- Email: [email protected]
Synthesis and electrochemical behaviour of GO doped ZrP nanocomposite membranes
Journal Pre-proof Synthesis and Electrochemical Behaviour of GO doped ZrP nanocomposite membranes Vanita Kumari, Rahul Badru, Sandeep Singh, Sandeep Kaushal, Prit Pal Singh
PII:
S2213-3437(20)30038-5
DOI:
https://doi.org/10.1016/j.jece.2020.103690
Reference:
JECE 103690
To appear in:
Journal of Environmental Chemical Engineering
Received Date:
28 August 2019
Revised Date:
9 January 2020
Accepted Date:
12 January 2020
Please cite this article as: Kumari V, Badru R, Singh S, Kaushal S, Singh PP, Synthesis and Electrochemical Behaviour of GO doped ZrP nanocomposite membranes, Journal of Environmental Chemical Engineering (2020), doi: https://doi.org/10.1016/j.jece.2020.103690
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2019 Published by Elsevier.
Synthesis and Electrochemical Behaviour of GO doped ZrP nanocomposite membranes
Vanita Kumari, Rahul Badru, Sandeep Singh, Sandeep Kaushal*& Prit Pal Singh*
Sri Guru Granth Sahib World University, Fatehgarh Sahib, Punjab, India
ro of
Address for Correspondence: Dr. Sandeep Kaushal Assistant Professor Department of Chemistry, Sri Guru Granth Sahib World University, Fatehgarh Sahib (Pb), India. Mobile No: +91-7009795652 Email: [email protected]
lP
re
-p
& Dr. Prit Pal Singh Professor and Head, Department of Chemistry, Sri Guru Granth Sahib World University, Fatehgarh Sahib (Pb), India. Mobile No: +91-84270-00415 Fax: +91-1763-234236, Email: [email protected] Abstract
In this study, new nanocomposite ion-exchange membranes were prepared by incorporating
na
graphene oxide (GO) in the inorganic matrix of zirconium phosphate (ZrP) by sol-gel method. The synthesized GO-ZrP membranes were characterized by X-ray diffraction, scanning
ur
electron microscopy (SEM) and transmission electron microscopy (TEM). Water content and ion exchange capacity were found to increase initially with increase in concentration of GO up
Jo
to 0.2 wt% and then decreased with further increase in concentration of GO. The electrochemical properties of prepared membranes like membrane potential, transport number, fixed charge density, permeability and ionic flux were explored. The fabricated membranes exhibited higher membrane potential, transport number and fixed charge density for monovalent ions (NaCl) than those for bivalent ions (BaCl2). These membranes exhibited lower permeability and ionic flux for bivalent ions as compared to those for monovalent ions. The conductivity measurements for both monovalent and bivalent ions were performed on the
nanocomposite membranes, and it was noticed that the conductivity of the membranes was higher for monovalent ions. Keywords: GO-ZrP nanocomposite; Electrochemical Studies; monovalent & bivalent ions; Transport number 1. Introduction Waste water treatment is picking up pace nowadays, to meet the ever increasing demand of drinking water owing to massive increase in population. Membrane separation technology retains a prime position in waste water treatment processes since long, due to its easy mode of operation and high efficiency [1]. It is one of the most reliable and frequently adopted methods
ro of
among diverse ways of water purification. Earlier, sole inorganic materials like zirconium antimonate, zirconium phosphate, tin arsenate and phosphate [2-5] and hydrous oxides of metals [6] were employed for the fabrication of purification membranes. But with advancement in technology, the composite materials, which exhibit enhanced porosity and stability [7], have
-p
almost replaced these sole inorganic materials in separation and purification procedures. Composites integrate two or more materials with desired characteristics, with the aim to
re
generate synergic effect. The composites in the light of their improved properties, find applications in diverse fields like electrochemistry, desalination, fuel cells, waste water
lP
treatment, removal of heavy metal ions and sensors [8-10]. Integration of different groups in the nanocomposite structures make them multifunctional and thus, these serve as better ionexchangers [11-13]. Consequently, the nanocomposite membranes manifest improved
na
electrochemical properties like high permeability, high flux and high charge density [14-15]. Numerous nanocomposite-based membranes have been reported in literature, for water purification [16-17]. Carbon based nanomaterials such as carbon nanotubes, graphene and
ur
graphene oxide have been observed to be promising dopants for membrane modifications in desired direction [18]. Previous work on membranes with GO as a dopant, demonstrates the
Jo
effectiveness of using GO as a modifier [19]. Graphene oxide (GO) is a porous material with a variety of oxygen functionalities which impart excellent electrochemical, mechanical, thermal and chemical properties to it [20-21]. It is worth mentioning that the majority of graphene oxide remains embedded in the bulk of the membrane [22-23] rendering it unavailable for surfacebased interactions. Since most of the applications of materials pertain to their surface phenomena, it is highly desirable to inculcate the dopant on the surface of nanocomposite, rendering the active sites available for ion exchange on the surface of the nanocomposite [24]. Zirconium phosphate is the material of choice as it belongs to an excellent class of inorganic
ion exchangers among tetravalent metal-acid salts [4,12]. It has recently been confirmed as a very good sorbent for heavy metals due to its high selectivity, thermal stability, and insolubility in water. In this context, the present study reports the doping of graphene oxide in zirconium phosphate, with the intention to synthesize a composite material with upgraded electrochemical properties. Membranes fabricated from the prepared composite material were evaluated for their electrochemical characteristics like membrane potential, transport number, fixed charge density, permeability and ionic flux. The results obtained highlight the potential of graphene oxide as a surface-active agent for the materials.
ro of
2. Experimental 2.1 Reagents and instruments
Zirconyl oxychloride, ortho-phosphoric acid (Loba Chemie, India) and graphite powder (Qualikems Lab, India) were used for synthesis. All other chemicals used were of AR grade,
-p
and used as such without further purification. Double distilled water (DDW) was used during the experiments. Standard solutions were prepared by direct weighing of AR grade reagents
re
using double distilled water (DDW). X-ray diffractometer (PAN Analytical, System No. DY 3190), surface scanning electron microscope (JEOl, JSM-6510LV), transmission electron microscope (MIC JEM 2100), digital potentiometer (Systronic 318), digital conductivity meter
lP
(Systronic, India) having platinum electrode as reference electrode and drop shape analyserDSA 25 were used for contact angle measurements.
na
2.2 Preparation of GO-ZrP nanocomposite
Zirconium phosphate was synthesized by sol-gel method [4]. Graphene oxide (GO) was prepared by modified Hummer’s method which involves both oxidation and exfoliation of
ur
graphite sheets [11]. GO-ZrP nanocomposite was prepared by sol-gel method. Powdered graphene oxide (GO) in different mass ratio was introduced into the ZrP gel and the mixture
Jo
was stirred at room temperature for 4 h at 60ºC using mechanical stirrer. Then the mixture was allowed to stand overnight. The nanocomposite was filtered under suction and washed with DDW to remove the unreacted part. The gel was then dried in an air oven at 80ºC. Five samples (S1–S5) were prepared by varying the concentration of graphene oxide (GO) in fixed quantity of zirconium phosphate (ZrP). 2.5 Preparation of membrane
The heterogeneous cation exchange membranes were fabricated by solution casting technique [16]. Polyvinylchloride (PVC) binder was dissolved in THF (THF: PVC = 20:1, v/w) in a flat bottom flask by stirring for 6 h, and a definite quantity of nanocomposite of 200 mesh size (nanocomposite: PVC = 1:1, w/w) was added to the polymeric solution (Table 1). The resulting solution was stirred for 30 min with a magnetic stirrer, followed by sonication for uniform dispersion of particles. The mixture was then poured into a glass ring fitted on a clean dry glass plate and kept overnight to allow the solvent evaporate. The membranes obtained were kept in DDW overnight and then in 0.5 M NaCl solution for 48 h. 2.6 Physical characterization of fabricated GO-ZrP nanocomposite membranes
ro of
2.6.1 Swelling
The swelling of the membrane was measured by a screw gauge by the already reported method [17].
-p
2.6.2. Porosity (ε)
Porosity is a measure of the volume of water incorporated in the cavities per unit membrane
mw md AL w
(1)
lP
re
volume, and is calculated from the following relation:
Where, mw and md are the mass (g) of wet and dry membrane, respectively. L is thickness of
na
the membrane, A is area of the membrane, and ρw is density of water [18]. 2.6.3 Water uptake by membrane
ur
The membrane was soaked in water and then blotted quickly with Whatman filter paper to remove surface moisture and weighed immediately. This membrane was then dried in vacuum
Jo
over P2O5 for 24h. Following equation was used to calculate the water content [19] Water Content (%) =
W wet W dry
100
(2)
W dry
Where, Wwet and Wdry are the masses (g) of the wet and the dry membrane, respectively. 2.6.4 Ion-exchange Capacity Ion-exchange capacity (IEC) of dry ZrP and differently doped GO-ZrP nanocomposite membranes were determined by batch method [25]. The synthesized membrane was treated
with HNO3 for 24h and then washed 2-3 times with demineralized water. After drying, membranes were dipped overnight in 0.1 M NaNO3 solution. The effluent is then titrated with 0.01M NaOH to estimate the amount of H+ ions substituted in the membrane by Na+ ions. Ion exchange capacity of the membrane was calculated by the formula: IEC
M V
meq g
1
(3)
W
Where, M is molarity and V is volume of NaOH consumed in mL and W is mass of GO-ZrP membrane (g).
ro of
2.6.5 Contact Angle Measurement The contact angle measurements between water droplets and pristine as well as GO-doped membranes dried at 120 ˚C were made by advance sessile drop method [26]. 2.8 Electrochemical Characterization of Fabricated Membranes
-p
2.8.1 Electrode assembly
The membrane potential was measured with a digital potentiometer. The membrane was pasted
re
with araldite at the centre of electrode assembly, which had two electrode chambers having cavities to introduce electrolyte solution and standard calomel electrode. The solution (1.0 M)
lP
of each of the electrolytes such as sodium chloride and barium chloride were filled in the chambers. The electrode assembly is depicted below:
na
Hg │ Hg2Cl2, Cl¯ ║soln. C1 │ Membrane │ soln. C2 ║ Cl¯, Hg2Cl2(s) │ Hg The concentration ratio of the electrolyte solutions taken for potential measurements was 10 i.e. C1/C2=10. The membrane potentials across the membranes were measured by using
ur
electrolyte solutions in the concentration range of 0.01 to 0.1 M [27].
Jo
2.8.2 Membrane potential and transport number The potential difference developed across the membrane was measured against Hg–Hg2Cl2, Cl¯ reference electrode on either side of the membrane, using a digital potentiometer. The electrolyte solution of next higher concentration was used to rinse the electrode chambers which were then filled with the same solution. The new potential difference was noted after 2 h during which the membrane attains equilibrium. The membrane potential measurements were reproducible to [25, 27]:
0.1 mV. The transport number
t
can be calculated by the following equation
E m 2 . 303
RT nF
( 2 t 1 ) log
C2
(4)
C1
where R is gas constant, F is Faraday’s constant, T is absolute temperature, C1 and C2 are the concentrations of electrolyte solutions in the test cell. 2.8.3 Permselectivity Permselectivity of the membrane can be expressed quantitatively, based on the migration of counter ions through the ion exchange membrane [6, 28]: t t
(5)
1 t
where Ps is the permselectivity of membrane,
t
and
t
ro of
Ps
refer to the transport number of counter
ions in the membrane and in free solution at same concentration, respectively. 2.8.3 Fixed charge density ( X )
-p
The fixed charge density denotes the electrical character of a membrane. The fixed charge density of the fabricated membrane for 1: 1 and 1: 2 electrolytes was evaluated by the following
1
1 1 2
1 Slope
(6)
lP
X
re
equation [25]:
where δ is the ratio C2/C1, α and β are constants.
na
2.9 Conductivity, ionic permeability and flux of ions The conductivity, ionic permeability and flux of ions were estimated by utilizing the test cell. NaCl or BaCl2 solution (0.1 M) was placed on one side of the cell and a 0.01M solution of the
ur
same electrolyte on its other side. A DC electrical potential with constant voltage (10V) was applied across the cell with platinum electrodes placed at the end of the compartments. The
Jo
variation of conductivity with time was measured using digital conductivity meter. During this experiment, the ions permeate into the permeation section through the membranes and hence, the conductivity of permeation section increases with time. Both the sections were re-circulated and stirred vigorously between two successive measurements to ensure the attainment of equilibrium in the two solution-membrane interfacial zones, and to minimize the effect of boundary layers. The permeation of ions can be determined from the slope of straight line plot of conductivity vs. time. According to first Fick’s law, the flux of ions through the membrane can be expressed as follows [20-21]
N P
C1 C 2
(7)
d
where, C1 and C2 are the concentrations of electrolyte solution on either side of the membranes, d is membrane thickness, P is the diffusion co-efficient of ions and N is ionic flux. N
V
dC
A
P
1
C1 C 2
dt
(8)
d
C 1 0 . 1 M , C 2 0 . 01 M , C 1 + C 2 0
0
= C 10
C 02 =0.11M
(9)
Where, A (m2) is the surface area of the membrane. By integrating the equation (8), we get 1
ln
2
(C 0 C 2 ) 1
0
2 PAt
(10)
Vd
ro of
(C 0 C 0 2 C 2 )
The diffusion coefficient and flux of cations in membrane phase were calculated from equation (10), and various parameters were determined by variation of conductivity in cathodic compartment [29].
-p
3. Results and discussion
Various samples of GO-ZrP nanocomposite membranes were synthesized by incorporating
re
different mass ratios of graphene oxide into the inorganic matrix of zirconium (IV) phosphate. The ion exchange capacity, thickness, water content and porosity of fabricated membranes is
lP
summarized in Table 1. It is clear from the data in Table 1 that membrane M-3 has maximum thickness, water content and ion exchange capacity among all the fabricated membranes.
Properties
0-GO (M-1)
0.1-GO (M-2)
0.2-GO(M-3)
0.3-GO (M-4)
0.4-GO (M-5)
0.47 ±0.02 5.23±0.13 2.47±0.05 0.17±0.02
0.44±0.04 5.35±0.15 2.51±0.04 0.22±0.01
0.53±0.02 6.89±0.11 5.29±0.03 0.26±0.03
0.49±0.04 5.70±0.16 5.71±0.05 0.23±0.02
0.42±0.03 5.41±0.14 5.66±0.04 0.18±0.02
Jo
ur
Thickness (mm) Water content (%) Porosity IEC (m equiv g-1)
na
Table 1: Properties of nanocomposite membranes
FTIR spectroscopic studies were carried out for various synthesized sample membranes M-1 to M-5, to confirm the incorporation of GO into the inorganic matrix of ZrP (Fig. 1). In the FTIR spectrum of pure zirconium phosphate, ionic phosphate stretching appears around 1000 cm-1 [30,31]. Peak around 700-800 cm-1 may be assigned to M-O stretching [32]. With the introduction of GO into the inorganic material, few more stretching peaks at 3850, 3750, 2350 cm-1 which are characteristic of GO, become clearly visible in the FTIR spectrum. Similarities
were noticed for all modified ZrP membranes. The peaks at 1000 and 1620 cm-1 were observed
re
-p
ro of
in all the membranes but the intensity was lower for samples M-2 to M-5.
lP
Fig. 1: FTIR spectra of fabricated membranes
The XRD pattern of fabricated membranes was recorded between 5° to 65° at 2ϴ, using Cu Kα radiation (Fig. 2). As can be seen from the XRD pattern of membrane M-1, there is appearance
na
of peak at 2ϴ = 19.7 which might be due to zirconium phosphate and binder present in the membrane phase [4, 33, 34]. It has been observed that with the enhanced additive loading of GO in the membrane phase (M-2 to M-5), the peak intensity at 2ϴ = 19.7 is greatly reduced
ur
and a new peak at 2ϴ = 9.5 appeared, which is attributed to the presence of GO in the membrane phase [35]. It is clear from the XRD patterns (Fig. 2) that the fabricated membranes are semi
Jo
crystalline in nature. Also, the intensity of the peak at 2ϴ = 9.5 is higher in M-3 than the other membranes, which may be due to the better interactions of GO at moderate concentration, with ZrP in the membrane phase.
ro of -p
re
Fig. 2 XRD patterns of the fabricated nano-composite membranes
SEM study was performed to predict the surface texture, homogeneity and cracks on the GO-
Jo
ur
na
lP
ZrP nanocomposite membrane (Fig. 3).
ro of -p
re
Fig. 3: SEM images of a) M-1, b) M-2, c) M-3, d) M-4, e) M-5 membranes and f) EDS spectra
lP
of nanocomposite
It is clear from the images that the GO particles are uniformly distributed throughout the membrane which has a smooth surface [24-27]. It has been observed that the increase of GO
na
content in the casting solution leads to the formation of voids and enlargement of channels in the membrane matrix. It was observed that the porous nature of nanocomposite membranes increases and cracks appear at the surface of membrane with increase of GO content in the
ur
membrane to 0.3wt%. Further, increase of GO content to 0.4wt% led to the decrease of porosity due to severe aggregation of nanoparticles in the membrane matrix. Such a deviation in the
Jo
porosity of membrane with the variation of GO content is likely to affect the physio-chemical properties of the fabricated membranes. The EDS spectra of the membrane confirm the presence of Zr, P, C and O elements in the membrane matrix.
ro of
-p
Fig. 4: FESEM images of cross-section of a) M-1, b) M-2, c) M-3, d) M-4, e) M-5
The cross-sectional images of fabricated membranes have been shown in Figure 4a-e. It is clear
re
from the images that the morphology of fabricated membranes has slightly changed with the increase in GO content. Moreover, the cross-sectional images confirm the regularity in the
Jo
ur
na
lP
porosity of the synthesized membranes.
ro of -p
re
Fig. 5: TEM images of a) M-1, b) M-2, c) M-3, d) M-4, e) M-5 nanocomposite membranes The water content increased from 5.23 to 6.89 % with the increase of GO content in the range
lP
0.1-0.3 wt%. This might be due to hydrophilic nature of added GO, expansion of flow channels in the membrane phase and increase in heterogeneity of the membrane that provides more free spaces for lodging of water molecules [36-37]. On the other hand, the properties of
na
nanocomposite membrane did not improve further with the increase of GO content in the membrane matrix. This may be attributed to the decrease in porosity of the membrane due to blocking of membrane flow channels at high additive loading of GO which diminishes the
ur
membrane water capacity and decreases the membrane hydrophilicity, leading to poor performance of the membrane. The appropriate water content in the membrane matrix leads to
Jo
better flow channels for ion traffic and enhances permselectivity of the membrane. It has been reported that the porosity also affects the transport properties and selectivity of the ion exchange membranes [38]. The membranes with large pore size lose the selectivity, and the pores smaller than ionic species behave like inaccessible pathways or non-conducting regions for ionic species [39]. In this work, similar trend of ion exchange capacity has been observed with variation in water content for the fabricated membranes. The ion exchange capacity of the nanocomposite membranes increased initially with the addition of GO as compared to pristine membrane. The cavities and voids are formed in the
bulk of membrane on incorporation of GO. Further increase of GO content in the casting solution did not enhance the ion exchange capacity of the membrane (Table 1). This might be due to the aggregation of particle clusters of GO, leading to partial blockage of cavities and voids in the membrane [40]. This observation was also supported by the decrease in porosity and water content of fabricated membranes with increased additive loading of GO. Hydrophilic character of pristine and graphene oxide doped membranes was determined by measuring the contact angle between membranes and water droplets. Distilled water was used as a probe in all experiments. Ten consecutive measurements were taken for every sample, to minimize the experimental error. It was observed that the pristine membrane is highly
ro of
hydrophobic in nature. Hydrophilicity of doped membranes was higher as compared to pristine membrane on doping the parent membrane with graphene oxide in different percentage ratios (0.1%-0.4%) which was supported by a drastic change in contact angle from 112º to 83º, respectively (Fig. 6). The increase in hydrophilic character is due to intense supra-molecular
π…π, CH…π interactions between -OH and -COOH
Jo
ur
na
lP
re
substituents on pristine ZrP and graphene oxide.
-p
hydrogen bonding OH…..H, C=O…..H,
Fig. 6: Effect of GO content on the membrane water contact angle
3.4 Electrochemical studies of GO-ZrP nanocomposite membranes 3.4.1 Membrane potential and transport numbers
The synthesized membranes were characterized electrochemically in monovalent (NaCl) and bivalent (BaCl2) ionic solutions. The variation of membrane potentials and transport numbers of Na+ and Ba2+ with concentration of electrolyte is shown in Fig. 7 and 8, respectively. Membrane potentials (Fig. 7) and transport numbers (Fig. 8) were found to be highest at different concentrations of both the electrolytes in membrane M-3 as compared to other membranes. This may be due to higher crystallinity of M-3, as compared to that of other membranes, which provides suitable ionic pathways for the movement of ions. It is important to mention that both the membrane potentials and transport numbers of Na+ and Ba2+ ions in different membranes under investigation follow the order: M-3 > M-4 > M-5 > M-
ro of
2 > M-1. The membrane potentials and transport numbers (mobility) of both the electrolytes in the membrane phase increase with increase in concentration of the electrolyte in all the membranes except M-1 up to a certain concentration, and then decrease with further increase
na
lP
re
-p
in concentration.
ur
Fig. 7. Effect of concentration of electrolyte on membrane potentials for a) alkali (Na+) and
Jo
b) alkaline earth metal (Ba2+) ions
The initial increase in membrane potential and transport numbers with increase in concentration of the electrolyte is attributed to the increase in number of free cations (counter ions) available for transport. With further increase in concentration of electrolyte, the number of free ions available for transport decreases due to increase in inter-ionic interactions at higher concentarion and concentration polarization phenomenon [25]. As a result, the membrane potential and transport numbers decrease as the concentartion of electrolyte was increased beyond a certain limit. Also, the membrane potential as well as the transport numbers were
found to be higher for Na+ as compared to those for Ba2+. The lower electrochemical values for bivalent ionic solutions may be due to the formation of stronger bonds by bivalent ions with the functional groups of the ion exchanger, which results in decrease of membrane potential, transport number and fixed charge density. The stronger electrostatic attraction between the bivalent ions and fixed oppositely charged sites prevents the dissociation of cations from the
-p
ro of
functional groups on the ion exchanger (Fig. 7b).
re
Fig. 8. Effect of concentration on the transport numbers for a) alkali (Na+) and b) alkaline earth metal (Ba2+) ions
lP
3.4.2 Permselectivity and fixed charge density ( X )
Permselectivity represents the ion selectivity of ion exchange membranes and is a measure of
na
the ease of migration of counter-ions through the membranes. The permselectivity (Fig. 9a) and fixed charge density (Fig. 9b) in different membrane compositions exhibit the same trend with variation in concentration of the electrolyte as followed by membrane potentials and
ur
transport numbers. The observed values of fixed charge density (Fig. 9b) indicate that larger part of internal fixed charge is inactive. The higher fixed charge density of the membrane for
Jo
Na+ is attributed to its smaller hydrated ionic radius as compared to that of Ba2+ ions.
ro of
Fig. 9. a) Variation of permselectivity with mean concentration of electrolyte for alkali metal ions; b) fixed charge density of different membranes for alkali and alkaline earth metal ions
-p
3.5 Ionic permeability and flux of ions
The ionic permeability and flux for Na+ ion enhanced with the increase in GO content up-to
re
0.2 wt% and then, a decrease in the values was observed with further increase in GO concentration (Fig. 10). The inoculation of GO into the membrane increased the surface
lP
hydrophilicity and thus facilitates the transportation of ions between the solution and the membrane phase, resulting in better ionic permeability and flux of the membrane. Moreover, the conducting behaviour of the membrane was enhanced by semi-conducting characteristics
na
of GO, which provides more conducting regions, and strengthened the electrical field around
Jo
ur
the modified membranes.
Fig. 10. Comparison of a) permeability and b) flux of monovalent and bivalent ions
The values of ion diffusion coefficients across the membrane indicate that at low wt% of GO, the control of the ion diffusion process across the membrane is kinetic (favorable diffusion and good even at low temperature), whereas at high% of GO, the process is energetically controlled (unfavorable diffusion and low at low temperature). 3.6 Ionic conductivity The ionic conductivity of fabricated membranes was studied and is depicted in Fig. 11. It was observed that the introduction of GO nanoparticles in the membrane matrix leads to increase of ionic conductivity slightly from M-1 to M-3. The enhancement in the conductivity might be
ro of
due to the presence of hydroxyl and carboxyl groups present on the GO particles. Interestingly, the ionic conductivity follows the same trend as that of membrane potential and transport
ur
na
lP
re
-p
numbers (Fig. 7 and 8).
Jo
Fig. 11. Variation of conductivity with time of prepared membranes for a) monovalent and b) bivalent ions It is apparent that 0.2wt% GO membrane (M-3) has good IEC, high membrane potential, transport number, fixed charge density and high porosity that might be the reason for the best conductivity of this membrane as compared to other membranes in the same series. Hence, the synergetic effect of the additive loading of GO and porosity might play an important role in affecting the overall membrane properties.
A comparison between electrochemical properties of fabricated membrane (M-3) in this study with some commercial reported membranes is given in Table 2. Table 2: A typical comparison between various properties of some commercial membranes and modified membrane in this work Water content (%)
Fixed Charge density
Transport Number
Permselectivity
Conductivity (Scm-1) /Resistancea
Ref.
Sulphonated 0.99 polyether sulphone (sPES) Neosepta 1.5-1.8 CMX
0.20
12.37
7.12
0.92
86.78
0.114
41
0.176
25
-
0.97
97
1.8-3.8 a
42
CMV
2.4
0.137
25
-
0.98
RALEX CMH-PES
2.34
0.764
31
-
0.946
Nafion 117
0.90
0.20
16
-
This research 0.26 (Sample 3)
0.53
6.89
63
Conclusion
2.9 a
43
94.7
11.33a
44 45
-p
95
-
97
1.5a
0.99
8.1
15.3
re
Resistance values (in Ωcm2)
ro of
Thickness (mm)
a
IEC (meq/g)
lP
Membrane
na
In the present study, GO doped ZrP composite cation exchange membranes were prepared by solution casting technique, using PVC as binder. Sonication was employed to achieve better homogeneity and electrochemical properties of the membrane matrix. Results revealed that
ur
with the increase of GO concentration in the casting solution, water uptake and ion exchange capacity of membranes increased initially up to 0.2wt% and then showed decreasing trend with
Jo
increase in additive loading of GO from 0.2 to 0.4 wt%. The membrane potential, transport number, fixed charge density and permselectivity values obtained with the fabricated membrane of the nanocomposite were found to be higher for monovalent cations (Na+) than those for bivalent cations (Ba2+) which may be attributed to the hindrance in the movement of bivalent ions. For both monovalent and bivalent ionic solutions, membrane permeability and flux were enhanced initially with the increase in GO concentration to 0.2wt% and then showed decreasing trend with more additive loading of GO. Moreover, the modified membranes containing GO showed better electrochemical properties in comparison to pristine membrane.
Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Author Contributions Section Contribution in this manuscript
1 Vanita Kumari in the research work.
She has done the synthesis and experimental work
2
Dr. Rahul Badru
Contributed in writing and spectroscopic studies.
3
Dr. Sandeep Singh
Contributed in contact angle measurement
ro of
Sr. No. Author Name
4 Dr. Sandeep Kaushal his supervision.
Proposed the work and all the work done under
5
Supervisor and assist in electrochemical studies.
Jo
ur
na
lP
re
-p
Dr. Prit Pal Singh
References
[1] J. Ran, L. Wu, Y. He, Z. Yang, Y. Wang, C. Jiang, L. Ge, E. Bakangura, T. Xu, Ion exchange membranes: New developments and applications, J. Membr. Sci., 522 (2017) 267–291. [2] M. M. A. Khan, Rafiuddin, Synthesis, estimation of stability in different media, electrochemical propertiesand potentiometric studies of PVC-based NP ion-exchange
Desalin Water Treat., 57 (2015) 18346-18353.
ro of
nanocomposite membrane for desalination and waste water treatment applications,
[3] C. Cornelius, C. Hibshman, E. Marand, Hybrid organic–inorganic membranes, Sep. Purif. Technol., 25 (2001) 181–193.
[4] S. Kaushal, P. K. Sharma, S. K. Mittal, P. Singh, Novel zinc oxide–zirconium (IV)
-p
phosphate nanocomposite as antibacterial material with enhanced ion exchange properties, J. Colloid Interface Sci., 7 (2015) 1-6.
re
[5] P.V. Vyas, P. Ray, S.K. Adhikary, B.G. Shah, R. Rangarajan, Studies of the effect ofvariation of blend ratio on permselectivity and heterogeneity of ion-
lP
exchangemembranes, J. Colloid Interface Sci., 257 (2003) 127–134. [6] G.S. Gohli, V.V. Binsu, V.K. Shahi, Preparation and characterization of monovalention selective polypyrrole nanocomposite ion-exchange membranes, J. Membr.
na
Sci., 280 (2006) 210–218.
[7] S.M. Hosseini, S.S. Madaeni, A.R. Khodabakhshi, Heterogeneous cation exchangemembrane: preparation, characterization and comparison of transport
ur
propertiesof mono and bivalent cations, Sep. Sci. Technol., 45 (2010) 2308–2321. [8] J. S. Lin, S. R. Kumar, W. T. Ma, C. M. Shih, L. W. Teng, C. C. Yang, S. J. Lu,
Jo
Gradiently distributed iron oxide@ graphene oxide nanofillers in quaternized polyvinyl alcohol composite to enhance alkaline fuel cell power density, J. Membr. Sci., 543 (2017) 28–39. [9] Y. Zhang, K. Su, Z. Li, Graphene oxide composite membranes cross-linked with urea for enhanced desalting properties, J. Membr. Sci., 563 (2018) 718–725. [10] Y. Zhang, S. Zhang, J. Gao, T. S. Chung, Layer-by-Layer Construction of Graphene Oxide (GO) Framework Composite Membranes for Highly Efficient Heavy Metal Removal, J. Membr. Sci., (2018) 230-237.
[11] C.O. M. Bareck, Q.T. Nguyen, S. Alexandre, I. Zimmerlin, Fabrication of ionexchange ultrafiltration membranes for water treatment. I. Semi-interpenetrating polymer networks of polysulfone and poly (acrylic acid), J. Membr. Sci., 278 (2006) 10–18. [12] V. K. Gupta, D. Pathania, P. Singh, B. S. Rathore, P. Chauhan, Cellulose acetate– zirconium (IV) phosphate nano-nanocomposite with enhanced photo-catalytic activity, Carbohydr. Polym., 95 (2013) 434– 440. [13] L. Stobinski, B. Lesiak, A. Malolepszy, M. Mazurkiewicz, B. Mierzwa, J. Zemek, P. Jiricek, I. Bieloshapka, Graphene oxide and reduced graphene oxide studied by the XRD,
ro of
TEM and electron spectroscopy methods, J. Electron Spectrosc. Relat. Phenom., 195 (2014) 145–154.
[14] M. E. Uddin, R. K. Layek, H. Y. Kim, N. H. Kim, D. Hui, J. H. Lee, Preparation and enhanced mechanical properties of non-covalently functionalized graphene oxide/cellulose acetate nanonanocomposites, Compos Part B-Eng., 90 (2016) 223-
-p
231.
[15] R. Hu, R. Zhang, Y. He, G. Zhao, H. Zhu, Graphene Oxide-in-Polymer
Membr. Sci., 564 (2018) 813–819.
re
Nanofiltration Membranes with Enhanced Permeabilityby Interfacial Polymerization, J.
lP
[16] S. M. Hosseini, E. Jashni, M. R. Jafari, B. Van der Bruggen, Z. Shahedi, Nanocomposite polyvinyl chloride-based heterogeneous cationexchangemembrane prepared by synthesized ZnQ2 nanoparticles: ionic behavior and morphological
na
characterization, J. Membr. Sci., 560 (2018) 1-10. [17] M. Arsalan, A Zehra, M.M.A. Khan, Preparation and characterization of Polyvinyl chloride-basednickelphosphate ion selective membrane and its application for removal of
ur
ions through water bodies, Groundw. Sustain. Dev., 8 (2019) 41-48. [18] M. M. A. Khan, Rafiuddin, Synthesis, electrochemical characterization, antibacterial
Jo
study and evaluation of fixed charge density of polystyrene based calcium-strontium phosphate nanocomposite membrane, Desalination, 284 (2012) 200–206. [19] M. M. A. Khan, Rafiuddin, Synthesis, characterization and antibacterial activity of polystyrene based Mg3 (PO4)2/Ca3 (PO4)2nanocomposite membrane, Desalination, 294 (2012) 74–81. [20] G. S. Lai, W. J. Lau, P. S. Goh, A. F. Ismail, N. Yusof, Y. H. Tan, Graphene oxide incorporated thin film nanocomposite nanofiltration membrane for enhanced salt removal performance, Desalination, 387 (2016) 14-24.
[21] R. Hu, R. Zhang, Y. He, G. Zhao, H. Zhu, Graphene oxide-in-polymer nanofiltration membranes with enhanced permeability by interfacial polymerization, J. Memb. Sci., 564 (2018) 813-819. [22] C. Shen, E. Barrios, L. Zhai, Bulk Polymer-Derived Ceramic Composites of Graphene Oxide, ACS Omega, 3 (2018) 4006-4016. [23] H. Li, L. Pan, C. Nie, Y. Liu, Z. Sun, Reduced graphene oxide and activated carbon composites for capacitive deionization, J. Mater. Chem., 22 (2012) 15556-15561. [24] F. Perreault, M. E. Tously, M. Elimelech, Thin-Film Composite Polyamide Membranes Functionalized with Biocidal Graphene Oxide Nanosheets, Environ. Sci.
ro of
Techno. Lett., 1 (2014) 71-76. [25] S. Kaushal, G. Singh, P. Singh, T. S. Kang, Synthesis and characterization of a tin (IV) antimonophosphate nano-composite membrane incorporating 1-dodecyl-3methylimidazolium bromide ionic liquid, RSC Adv., 7 (2017) 12561–12569.
[26] M. Nemati, S. M. Hosseini, M. Shabanian, Novel electrodialysis cation exchange
removal, J. Hazard Mater. 337 (2017) 90-104.
-p
membrane prepared by 2-acrylamido-2-methylpropane sulfonic acid; Heavy metal ions
re
[27] M. M. A. Khan, Rafiuddin, Inamuddin, PVC based polyvinyl alcohol zinc oxide nanocomposite membrane: Synthesis and electrochemical characterization for heavy
lP
metal ions, J. Ind. Eng. Chem., 19 (2013) 1365–1370.
[28] X. Li, Z. Wang, H. Lu, C. Zhao, H. Na, C. Zhao, Electrochemical properties of sulfonated-PEEK used for ion exchange membranes, J. Membr. Sci., 254 (2005) 147–
na
155.
[29] S.M. Hosseini, S.S. Madaeni, A.R. Khodabakhshi, Preparation and characterization of ABS/HIPS heterogeneous cation exchange membranes with various blend ratios of
ur
polymer binder, J. Membr. Sci., 351 (2010) 178–188. [30] C. N. R. Rao, Chemical Applications of Infrared Spectroscopy, J. Chem. Educ., 42
Jo
(1965) 117-118.
[31] V. K. Gupta, D. Pathania, N. C. Kothiyal, G. Sharma, Polyaniline zirconium (IV) silicophosphate nanocomposite for remediation of methylene blue dye from waste water, J. Mol. Liq., 190 (2014) 139–145. [32] A. Nilchi, M. G. Maragheh, A. Khanchi, M. A. Farajzadeh, A. A. Aghaei, Synthesis and ion-exchange properties of crystalline titanium and zirconium phosphates, J. Radioanal. Nucl. Ch., 261 (2004) 393-400.
[33] C. C. Yang, G.M. Wu, Study of microporous PVA/PVC composite polymer membrane and it application to MnO2 capacitors, Mater. Chem. Phys., 114 (2009) 948– 955. [34] B. M. Mosby, A. Diaz, V. Bakhmutov, A. Clearfield, Surface Functionalization of Zirconium Phosphate Nanoplatelets for the Design of Polymer Fillers, ACS Appl. Mater. Interfaces, (2014), 585−592. [35] M. Singh, S. Kaushal, P. Singh, J. Sharma, Boron doped graphene oxide with enhanced photocatalytic activity for organic pollutants, J. Photoch. Photobio. A, 364 (2018) 130–
ro of
139. [36] H. M. Hegab, Y. Wimalasiri, M. Ginic-Markovic, L. Zou, Improving the fouling resistance of brackish water membranes via surface modification with graphene oxide functionalizedchitosan, Desalination, 365 (2015) 99–107.
[37] J. O. Titiloye, I. Hussain, Synthesis and characterization of silicalite-1/carbon-
-p
graphite membranes, J. Colloid Interface Sci., 318 (2008) 50–58.
[38] J. H. Choi, S.H. Moon, Pore size characterization of cation-exchange membranes by
re
chronopotentiometry using homologous amine ions, J. Membr. Sci., 191 (2001) 225–236. [39] K. Sollner, An Outline of the Basic Electrochemistry of Porous Membranes, J.
lP
Dental Res., 53 (1974) 267–279.
[40] C. Klaysom, R. Marschall, L. Wang, B. P. Ladewig, G. Q. Max Lu, Synthesis of nanocomposite ion-exchange membranes and their electrochemical properties for
na
desalination applications, J. Mater. Chem., 20 (2010) 4669–4674. [41] C. Klaysom, R. Marschall, L. Wang, B. P. Ladewig, G. Q. M. Lu, Synthesis of composite ion-exchange membranes and their electrochemical properties for
ur
desalination applications, J. Mater. Chem., 20 (2010) 4669-4674. [42] J. H. Choi, H. J. Lee, S. H. Moon, Effects of Electrolytes on the Transport
Jo
Phenomena in a Cation-Exchange Membrane, Colloid. Interfac. Sci., 238 (2001) 188195.
[43] E. Güler, R. Elizen, D. A. Vermaas, M. Saakes, K. Nijmeijer, Performancedetermining membrane properties in reverse electrodialysis, J. Memb. Sci., 446 (2013) 266–276. [44] P. Dligolecki, K. Nymeijer, S. Metz, M. Wessling, Current status of ion exchange membranes for power generation from salinity gradients, J. Memb. Sci., 319 (2008) 214–222.
Jo
ur
na
lP
re
-p
ro of
[45] A. Lehmani, P. Turq, M. Perie, J. Perie, J. P. Simonin Ion transport in Nafion 117 membrane, J. Electroanal. Chem., 428 (1997) 81-89
PII:
S2213-3437(20)30038-5
DOI:
https://doi.org/10.1016/j.jece.2020.103690
Reference:
JECE 103690
To appear in:
Journal of Environmental Chemical Engineering
Received Date:
28 August 2019
Revised Date:
9 January 2020
Accepted Date:
12 January 2020
Please cite this article as: Kumari V, Badru R, Singh S, Kaushal S, Singh PP, Synthesis and Electrochemical Behaviour of GO doped ZrP nanocomposite membranes, Journal of Environmental Chemical Engineering (2020), doi: https://doi.org/10.1016/j.jece.2020.103690
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2019 Published by Elsevier.
Synthesis and Electrochemical Behaviour of GO doped ZrP nanocomposite membranes
Vanita Kumari, Rahul Badru, Sandeep Singh, Sandeep Kaushal*& Prit Pal Singh*
Sri Guru Granth Sahib World University, Fatehgarh Sahib, Punjab, India
ro of
Address for Correspondence: Dr. Sandeep Kaushal Assistant Professor Department of Chemistry, Sri Guru Granth Sahib World University, Fatehgarh Sahib (Pb), India. Mobile No: +91-7009795652 Email: [email protected]
lP
re
-p
& Dr. Prit Pal Singh Professor and Head, Department of Chemistry, Sri Guru Granth Sahib World University, Fatehgarh Sahib (Pb), India. Mobile No: +91-84270-00415 Fax: +91-1763-234236, Email: [email protected] Abstract
In this study, new nanocomposite ion-exchange membranes were prepared by incorporating
na
graphene oxide (GO) in the inorganic matrix of zirconium phosphate (ZrP) by sol-gel method. The synthesized GO-ZrP membranes were characterized by X-ray diffraction, scanning
ur
electron microscopy (SEM) and transmission electron microscopy (TEM). Water content and ion exchange capacity were found to increase initially with increase in concentration of GO up
Jo
to 0.2 wt% and then decreased with further increase in concentration of GO. The electrochemical properties of prepared membranes like membrane potential, transport number, fixed charge density, permeability and ionic flux were explored. The fabricated membranes exhibited higher membrane potential, transport number and fixed charge density for monovalent ions (NaCl) than those for bivalent ions (BaCl2). These membranes exhibited lower permeability and ionic flux for bivalent ions as compared to those for monovalent ions. The conductivity measurements for both monovalent and bivalent ions were performed on the
nanocomposite membranes, and it was noticed that the conductivity of the membranes was higher for monovalent ions. Keywords: GO-ZrP nanocomposite; Electrochemical Studies; monovalent & bivalent ions; Transport number 1. Introduction Waste water treatment is picking up pace nowadays, to meet the ever increasing demand of drinking water owing to massive increase in population. Membrane separation technology retains a prime position in waste water treatment processes since long, due to its easy mode of operation and high efficiency [1]. It is one of the most reliable and frequently adopted methods
ro of
among diverse ways of water purification. Earlier, sole inorganic materials like zirconium antimonate, zirconium phosphate, tin arsenate and phosphate [2-5] and hydrous oxides of metals [6] were employed for the fabrication of purification membranes. But with advancement in technology, the composite materials, which exhibit enhanced porosity and stability [7], have
-p
almost replaced these sole inorganic materials in separation and purification procedures. Composites integrate two or more materials with desired characteristics, with the aim to
re
generate synergic effect. The composites in the light of their improved properties, find applications in diverse fields like electrochemistry, desalination, fuel cells, waste water
lP
treatment, removal of heavy metal ions and sensors [8-10]. Integration of different groups in the nanocomposite structures make them multifunctional and thus, these serve as better ionexchangers [11-13]. Consequently, the nanocomposite membranes manifest improved
na
electrochemical properties like high permeability, high flux and high charge density [14-15]. Numerous nanocomposite-based membranes have been reported in literature, for water purification [16-17]. Carbon based nanomaterials such as carbon nanotubes, graphene and
ur
graphene oxide have been observed to be promising dopants for membrane modifications in desired direction [18]. Previous work on membranes with GO as a dopant, demonstrates the
Jo
effectiveness of using GO as a modifier [19]. Graphene oxide (GO) is a porous material with a variety of oxygen functionalities which impart excellent electrochemical, mechanical, thermal and chemical properties to it [20-21]. It is worth mentioning that the majority of graphene oxide remains embedded in the bulk of the membrane [22-23] rendering it unavailable for surfacebased interactions. Since most of the applications of materials pertain to their surface phenomena, it is highly desirable to inculcate the dopant on the surface of nanocomposite, rendering the active sites available for ion exchange on the surface of the nanocomposite [24]. Zirconium phosphate is the material of choice as it belongs to an excellent class of inorganic
ion exchangers among tetravalent metal-acid salts [4,12]. It has recently been confirmed as a very good sorbent for heavy metals due to its high selectivity, thermal stability, and insolubility in water. In this context, the present study reports the doping of graphene oxide in zirconium phosphate, with the intention to synthesize a composite material with upgraded electrochemical properties. Membranes fabricated from the prepared composite material were evaluated for their electrochemical characteristics like membrane potential, transport number, fixed charge density, permeability and ionic flux. The results obtained highlight the potential of graphene oxide as a surface-active agent for the materials.
ro of
2. Experimental 2.1 Reagents and instruments
Zirconyl oxychloride, ortho-phosphoric acid (Loba Chemie, India) and graphite powder (Qualikems Lab, India) were used for synthesis. All other chemicals used were of AR grade,
-p
and used as such without further purification. Double distilled water (DDW) was used during the experiments. Standard solutions were prepared by direct weighing of AR grade reagents
re
using double distilled water (DDW). X-ray diffractometer (PAN Analytical, System No. DY 3190), surface scanning electron microscope (JEOl, JSM-6510LV), transmission electron microscope (MIC JEM 2100), digital potentiometer (Systronic 318), digital conductivity meter
lP
(Systronic, India) having platinum electrode as reference electrode and drop shape analyserDSA 25 were used for contact angle measurements.
na
2.2 Preparation of GO-ZrP nanocomposite
Zirconium phosphate was synthesized by sol-gel method [4]. Graphene oxide (GO) was prepared by modified Hummer’s method which involves both oxidation and exfoliation of
ur
graphite sheets [11]. GO-ZrP nanocomposite was prepared by sol-gel method. Powdered graphene oxide (GO) in different mass ratio was introduced into the ZrP gel and the mixture
Jo
was stirred at room temperature for 4 h at 60ºC using mechanical stirrer. Then the mixture was allowed to stand overnight. The nanocomposite was filtered under suction and washed with DDW to remove the unreacted part. The gel was then dried in an air oven at 80ºC. Five samples (S1–S5) were prepared by varying the concentration of graphene oxide (GO) in fixed quantity of zirconium phosphate (ZrP). 2.5 Preparation of membrane
The heterogeneous cation exchange membranes were fabricated by solution casting technique [16]. Polyvinylchloride (PVC) binder was dissolved in THF (THF: PVC = 20:1, v/w) in a flat bottom flask by stirring for 6 h, and a definite quantity of nanocomposite of 200 mesh size (nanocomposite: PVC = 1:1, w/w) was added to the polymeric solution (Table 1). The resulting solution was stirred for 30 min with a magnetic stirrer, followed by sonication for uniform dispersion of particles. The mixture was then poured into a glass ring fitted on a clean dry glass plate and kept overnight to allow the solvent evaporate. The membranes obtained were kept in DDW overnight and then in 0.5 M NaCl solution for 48 h. 2.6 Physical characterization of fabricated GO-ZrP nanocomposite membranes
ro of
2.6.1 Swelling
The swelling of the membrane was measured by a screw gauge by the already reported method [17].
-p
2.6.2. Porosity (ε)
Porosity is a measure of the volume of water incorporated in the cavities per unit membrane
mw md AL w
(1)
lP
re
volume, and is calculated from the following relation:
Where, mw and md are the mass (g) of wet and dry membrane, respectively. L is thickness of
na
the membrane, A is area of the membrane, and ρw is density of water [18]. 2.6.3 Water uptake by membrane
ur
The membrane was soaked in water and then blotted quickly with Whatman filter paper to remove surface moisture and weighed immediately. This membrane was then dried in vacuum
Jo
over P2O5 for 24h. Following equation was used to calculate the water content [19] Water Content (%) =
W wet W dry
100
(2)
W dry
Where, Wwet and Wdry are the masses (g) of the wet and the dry membrane, respectively. 2.6.4 Ion-exchange Capacity Ion-exchange capacity (IEC) of dry ZrP and differently doped GO-ZrP nanocomposite membranes were determined by batch method [25]. The synthesized membrane was treated
with HNO3 for 24h and then washed 2-3 times with demineralized water. After drying, membranes were dipped overnight in 0.1 M NaNO3 solution. The effluent is then titrated with 0.01M NaOH to estimate the amount of H+ ions substituted in the membrane by Na+ ions. Ion exchange capacity of the membrane was calculated by the formula: IEC
M V
meq g
1
(3)
W
Where, M is molarity and V is volume of NaOH consumed in mL and W is mass of GO-ZrP membrane (g).
ro of
2.6.5 Contact Angle Measurement The contact angle measurements between water droplets and pristine as well as GO-doped membranes dried at 120 ˚C were made by advance sessile drop method [26]. 2.8 Electrochemical Characterization of Fabricated Membranes
-p
2.8.1 Electrode assembly
The membrane potential was measured with a digital potentiometer. The membrane was pasted
re
with araldite at the centre of electrode assembly, which had two electrode chambers having cavities to introduce electrolyte solution and standard calomel electrode. The solution (1.0 M)
lP
of each of the electrolytes such as sodium chloride and barium chloride were filled in the chambers. The electrode assembly is depicted below:
na
Hg │ Hg2Cl2, Cl¯ ║soln. C1 │ Membrane │ soln. C2 ║ Cl¯, Hg2Cl2(s) │ Hg The concentration ratio of the electrolyte solutions taken for potential measurements was 10 i.e. C1/C2=10. The membrane potentials across the membranes were measured by using
ur
electrolyte solutions in the concentration range of 0.01 to 0.1 M [27].
Jo
2.8.2 Membrane potential and transport number The potential difference developed across the membrane was measured against Hg–Hg2Cl2, Cl¯ reference electrode on either side of the membrane, using a digital potentiometer. The electrolyte solution of next higher concentration was used to rinse the electrode chambers which were then filled with the same solution. The new potential difference was noted after 2 h during which the membrane attains equilibrium. The membrane potential measurements were reproducible to [25, 27]:
0.1 mV. The transport number
t
can be calculated by the following equation
E m 2 . 303
RT nF
( 2 t 1 ) log
C2
(4)
C1
where R is gas constant, F is Faraday’s constant, T is absolute temperature, C1 and C2 are the concentrations of electrolyte solutions in the test cell. 2.8.3 Permselectivity Permselectivity of the membrane can be expressed quantitatively, based on the migration of counter ions through the ion exchange membrane [6, 28]: t t
(5)
1 t
where Ps is the permselectivity of membrane,
t
and
t
ro of
Ps
refer to the transport number of counter
ions in the membrane and in free solution at same concentration, respectively. 2.8.3 Fixed charge density ( X )
-p
The fixed charge density denotes the electrical character of a membrane. The fixed charge density of the fabricated membrane for 1: 1 and 1: 2 electrolytes was evaluated by the following
1
1 1 2
1 Slope
(6)
lP
X
re
equation [25]:
where δ is the ratio C2/C1, α and β are constants.
na
2.9 Conductivity, ionic permeability and flux of ions The conductivity, ionic permeability and flux of ions were estimated by utilizing the test cell. NaCl or BaCl2 solution (0.1 M) was placed on one side of the cell and a 0.01M solution of the
ur
same electrolyte on its other side. A DC electrical potential with constant voltage (10V) was applied across the cell with platinum electrodes placed at the end of the compartments. The
Jo
variation of conductivity with time was measured using digital conductivity meter. During this experiment, the ions permeate into the permeation section through the membranes and hence, the conductivity of permeation section increases with time. Both the sections were re-circulated and stirred vigorously between two successive measurements to ensure the attainment of equilibrium in the two solution-membrane interfacial zones, and to minimize the effect of boundary layers. The permeation of ions can be determined from the slope of straight line plot of conductivity vs. time. According to first Fick’s law, the flux of ions through the membrane can be expressed as follows [20-21]
N P
C1 C 2
(7)
d
where, C1 and C2 are the concentrations of electrolyte solution on either side of the membranes, d is membrane thickness, P is the diffusion co-efficient of ions and N is ionic flux. N
V
dC
A
P
1
C1 C 2
dt
(8)
d
C 1 0 . 1 M , C 2 0 . 01 M , C 1 + C 2 0
0
= C 10
C 02 =0.11M
(9)
Where, A (m2) is the surface area of the membrane. By integrating the equation (8), we get 1
ln
2
(C 0 C 2 ) 1
0
2 PAt
(10)
Vd
ro of
(C 0 C 0 2 C 2 )
The diffusion coefficient and flux of cations in membrane phase were calculated from equation (10), and various parameters were determined by variation of conductivity in cathodic compartment [29].
-p
3. Results and discussion
Various samples of GO-ZrP nanocomposite membranes were synthesized by incorporating
re
different mass ratios of graphene oxide into the inorganic matrix of zirconium (IV) phosphate. The ion exchange capacity, thickness, water content and porosity of fabricated membranes is
lP
summarized in Table 1. It is clear from the data in Table 1 that membrane M-3 has maximum thickness, water content and ion exchange capacity among all the fabricated membranes.
Properties
0-GO (M-1)
0.1-GO (M-2)
0.2-GO(M-3)
0.3-GO (M-4)
0.4-GO (M-5)
0.47 ±0.02 5.23±0.13 2.47±0.05 0.17±0.02
0.44±0.04 5.35±0.15 2.51±0.04 0.22±0.01
0.53±0.02 6.89±0.11 5.29±0.03 0.26±0.03
0.49±0.04 5.70±0.16 5.71±0.05 0.23±0.02
0.42±0.03 5.41±0.14 5.66±0.04 0.18±0.02
Jo
ur
Thickness (mm) Water content (%) Porosity IEC (m equiv g-1)
na
Table 1: Properties of nanocomposite membranes
FTIR spectroscopic studies were carried out for various synthesized sample membranes M-1 to M-5, to confirm the incorporation of GO into the inorganic matrix of ZrP (Fig. 1). In the FTIR spectrum of pure zirconium phosphate, ionic phosphate stretching appears around 1000 cm-1 [30,31]. Peak around 700-800 cm-1 may be assigned to M-O stretching [32]. With the introduction of GO into the inorganic material, few more stretching peaks at 3850, 3750, 2350 cm-1 which are characteristic of GO, become clearly visible in the FTIR spectrum. Similarities
were noticed for all modified ZrP membranes. The peaks at 1000 and 1620 cm-1 were observed
re
-p
ro of
in all the membranes but the intensity was lower for samples M-2 to M-5.
lP
Fig. 1: FTIR spectra of fabricated membranes
The XRD pattern of fabricated membranes was recorded between 5° to 65° at 2ϴ, using Cu Kα radiation (Fig. 2). As can be seen from the XRD pattern of membrane M-1, there is appearance
na
of peak at 2ϴ = 19.7 which might be due to zirconium phosphate and binder present in the membrane phase [4, 33, 34]. It has been observed that with the enhanced additive loading of GO in the membrane phase (M-2 to M-5), the peak intensity at 2ϴ = 19.7 is greatly reduced
ur
and a new peak at 2ϴ = 9.5 appeared, which is attributed to the presence of GO in the membrane phase [35]. It is clear from the XRD patterns (Fig. 2) that the fabricated membranes are semi
Jo
crystalline in nature. Also, the intensity of the peak at 2ϴ = 9.5 is higher in M-3 than the other membranes, which may be due to the better interactions of GO at moderate concentration, with ZrP in the membrane phase.
ro of -p
re
Fig. 2 XRD patterns of the fabricated nano-composite membranes
SEM study was performed to predict the surface texture, homogeneity and cracks on the GO-
Jo
ur
na
lP
ZrP nanocomposite membrane (Fig. 3).
ro of -p
re
Fig. 3: SEM images of a) M-1, b) M-2, c) M-3, d) M-4, e) M-5 membranes and f) EDS spectra
lP
of nanocomposite
It is clear from the images that the GO particles are uniformly distributed throughout the membrane which has a smooth surface [24-27]. It has been observed that the increase of GO
na
content in the casting solution leads to the formation of voids and enlargement of channels in the membrane matrix. It was observed that the porous nature of nanocomposite membranes increases and cracks appear at the surface of membrane with increase of GO content in the
ur
membrane to 0.3wt%. Further, increase of GO content to 0.4wt% led to the decrease of porosity due to severe aggregation of nanoparticles in the membrane matrix. Such a deviation in the
Jo
porosity of membrane with the variation of GO content is likely to affect the physio-chemical properties of the fabricated membranes. The EDS spectra of the membrane confirm the presence of Zr, P, C and O elements in the membrane matrix.
ro of
-p
Fig. 4: FESEM images of cross-section of a) M-1, b) M-2, c) M-3, d) M-4, e) M-5
The cross-sectional images of fabricated membranes have been shown in Figure 4a-e. It is clear
re
from the images that the morphology of fabricated membranes has slightly changed with the increase in GO content. Moreover, the cross-sectional images confirm the regularity in the
Jo
ur
na
lP
porosity of the synthesized membranes.
ro of -p
re
Fig. 5: TEM images of a) M-1, b) M-2, c) M-3, d) M-4, e) M-5 nanocomposite membranes The water content increased from 5.23 to 6.89 % with the increase of GO content in the range
lP
0.1-0.3 wt%. This might be due to hydrophilic nature of added GO, expansion of flow channels in the membrane phase and increase in heterogeneity of the membrane that provides more free spaces for lodging of water molecules [36-37]. On the other hand, the properties of
na
nanocomposite membrane did not improve further with the increase of GO content in the membrane matrix. This may be attributed to the decrease in porosity of the membrane due to blocking of membrane flow channels at high additive loading of GO which diminishes the
ur
membrane water capacity and decreases the membrane hydrophilicity, leading to poor performance of the membrane. The appropriate water content in the membrane matrix leads to
Jo
better flow channels for ion traffic and enhances permselectivity of the membrane. It has been reported that the porosity also affects the transport properties and selectivity of the ion exchange membranes [38]. The membranes with large pore size lose the selectivity, and the pores smaller than ionic species behave like inaccessible pathways or non-conducting regions for ionic species [39]. In this work, similar trend of ion exchange capacity has been observed with variation in water content for the fabricated membranes. The ion exchange capacity of the nanocomposite membranes increased initially with the addition of GO as compared to pristine membrane. The cavities and voids are formed in the
bulk of membrane on incorporation of GO. Further increase of GO content in the casting solution did not enhance the ion exchange capacity of the membrane (Table 1). This might be due to the aggregation of particle clusters of GO, leading to partial blockage of cavities and voids in the membrane [40]. This observation was also supported by the decrease in porosity and water content of fabricated membranes with increased additive loading of GO. Hydrophilic character of pristine and graphene oxide doped membranes was determined by measuring the contact angle between membranes and water droplets. Distilled water was used as a probe in all experiments. Ten consecutive measurements were taken for every sample, to minimize the experimental error. It was observed that the pristine membrane is highly
ro of
hydrophobic in nature. Hydrophilicity of doped membranes was higher as compared to pristine membrane on doping the parent membrane with graphene oxide in different percentage ratios (0.1%-0.4%) which was supported by a drastic change in contact angle from 112º to 83º, respectively (Fig. 6). The increase in hydrophilic character is due to intense supra-molecular
π…π, CH…π interactions between -OH and -COOH
Jo
ur
na
lP
re
substituents on pristine ZrP and graphene oxide.
-p
hydrogen bonding OH…..H, C=O…..H,
Fig. 6: Effect of GO content on the membrane water contact angle
3.4 Electrochemical studies of GO-ZrP nanocomposite membranes 3.4.1 Membrane potential and transport numbers
The synthesized membranes were characterized electrochemically in monovalent (NaCl) and bivalent (BaCl2) ionic solutions. The variation of membrane potentials and transport numbers of Na+ and Ba2+ with concentration of electrolyte is shown in Fig. 7 and 8, respectively. Membrane potentials (Fig. 7) and transport numbers (Fig. 8) were found to be highest at different concentrations of both the electrolytes in membrane M-3 as compared to other membranes. This may be due to higher crystallinity of M-3, as compared to that of other membranes, which provides suitable ionic pathways for the movement of ions. It is important to mention that both the membrane potentials and transport numbers of Na+ and Ba2+ ions in different membranes under investigation follow the order: M-3 > M-4 > M-5 > M-
ro of
2 > M-1. The membrane potentials and transport numbers (mobility) of both the electrolytes in the membrane phase increase with increase in concentration of the electrolyte in all the membranes except M-1 up to a certain concentration, and then decrease with further increase
na
lP
re
-p
in concentration.
ur
Fig. 7. Effect of concentration of electrolyte on membrane potentials for a) alkali (Na+) and
Jo
b) alkaline earth metal (Ba2+) ions
The initial increase in membrane potential and transport numbers with increase in concentration of the electrolyte is attributed to the increase in number of free cations (counter ions) available for transport. With further increase in concentration of electrolyte, the number of free ions available for transport decreases due to increase in inter-ionic interactions at higher concentarion and concentration polarization phenomenon [25]. As a result, the membrane potential and transport numbers decrease as the concentartion of electrolyte was increased beyond a certain limit. Also, the membrane potential as well as the transport numbers were
found to be higher for Na+ as compared to those for Ba2+. The lower electrochemical values for bivalent ionic solutions may be due to the formation of stronger bonds by bivalent ions with the functional groups of the ion exchanger, which results in decrease of membrane potential, transport number and fixed charge density. The stronger electrostatic attraction between the bivalent ions and fixed oppositely charged sites prevents the dissociation of cations from the
-p
ro of
functional groups on the ion exchanger (Fig. 7b).
re
Fig. 8. Effect of concentration on the transport numbers for a) alkali (Na+) and b) alkaline earth metal (Ba2+) ions
lP
3.4.2 Permselectivity and fixed charge density ( X )
Permselectivity represents the ion selectivity of ion exchange membranes and is a measure of
na
the ease of migration of counter-ions through the membranes. The permselectivity (Fig. 9a) and fixed charge density (Fig. 9b) in different membrane compositions exhibit the same trend with variation in concentration of the electrolyte as followed by membrane potentials and
ur
transport numbers. The observed values of fixed charge density (Fig. 9b) indicate that larger part of internal fixed charge is inactive. The higher fixed charge density of the membrane for
Jo
Na+ is attributed to its smaller hydrated ionic radius as compared to that of Ba2+ ions.
ro of
Fig. 9. a) Variation of permselectivity with mean concentration of electrolyte for alkali metal ions; b) fixed charge density of different membranes for alkali and alkaline earth metal ions
-p
3.5 Ionic permeability and flux of ions
The ionic permeability and flux for Na+ ion enhanced with the increase in GO content up-to
re
0.2 wt% and then, a decrease in the values was observed with further increase in GO concentration (Fig. 10). The inoculation of GO into the membrane increased the surface
lP
hydrophilicity and thus facilitates the transportation of ions between the solution and the membrane phase, resulting in better ionic permeability and flux of the membrane. Moreover, the conducting behaviour of the membrane was enhanced by semi-conducting characteristics
na
of GO, which provides more conducting regions, and strengthened the electrical field around
Jo
ur
the modified membranes.
Fig. 10. Comparison of a) permeability and b) flux of monovalent and bivalent ions
The values of ion diffusion coefficients across the membrane indicate that at low wt% of GO, the control of the ion diffusion process across the membrane is kinetic (favorable diffusion and good even at low temperature), whereas at high% of GO, the process is energetically controlled (unfavorable diffusion and low at low temperature). 3.6 Ionic conductivity The ionic conductivity of fabricated membranes was studied and is depicted in Fig. 11. It was observed that the introduction of GO nanoparticles in the membrane matrix leads to increase of ionic conductivity slightly from M-1 to M-3. The enhancement in the conductivity might be
ro of
due to the presence of hydroxyl and carboxyl groups present on the GO particles. Interestingly, the ionic conductivity follows the same trend as that of membrane potential and transport
ur
na
lP
re
-p
numbers (Fig. 7 and 8).
Jo
Fig. 11. Variation of conductivity with time of prepared membranes for a) monovalent and b) bivalent ions It is apparent that 0.2wt% GO membrane (M-3) has good IEC, high membrane potential, transport number, fixed charge density and high porosity that might be the reason for the best conductivity of this membrane as compared to other membranes in the same series. Hence, the synergetic effect of the additive loading of GO and porosity might play an important role in affecting the overall membrane properties.
A comparison between electrochemical properties of fabricated membrane (M-3) in this study with some commercial reported membranes is given in Table 2. Table 2: A typical comparison between various properties of some commercial membranes and modified membrane in this work Water content (%)
Fixed Charge density
Transport Number
Permselectivity
Conductivity (Scm-1) /Resistancea
Ref.
Sulphonated 0.99 polyether sulphone (sPES) Neosepta 1.5-1.8 CMX
0.20
12.37
7.12
0.92
86.78
0.114
41
0.176
25
-
0.97
97
1.8-3.8 a
42
CMV
2.4
0.137
25
-
0.98
RALEX CMH-PES
2.34
0.764
31
-
0.946
Nafion 117
0.90
0.20
16
-
This research 0.26 (Sample 3)
0.53
6.89
63
Conclusion
2.9 a
43
94.7
11.33a
44 45
-p
95
-
97
1.5a
0.99
8.1
15.3
re
Resistance values (in Ωcm2)
ro of
Thickness (mm)
a
IEC (meq/g)
lP
Membrane
na
In the present study, GO doped ZrP composite cation exchange membranes were prepared by solution casting technique, using PVC as binder. Sonication was employed to achieve better homogeneity and electrochemical properties of the membrane matrix. Results revealed that
ur
with the increase of GO concentration in the casting solution, water uptake and ion exchange capacity of membranes increased initially up to 0.2wt% and then showed decreasing trend with
Jo
increase in additive loading of GO from 0.2 to 0.4 wt%. The membrane potential, transport number, fixed charge density and permselectivity values obtained with the fabricated membrane of the nanocomposite were found to be higher for monovalent cations (Na+) than those for bivalent cations (Ba2+) which may be attributed to the hindrance in the movement of bivalent ions. For both monovalent and bivalent ionic solutions, membrane permeability and flux were enhanced initially with the increase in GO concentration to 0.2wt% and then showed decreasing trend with more additive loading of GO. Moreover, the modified membranes containing GO showed better electrochemical properties in comparison to pristine membrane.
Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Author Contributions Section Contribution in this manuscript
1 Vanita Kumari in the research work.
She has done the synthesis and experimental work
2
Dr. Rahul Badru
Contributed in writing and spectroscopic studies.
3
Dr. Sandeep Singh
Contributed in contact angle measurement
ro of
Sr. No. Author Name
4 Dr. Sandeep Kaushal his supervision.
Proposed the work and all the work done under
5
Supervisor and assist in electrochemical studies.
Jo
ur
na
lP
re
-p
Dr. Prit Pal Singh
References
[1] J. Ran, L. Wu, Y. He, Z. Yang, Y. Wang, C. Jiang, L. Ge, E. Bakangura, T. Xu, Ion exchange membranes: New developments and applications, J. Membr. Sci., 522 (2017) 267–291. [2] M. M. A. Khan, Rafiuddin, Synthesis, estimation of stability in different media, electrochemical propertiesand potentiometric studies of PVC-based NP ion-exchange
Desalin Water Treat., 57 (2015) 18346-18353.
ro of
nanocomposite membrane for desalination and waste water treatment applications,
[3] C. Cornelius, C. Hibshman, E. Marand, Hybrid organic–inorganic membranes, Sep. Purif. Technol., 25 (2001) 181–193.
[4] S. Kaushal, P. K. Sharma, S. K. Mittal, P. Singh, Novel zinc oxide–zirconium (IV)
-p
phosphate nanocomposite as antibacterial material with enhanced ion exchange properties, J. Colloid Interface Sci., 7 (2015) 1-6.
re
[5] P.V. Vyas, P. Ray, S.K. Adhikary, B.G. Shah, R. Rangarajan, Studies of the effect ofvariation of blend ratio on permselectivity and heterogeneity of ion-
lP
exchangemembranes, J. Colloid Interface Sci., 257 (2003) 127–134. [6] G.S. Gohli, V.V. Binsu, V.K. Shahi, Preparation and characterization of monovalention selective polypyrrole nanocomposite ion-exchange membranes, J. Membr.
na
Sci., 280 (2006) 210–218.
[7] S.M. Hosseini, S.S. Madaeni, A.R. Khodabakhshi, Heterogeneous cation exchangemembrane: preparation, characterization and comparison of transport
ur
propertiesof mono and bivalent cations, Sep. Sci. Technol., 45 (2010) 2308–2321. [8] J. S. Lin, S. R. Kumar, W. T. Ma, C. M. Shih, L. W. Teng, C. C. Yang, S. J. Lu,
Jo
Gradiently distributed iron oxide@ graphene oxide nanofillers in quaternized polyvinyl alcohol composite to enhance alkaline fuel cell power density, J. Membr. Sci., 543 (2017) 28–39. [9] Y. Zhang, K. Su, Z. Li, Graphene oxide composite membranes cross-linked with urea for enhanced desalting properties, J. Membr. Sci., 563 (2018) 718–725. [10] Y. Zhang, S. Zhang, J. Gao, T. S. Chung, Layer-by-Layer Construction of Graphene Oxide (GO) Framework Composite Membranes for Highly Efficient Heavy Metal Removal, J. Membr. Sci., (2018) 230-237.
[11] C.O. M. Bareck, Q.T. Nguyen, S. Alexandre, I. Zimmerlin, Fabrication of ionexchange ultrafiltration membranes for water treatment. I. Semi-interpenetrating polymer networks of polysulfone and poly (acrylic acid), J. Membr. Sci., 278 (2006) 10–18. [12] V. K. Gupta, D. Pathania, P. Singh, B. S. Rathore, P. Chauhan, Cellulose acetate– zirconium (IV) phosphate nano-nanocomposite with enhanced photo-catalytic activity, Carbohydr. Polym., 95 (2013) 434– 440. [13] L. Stobinski, B. Lesiak, A. Malolepszy, M. Mazurkiewicz, B. Mierzwa, J. Zemek, P. Jiricek, I. Bieloshapka, Graphene oxide and reduced graphene oxide studied by the XRD,
ro of
TEM and electron spectroscopy methods, J. Electron Spectrosc. Relat. Phenom., 195 (2014) 145–154.
[14] M. E. Uddin, R. K. Layek, H. Y. Kim, N. H. Kim, D. Hui, J. H. Lee, Preparation and enhanced mechanical properties of non-covalently functionalized graphene oxide/cellulose acetate nanonanocomposites, Compos Part B-Eng., 90 (2016) 223-
-p
231.
[15] R. Hu, R. Zhang, Y. He, G. Zhao, H. Zhu, Graphene Oxide-in-Polymer
Membr. Sci., 564 (2018) 813–819.
re
Nanofiltration Membranes with Enhanced Permeabilityby Interfacial Polymerization, J.
lP
[16] S. M. Hosseini, E. Jashni, M. R. Jafari, B. Van der Bruggen, Z. Shahedi, Nanocomposite polyvinyl chloride-based heterogeneous cationexchangemembrane prepared by synthesized ZnQ2 nanoparticles: ionic behavior and morphological
na
characterization, J. Membr. Sci., 560 (2018) 1-10. [17] M. Arsalan, A Zehra, M.M.A. Khan, Preparation and characterization of Polyvinyl chloride-basednickelphosphate ion selective membrane and its application for removal of
ur
ions through water bodies, Groundw. Sustain. Dev., 8 (2019) 41-48. [18] M. M. A. Khan, Rafiuddin, Synthesis, electrochemical characterization, antibacterial
Jo
study and evaluation of fixed charge density of polystyrene based calcium-strontium phosphate nanocomposite membrane, Desalination, 284 (2012) 200–206. [19] M. M. A. Khan, Rafiuddin, Synthesis, characterization and antibacterial activity of polystyrene based Mg3 (PO4)2/Ca3 (PO4)2nanocomposite membrane, Desalination, 294 (2012) 74–81. [20] G. S. Lai, W. J. Lau, P. S. Goh, A. F. Ismail, N. Yusof, Y. H. Tan, Graphene oxide incorporated thin film nanocomposite nanofiltration membrane for enhanced salt removal performance, Desalination, 387 (2016) 14-24.
[21] R. Hu, R. Zhang, Y. He, G. Zhao, H. Zhu, Graphene oxide-in-polymer nanofiltration membranes with enhanced permeability by interfacial polymerization, J. Memb. Sci., 564 (2018) 813-819. [22] C. Shen, E. Barrios, L. Zhai, Bulk Polymer-Derived Ceramic Composites of Graphene Oxide, ACS Omega, 3 (2018) 4006-4016. [23] H. Li, L. Pan, C. Nie, Y. Liu, Z. Sun, Reduced graphene oxide and activated carbon composites for capacitive deionization, J. Mater. Chem., 22 (2012) 15556-15561. [24] F. Perreault, M. E. Tously, M. Elimelech, Thin-Film Composite Polyamide Membranes Functionalized with Biocidal Graphene Oxide Nanosheets, Environ. Sci.
ro of
Techno. Lett., 1 (2014) 71-76. [25] S. Kaushal, G. Singh, P. Singh, T. S. Kang, Synthesis and characterization of a tin (IV) antimonophosphate nano-composite membrane incorporating 1-dodecyl-3methylimidazolium bromide ionic liquid, RSC Adv., 7 (2017) 12561–12569.
[26] M. Nemati, S. M. Hosseini, M. Shabanian, Novel electrodialysis cation exchange
removal, J. Hazard Mater. 337 (2017) 90-104.
-p
membrane prepared by 2-acrylamido-2-methylpropane sulfonic acid; Heavy metal ions
re
[27] M. M. A. Khan, Rafiuddin, Inamuddin, PVC based polyvinyl alcohol zinc oxide nanocomposite membrane: Synthesis and electrochemical characterization for heavy
lP
metal ions, J. Ind. Eng. Chem., 19 (2013) 1365–1370.
[28] X. Li, Z. Wang, H. Lu, C. Zhao, H. Na, C. Zhao, Electrochemical properties of sulfonated-PEEK used for ion exchange membranes, J. Membr. Sci., 254 (2005) 147–
na
155.
[29] S.M. Hosseini, S.S. Madaeni, A.R. Khodabakhshi, Preparation and characterization of ABS/HIPS heterogeneous cation exchange membranes with various blend ratios of
ur
polymer binder, J. Membr. Sci., 351 (2010) 178–188. [30] C. N. R. Rao, Chemical Applications of Infrared Spectroscopy, J. Chem. Educ., 42
Jo
(1965) 117-118.
[31] V. K. Gupta, D. Pathania, N. C. Kothiyal, G. Sharma, Polyaniline zirconium (IV) silicophosphate nanocomposite for remediation of methylene blue dye from waste water, J. Mol. Liq., 190 (2014) 139–145. [32] A. Nilchi, M. G. Maragheh, A. Khanchi, M. A. Farajzadeh, A. A. Aghaei, Synthesis and ion-exchange properties of crystalline titanium and zirconium phosphates, J. Radioanal. Nucl. Ch., 261 (2004) 393-400.
[33] C. C. Yang, G.M. Wu, Study of microporous PVA/PVC composite polymer membrane and it application to MnO2 capacitors, Mater. Chem. Phys., 114 (2009) 948– 955. [34] B. M. Mosby, A. Diaz, V. Bakhmutov, A. Clearfield, Surface Functionalization of Zirconium Phosphate Nanoplatelets for the Design of Polymer Fillers, ACS Appl. Mater. Interfaces, (2014), 585−592. [35] M. Singh, S. Kaushal, P. Singh, J. Sharma, Boron doped graphene oxide with enhanced photocatalytic activity for organic pollutants, J. Photoch. Photobio. A, 364 (2018) 130–
ro of
139. [36] H. M. Hegab, Y. Wimalasiri, M. Ginic-Markovic, L. Zou, Improving the fouling resistance of brackish water membranes via surface modification with graphene oxide functionalizedchitosan, Desalination, 365 (2015) 99–107.
[37] J. O. Titiloye, I. Hussain, Synthesis and characterization of silicalite-1/carbon-
-p
graphite membranes, J. Colloid Interface Sci., 318 (2008) 50–58.
[38] J. H. Choi, S.H. Moon, Pore size characterization of cation-exchange membranes by
re
chronopotentiometry using homologous amine ions, J. Membr. Sci., 191 (2001) 225–236. [39] K. Sollner, An Outline of the Basic Electrochemistry of Porous Membranes, J.
lP
Dental Res., 53 (1974) 267–279.
[40] C. Klaysom, R. Marschall, L. Wang, B. P. Ladewig, G. Q. Max Lu, Synthesis of nanocomposite ion-exchange membranes and their electrochemical properties for
na
desalination applications, J. Mater. Chem., 20 (2010) 4669–4674. [41] C. Klaysom, R. Marschall, L. Wang, B. P. Ladewig, G. Q. M. Lu, Synthesis of composite ion-exchange membranes and their electrochemical properties for
ur
desalination applications, J. Mater. Chem., 20 (2010) 4669-4674. [42] J. H. Choi, H. J. Lee, S. H. Moon, Effects of Electrolytes on the Transport
Jo
Phenomena in a Cation-Exchange Membrane, Colloid. Interfac. Sci., 238 (2001) 188195.
[43] E. Güler, R. Elizen, D. A. Vermaas, M. Saakes, K. Nijmeijer, Performancedetermining membrane properties in reverse electrodialysis, J. Memb. Sci., 446 (2013) 266–276. [44] P. Dligolecki, K. Nymeijer, S. Metz, M. Wessling, Current status of ion exchange membranes for power generation from salinity gradients, J. Memb. Sci., 319 (2008) 214–222.
Jo
ur
na
lP
re
-p
ro of
[45] A. Lehmani, P. Turq, M. Perie, J. Perie, J. P. Simonin Ion transport in Nafion 117 membrane, J. Electroanal. Chem., 428 (1997) 81-89