Enhancement in Performance of the PVC / Nanoclay Mixed Matrix Nanofiltration Membrane

doi:10.21203/rs.3.rs-1741723/v1

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Enhancement in Performance of the PVC / Nanoclay Mixed Matrix Nanofiltration Membrane

https://doi.org/10.21203/rs.3.rs-1741723/v1

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Mixed matrix membranes are considered as a novel generation of membranes that have favorable separation and stability properties of inorganic and polymeric membranes at the same time. In this study, the effects of presence of clay nanoparticles (CNs) on the enhancement of properties and performance of PVC nanofiltration membranes were investigated. FTIR, AFM, XRD, EDS, and FESEM analyses were used to evaluate the mixed matrix membranes. Significant improvements in the membrane hydrophilicity, porosity, permeation flux, and rejection were observed by incorporating CNs. The highest rejection of 94.8% was obtained with mixed matrix membranes containing 2 wt% of CNs. The permeation flux of this membrane was enhanced by 75% relative to the neat membrane.

Mixed matrix membranes

Nanofiltration

Clay nanoparticles

Permeation

Rejection

In the current century, we face two major challenges including the provision of sustainable sources of water and cost-effective clean energy; two highly interdependent sources. With the continuous reduction in available freshwater sources, membrane technologies as environmentally friendly processes have attracted much attention in recent years. However, enhanced membranes with high flux and high salt rejection are required to develop this technology. Such membranes, are less exposed to fouling and are more resistant to chemical environments, especially chlorination^1,5. So, the synthesis of appropriate membranes can lead to the development of the membrane application in water desalination and treatment.

Synthesis of the mixed matrix membrane can be an effective technique to enhance the properties and performance of the membranes. The mixed matrix membranes are composed of a continuous polymer phase and dispersed inorganic porous particles².

Dispersion of inorganic particles in the organic phase improves not only the transfer properties of a membrane but also its mechanical and thermal properties³. The simplicity of fabrication of these membranes over inorganic ones is proof of the advantage of this type of membrane. A large number of studies have shown that the separation efficiency of mixed matrix membranes is significantly higher than that of polymeric membranes. The purpose of combining polymeric and inorganic materials and the synthesis of mixed matrix membranes is to achieve better selectivity and permeability^4,7.

The composition of mineral nanoparticles in the polymeric matrix can better the hydrophilicity, porosity, chemical, pore size, mechanical, thermal, permeability/rejection, and anti-fouling properties of the polymeric membranes^5,8. Various nanoparticles have been used to synthesize the mixed matrix membranes, including clay minerals⁶, carbon nanoparticles⁷, titanium oxide⁸, silica⁹, silver¹⁰, and so on. Many studies have reported the improvement of polymeric membranes by combining different nanomaterials. However, it is not yet clear which of these nanoparticles is more appropriate for membrane modification¹¹.

CNs have attracted much attentions as an additive for enhancing membrane properties and performance. Unlimited resources in nature, low cost, flat layer structure (resulting in high aspect ratio), high efficiency, and ion exchange capacity are remarkable features of CNs. The extent and mode of dispersion of clay layers in the polymer network are key factors affecting the membrane's physical and mechanical properties^{12, 13}.

Anadão et al.¹⁴ Investigated the addition of CNs to polystyrene (PS) membranes, which resulted in increased hydrophilicity and thermal / mechanical stability. Ma et al.¹⁵ reported that the addition of CNs and polyethylene glycol (PEG) to PS membranes enhanced the number of large pores in the skin layer, and Reduced the mechanical resistance of the membrane. Rodrigues et al.¹⁶ studied the effect of CNs on the performance and structure of mixed matrix polysulfone ultrafiltration membranes in the presence and absence of polyethylene oxide (PEO) as the pore former. The use of CNs improved the thermal / mechanical resistance and permeability of the membrane with minimal loss in rejection. In an observation carried out by way of Rajabi et al.¹⁷, the structure and performance of polyvinyldin fluoride (PVDF) membranes containing CNs were investigated. The results showed that the surface hydrophilicity of all mixed matrix membranes was significantly improved compared to the base PVDF. Also, the mixed matrix membrane exhibited higher surface porosity and hardness than the base PVDF membranes. Sunil et al.¹⁸ investigated the use of new Al-Ti₂O₆ nanoparticles in PS composite membranes to remove heavy metal ions. Membrane hydrophilicity was measured by the contact angle, water absorption, and water flux. Kusworo et al.¹⁹ studied the intensification of separation and anti-fouling performance of PSf membranes containing graphene oxide (GO) and zinc oxide (ZnO) nanoparticles for treatment of oil refinery wastewater. The addition of GO and ZnO nanoparticles decreased the water contact angle and improved the water absorption capacity compared with the neat PSF membrane. The application of mixed matrix membranes also resulted in the higher permeation flux and contaminants removal in comparison with the base membrane. Rabiee et al.²⁰ showed that the presence of ZnO nanoparticles in the PVC membrane matrix increases the permeation of pure water, restores flux, porosity, and increases the rejection of bovine serum albumin (BSA) solution. Zhang et al.²¹ investigated polyvinylidene fluoride (PVDF) ultrafiltration membranes for high permeability with polydopamine-modified TiO₂ nanoparticles. The results showed that hydrophilicity and water flux relative to the base membrane increased significantly.

One of the most common polymers that can be used in membrane fabrication is Polyvinyl chloride (PVC). This polymer has high hardness, and high mechanical and chemical resistance²². The effects of the incorporation of CNs as an additive on the properties and performance of PVC nanofiltration membranes have not been studied. In this study, the synthesis of PVC and PVC/ CNs membranes was carried out using the phase inversion technique. The membrane's structures and properties were investigated by using FESEM, AFM, XRD, and contact angle techniques in presence of CNs. The effects of nanoparticle concentrations on the membrane properties (hydrophilicity, pore size, and porosity) and performance (permeation flux and rejection) were studied.

Selecting the best neat membrane. The effect of polymer concentration (wt%) on the permeation flux and rejection are provided in Table 1.

Table 1

The flux of permeation and rejection at different PVC concentrations.
Membrane	PVC (%)	Water permeate flux ( kg.m^− 2h^− 1)	Rejection (%)
M1	13	68.90	51.5
M2	14	57.36	69.0
M3	15	46.53	71.0
M4	16	36.97	73.0
M5	17	23.95	86.0
M6	18	7.24	83.0

As shown in Table 1, the highest water flux is related to M1 which is synthesized with a PVC concentration of 13 wt%. On the other hand, this membrane exhibits the lowest rejection among the synthesized membranes. The highest rejection (86%) is obtained at a PVC concentration of 17 wt%. However, this membrane (M5) doesn’t show the highest flux of permeation. The best performance among the six lab-made membranes belongs to M5, which shows the highest rejection and a relatively high permeation (Table 1).

The effects of CNs on membrane structure and performance. The results of water permeation through mixed matrix membranes (M5-1 to M5-3) are provided in Table 2. The highest permeation and rejection is obtained by membrane M5-2.

Table 2

Performance results of mixed matrix membranes
Membrane	Nanoparticles (%)	Water permeate flux ( kg.m^− 2h^− 1)	Rejection (%)
M5	0	23.95	86.00
M5-1	1	35.62	89.25
M5-2	2	40.72	94.78
M5-3	3	38.19	91.19

Figure 1 shows the flux of water permeation for mixed matrix membranes containing different concentrations of CNs. Enhancement in the flux of permeation and rejection of mixed matrix membranes can be explained by FESEM images and contact angle results.

As can be seen, the flux of membrane M5-3 has decreased compared to membrane M5-2, due to the accumulation of CNs on the surface of the M5-3 membrane (Fig. 4c). The accumulation of nanoparticles on the membrane surface can be clearly apperceived in Fig. 4c. As a result, according to Table 2, it was observed that the highest water flux and also the highest rejection related to the M5-2 mixed matrix membrane. Figure 2 shows the results of contact angle of neat as well as the mixed matrix membranes. As we know, the contact angle indicates the degree of hydrophilicity of the membrane surface, and factors such as porosity, functional groups, surface charge, and membrane roughness affect the contact angle^18,23. The lower the contact angle, the greater the hydrophilicity. Reduction of the contact angles of the mixed matrix nanofiltration membranes are observed due to the presence of hydroxyl groups, extremely hydrophilic, and very high porosity of CNs^24,26. CNs showed good dispersion at low concentrations in the polymeric matrix. However, by increasing the clay concentration beyond 3 wt%, part of nanoparticles accumulated on the membrane surface. Increasing the viscosity of the polymeric solution at high concentrations of nanoparticles affects the mechanism of membrane formation. The latter increase leads to an increase in the thickness of the top layer and a denser structure with lower porosity is formed. Lower porosity causes higher roughness and also lower surface hydrophilicity^25,10. Higher roughness can be explained by accumulation of nanoparticles on the membrane surface (Fig. 4c). As can be seen in Figs. 4e and 4f, upon increasing the nanoparticles' concentration from 2 to 3 wt%, the thickness of the top layer increased. Furthermore, the porosity decreases and pore size increases (Table 3). As such, the flux of permeation and rejection of M5-3 decreases comparted with M5-2. Generally, the membrane porosity increases and the pore size decreases in the presence of CNs. Embedding hydrophilic CNs in the PVC membrane increases the DMF/THF-water exchange rate and creates a porous structure. As the concentration of nanoparticles increases, the porosity and pore size of the membranes increases. However, by further increasing the amount of nanoparticles, these nanoparticles accumulate on the membrane surface and reduce the porosity and pore size. The addition of nanoparticles created more gaps between the hydrophilic groups on the CNs and the hydrophobic chains of PVC, which led to the creation of a more porous structure^26–28.

Table 3

Porosity and average pore size
Membrane	Porosity (%)	Average pore radius (nm)
M5	74.33	8.4
M5-1	80.11	4.3
M5-2	89.67	1.8
M5-3	85.29	2.7

The FTIR spectra of the mixed matrix membrane with nanoclay concentration of 2 wt% is shown in Fig. 3. The C-Cl peak at 600 cm^− 1, CCl-H peak at 950 cm^− 1, and CH₂ peak at 2900 cm^− 1 are strong identifications of PVC, which are present in both PVC and PVC/nanoclay membranes²⁹.

For CNs, the peaks in the range of 1100, 1250, 3240, and 3450 are related to the Si-O stretching bond (silicon group), the -COOC- stretching bond, and the -OH stretching bond, and the -OH stretching bond (hydroxyl group), respectively^30,31. According to the above interpretations, it can be concluded that CNs have been well dispersed on the membrane structure.

Incorporation of nanoparticles as a hydrophilic additive affects the kinetics and thermodynamics of the phase inversion process, which leads to different morphologies of the synthesized membrane³². SEM show that the number of pores increases with the composition of CNs (Fig. 4e). Compared to neat PVC nanofiltration membranes, the mixed matrix membrane provides a surface with a porous structure and no roughness (AFM analysis, Fig. 5).

Also decrease in roughness can be observed in the mixed matrix membrane containing 2 wt% of CNs (Fig. 4b) compared to the neat membrane (Fig. 4a).

One of the important morphological features that can affect the performance of the membrane is the structure of the inner pores of the membrane³³. The effect of additives on the internal morphology of the membrane was investigated by cross-sectional FESEM analysis of the membrane. According to the cross-sectional images, it was observed that the membranes have a normal asymmetric and porous structure with a thin top layer (less than 2.5 µm) followed by a layer with a finger structure and macro-sized cavities (Figs. 4d, 4e, 4f). The morphology of the mixed matrix membranes containing CNs is characterized by a coarse surface layer of pores, a bottom layer having a spongy pore-like structure with fine pores, and an intermediate layer with finger-like pores and fine pores (Figs. 4e, 4f)^14,16,34. The structure of the inner cavities of the membrane is significantly affected after adding CNs. CNs has a layered structure (Fig. 8) and in interaction with the polymer, its layers are separated and distributed throughout the polymeric matrix^15,35. The presence of CNs in the polymer solution makes the solution more thermodynamically unstable, which leads to rapid phase separation during immersion in the coagulation bath. Increasing the affinity of insoluble polymer solution due to the presence of hydrophilic groups in the membrane structure leads to faster polymer deposition. As a result, the growth of the top layer is reduced and the formation of finger pores under the layer is improved, and eventually, a more porous structure is formed (Figs. 4d and 4e). FESEM images of the cross-sectional area of the mixed matrix confirms the presence of CNs in the membrane structure^17,36.

The cross-sectional size of the finger cavities of the mixed matrix membranes with the nanoparticles is larger than that of the neat membrane (Figs. 4e, 4f compare with Fig. 4d). Since CNs have a high tendency to absorb water, the exchange rate of solvent-nonsolvent as a key factor of membrane formation mechanism can be reduced³⁷. Fast phase inversion and the formation of the membrane surface layer prevent the penetration of solvents to coagulation bath and as a result increase the time of solvent-nonsolvent exchange. This leads to more growth of the polymer-free phase, and eventually larger cavities are formed in the sub-layer of the membrane, which leads to increased membrane porosity^16,38,39.

Using three-dimensional surface images, the surface roughness of the membranes was also investigated (Fig. 5). The dark areas and the light areas are related to the valleys and peaks of the membrane surface, respectively. According to the results, it was observed that the incorporation of nanoparticles leads to a significant reduction in surface roughness. The rather uniform dispersal of nanoparticles on the membrane surface and the probabilistic scattering of the nanoparticles to the membrane surface as result of their low-densities formed a smoother surface for the mixed matrix membrane. The surface morphology in the images also shows that the CNs are relatively dispersed uniformly in the polymeric solution, which reduces the roughness of the membrane surface. Surface roughness is considered a criterion for the membrane surface deposition. The results of roughness analysis certified the efficiency of the mixed matrix membranes in eliminating scale and adsorbent from the membrane surface (increasing membrane permeation flux and decreasing membrane fouling). One of the reasons for rougher surfaces could be the effects of increased colloidal interactions and adsorption on the membrane surface^39,40.

Membrane surface roughness parameters such as mean surface roughness (Ra), mean second root roughness (R_q), maximum profile valley depth (R_v), and maximum peak profile height (R_p) are given in Table 4.

Table 4

Surface roughness parameters
Membrane	R_p (nm)	R_v (nm)	R_q (nm)	R_a (nm)
M5	35.2841	-43.2945	10.8915	8.6482
M5-2	24.0874	-21.2481	6.6390	5.1642

XRD test is a non-destructive method with multiple applications that provide comprehensive information on the chemical composition as well as the crystalline structure of both natural and industrial materials⁴¹. XRD analysis was used to characterize and confirm the crystal structure of the mixed matrix membrane in the presence of CNs. As shown in Fig. 6, the XRD pattern contains a peak at 2θ = 25º for pure PVC, 2θ = 24.9º for M5-1, and 2θ = 22º for M5-2. In other words, the above results show that the silicates of the CN layer are located in the PVC matrix and shows that the CNs do not change the crystal structure of PVC in the membrane. It was also observed that the neat membrane curve refers to a non-crystalline or amorphous polymer and remains unchanged compared to the XRD pattern of the origin polymer. It is also observed that for the membranes containing nanoparticles, the characteristic peaks of montmorillonite in the presence of membrane curves were not detected, indicating a peeled and/or partially peeled structure. The reason why the characteristic peak of montmorillonite does not appear can be attributed to the efficient fusion of polymer chains between the clay layers^13,15,42.

EDAX spectroscopy was performed to obtain the elemental composition of the membrane. X-ray energy dispersive spectroscopy was performed to confirm the outer surface of the membranes to confirm FESEM micrographs. Figure 7 shows the EDAX spectrum and the composition of the specified elements in the mixed matrix membrane. The corresponding atomic fractions are shown in Table 5. As the results in Table 6 reveal, silicon (Si) scattered on the outer surface of the membrane indicates the presence of CNs in the polymer matrix. The presence of Si can increase the hydrophilicity and porosity of the membrane. The micrographs also show the uniform dispersion of the nanoparticles in the PVC matrix (membrane surface without cracks).)^16,44.

Table 5

Elemental analysis of the M5-2 membrane.
Element	Atom (%)	Mass Norm (%)	Mass (%)
Cl	94.82	95.69	31.90
Si	4.65	3.72	1.24
K	0.53	0.59	0.20
Ca	0.00	0.00	0.00
Sum	100.00	100.00	33.34

A comparison between the lab-made mixed matrix membrane with the previous reported studies reveals an enhancement in the performance of the synthesized membrane (Table 6). As can be seen, appropriate fluxes of rejection and permeation were simultaneously obtained with PVC/ nanoclay mixed matrix nanofiltration membrane. In other researches, rejection and permeation flux have not increased simultaneously. Reference 46, which has a higher rejection, show much less permeation flux than the current lab-made membrane. Only ref. 48 reported simultaneous enhancement in both permeation flux and rejection by incorporation of ZnO, which is much more expensive nanoparticles than nanoclay. In other words, in the current study, permeation flux and rejection are improved simultaneously by using a low cost and unlimited natural resources nanoparticle as an additive.

Table 6: Comparison between the present study and some recent studies

Reference	Contact angle	Rejection (%)		Permeation flux ( kg.m^-2h^-1)	NP		Membrane type
¹²	66.0	88.0	48.50		Clay	PVDF
¹⁶	65.0	94.7	23.00		Clay	PS
⁴⁵	59.5	91.2	19.40		SiO₂	PES
⁴⁵	64.3	89.5	16.20		ZnO	PES
⁴⁵	55.3	88.2	23.32		GO	PES
⁴⁵	60.5	96.9	18.20		Al₂O₃	PES
⁴⁶	32.0	92.6	64.23		Ge-TA	PES-PVP
⁴⁷	28.0	98.9	166.73		ZnO	PEES
Lab made membrane	63.3	94.8	40.71		Clay	PVC

Due to the desirable properties of CNs, such as unlimited resources in nature and shell structure, if properly distributed and uniformly dispersed in the polymeric matrix, these nanoparticles can effectively improve the properties and performance of the membrane. The PVC nanofiltration membranes and mixed matrix membranes with CNs were synthesized via phase inversion method. The effects of CNs concentration on the pore size, porosity, contact angle, permeation flux, and rejection of the mixed matrix membranes were investigated. The main results can be summarized as follows:

CNs showed good dispersion at low concentrations in the polymeric solution and consequently in the mixed matrix membrane. However, accumulation of nanoparticles on membrane surface occur with increasing concentration of CNs beyond 3 wt%. FESEM images confirm this observation.

The permeation flux enhanced with increasing the concentration of CNs, due to the increasing porosity as well as hydrophilicity of the synthesized mix matrix membranes.

By incorporating CNs, significant improvements in the membrane hydrophilicity and pure water flux were observed. Also, the presence of montmorillonite affected on the mean pore size and overall porosity of the membranes.

The FESEM and EDX analysis confirmed the good dispersion of the nanoclay particles in the polymeric matrix. Also FESEM cross-section images of mixed matrix nanofiltration membranes indicate the formation of membranes with thinner skin layer and larger macrovoids compared to the neat membranes. Furthermore, decreasing the surface roughness and increasing the pore size of PVC/nanoclay membranes were confirmed by AFM analyses.

Materials. Polyvinylchloride (Arvand Petrochemical, Iran) was used as the polymeric matrix. Dimethylformamide (DMF) and tetrahydrofuran (THF) (Merck, Germany, 99% purity) were used as solvents for membrane synthesis. Non-woven filter paper (Ahlstrom filtration Co., Helsinki, Finland) was prepared as a support layer. CNs (Sigma Aldrich Co.) were used as additive to the polymer matrix (montmorillonite K10 with an average particle size of 100 nm and a surface area of 220 m²/g). The chemical structure of this nanoclay is shown in Fig. 8. Magnesium chloride hexahydrate (MgCl₂.6H₂O) was purchased from Merck (Germany) and was used to evaluate the performance of membranes.

Preparation of membranes

Synthesis of PVC membranes. PVC nanofiltartion membranes were prepared via the non-solvent induced phase separation (NIPS) method. Accordingly, a completely uniform solution of the polymer in the appropriate solvent was prepared. For the synthesis of a neat membrane, an appropriate amount of PVC (wt.%) was added to a mixture of DMF (wt.%) and THF (wt. %) as solvent. The polymeric solution was stirred for 24 h at 30°C. To remove air bubbles, the solution was kept for 24 h at room temperature without stirring prior to casting. The polymeric solution was cast on non-woven support using an automatic casting machine (Sepantashrif Co., Iran) with a thickness of 200 µm. The casted film was immersed in a coagulation bath (distilled water). The structure of the membrane was formed after wet phase inversion.

Synthesis of mixed matrix membranes. After obtaining the best neat membrane (with the highest rejection and high permeation flux), different amounts of CNs (1, 2, and 3 wt%) were added to the mixture of DMF (53 wt%) and THF (30 wt%) and the solution was stirred for 30 min. To ensure the appropriate dispersion of particles, the mixture was put in an ultrasonic device (Parsnahand Company, Iran) for 30 min. After obtaining uniform dispersion of particles in the solution, PVC (17 wt%) was added to the prepared mixture. The mixture was further stirred for 24 h at 30 C and was rested at room temperature for another 12 h for the removal of any bubble before casting. The solution was cast on a support with an automatic casting machine. The casted membrane was immediately immersed in a distilled water bath at 25 ° C. The names and compositions of the synthesized membranes are given in Table 7.

The prepared membrane Samples were cut into the desired size and then kept for 60 min in an oven at 50°C.

Table 7

Name and composition of the prepared lab-made membranes.
Membranes	PVC (wt%)	DMF (wt%)	THF (wt%)	Nano clay (wt%)
M1 M2	13 14	57 56	30 30	- -
M3 M4	15 16	55 54	30 30	- -
M5 M6	17 18	53 52	30 30	- -
M5-1 M5-2	17 17	53 53	30 30	1 2
M5-3	17	53	30	3

Membranes Characterization

FTIR analysis. FTIR (FTIR-8400S, Shimadzu, Japan) was used for the analysis, under ATR mode. The membrane was scanned in the range of 3500–700 cm^− 1 wave number. Transmittance mode was used for determination of the FTIR spectrum of all samples.

Contact angle analysis. Membrane hydrophilicity was investigated by contact angle technique. Contact angle measurements were performed by Dataphysics, OCA 15 plus, Germany.

X-ray diffraction (XRD). The X-ray jump measurement is carried out to investigate the generality of the crystal structure from the fixed lattice, lattice geometry, crystal phase, crystal size, single-crystal orientation, stress, lattice and so on. The D8 advanced XRD apparatus (Bruker Company, Germany) was used for XRD analysis.

AFM analysis. Atomic force microscopy was used to analyze the membrane surface roughness. In this technique, weak forces such as van der Waals forces and the capillary between the tip of the probe and the sample surface are used to form a topographic image of the sample surface⁴⁹. Nanosurf Mobile device made by Nanosurf Company, Switzerland was used.

EDS analysis. X-ray energy diffraction spectroscopy (Bruker, Germany) was used to analyze the structural and chemical properties of the membranes.

Porosity and pore size. Overall porosity (ɛ) was measured using the following Eq. ⁵⁰:

where, W₁ and W₂ are the wet and dry membrane weights (g), respectively. Also A is the effective membrane surface area (m²), ρ_w is water density (0.998 g/cm³), and L is the dry membrane thickness. Dry and wet methods were used to measure the membrane porosity. In this way, the weight of the wet membrane was measured, then the membrane was placed between two wipes to remove the surface water; the sample was then placed in an oven at 50° C for 4 h. Its dry weight was then recorded. Finally, the percentage of total porosity of the membrane was set according to Equation (1).

The average pore size (nm) of the membrane was calculated by the Guerout-Elford-Ferry equation⁵⁰:

\({Г}_{m}=\sqrt{\frac{\left(2.9-1.75ԑ\right)*8\eta LQ}{ԑA\varDelta P}}\)

(2)

Where, η is water viscosity (8.9 * 10^− 4 Pa.s, 25ºC), and Q is the volumetric flow rate of water (m³.s^− 1).

FESEM analysis. FESEM (KYKY, EM8000, China) was used to examine the membrane structure. Images were taken from the surface and cross-section of the membranes. The membranes were cut into the desired size and broken in liquid nitrogen. The membranes were coated with gold and placed on the base. After these steps, membranes were placed in the device to take FESEM images.
Evaluation of the membrane performance. A nanofiltration setup was used to investigate the membrane permeation flux and rejection. The setup consists of feed tank, cooling system, pump (PLM100RB14, Lowara, Italy), membrane module, pressure gauge, flow meter, pressure and flow control valves, and automatic panel indicating the temperature of the feed tank and connections (Fig. 9). In all experiments, MgCl₂.6H₂O solution with a concentration of 1500 ppm was used as the feed solution. The operating conditions were set as pressure of 7 bar, feed flow rate of 100 L/h, temperature of 25°C, and the duration of the experiment was 2 h. To determine the time of reaching the steady-state condition, at the beginning of each experiment, the weight of the permeate solution was measured at short intervals and the flux was calculated. After reaching a constant value, the weight of the permeate solution was measured every 5 min. Upon termination of the experiment, a volume of the permeate was collected to analyze its salt concentration. After each experiment, the apparatus was thoroughly washed with distilled water and drained.

The permeation flux ((kg / m²h) J) was calculated using Eq. (3)⁵¹:

\(\text{J}=\frac{\text{W}}{\text{A}{\Delta }\text{t}}\)

(3)

where W is the weight of the permeate (kg), A is the effective membrane surface area (m²) and Δt is time (h).

The salt rejection was also calculated using Eq. (4)⁵¹:

\(\text{R}=\frac{{\text{C}}_{\text{f}}-{\text{C}}_{\text{p}}}{{\text{C}}_{\text{f}}}\times 100\)

(4)

where C_f is the salt concentration in the feed and C_p is the salt concentration in the permeate.

Inductively Coupled Plasma spectroscopy (Shimadzu ICP-7000, Japan) was used to measure the concentration of magnesium ions in the permeate.

Data Availability: All data generated during this study are included in this manuscript. The data are available in the [Science Data Bank] repository, [https://www.scidb.cn/s/BR3qQr],

Data DOI:10.57760/sciencedb.j00053.00024

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Enhancement in Performance of the PVC / Nanoclay Mixed Matrix Nanofiltration Membrane

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