interactions with CA/PEG300 as
213
the chains become regimented and more packed in nature.
214
4.2. Thermogravimetric analysis
cr
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210
Thermogravimetric analyzer was used to analyzethethermal decomposition properties of
216
CA/PEG300 and SNP conjugated PM-SNPs synthesized membranesas shown in Fig.3 (b). Three
217
main decomposition steps areshown by each curve of TGA. Thermograms of PM showed that
218
the first step took place between 30-250 ̊ C and the decomposition was akin to the volatile
219
matter volatilization and/or the evaporation of residual absorbed water. The second step showed
220
that deacetylation and major degradation of CA/PEG300 polymer matrix chainsoccurred
221
from250-395 ̊ C (Shieh and Chung 1998; Lucena, V. de Alencar et al. 2003). The third
222
stepoccurred from395to 800 ̊ C which implied to the carbonization of degraded products to
223
residue. Similarly, for all conjugated PM-SNPs membranes, the TGA curve of PM-S5 was
224
thermally more stable as compared to the other PM and PM-SNPs; 20 and 70 wt.% loss of PM
225
membrane was at 274.72and 363.04 ̊ C which increased up to309.76and 398.4 ̊ C in PM-S5,
226
respectively. The results showed that the thermal stability of the SNP conjugated PM-SNPs
227
membranes were higher than that of PM membrane exhibiting the improvement in thermal
228
properties.
Ac ce pt e
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4.3 Scanning electron microscopy
an
231
The scanning electron micrographs of PM membrane andconjugated PM-SNPs
233
membranes with different SNP loadings are shown in Fig.4(a,b).It reflected the dense
234
asymmetric morphology of the membranes, with top layer and cross sectional layer revealed that
235
the surface morphologies of the membranes were transmuted significantly with the addition of
236
SNP. The top surface morphologies (Fig. 4(a))showedthatthemesoporous, nano-size silica
237
particles were distributed in the PM-SNPs membranes. The interaction of SNP with polymer
238
matrix disrupted the polymeric chains mobility ensuing in the formation of macroscopic
239
defects(Arthanareeswaran, Sriyamuna Devi et al. 2008). As the concentration wasincreased, the
240
defects of mottled surface were filled with agglomerates of SNPs.
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243
Ac ce pt e
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4.4 Atomic force microscope
244
Surface topography of the PM and PM-SNPs membranes were calculated from AFM as
245
shown inthe 2-dimensional surface images (Fig. 5). The consistent valley and ridge like structure
246
is shown in CA/PEG300 polymer matrix membrane.Morphological improvement in membrane
247
structure were generated by the reactive functionalities of polyethylene glycol (-OH group). The
248
roughness parameter was increased with increase in valleys and ridges(Yin, Kim et al. 2012).
249
The membrane with more roughness and elevated regions provided greater membrane surface
250
area and also more active sites were available for adsorption on the membranes(Khulbe, Feng et
251
al. 2007).
17
Page 17 of 38
252
The conjugation of different amounts of SNP ensured the roughness in the valleys and
253
ridges of the RO membrane. The increase in conjugation of SNP increased the average and root
254
mean square roughness (Ra and Rms) of the surface except for PM-S3 as given in Table1. Membrane fouling and the surface roughness were strongly interlinked. It was observed
256
that hydrophilic RO membranes with smooth surfaces were less prone to fouling as compared to
257
the rougher membranes that accumulated in the “valleys”. In PM-S1 to PM-S4 membranes, there
258
was increase in Ra, as compared to PM and showed increased permeation flux. However, the
259
particles preferentially of PM-S5rough membranes resulted in “valley clogging” which caused
260
decline in permeation flux than in smooth membranes(Elimelech, Xiaohua et al. 1997;
261
Vrijenhoek, Hong et al. 2001). The reason acclaimed was a decrease in the electrostatic repulsion
262
between SNP and the surface of themembrane, resulting in the experience of greater adhesion
263
force in the valley regions(Richard Bowen and Doneva 2000).
cr
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d Ac ce pt e
264
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255
18
Page 18 of 38
ip t cr us
4.6 Water Content
an
265
Water content (WC)analysis is the studyof hydrophilicity of the PM-SNPs membranes
267
that exhibited a rapid increase in absorbed water content due to the hydrophilic nature of the
268
membranes. The WC % of the membrane exhibited the hydrophilic nature of the membrane. WC
269
analysis of the membranes attributed to the absorption mechanism caused by the diffusion
270
process controlled by the affinity between the polymer chains and water molecules(external
271
media). The hydrophilic nature of PEG300 in the membranes acted as a driving force for
272
sorption of water into the polymer membrane matrix. These absorption properties of the
273
membranes played an important role in RO performance processes, which affected the
274
membranes permeation flux. Equation 3 was used to calculate the water content (%) ofPM
275
membrane (without SNPs) i.e. 64.2 % as shown in Table 1. In case of 0.1 wt% of SNPs, the
276
water content (%) showed the value of 80.8 %. When SNP contents was0.4 wt%, WC further
277
increased to 92.1 %. Whereas, for SNPs with 0.5 wt%,WC wasdeclined to 90.2%.Similar
278
increase in WC wasreportedin literature (Lv, C.S., et. al 2007).
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Page 19 of 38
280
4.6 Reverse osmosis membrane performance test for flux and MgSO4 rejection The permeation flux of PM and all conjugated PM-SNPs membranes were considered at
282
a pressure of 6.0 bar(osmotic pressure of feed solution is0.7095 bar)for 8 h. The permeation flux
283
and MgSO4rejectionof polymer matrix PM membranes were measured using Equations 4 and5,
284
respectively and are shown in Fig 6(c) and (d). In these membranes,PM3 showed a determined
285
flux of 2.06L/m2.h, whereas,it exhibited minimum MgSO4 rejection ability of 56%.On the
286
contrary, PM membrane had 72% MgSO4 rejection and has the flux of 1.74L/m2.h.
us
cr
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281
The PM3 membrane, with the highest flux, showed reduced salt rejection (%) though PM
288
membrane with the lowest permeation flux had a prominent MgSO4 rejection capacity as shown
289
in Fig 6 (c). The solution diffusion model can better elucidate the transport mechanismof the
290
membranes. It pragmatically involved three steps: surface sorption, under pressure diffusion into
291
dense membrane structure and lastly the desorption phenomenon. PEG300 hydrophilic nature
292
acted as driving force for water sorption into the membrane(Burghoff, Lee et al. 1980; Mazid
293
1984). Desaltingnature ofCA was a reason that PM had maximum abilityof MgSO4 rejection
294
(Chakrabarty, Ghoshal et al. 2008). When membrane pertained to the highest MgSO4 rejection
295
efficiency,the flux at the same time was reduced, limiting to the varying amount of CA and
296
PEG300.
297
membranes(Arthanareeswaran, Mohan et al. 2010).PM3 membrane, with highest quantity of
298
PEG300, showed increase in flux, but at the same time detrimental to MgSO4 rejection. This
299
might be accredited to the voidformation inmembrane, which permitted the passage of salt with
300
water(Bai, Zhou et al. 2012; Safarpour, Khataee et al. 2015). Moreover, the diffusion rate of
301
water molecules was accelerated by the existence of hydrophilic nature of PEG300. The
302
tendency of pore formation was increased withincrease in PEG300 content and consequently
Ac ce pt e
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The
hydrophilic
nature
of
PEG300
acted
as
pore
former
in
the
20
Page 20 of 38
theenhancement in the permeation flux. It was observed that with increase in transmembrane
304
pressure (3.0 - 6.0 bar),the flux was decreased linearly as indicated in Fig. 6(a). Similar results
305
have been shownin the reported data(Pendergast and Hoek 2011). The decrease of permeation
306
flux with time,for PM even at high range pressure was ascribed to the compaction phenomena
307
occurring onthe surface of the membrane as shown in Fig. 6(b). The rearrangement of polymeric
308
chains occurred under pressure because of the compaction phenomena of the membranes
309
thatchangesthe membrane structure and decreases the permeation flux.
us
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303
PM membrane was further selected for conjugation with SNPon the basis of
311
MgSO4rejection. The permeation flux andMgSO4 rejection of conjugated PM-SNPs membranes
312
are depicted in Fig. 6(c) and 6(d).The permeability of PM-SNP membrane was increased with
313
increase in the conjugation of SNP. The permeation flux of conjugated membranes was
314
increasedforPM-S4,but it was decreased in PM-S5. The reason might acclaimed to the
315
agglomeration of SNP in the membrane.PM-S4 membrane has highest flux of 2.38L/m2.h.
316
Similar results have been reported by Yin et al. for silica incorporation in polyamide membranes,
317
which showed that the addition of silica nanoparticles have increased the flux(Yin, Kim et al.
318
2012).The conjugation of silica particles in CA/PEG300 polymer matrix membrane disrupted the
319
packing of polymer chains by forming microporous defects between polymer interface and
320
inorganic particles. The MgSO4 rejection increased from 72 to 95% for PM to PM-S4
321
membranes as a result of incorporation of mesoporous silica nanoparticles(Zou, Vidalis et al.
322
2011).However, a slight decrease in the permeation flux was observed at highest SNPs loading
323
(0.5 wt%). This slight decrease of flux with highest loadingattributed to the agglomeration of
324
SNPs in certain locations which affected the MgSO4 rejection and permeation flux.
Ac ce pt e
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21
Page 21 of 38
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327
Ac ce pt e
325
328
329
330
22
Page 22 of 38
331
Conclusion FTIR spectra of SNPs conjugated PM membranes confirmed the impregnation of SNPs
333
within the PM-SNPs membranes. The thermal stabilityof the SNPs conjugated PM-SNPs
334
membranes were higher than PM membrane.
ip t
332
The observed trendin water flux and MgSO4 rejectionwasrationalized by viewing the
336
polymer matrix (PM)as a medium for conjugation with SNPs. The crucial common features of
337
PM-S4 membrane showingthe highestMgSO4 rejection could bedue tosurface roughness in the
338
membranes that helped preventing formation of non-selective nanochannels or nanopores, and
339
the presence of hydrogen-bonding affinitythat facilitated transport of water.It was observed that
340
0.1–0.5 wt% conjugation of SNPs into CA/PEG300 PM-SNPs manifestly increased the MgSO4
341
rejection at operating pressure of 6.0 bar (osmotic pressureof feed solution is 0.7095 bar) and at
342
40 ̊ C. Therefore, these resultssuggestedthat the PM-S4 among conjugated PM-SNPs
343
membranes is a promising candidate fornanoscale molecule transport device and water
344
desalination.
345
Acknowledgements
346
The authors express their cordial gratitude to the team of Department of Polymer Engineering
347
and Technology, University of the Punjab, for their co-operation during the execution of this
348
research project.
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350
351
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Page 23 of 38
352
References
354 355
AlTaee, A. and A. O. Sharif (2011). "Alternative design to dual stage NF seawater desalination using high rejection brackish water membranes." Desalination273(2–3): 391-397.
ip t
353
356
Arthanareeswaran, G., D. Mohan, et al. (2010). "Preparation, characterization and performance studies of ultrafiltration membranes with polymeric additive." Journal of Membrane Science350(1): 130-138.
360 361 362 363
Arthanareeswaran, G., K. Srinivasan, et al. (2004). "Studies on cellulose acetate and sulfonated poly (ether ether ketone) blend ultrafiltration membranes." European polymer journal40(4): 751762.
364 365 366 367
Arthanareeswaran, G., T. K. Sriyamuna Devi, et al. (2008). "Effect of silica particles on cellulose acetate blend ultrafiltration membranes: Part I." Separation and Purification Technology64(1): 38-47.
368 369 370 371
Bai, H., Y. Zhou, et al. (2012). "The permeability and mechanical properties of cellulose acetate membranes blended with polyethylene glycol 600 for treatment of municipal sewage." Procedia Environmental Sciences16: 346-351.
372 373 374
Boom, R., I. Wienk, et al. (1992). "Microstructures in phase inversion membranes. Part 2. The role of a polymeric additive." Journal of Membrane Science73(2): 277-292.
375 376 377
Bottino, A., G. Capannelli, et al. (2001). "Preparation and properties of novel organic–inorganic porous membranes." Separation and Purification Technology22: 269-275.
378 379 380 381
Burghoff, H. G., K. Lee, et al. (1980). "Characterization of transport across cellulose acetate membranes in the presence of strong solute–membrane interactions." Journal of applied polymer science25(3): 323-347.
382 383 384
Castro, R. P., H. G. Monbouquette, et al. (2000). "Shear-induced permeability changes in a polymer grafted silica membrane." Journal of Membrane Science179(1): 207-220.
385 386 387
Chakrabarty, B., A. Ghoshal, et al. (2008). "Effect of molecular weight of PEG on membrane morphology and transport properties." Journal of Membrane Science309(1): 209-221.
Ac ce pt e
d
M
an
us
cr
357 358 359
388 24
Page 24 of 38
Chen, W., Y. Su, et al. (2010). "In situ generated silica nanoparticles as pore-forming agent for enhanced permeability of cellulose acetate membranes." Journal of Membrane Science348(1): 75-83.
392 393 394 395
Chen, Z., M. Deng, et al. (2004). "Preparation and performance of cellulose acetate/polyethyleneimine blend microfiltration membranes and their applications." Journal of Membrane Science235(1): 73-86.
396 397
Cheryan, M. (1998). Ultrafiltration and microfiltration handbook, CRC press.
398 399
Dietrich O. Hummel (2002). Analysis of Spectrometric Methods, Atlas of Plastic Additives, Springer, Page 46.
cr
ip t
389 390 391
us
400
Drioli, E. and L. Giorno (2010). Comprehensive membrane science and engineering, Newnes.
402 403 404 405
Elimelech, M., Z. Xiaohua, et al. (1997). "Role of membrane surface morphology in colloidal fouling of cellulose acetate and composite aromatic polyamide reverse osmosis membranes." Journal of Membrane Science127(1): 101-109.
406 407 408
Greenlee, L. F., D. F. Lawler, et al. (2009). "Reverse osmosis desalination: Water sources, technology, and today's challenges." Water Research43(9): 2317-2348.
409 410 411
Innocenzi, P. (2003). "Infrared spectroscopy of sol–gel derived silica-based films: a spectramicrostructure overview." Journal of Non-Crystalline Solids316(2–3): 309-319.
412 413
Jean-Pierre, J., G. Christian, et al. "SYNTHETIC POLYMERIC MEMBRANES."
414 415 416
Khulbe, K. C., C. Feng, et al. (2007). Synthetic polymeric membranes: characterization by atomic force microscopy, Springer.
M
d
Ac ce pt e
417
an
401
418
Kunst, B., Đ. Škevin, et al. (1976). "A light‐scattering and membrane formation study on
419
concentrated cellulose acetate solutions." Journal of applied polymer science20(5): 1339-1353.
420 421 422
Kutowy, O. and S. Sourirajan (1975). "Cellulose acetate ultrafiltration membranes." Journal of applied polymer science19(5): 1449-1460.
423 25
Page 25 of 38
Lee, K. P., T. C. Arnot, et al. (2011). "A review of reverse osmosis membrane materials for desalination—Development to date and future potential." Journal of Membrane Science370(1– 2): 1-22.
427 428 429 430
Li, J., K. Nagai, et al. (1995). "Preparation of polyethyleneglycol (PEG) and cellulose acetate (CA) blend membranes and their gas permeabilities." Journal of applied polymer science58(9): 1455-1463.
431 432 433 434
Lin, D.-J., C.-L. Chang, et al. (2003). "Effect of salt additive on the formation of microporous poly (vinylidene fluoride) membranes by phase inversion from LiClO< sub> 4/Water/DMF/PVDF system." Polymer44(2): 413-422.
435 436 437
Liu, C. and R. Bai (2005). "Preparation of chitosan/cellulose acetate blend hollow fibers for adsorptive performance." Journal of Membrane Science267(1–2): 68-77.
438 439 440 441
Liu, S., K. Li, et al. (2003). "Preparation of porous aluminium oxide (Al2O3) hollow fibre membranes by a combined phase-inversion and sintering method." Ceramics International29(8): 875-881.
442 443 444
Lucena, M. d. C. C., A. E. V. de Alencar, et al. (2003). "The effect of additives on the thermal degradation of cellulose acetate." Polymer Degradation and Stability80(1): 149-155.
M
an
us
cr
ip t
424 425 426
Lv, C.S., Yanlei Wang, et al. (2007). “Enhanced permeation performance of cellulose acetate ultrafiltration membrane by incorporation of Pluronic F127”.Journal of Membrane Science,. 294(1): 68-74.
449 450 451
Ma, J., Z. Wang, et al. (2009). "A study on the multifunction of ferrous chloride in the formation of poly (vinylidene fluoride) ultrafiltration membranes." Journal of Membrane Science341(1): 214-224.
452 453 454 455
Mahendran, R., R. Malaisamy, et al. (2004). "Preparation, characterization and effect of annealing on performance of cellulose acetate/sulfonated polysulfone and cellulose acetate/epoxy resin blend ultrafiltration membranes." European polymer journal40(3): 623-633.
456 457 458
Mazid, M. (1984). "Mechanisms of transport through reverse osmosis membranes." Separation Science and Technology19(6-7): 357-373.
459 460 461 462
Österberg, E., K. Bergström, et al. (1993). "Comparison of polysaccharide and poly (ethylene glycol) coatings for reduction of protein adsorption on polystyrene surfaces." Colloids and Surfaces A: Physicochemical and Engineering Aspects77(2): 159-169.
Ac ce pt e
d
445 446 447 448
463 26
Page 26 of 38
Pendergast, M. M. and E. M. Hoek (2011). "A review of water treatment membrane nanotechnologies." Energy & Environmental Science4(6): 1946-1971.
466 467 468 469
Razmjou, A., J. Mansouri, et al. (2011). "The effects of mechanical and chemical modification of TiO< sub> 2 nanoparticles on the surface chemistry, structure and fouling performance of PES ultrafiltration membranes." Journal of Membrane Science378(1): 73-84.
470 471 472 473
Reuvers, A. J. and C. A. Smolders (1987). "Formation of membranes by means of immersion precipitation : Part II. the mechanism of formation of membranes prepared from the system cellulose acetate-acetone-water." Journal of Membrane Science34(1): 67-86.
474 475 476 477
Richard Bowen, W. and T. A. Doneva (2000). "Atomic force microscopy studies of membranes: effect of surface roughness on double-layer interactions and particle adhesion." Journal of colloid and interface science229(2): 544-549.
us
cr
ip t
464 465
Sabir, A., A. Islam, et al. (2015). "Novel polymer matrix composite membrane doped with fumed silica particles for reverse osmosis desalination." Desalination368: 159-170.
484 485 486
Safarpour, M., A. Khataee, et al. (2015). "Thin film nanocomposite reverse osmosis membrane modified by reduced graphene oxide/TiO2 with improved desalination performance." Journal of Membrane Science489: 43-54.
487 488 489
Sajitha, C., R. Mahendran, et al. (2002). "Studies on cellulose acetate–carboxylated polysulfone blend ultrafiltration membranes––Part I." European polymer journal38(12): 2507-2511.
490 491 492
Shashidhara, G., K. Guruprasad, et al. (2002). "Miscibility studies on blends of cellulose acetate and nylon 6." European polymer journal38(3): 611-614.
493 494 495 496
Shieh, J.-J. and T. S. Chung (1998). "Effect of liquid-liquid demixing on the membrane morphology, gas permeation, thermal and mechanical properties of cellulose acetate hollow fibers." Journal of Membrane Science140(1): 67-79.
497 498 499
Su, J., Q. Yang, et al. (2010). "Cellulose acetate nanofiltration hollow fiber membranes for forward osmosis processes." Journal of Membrane Science355(1): 36-44.
500 501 502 503
Takahashi, H., B. Li, et al. (2000). "Catalytic activity in organic solvents and stability of immobilized enzymes depend on the pore size and surface characteristics of mesoporous silica." Chemistry of Materials12(11): 3301-3305.
an
478 479 480 481 482 483
Ac ce pt e
d
M
Sabir, A., M. Shafiq, et al. (2015). "Fabrication of tethered carbon nanotubes in cellulose acetate/polyethylene glycol-400 composite membranes for reverse osmosis." Carbohydrate Polymers132: 589-597.
27
Page 27 of 38
Vrijenhoek, E. M., S. Hong, et al. (2001). "Influence of membrane surface properties on initial rate of colloidal fouling of reverse osmosis and nanofiltration membranes." Journal of Membrane Science188(1): 115-128.
508 509 510
Wara, N. M., L. F. Francis, et al. (1995). "Addition of alumina to cellulose acetate membranes." Journal of Membrane Science104(1): 43-49.
511 512 513
Wu, H., J. Mansouri, et al. (2013). "Silica nanoparticles as carriers of antifouling ligands for PVDF ultrafiltration membranes." Journal of Membrane Science433: 135-151.
514 515 516
Wu, Y., Y. Kong, et al. (1992). "Surface-modified hydrophilic membranes in membrane distillation." Journal of Membrane Science72(2): 189-196.
517 518 519 520
Yan, L., Y. S. Li, et al. (2005). "Preparation of poly (vinylidene fluoride)(pvdf) ultrafiltration membrane modified by nano-sized alumina (Al< sub> 2 O< sub> 3) and its antifouling research." Polymer46(18): 7701-7706.
521 522 523 524
Yang, Y., H. Zhang, et al. (2007). "The influence of nano-sized TiO< sub> 2 fillers on the morphologies and properties of PSF UF membrane." Journal of Membrane Science288(1): 231238.
525 526 527 528
Yin, J., E.-S. Kim, et al. (2012). "Fabrication of a novel thin-film nanocomposite (TFN) membrane containing MCM-41 silica nanoparticles (NPs) for water purification." Journal of Membrane Science423–424(0): 238-246.
529 530 531 532
Zafar, M., M. Ali, et al. (2012). "Effect of additives on the properties and performance of cellulose acetate derivative membranes in the separation of isopropanol/water mixtures." Desalination285(0): 359-365.
533 534 535 536
Zavastin, D., I. Cretescu, et al. (2010). "Preparation, characterization and applicability of cellulose acetate–polyurethane blend membrane in separation techniques." Colloids and Surfaces A: Physicochemical and Engineering Aspects370(1–3): 120-128.
537 538 539 540
Zhang, S., K. Y. Wang, et al. (2010). "Well-constructed cellulose acetate membranes for forward osmosis: Minimized internal concentration polarization with an ultra-thin selective layer." Journal of Membrane Science360(1–2): 522-535.
541 542 543
Zou, H., S. Wu, et al. (2008). "Polymer/silica nanocomposites: preparation, characterization, properties, and applications." Chem. Rev108(9): 3893-3957.
Ac ce pt e
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Zou, L., I. Vidalis, et al. (2011). "Surface hydrophilic modification of RO membranes by plasma polymerization for low organic fouling." Journal of Membrane Science369(1–2): 420-428.
547
Figure and Scheme Captions
549
Scheme: Intermolecular hydrogen acetate/polyethylene glycol 300.
552
Fig.1. Flow sheet diagram of reverse osmosis/pervaporation rig.
553
Fig.2. FTIR spectra of PM and conjugated PM-SNPs membranes
554
Fig.3(a).DSC curves of PM and conjugated PM-SNPs membranes
555
Fig.3(b).TGA curves of PM and conjugated PM-SNPs membranes
556 557
Fig.4. SEM micrographs of PM and conjugated PM-SNPs membranes (a) top surface and (b) cross-section.
558
Fig.5. AFM images (3-dimensional) of PM and conjugated PM-SNPs membranes.
559
Fig.6(a).Relationship between pressure and permeation flux of PM, PM(1-3) membranes.
560
Fig.6(b).Permeation flux of PM and conjugated PM-SNPs membrane with time
561 562
Fig.6(c).Effect of CA/PEG300 concentration on permeation flux and salt rejection of the membrane.
563 564
Fig.6(d).Effect of SNPs(0.1-0.5wt%) conjugation on PM-SNPs for permeation flux and salt rejections.
567
conjugated
SNP
and
cellulose
us
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d
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566
between
cr
550 551
565
bonding
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548
568
Table 1
569
Effect of concentration CA/PEG300, SNPs, water contentand AFM roughness values of the
570
membranes at 6.0 bar(osmotic pressure 0.7095 bar) Polymer Matrix Membranes
Conjugated PM-SNPs
AFM- Roughness values
Membrane
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Membrane CA/PEG300 Water Membrane SNP Water Membrane Average Root Type Content Sample loading Content mean Type Roughness (%) square (wt.%) (%) Ra (nm) roughness Rms (nm)
85/15
64.2
PM-S1
0.1
80.8
PM
47.54
61.38
PM1
75/25
68.7
PM-S2
0.2
83.2
PM-S1
38.84
46.18
PM2
65/35
75.2
PM-S3
0.3
88.4
PM-S2
53.01
67.3
PM3
55/45
77.1
PM-S4
0.4
92.1
PM-S3
46.72
56.75
PM-S5
0.5
90.2
PM-S4
106.14
128.7
PM-S5
131.89
153.04
cr
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571
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PM
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572
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