Essay: Performance enhancement of PA-TFC RO membrane by using magnesium silicate nanoparticles

Abstract:
This study focus on to the change of the execution of polyamide (PA) thin-film composite (TFC) reverse osmosis (RO) membrane utilizing surface alteration by MgSiO3 nanoparticles. This has been an expert by means of holding of the practical grafting of PA layer with magnesium silicate nanoparticles (MgSiO3) in the presence of 2-acylamido 2-methyl propane sulphonic acid (AMPS) as condensing monomer. To confirm the presence of MgSiO3 nanoparticles and to inspect the morphology of the TFC nanoparticles layer SEM, FT-IR, XRD, TGA and DMA analysis were used.. The outcomes demonstrated that the AMPS are effectively joined on the TFC film surface with an upgrade in thermal and mechanical decencies contrasted with pristine TFC layer. Besides, the contact angel estimations demonstrate an increase in the hydrophilicity of the thin film surface by the addition of nanoparticles. The water flux and salt rejection of the modified membranes were 25 L/m2h and 95.5%, respectively.
Keywords: Membrane performance, Reverse osmosis, Water desalination, Thin film composite, Magnesium silicate nanoparticle.
1. Introduction
water prerequisites are constantly expanding because of inhabitance increase (The ask for water has develop, twice as quick as population)[1], and enhancing gauges of manor and in addition the legislative approach to support industrialization, adjacent to that the environmental change impact and the current of physical water shortage, numerous areas in the circle have-not great crisp drinking water, particularly, in the Middle East district, a definitive water-rare zone of the world [2].
Egypt as one illustration has achieved a state where the arrangement of water accessible is incomparable cutoff points on its occupant financial improvement. As a sign of shortage in outright terms, frequently the edge estimation of (1000m3/capita/year), is utilized. Egypt has passed that edge as of now in the nineties. As a limit of total shortage (500m3/ca/yr) is utilized, this will be clear with populace forecast for 2025 which will get Egypt down to 500m3/ca/yr [3].
Desalination has a considerable part in water maintainability for some nations concerning the world that supply a safe and extreme wellspring of water particularly in beach front zones, where ,around 23% of the circle populace lives inside 100 km of the ocean and populace densities in waterfront districts are around three circumstances more than the mainstream normal [4]
Membrane technology shared about 63.7% of the total power of secular desalted water; legitimize the significance of membrane technologies in this application [5]. Membrane-established filtration is the current leading energy-efficient technology for the cleanup and desalination of brackish water, recycled water, and arid seawater. Membrane-established filtration is also capable of removing serious pollution, such as arsenic, as well as poisonous organic compounds [6].
Commercial interest in Reverse Osmosis tech¬nology is growing globally due to continuous process improvements, which in turn lead to important cost reductions. These advances include developments in films accessories and module layout, process design, feed pretreatment, energy recovery, and reduction in energy consumption [7]. A noteworthy test for membrane innovation is the inborn tradeoff between layer selectivity and permeability. The lifted vitality depletion is a huge hindrance to the wide usage, of weight driven procedures of the film [8]. In addition, it was elucidated that desalted water aliment can be miniature if membranes with rising permeability are applied, even if they display rising of the salt transit [9].
Use of nanotechnology is one of the quickly creating sciences. As demand for fresh drinking water continues to raise, nanotechnology can participate noticeable development and improvement to water treatment process [9]. Now, desalination membranes set up on the fuse of nanomaterials are realistic available, with others either close market start or in the methodology of being advanced [10]. Beginning tests recommend the novel layers have double the yield, or consume half lower vitality, shortening the aggregate cost of desalinated water by as a considerable measure as 25%[11].
Incorporation of functional nanomaterials inside membranes gives a great chance to develop the membrane permeability, fouling impedance, mechanical ,ther-mal stability as well to grant new assignment for contaminant degradation and self-cleaning[12].There is a tremendous potential for the manufacture of the mixed-matrix membrane (MMM) through the dispersion of inorganic winds in the thin polymeric layers has been performed during interfacial polym¬erization using various kinds of nanostructured materials, such as zeolite, silica, carbon nano¬tubes, and metal oxide nanoparticles, which will significantly impact desalination technologies. Incorporation of these advanced nanomaterials in the polymer matrix promises to resolve trouble, such as fouling and poor process environment compatibility, encountered when utilizing traditional polymer membranes. Mixed-matrix membrane has demonstrated outstanding desalination properties with great water flux and salt dismissal, and low biofouling potential [9]. One of the clef parameters for the successful implementation of nanocomposite Mixed-matrix membranes (MMMs) is to improve the dispersion of inorganic nanomaterial fillers in the polymer matrix through the foundation of specific interaction amidst the two phases [13]. Unfortunately, the dispersion of nanofiller is hindered by poor interfacial com¬patibility of the agglomerated nanofiller with the polymer, hence resulting in the fashioning of unselective spaces in the membranes. Weak interaction between these two phases could likewise disparagingly advancement to the leaking of the nanofiller through the membrane purifying process and after long operation. Possibilities of the nanofiller leaching from the MMM would decrease the membrane lifetime and raise concerns with regard to potential environmental and health risks related with the removal of nanomaterials [14]. MMMs had the capability to be prepared by directly coating or depositing inorganic particles upon the membrane surface. PA membrane materials are susceptible to chemical and physical hurt and also inorganic membranes materials, are more robust and can operate in process extremes of both temperature and pressure with greater resilience to chemical attack from liquids like natural solvents or potentially cleaning specialists than polymeric membranes [9]. In this study, we development of MMMs by making a surface modification via attachment of inorganic nanoparticles like magnesium silicate nanoparticles (MgSiO3 NPs) as a covering layer over a routine TFC membrane to join the two exceptional elements of natural and inorganic materials–high possibility of natural polymers and elite, as far as brilliant thermal and chemical stabilities, high selectivity and high permeability of inorganic materials.
In this work MgSiO3NPs incorporated with 2-acrylamido-2-methylepropane sulfonic acid (AMPS) grafting solution was successfully synthesized using the redox grafting technique, perfecting surface coating with nanoparticles and enhance application ofPA(TFC) membranes.The chemical structure and the morphology of the membrane grafted and modified with nanoparticles were studied and characterized by/ X-ray diffraction (X-ray), infrared spectroscopy (FTIR), Scanning electron microscope (SEM), thermal analysis (TGA), assessments of mechanical property, and contact angle (CA) determination.Optimization of the amount of MgSiO3NPs incorporated onto the TFC surface was proposed leading to the best RO membrane performance.
2. Experimental
2.1. Materials
Polysulfone pellets Udel P-3500 were supplied by Solvay advanced polymer, USA, N,N-dimethylacetamide (DMA) were supplied from (Sigma-Aldrich). metaphenylenediamine (MPDA), trimesoyl chloride (TMC), triethyl amine (TEA), (+)-10-champhor sulfonic acid (CSA), sodium lauryl sulfate (SLS), 2-acrylamido-2-methyl propane sulfonic acid (AMPS), potassium persulfate ≥ 99.0%, sodium metabisulfite ≥ 99.0%, and a commercial form of nano-magnesium silicate (MgSiO3) (diameter of particles about 15 nm) was afforded from Dixiang Chemical Engineering Co., Ltd. (Shanghai, China). Other reagents such as n-hexane, sodium chloride (NaCl) are of analytical grade, and pure water with a conductivity less than 5µs/cm was produced by a two-stage reverse osmosis system.
2.2. Characterization of MgSiO3 NPs.
Scanning electron microscope (SEM Model Quanta FEG) connected with EDX Unit, with accelerating voltage 30 K.V., magnification 250x up to 20000x and resolution for gun 1m also XRD analysis utilizing (Shimadzu X-ray) diffractometer, (Model XD 490 Shimadzu, Kyoto, Japan) and FTR-IR analysis (Nicolet avator 230 spectrometer) at room temperature were used to characterize the morphology of MgSiO3 NPs.
2.3. Preparation of microporouspolysulfone support membrane
PS casting solution was prepared by dissolving 15 wt. % PSF in DMA at 80–90 ◦C with continuous stirring. The resultant polysulfone solution was molding onto a glass tray and coagulates in a water bath. After 10 min of gelation, the resulting PSF membrane was removed from the gelation bath and washed with bi-distilled water to remove the residual DMA. The prepared PSF support membrane was saved in distilled water for at minimal 24 hr before use. The membrane was then posterior utilized as a support milieu for TFC membrane production.
2.4. Manufacture of thin film composite membranes
Thin film coating was synthetic / fabricated to deposit the active thin layer of polyamide (PA) over the porous PSF bolester membrane. Aromatic polyamide TFC RO membranes were synthesized by the interfacial polymerization of MPD (2.0 wt. %) in aqueous phase and Trimethoyl chloride (0.15 wt. %) in organic phase (n-hexane), CSA (4.0 wt. %), SLS (0.15 wt. %), and TEA (3 wt. %), were combined into the aqueous phase. CSA and SLS were used to improve the absorption of MPD in microporous polysulfone support membrane. TEA hurried the MPD–TMC reaction by eliminating hydrogen halide created during amide bond formation [15]. Firstly, the support membrane was soaked with MPD solution for two minutes. The overabundance solution was removed by a rubber roller. Then the support membrane covered with 0.15 wt % of TMC-hexane solution for the 60s, followed by rinsing with n-hexane and cured at 80 ◦C for 10min. This resulted in formation of ultra-thin aromatic polyamide film over the support membrane that was denoted as “parent membrane” in this work. The membranes then washed and preserved in deionized water before characterization tests or application studies.
2.5. Fabrication of MgSiO3 NPs modified AMPS-g-TFC membranes.
Firstly redox grafting was performed utilizing a blend of redox initiators consisting of potassium persulfate K2S2O8 (2% of monomers) and sodium metabisulfite Na2S2O5 (1/3 of K2S2O8) on a newly fabricated TFC flat sheet membrane for about 20 minutes. Secondly a different mixture of various concentrations of (AMPS) monomer (2.5-15%) and (MgSiO3) nano-particles (0.005-0.1% of monomer concentration) were sonicated for one hour, then added to the above initiated TFC flat sheet membrane, and immediately put in the oven to complete the reaction at various temperatures and different times (Scheme 1).
2.6. Membrane characterization
Membranes used for chemical and morphological analysis are washed with Di water and dried before characterization. The thin film composite RO membrane surface was characterized by Fourier transform infrared (FT-IR) made with a (Nicolet avator 230 spectrometer) at room temperature. Irtran crystal at 45◦ angle of incidence employed for FT-IR analysis of different samples. Scanning electron microscopy (SEM) with (SEM Model Quanta FEG) connected with EDX Unit, with accelerating voltage 30 K.V., magnification 250x up to 20000x and resolution for gun 1m was used for examination of membrane morphology. Samples are coated with gold. X-ray diffraction patterns were performed utilizing (Shimadzu X-ray) diffractometer, (Model XD 490 Shimadzu, Kyoto, Japan) with a nickel filter and Cu-Kα radiation tube. Thermal stability and water content of the fabricated membranes were done using a (Shimadzu DT-60H thermal analyzer, Shimadzu, Kyoto, Japan). The films measured from 25˚C to 1000°C with a rate heating equal 15 deg /min. Dynamic Mechanical Analysis (DMA) mechanical proprieties where tensile strength and elongation of membranes were determined by a universal mechanical testing instrument (DMATAQ800) (Film tension clamp) of different membranes under study. Measurements were executed at room temperature and a strain rate of 50 mm min-1 was utilized. For all membrane, at least three specimen tests were examined. Also, the surface hydrophilicity of the films was particulate by the estimation of the water contact edge with a contact point goniometer from (VCA Video Contact Angle System, Kr ÜssDSA25B, Germany) at room temperature, at least, six estimations at various locales were procured for each layer.
2.7. Performance test
ALFA LAVAL pilot-scale laboratory unit for membrane filtration (Model LabUnit M20) was used for testing the performance of synthesized reverse osmosis membranes (Fig. 1). Flat sheet layers with a viable region of 0.018 m2 were set in the test instrument with the polyamide dynamic layer confronting the bolster water. All film tests were carried and tried at least twice with a sum of three layers tests for RO execution, the normal outcomes were taken, the volume of penetrate were taken in 1 hr and the flux communicated regarding (L/m2h).The standard conductivity meter was utilized to assess the salt fixations in the nourish and the pervade water for setting film effectiveness as given below:
(1)
Where Cf and Cp are the salt concentration in the feed water and in permeate flux, respectively.
3. Results and discussion
3.1. MgSiO3 NPs characteristics
It was clear from SEM image in Fig.2, MgSiO3 NPs are well distributed, of spherical morphology and of very small and highly agglomerated particles with a rounded shape.The functional groups of the MgSiO3 NPs were resolved using the FTIR spectrum as shown in Fig.3. A peak at 3697 cm−1 is characteristic to Mg–OH stretching, broadening peak near 3437 cm−1 attributable to H-bonding of coordinated water and the strong peak at 1017 with a shoulder band at 878 cm−1 is due to the presence of Si–O stretching vibrations, while the Mg–O vibrations occur at 462 cm-1[16]. X-ray diffraction displays crystalline structures (Fig. 4), where, three minor peaks demonstrate that the materials have identical patterns of crystalline nature.Also, the three minor peaks evidenced at 18–38, 51 and 58–62 °2θ were pointed out to MgSiO3 NPs.
3.2. Spectroscopic characterizations of PSF, TFC, AMPS-g-TFC and MgSiO3 NPs modified AMPS-g-TFC membranes.
FTIR was performed to describe the successful preparation of TFC membranes onto the PSF support layer, to verify the successful graft polymerizations of AMPS onto TFC membranes, and to determine the functional groups in the MgSiO3 NPs modified AMPS-g-TFC membrane.Figure 5, shows the characteristic peaks of PSF support layer and shows bands at737.1, 851.9, 1013, 1151.78, 1484 and 1579 cm-1 corresponding to (aromatic hydrogen), isolated aromatic hydrogen, ether group, sulfonic group, alkane groups and C-H aromatics respectively [17,18]. While/ in the TFC membrane Fig.5 elucidate different new peak bands appeared indicating the coating of PA barrier layer onto the PSF support layer. Two peak bands appear around 1597 cm–1 and 1248 cm–1 for the C=O stretching vibration and C-N group of the amide II on TFC membrane, respectively [19].The spectrum reveals that there is a strong band around 1675.8cm-1, which is characteristic of C=O band of an amide group (amide I). Also, a small peak at 1777.09 cm-1 which corresponded to C=O stretching (acid). The stretching peak at 3341 to 3473cm-1 can be assigned to N-H and O-H which overlapped together [20,21].The FTIR spectra of the AMPS-g-TFC membranes was also shown in Fig.5, in addition to the NH2 and C=O bands for TFC membrane, we found characteristic absorption peak of AMPS units at 1294 cm-1 due to the S-O group in the sulfonic acid (SO2) asymmetric and at 1152 cm-1 due to symmetric bands of(S-O) both referred by [21], who report 1250–1150 and 1100–1000 cm-1, respectively. The stretching band of OH group for sulfonic acid corresponds at 3000 cm-1. As indicated in Scheme (1), the C=O in the amide group stretched to a lower frequency peak (~1654cm-1) forming hydrogen bonds with N-H groups at the possible grafting sites on the surface of TFC membrane [22]. The new band, located at ~1740cm-1, and representing the appearance of the carbonyl (C=O) group is mainly attributed to the dimmers of AMPS [21]. Peaks appearing between the band range of ~2890 to ~3000 cm–1 corresponds to –CH2 and –CH3 stretching vibrations from AMPS. The AMPS grafting process happen at the possible grafting sites of –OH and –NH groups assimilated in the chemical structure of the TFC membrane compound I. The FTIR spectrum of the AMPS-g-TFC show that all bands of –OH and –NH have been overlapped together into one line, constructing a large peak plateau between ~3161-3892 cm–1 Fig.5. The construction of this plateau is normally associated with a stretching vibration and banding shift of –OH and –NH due to the development of AMPS-g-TFC compound II,(Scheme2).The spectrum of the MgSiO3 NPs modified AMPS-g-TFC membrane is shown in Fig.5, by comparing the MgSiO3 NPs modified AMPS-g-TFC membrane with the pure TFC membrane indicates that/ there is a new stretching vibration band that appears at approximately 1904 cm-1 is due to Si-O stretching vibrations for MgSiO3 NPs[23]. The appearance of hydroxyl (–OH) group peak around 3567.1 cm-1, is due to the formation of the intramolecular hydrogen bond between the carbonyl groups (CO-) of AMPS and the hydroxyl group on the surface of the MgSiO3 NPs, Scheme (1). The AMPS is flexible, and the hydroxyl groups on the surface of the MgSiO3 NPs can easily find a carbonyl group to form the hydrogen bond that will be stabilized on the membrane surface. The stretching vibration peak, appearing at ~1778 cm-1, is mainly attributed to the dimmers of AMPS. The incorporation of MgSiO3NPs into the AMPS grafting solution is inferred by the shift of the carbonyl peak due to electron acceptance from the Mg atoms. This shift is consequent to the interaction occurred between the sulfonic group (SO2) and carbonyl groups contained in the AMPS. Finally, these peaks indicate the successful incorporation of MgSiO3 NPs on the surface of the AMPS-TFC membrane.
Investigation of surface nature of the PSF and the TFC membranes and illustration the difference in the structure pattern between the AMPS-g-TFC and MgSiO3 NPs modified AMPS-g-TFC and that may take place during grafting with the AMPS, as well as after combination of the MgSiO3 NPs into the TFC membrane were done by X-ray diffraction (XRD) technique .In Fig.6, the characteristic diffraction peak for pure PSF is observed at 2θ value of 18.00. The spectrum showed the highly amorphous nature of PSF [24]. The broad peak at 18.00 (2θ) appeared with low crystallinity, while the x-ray diffraction peak of TFC membrane appears at 2θ value of 18.01. The curves of TFC were broad with low intensity centered on 18 of 2θ, which emphasize the semicrystalline nature of the composite membrane [25]. The crystalline area in the TFC is due to the polyamide skin layer and the amorphous regions are due to PSF support layer. The broad peak center on every X-ray formula was referred to the average intersegmental distance of polymer main chains [26]. Fig.6, shows the XRD pattern of AMPS-g-TFC membranes are crystalline in nature, and show three crystalline peaks at 2θ angles of 26.2, 38,1 and 44.4 with the combination of the dispersion peak of amorphous PS, nevertheless indicates that their locations are slightly shifted [27]. The MgSiO3NPs modified AMPS-g-TFC membrane shows six crystalline characteristic peaks at 2θ angles in addition to the main characteristic peaks of MgSiO3 NPs with values of 2θ equal 10.2, 17.80, 18.31, 38.1, 44.4 and 54,6. The XRD pattern shows that MgSiO3 NPs remain in the grafting layer of the membrane surface; however, all characteristic peaks in the grafting layer were shifted to slightly lower angles which compared with those of MgSiO3 NPs. This shift may be due to slight interactions between MgSiO3NPs and the AMPS on the modified grafting layer. Table 1, detect the comparison in terms of peak position, relative intensity, FWHM and d-space in the AMPS-g-TFC and MgSiO3NPs modified AMPS-g-TFC membranes.
3.3. Microscopic characterizations of the PSF support layer, PSF/TFC, and TFNC membrane.
The surface morphology of each membrane, i PSF, TFC, AMPS-g-TFC and MgSiO3NPs modified AMPS-g-TFC membranes were characterized by SEM as shown in Fig.7. Figure 7(a), shows the PSF support layer is porous, and showing that PSF has a sponge–structured which can afford high pressure. Figure7 (b) shows the surface of a TFC layer, where a dense structure had a “ridge and valley” structure characteristic of the typical of PA films was monitored. The AMPS-g-TFC grafting shows nodules/ and roughly surface as in figure7(c). Additional of MgSiO3NPs in the grafting solution lead to rougher membrane surfaces, showed the presence of nanoparticles, confirming the attachment of MgSiO3 NPs on the surface of membrane, which exhibits increased pore density and pore size as present in Fig.7(d). It is believed that the addition of MgSiO3NPsimproves the membranes surface properties and the expansion of MgSiO3 NPs enhances the layers surface properties and creates new stream ways through the thin layer, bringing on an increment in water sorption and permeability. Additionally, the cross-sectional SEM images of AMPS-g-TFC and MgSiO3 NPs modified AMPS-g-TFC membranes appeared in Fig 8, (a,b) which show that the surface modification achieved by this study results in a small increase in the membrane thickness compared to original TFC membrane.
3.4. Mechanical properties of the synthetic membranes:
` The mechanical properties of PSF, TFC, AMPS-g-TFC and MgSiO3 NPs modified AMPS-TFC membranes have been studied, and the stress-strain figures are shown in Figure 9. The AMPS-g-TFC and MgSiO3NPs modified AMPS-g-TFC membranes show improved tensile strength (Mpa), elongation break (%), and significantly increased Young’s modulus values when contrast to pristine TFC membranes. The markedly increasing tensile strength of modified membranes could be attributed to two reasons: First, chemical bonding between the MgSiO3 particles, AMPS and TFC matrix, which has been illustrated by FTIR. The chemical bond could transfer load efficiently from the TFC matrix to rigid nano-MgSiO3 particles; consequently, it enhanced the tensile strength and modulus. Second, the uniform dispersion of nano-MgSiO3 particles throughout the TFC matrix, i.e., rigid particles in the delicate lattice prompts to an expansion in firmness. When cracks occur, the progress of the cracks can be prevented by the dispersed particles of the polymer matrix [22]. Homogeneous and relative smaller particle size of silica, as can be spotted in SEM analysis, ensure the efficiency absorbing of mechanical energy, hence increasing the mechanical properties [27, 28].
3.5. Hydrophilicity of the membranes
The technique of contact angle (θ) is used to detect the information regarding membrane surface energy behavior such as (Van der Waals, Lewis acid-base) for detailed interfacial dissection for qualitatively measuring the wettability, or hydrophobicity / hydrophilicity, of the membrane surface. A lower value of contact angle indicates a higher hydrophilicity as a greater tendency for water molecules to wet the membrane surface existed [29]. Figure10. Shows the contact angle (θ) measurements of PSF, TFC, AMPS-g-TFC and/ MgSiO3 NPs modified AMPS- g-TFC membranes. From Fig.10 the PSF substrate shows contact angle measurement equal 72.8° this indicated initial impedance against the water molecules and relatively hydrophobic properties. After interfacial polymerization, the hydrophilicity of TFC membrane was improved, and it decreased to 68.3° this indicated that the PA layer was moderately hydrophilic, with modification of the TFC membranes by monomer AMPS grafting, the contact angle reached 62.1°. The low contact angle of the AMPS-g-TFC membrane indicated more hydrophilic properties because of the presence of polar and hydrophilic groups of sulfonic acids in the AMPS monomer structure. However, MgSiO3 NPs modified AMPS- g-TFC membrane shows a lower contact angle of approximately 45.9° at 25˚C; show the superior surface hydrophilicity due to the existing of free silanol species still present at their surfaces. The improved hydrophilicity of the MgSiO3 NPs modified AMPS-g-TFC membrane may be due to the presence of free silicate groups as an active hydrophilic functional groups on the surface of membrane, that causes higher interaction in water and surface, though tightly bonded through Si-OH groups. The considerable increscent in membrane hydrophilicity resulted in increased permeability of the membrane modified with nanoparticles.
3.6. Thermal stability of the membranes
Thermo-gravimetric analysis (TGA) was performed for PSF, TFC, AMPS-g-TFC, and MgSiO3 NPs modified AMPS-g-TFC membranes under nitrogen atmosphere as shown in Figure11, which shows a degradation behavior of different membranes. It can be observed that both PSF and TFC membrane goes through thermal decomposition in two main stages.The first stage at 451.4-561.97°C and 304.70-551.94°C for PSF and TFC respectively, this could be regarded to the sulfonic group in chains of the polymer[30]. However, the second weight loss stage occurred above 729.9°C and 760°C is corresponding to the splitting of the polymer main chain as the S=O group in the main chain of PSF appears to form inter-molecular hydrogen bonds with water. A weight loss in TFC membranes occurs above 760 °C is corresponding to the splitting of carbon atoms above 600°C. The resulting weight loss is due to polymer chemical structure, which composed of both amide groups and aromatic rings, generally known to be highly reluctant to increases in temperature [31].
The TGA of AMPS-g-TFC membrane shows an increase in thermal stability by comparing to pure TFC membrane, which possibly due to the presences of more bonded amide and sulphonic groups in AMPS monomer. The TGAcurve of MgSiO3 NPs modified AMPS-g-TFC membrane shown in Fig 11, indicate that thermal degradation was shifted to a higher temperature than pure AMPS-g-PATFC. The first weight loss, between 490-610°C, with an increase of more than 50°C is fundamentally due to the binding water where/ the incorporation of MgSiO3NPs strengthened chemical bonds within the polymeric backbone which is confirmed by using FTIR test. The second weight loss, between 630-790 and 820◦C,may be attributed due to the elimination of, SO3, and SO2molecule from the grafted polymer[32].The TGA results indicate that the incorporation of MgSiO3 NPs significantly enhances the thermal stability of the AMPS-g-TFC membrane.
3.7. Performance evaluation
Membrane performance enhancement for desalination by surface coating with magnesium silicate nanoparticles using the free radical grafting technique and assessed the membrane performance including permeate flux and salt rejection are the main target of this work. In this study, various parameters were studied such as the concentration of AMPS monomer, the concentration of MgSiO3 NPs, grafting time and temperature to get the optimum condition necessary to prepare the best suitable MgSiO3 NPs modified AMPS-g-TFC membrane for desalination of water which compared with pristine PA -TFC membrane which have 89.7% salt rejection and water flux 17.6 L/m2h at water salinity 2000ppm and at pressure15 bar.
3.7.1. Concentration of monomer AMPS and MgSiO3 NPs.
Figures (12& 13), show water flux and the salt rejection of prepared membranes with different concentrations of AMPS monomer,& MgSiO3 NPs respectively. It is observed that both water flux and salt rejection increases with nanomaterial concentration increasing. Then, for higher concentrations, it decrease, this results can be clarified as the increasing of coating layers on the membrane could reduce the permeation flux. Also, the reduction in the salt rejection may be due to some coating layers could minimize the surface charge due to the concealment, which then minimizes the salt rejection due to the Donnan effect phenomena [33]. The results reflect the existence of an optimum concentration of AMPS monomer& MgSiO3 NPs.
3.7.2. Grafting time and temperature.
By over increasing in grafting time or curing temperature as in Fig. 14&15, membranes water flux, and salt rejection have been decreased, this may be due to The decreasing of interchain hydrogen bonds as large amount of AMPS molecules were incorporated into aromatic polyamide chains, which may increase the polymer chain mobility,causing conformational alteration of aromatic polyamide chains.It may also cause local collapse or compaction in the modified membrane surface and finally result in increased passage of both water and salt [34].
3.8. Application of the resulting MgSiO3 NPs modified AMPS-g-TFC membrane on sea water and different ground water salinity.
A seawater sample from a beach well located in Cleopatra region, Marsa Matrouh, and a groundwater samples collected from different sites on the northwestern coast in Egypt were used as a feed source in the RO pilot scale unit using the prepared sheets of MgSiO3 NPs modified AMPS-g-TFC membrane.
The different kind of both feed water and the corresponding product water through the Lab. RO unit was tested for major ion constituents to determine the efficiency of the membranes under different applied pressure, at a temperature (25°C), and flow rate (5 L/min), a brief result of feed and product water analysis results are observed in Table (2). From results the salt rejections of bivalent ions (Mg2+ and SO42-) are higher than that of monovalent ions (Na+ and Cl-) for cations and anions, where the retention for the bivalent anions is fewer than cations. This can be demonstrated by the mass transfer coefficients for divalent ions are lower than those for themonovalent ions and hence higher values for solute separations with respect to divalent ions [35]. Additionally, the degree of hydration which is a function of both size and charge/ being higher for small ions with a large charge, since there is a strong interaction of the solute ions with water molecules (ion-dipole influence) [36]. So that, the rejection of different ions is in the order:
R HCO3- > R SO42-> R Cl- and R Mg2+> R Ca2+> R Na+.
By applying, different pressure on the prepared composite membranes of MgSiO3 NPs modified AMPS-g-TFC membrane with different water types as in Table (3) and Figs. (16, 17) the results of both water flux and salt rejection increase gradually as an operation pressure increases, and by the further increasing of the operation pressure water flux increases dramatically comparing with increasing in salt rejection. It can be clarified by the way that, permeate is directly corresponding to the net wrking pressure and the solute diffusion across the membrane [37, 38]. By analyzing the metal concentration in the permeate flux of the applicant water which applied on MgSiO3 NPs modified AMPS-g-TFC membrane, we observed that, there is no release of both magnesium and silicon which confirms that, MgSiO3 NPs attached to thin film composite membrane via a chemical bond. Application results demonstrate that MgSiO3 NPs modified AMPS-g-TFC membrane show high desalination performance under different operating conditions and can be use as an applicable good modification for PA TFC membrane with modified properties.
4. Conclusions
MgSiO3 NPs were attached to the surface of TFC membrane with AMPS monomer as a bridging agent via free radical grafting technique. MgSiO3 NPs modified AMPS-g-TFC membrane showed good mechanical and thermal stability while was high hydrophilic, with an increase in water contact angle (~45.9°). The modified composite membrane and its morphology were also examined using FT-IR, XRD, and SEM. The performance of the modified membranes was evaluated with respect to water flux, salt rejection. The new membrane presented a water flux of 28.2 L/m2•h and a salt rejection of ≥95.5%were obtained for a saline water (2000 ppm of NaCl) at a modified membrane pressure 15 bar with a 32% increase in water flux was fulfill when compared to the pristine TFC membrane. This study demonstrates that the MgSiO3 NPs modified AMPS-g-TFC membrane can significantly enhance selectivity, permeability and hydrophilic properties of the surface of membranes for water desalination.
References
1) UNEP (2012) http://na.unep.net/geas/newsletter/images/Jan-12/Figure1.png
2) Seckler, William D. World water demand and supply, 1990 to 2025: Scenarios and issues. Vol. 19. Iwmi, 1998.‏
3) Ministry of Water Resources and Irrigation, Water Scarcity in Egypt, February 2014.
4) Parry M L. Contribution of working group II to the fourth assessment report of the intergovernmental panel on climate change, 2007. Climate Change 2007: Working Group II: Impacts, Adaptation and Vulnerability (2007).
5) Intelligence, Global Water. Desal Data. com. 2013.
6) Savage N.. Nanotechnology Application for Clean Water, 77–93, 2009, Norwich: William Andrew Inc.
7) Lee, Peng K, Tom C A, Mattia D. A review of reverse osmosis membrane materials for desalination—development to date and future potential. Journal of Membrane Science. 2011; 370 (1): 1-22.‏
8) Peñate, Baltasar, García-Rodríguez L. Current trends and future prospects in the design of seawater reverse osmosis desalination technology. Desalination. 2012; (284) : 1-8.
9) Hilal, N, Ismail A F, Wright C J, eds. Membrane fabrication. CRC Press, 2015.‏
10) Sean G P, Cheer N P, Ismai A Fl, Current Progress of Nanomaterial/Polymer Mixed-Matrix Membrane for Desalination, Membrane Fabrication, 2015, Chapter 14. 489–510.
11) Li, Bo J, Zhu J, Zheng M. Morphologies and properties of poly (phthalazinone ether sulfone ketone) matrix ultrafiltration membranes with entrapped TiO2 nanoparticles.\” Journal of applied polymer science. 2007; 103(6): 3623-3629.‏
12) Qu, Xiaolei, Alvarez P J J, Li Q. \”Applications of nanotechnology in water and wastewater treatment.\” Water research 2013; 47(12): 3931-3946.‏
13) Arsuaga, María J. \”Influence of the type, size, and distribution of metal oxide particles on the properties of nanocomposite ultrafiltration membranes.\” Journal of membrane science 2013; 428: 131-141.‏
14) Kango, Sarita. Surface modification of inorganic nanoparticles for development of organic–inorganic nanocomposites—a review.\” Progress in Polymer Science. 2013; 38(8) 1232-1261.‏
15) Kim, Ho S, Kwak S, Suzuki T. \”Positron annihilation spectroscopic evidence to demonstrate the flux-enhancement mechanism in morphology-controlled thin-film-composite (TFC) membrane.\” Environmental science & technology 2005; 39(6): 1764-1770.‏
16) Ali I M, Kotp Y H, El-Naggar I M. Thermal stability, structural modifications and ion exchange properties of magnesium silicate. Desalination. 2010; 259(1): 228-234.‏
17) Socrates, G. \”Infrared Characteristic Frequencies, 2nd-Ed.\” (1994).‏
18) Kwon, Young N, Tang C Y, Leckie J O. Change of membrane performance due to chlorination of crosslinked polyamide membranes. Journal of applied polymer science. 2006; 102(6): 5895-5902.‏
19) Lee, Soo H. Polyamide thin-film nanofiltration membranes containing TiO2 nanoparticles. Desalination. 2008; 219(1): 48-56.‏
20) Sridhar S, Smitha B, Aminabhavi T M. Separation of carbon dioxide from natural gas mixtures through polymeric membranes – a review. Separation& Purification Reviews. 2007; 36(2): 113-174.‏
21) Rao C N R. Chemical applications of infrared spectroscopy; Academic Press: New York, 1963.
22) Isawi H, El-Sayed M H, Feng H, Shawky H, Abdel Mottaleb M S, Surface nanostructuring of thin film composite membranes via grafting polymerization and incorporation of ZnO nanoparticles, Applied Surface Science. 2016.
23) Dechant R, Danz W, Kimmer R, Schmolke Ultrarotspektroskopischeuntersuchungen an polymeren. (1972).‏
24) Riccardi C S. Preparation of CeO2 by a simple microwave–hydrothermal method. Solid State Ionics. 2009; 180 (2): 288-291.‏
25) Padmavathi, Rajangam, Karthikumar R, Sangeetha D. Multilayered sulphonated polysulfone/silica composite membranes for fuel cell applications. Electrochimica Acta. 2012; (71): 283-293.
26) Kang Y S, Lee S, Kim Y U, Shim S J. Kang YS, Lee SW, Kim UY, Shim YS. Pervaporation of water–ethanol mixtures through crosslinked and surface-modified poly (vinyl alcohol) membrane. J Memb Sci. 1990; 51: 215-226.
27) Li, Lei. Polyamide thin film composite membranes prepared from 3, 4′, 5-biphenyl triacyl chloride, 3, 3′, 5, 5′-biphenyl tetraacyl chloride and m-phenylenediamine. Journal of Membrane Science. 2007; 289(1): 258-267.‏
28) Li J, Suo J, Deng R .State Key Laboratory of Mould Technology, Institute of Material Science and Engineering Huazhong University of Science and Technology, Luo-Yu Road 1037Wuhan, Hubei 430074, PR China2010.
29) Water Research Foundation, Evaluation of Membrane Characterization Methods 4102 (2012).
30) Liu, Feng Y, Yu Q C, Wu Y H. Preparation and proton conductivity of composite membranes based on sulfonated poly (phenylene oxide) and benzimidazole. Electrochimica Acta. 2007; 52(28): 8133-8137.‏
31) Villar-Rodil S, Paredes J I , Martınez-Alonso A, Tascon J M D. Atomic force microscopy and infrared spectroscopy studies of the thermal degradation of Nomex aramid fibers. Chemistry of Materials. 2001; (13): 4297–4304.
32) Srivastava, Arti, Mandal P, Kumar R. Solid state thermal degradation behaviour of graft copolymers of carboxymethyl cellulose with vinyl monomers. International journal of biological macromolecules 2016; (87): 357-365.‏
33) Xu, Guo-Rong, Wang J, Li C. Strategies for improving the performance of the polyamide thin film composite (PA-TFC) reverse osmosis (RO) membranes: surface modifications and nanoparticles incorporations. Desalination 2013; (328) : 83-100.‏
34) Wei, Xinyu. Surface modification of commercial aromatic polyamide reverse osmosis membranes by graft polymerization of 3-allyl-5, 5-dimethylhydantoin. Journal of Membrane Science. 2010; 351(1): 222-233.‏
35) Khayet M, Mengual J. I. Effect of salt type on mass transfer in reverse osmosis thin film composite membranes. Desalination 2004; (168): 383-390.‏
36) Ghiu, Silvana M S, Carnahan R P, Barger M. Mass transfer in RO TFC membranes-dependence on the salt physical and thermodynamic parameters. Desalination. 2003; 157(1): 385-393.‏
37) Zhou Y, Yu S, Liu M, Gao C. Preparation and characterization of polyamide-urethane thin-film composite membrane. Desalination. 2005; 180: 189-196.
38) Liu M, Wu D, Yu S, Gao C. Influence of the polyacyle chloride structure on the reverse osmosis performance, surface properties and chlorine stability of the thin-film composite polyamide membranes, J. Membrane Science. 2009; 326: 205-214.