Enhanced properties of PVDF membranes using green Ag-nanoclay composite nanoarchitectonics

Introduction. Polyvinylidene fluoride (PVDF) is widely used in various industries, particularly in water treatment, owing to its effectiveness as an ultrafiltration membrane. Fouling can occur on PVDF membranes during the treatment of aqueous solutions containing natural organic matter in water treatment. Nanofillers can be added to PVDF membranes to improve their durability for more water treatment applications Objectives. This study aimed to enhance the mechanical and anti-biofouling properties of PVDF membranes while maintaining the flux and rejection rates. Methods. A green method was used to synthesize the Ag-Nanoclay nanocomposite for integration into a PVDF polymer membrane. P. argentea extract was employed as a reducing and stabilizing agent for the synthesis of Ag-Nanoclay nanocomposites. The synthesized Ag-Nanoclay nanocomposite was characterized using the X-Ray Diffration (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscope (SEM). The phase inversion method was used to prepare the PVDF membranes and 1 wt% and 3 wt% Ag-Nanoclay nanocomposite membranes. The structures, morphologies, performances and mechanical and antibacterial proeprties of the prepared membranes were characterized. Results. The synthesized Ag-Nanoclay consisted of Ag Nanoparticles linked to nanoclay platelets with flavonoids from plant extracts. Incorporating the Ag-Nanoclay nanocomposite into the PVDF membrane resulted in minor increases in the pore size, roughness, and hydrophobicity of the membrane. However, these effects did not significantly affect the flux and rejection rates, which showed little improvement. The 1 wt% loading significantly improved the tensile strength by 67%, whereas it decreased by 50% at 3 wt% loading. Both loading levels demonstrated excellent antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), with sterilization rates exceeding 99%. Conclusions. Addition of Ag-Nanoclay to PVDF membranes is a promising strategy for developing advanced membranes with improved mechanical properties and anti-biofouling characteristics.


Introduction
Water scarcity is increasing owing to climate change, urbanization, and population growth [1].New water sources, such as desalination and recycled water, are in high demand to address these problems [2].Membranes enable access to new water sources [3].Membrane technology is vital in many industries including medicine, food, pharmaceuticals, biotechnology, and chemicals [4].It is also used for wastewater purification, industrial effluent treatment, and domestic water purification [5].Membranes offer an economical and flexible alternative to conventional separation processes with high impurity removal capacity [6].Polymers used as water-treatment membranes must be durable and have a suitable pore size [7].Common low-pressure membrane polymers include polypropylene (PP), polytetrafluoroethylene (PTFE), polysulfone (PSf), and Polyvinylidene fluoride PVDF [3].
PVDF is a popular material for ultrafiltration (UF) membranes in various industries, including nuclear waste processing, pulp and paper, and chemical processing [8].PVDF-based nanocomposite thin films can enhance properties such as those relevant to piezoelectric nanogenerators, energy harvesting [9,10], water filtration devices, sensors, and actuators, as well as biomedical applications [11].
It is also hydrophilic and has a controllable porosity for microfiltration (MF) and UF applications in water treatment.PVDF MF and UF membranes were fabricated using phase inversion.However, its crystalline nature makes the process complex and different crystalline phases can affect the material's properties.Researchers are working on incorporating nanofillers to improve the durability of PVDF membranes for more water treatment applications [3].Nanomaterials enhance the performance of polymer nanocomposite membranes for water treatment [12].These enhancements lead to better permeability of water; increased ability to reject salt; improved removal of contaminants; higher selectivity; greater hydrophilicity; increased porosity; better antifouling; improved antimicrobial properties [13]; and enhanced mechanical, thermal, and chemical stability [14].
Fouling can occur on PVDF membranes during the treatment of aqueous solutions containing natural organic matter in water treatment [15].Increasing the hydrophilicity of a membrane can enhance its resistance to fouling [16].Numerous studies have focused on enhancing the hydrophilicity of PVDF membranes using different methods such as incorporating them with inorganic nanoparticles [17].
Membrane technologies have extensively investigated the catalytic, electrical, optical, and antibacterial properties of AgNPs [42].AgNPs are incorporated into membranes, resulting in high levels of antimicrobial activity, electroconductivity, photocatalytic degradation, and thermal response [43].
Different types of clay, such as bentonite, have been used as fillers in polymers to improve their properties [44].Bentonite is a type of clay composed mostly of montmorillonite formed from volcanic ash.It exhibits notable swelling and viscosity characteristics and is used in various industries [45].It is an excellent adsorbent and membrane modifier agent owing to its high surface area, surface negative charge, and thermal resistance.It is affordable and provides an excellent performance [46].
Adding clay to the matrix of polymer nanocomposite membranes enhances their mechanical, optical, barrier, and flame resistance properties.They are also economical and effective for filtering pollutants from water [47].
This study aims to enhance the mechanical and anti-biofouling properties of polyvinylidene fluoride (PVDF) membranes.This was achieved by synthesizing an Ag-Nanoclay nanocomposite using a green method, and to our knowledge, this is the first Ag-Nanoclay nanocomposite being prepared using the green method.The synthesized Ag-Nanoclay nanocomposite was then incorporated into a PVDF membrane.The results of this study demonstrate the efficacy of this approach in improving membrane performance.Ag-Nanoclay is a promising strategy for developing advanced membranes with improved mechanical properties and antibiofouling characteristics.

Synthesis of Ag-Nanoclay nanocomposite 2.2.1.1. Aqueous extract preparation
The aerial parts of Paronychia argentea Lam were subjected to a process of drying in an oven that was set between 50 °C-70 °C.The dried parts were crushed to form a fine powder, which was stored in a desiccator for future use.Next, 5 g of dry Paronychia argentea Lam powder was mixed with 100.0 ml of deionized water.The aqueous extract was heated for 20 min and filtered through Whatman filter paper No.1.Finally, it was again filtered through a syringe filter (0.45 m) [37,48].

Ag-Nanoclay preparation
Nanoclay (0.25 g) was added to 8.0 ml of Paronychia argentea Lam extract, and the mixture was sonicated for 15 min.Then, 50.0 ml of a 3.0 mM solution of AgNO 3 was added dropwise to the mixture at a rate of 2.0 ml/h using a Pasteur pipette.The AgNO 3 solution experienced a color change from clear to dark brown, which implied the formation of an Ag-nanoclay nanocomposite.The resulting Ag-Nanoclay suspension was dried using a freeze dryer (CHRIST, ALPHA 2-4 lD PLUS, New York, NY, USA).

Membranes casting
Two different weights of Ag-Nanoclay (0.11 g and 0.33 g) were mixed with 38.17 g of DMAA to produce a PVDF Ag-Nanoclay membrane with 1% and 3% concentrations.For both Ag-Nanoclay solutions, 11 g of PVDF and 0.5 g of PVP were gradually added while stirring at 100.0 rpm for 6.0 h in the temperature range of 70 °C-80 °C.The fluid was degassed for 12 h on a glass plate to create a gel, followed by film casting.The film was left in distilled water at room temperature until a membrane was formed through phase inversion.After washing to remove any residual solvent, the membranes were stored in a distilled water bath until testing and characterization.Pure PVDF membranes were produced using the same process as that without Ag-Nanoclay.
The preparation steps of PVDF membranes are shown in Scheme 1.

Ag-Nanoclay nanocomposite and PVDF-Ag-Nanoclay membrane characterization
The Ag-Nanoclay suspension and prepared membranes were examined using various techniques.A UV-vis spectrometer (Cary 100, Santa Clara, California, USA) was used to check the formation of Ag-Nanoclay.The percentage conversion of Ag + to AgNPs in Ag-Nanoclay was determined using inductively coupled plasma/ Scheme 1.The preparation of PVDF membranes.
atomic emission spectroscopy (ICP/AES) from GBC E1475 (Hampshire, MA, USA).X-ray diffraction (XRD) was conducted using an X-ray Diffraction device (XRD) (Rigaku Ultima IV/Japan), with a Cu K X-ray tube operating at 40 kV, 20 mA, a scanning speed of 3000 °/min at a 0.02-step size ranging from 3°to 90°, was used to examine the crystalline structure of PVDF and the nanofiller.Fourier-transform Infrared Spectroscopy (FTIR) (PerkinElmer, Waltham, MA, USA) was used to study the functional groups of the prepared Ag-Nanoclay nanocomposites.The size and shape of the nanoparticles, as well as the pore size and surface morphology of the membranes, were investigated using a scanning electron microscope (SEM) (Quanta FEG 450, Netherlands).Atomic force microscopy (AFM) was used to examine the superficial topology of the membranes.An AIST-NT SmartSPM 1000 scanning probe microscope was used for this purpose.The mode of operation for the microscope was in non-contact mode using NSC14/Al BC.Si tops at a resonance frequency of 160 KHz.The scan rate was in the range of 0.3-1 KHz.Surface hydrophilicity was assessed through the application of the sessile drop method using a contact angle meter from Biolin Scientific's Attension brand based in Manchester, UK.The porosity of the membranes was determined using gravimetric techniques.Three samples of each membrane type (PVDF-PURE and 1% and 3% PVDF-Ag-Nanoclay) were saturated with deionized water.Excess water was then wiped from the surfaces using filter paper, and the samples were weighed (m 1 ).After 48 h of drying at room temperature, the membrane weights were determined (m 2 ).Equation (1) was used to calculate the membrane porosity Where ε: Membrane porosity, m 1 : Wet sample weight, m 2 : Dry sample weight, ρH 2 O: Density of deionized water (1.0 g cm −3 ), and ρP: Density of polymer (PVDF) (1.74 g cm −3 ).

Performance of PVDF and PVDF Ag-Nanoclay membranes 2.2.3.1. Flux and rejection
The dead-end cell system (HP4750; Sterlitech, Auburn, WA, USA) was used to determine the pure water flux and BSA rejection for membranes with an area of 14.6 cm 2 , 0.5 g L −1 BSA at 1.0 bar transmembrane pressure at room temperature.Deionized Water was used to determine the flux rate.At a wavelength of 278.0 nm, UV-vis spectrophotometry (Cary 100, Santa Clara, California, USA) was used to determine the BSA concentration permeation and feed solution.
The following equations (2) and (3), were used to calculate the permeability flux (Jw) and BSA rejection (R): where v (L) is the water permeate volume, A (m 2 ) is the membrane effective area, ΔT (h) is the permeability time, C P the concentration of BSA permeated, C F : Feed solution.
C F was kept at 0.5 g L −1 in a permeation solution, and C P was checked at 4.0 ml [49].

Tensile performance testing
Electromechanical Universal Tensile testing (BMT-E Series, BESMAK, Kazan, Turkey) was used to test the tensile performance of the membrane.A tensile rate of 5 mm min −1 was used in the study.An average of five trials was obtained for each sample.

Evaluation of the antibacterial efficiency for synthesized Ag-Nanoclay
The antibacterial efficiency of the synthesized Ag-Nanoclay powder was examined before its incorporation into the membrane matrix using the liquid medium method against E. coli (ATCC no.8739) and S. aureus (ATCC no.

25913).
The concentration of each bacterium was adjusted to approximately 6 × 10 6 cells/ml.The antibacterial effects of Ag-Nanoclay were investigated at four concentrations (300, 400, 500, and 600 ppm).In four-cell culture flasks, 8 ml of broth was added to each flask.Subsequently, 3, 4, 5, and 6 mg of Ag-Nanoclay were introduced into the four flasks.The four flasks were placed in a sonicator to suspend the nanoparticles in the broth.The total volume for each flask was adjusted to 10 ml by adding 2 ml of bacteria at a concentration of 6 × 10 6 bacteria/ml.The nutrient broth was used as a negative control for each tested bacterium, while the positive control contained the tested bacteria at the same concentration as the samples.All flasks were incubated overnight in a shaker at 37 °C.The next day, 200 μl of each concentration for both types of bacteria was pipetted into a 96-well plate, including standard concentrations, and then detected using an ELISA reader.Each concentration of the standard solution was prepared by suspending it in Ag-Nanoclay in 10 ml broth [50].
The optical density (OD) of the bacteria at 600 nm was used to determine bacterial growth, and the inhibition ratios were determined using equation (4): The control OD resulted from bacteria without Ag-Nanoclay, while the tested OD was from bacteria with Ag-Nanoclay [51].

Antibacterial activity for membrane
The antibacterial activity of the membranes was tested according to the standard 'ISO 22196:2007 Plastics-Measurement of antibacterial activity on plastic surfaces'.

Culture media and solutions preparation
Nutrient agar, 28.0 grams of nutrient agar was dissolved in 1.0 liter of deionized water.To prepare the nutritious broth, 13.0 grams of nutrient broth was mixed in 1.0 liter of deionized water.SCDLP broth, which is soybean casein digest broth with lecithin and polyoxyethylene sorbitan monooleate, was prepared by mixing 3.0 grams of soybean peptone, 17.0 grams of casein peptone, 5.0 grams of sodium chloride, 2.5 grams of disodium hydrogen phosphate, 2.5 grams of glucose, 7.0 grams of nonionic surfactant, and 1.0 gram of lecithin in 1.0 liter of deionized water.The pH was adjusted to 6.8-7.2 using a phosphate buffer solution.Phosphate-buffered physiological saline was prepared by dissolving 8.5 g of sodium chloride (1.0 l of deionized water.Physiological saline was used to dilute the phosphate buffer solution to an 800-fold volume.All the media were sterilized by autoclaving.Each medium was dissolved in deionized water with a conductivity of less than one μS/cm.

Membrane samples preparation
Three PVDF-Ag-Nanoclay membrane samples measuring (2.2 × 2.2) cm 2 were used with six control membrane samples (PVDF-Pure), all with the exact dimensions.Half of the untreated samples (PVDF-pure) were immediately washed with 10.0 ml of SCDLP buffer.Then, SCDLP was serially diluted in phosphate buffer until it was ten times smaller.After dilution, 100 μl was collected and grown on plate count agar for 24.0 h at 37.0 °C.After washing in SCDLP buffer, the surviving pieces were diluted, cultured, and incubated as with the untreated samples.Equation (5) was used to determine the number of viable bacteria for each membrane sample.
where: N: Number of viable bacteria found in each cm 2 of the tested membrane sample.C: The average plate counts for each set of duplicate or triplicate plates D: Plates counted dilution factor.V: SCDLP volume (ml) added to the membrane samples.A: The cover film surface area (mm 2 ).
The sterilization ratio was determined using equation (6): where R is the sterilization ratio, A is the number of viable bacteria per cm 2 on the membrane of the untreated sample (PVDF-Pure), and B is the number of viable bacteria per cm 2 on the membrane of the treated sample (PVDF-Ag-Nanoclay) [52].This method was applied to two types of PVDF-Ag-Nanoclays (1% and 3%).Characterization of Ag-Nanoclay and PVDF-Ag-Nanoclay nanocomposites are shown in Scheme 2.

Characterization of synthesized Ag-Nanoclay nanocomposite and PVDF membranes
The formation of Ag-Nanoclay was confirmed by characterizing the absorption in the UV-vis spectrum.
Figure 1 shows the spectrum of the Ag-Nanoclay.A broad peak of around 450 nm appeared, related to AgNPs, which agrees with other studies that prepared AgNPs using plant extracts [37,53].However, the broad peak was due to the low AgNP content in the Ag-Nanoclay nanocomposite.This was further confirmed by the ICP analysis result.Also, the broad peak indicated a heterogeneous size distribution of AgNPs, further confirmed by the SEM results.Table 1 shows the results of the ICP analysis, which was used to examine the content of Ag+ in the prepared nanocomposite.This explains the broad peak of AgNPs in the prepared nanocomposite because only 59.5% of Ag + was converted into AgNPs in the prepared Ag-Nanoclay nanocomposite.For the PVDF membranes, a peak at 20.6 for pure PVDF and PVDF-Ag-Nanoclay nanocomposites is ascribed to β-crystalline [45], which indicates that adding Ag-Nanoclay to PVDF does not affect the PVDF crystal structure, which is the β crystal in all PVDF.However, Hosseini et al (2017) [45] found that the PVDF crystal changed from α-crystalline to β-crystalline upon adding MWCNT-Nanoclay to electrospun PVDF [57].On the other hand, the PVDF containing Ag-Nanoclay nanocomposite showed a significant increase in the 2θ related to (111) of the nanoclay from 4.5°to 14°.This indicates that the average d-spacing has decreased from 1.96 nm to 0.63 nm.This means that the PVDF molecules interacted with the Ag-nanoclay particles, leading to a more compact arrangement and a more ordered and closely packed structure.
The results of the FT-IR analysis of the Paronychia argentea extract, nanoclay, and Ag-Nanoclay nanocomposite are shown in figure 3. The nanoclay was surface modified with trimethylstearyl ammonium.FTIR revealed the differences that occurred in the nanoclay structure after modification, either by the modification of the organic cation (trimethyl stearyl ammonium) or by incorporating the Ag Nps that were prepared and stabilized using Paronychia argentea extract within the layered silicate.The FTIR spectra show characteristic peaks corresponding to the functional groups of the nanoclay and confirm the interactions between the clay layers and the Ag NPs.The spectra of modified nanoclay differ from those of natural nanoclay [58].However, they are consistent with the primary functional groups found in modified nanoclays [59].The stretching peak of OH was present in the range of 3489-3559 cm −1 .The silicate structure bands of Si-O-Si were located in the region of 1152 and 1083 cm −1 .The peak at 381 cm −1 is assigned to the symmetric vibration of Si-O; the observed peak shifts can be attributed to the presence of organic cations (trimethyl stearyl ammonium) within the nanoclay layers [59,60].The bands at 2530 and 2357 cm −1 represent the symmetric and asymmetric stretching vibrations of -CH 3 and -CH 2 supporting the intercalation of organic molecules from the organic ammonium cations and organic molecules that stabilized the AgNPs.The Ag-Nanoclay spectra contain characteristic peaks corresponding to the nanoclay with additional peaks at 449 and 471, confirming the incorporation of the AgNPs within the nanoclay layers.In addition, the enhancement of the OH stretching peaks (3489-3559 cm −1 ) is attributed to the presence of capping organic molecules at the surface of the AgNPs from the P Argenta plant extract [37,60].The presence of peaks corresponding to silicates in nanoclay, organic molecules in the plant extract, and AgNPs together in the Ag-Nanoclay composite confirm its successful synthesis and confirm that the organic molecules in the plant extract were not only used as reducing agents for Ag ions to AgNPs, but they also became a constituent of the Ag-Nanoclay composite.SEM was used to determine the shape and size of the prepared AgNanclay nanocomposite. Figure 4 shows bentonite platelets covered with AgNPs distributed non-homogenously on their surfaces, with sizes ranging from to 20-60 nm, on clay layers with lateral dimensions of 1000 nm.The result was consistence with the broad peak in UV-vis spectroscopy due to the non-homogeneity in size.The non-homogenous distribution of AgNPs  on the clay layers can be related to the fact that the clay layers lateral dimensions are much larger than that of AgNPs, which make it difficult to cover the whole surface of the nanoclay homogenously.Similar results showed the non-homogeneous distribution of nanoparticles on layers by Atarod et al (2016), who synthesized Fe 3 O 4 /Graphene Oxide nanocomposites using green methods [61].
P. argentea species found in Jordan are known to contain high levels of phenolic compounds, flavonoids, and oleanane saponins [62].The two primary flavonoids present in P. argentea are quercetin and isorhamnetin [63].Besides reducing the silver ions into silver nanoparticles, the green synthesis method enables conjugation between the AgNPs and the functional groups in the plant extract, such as flavonoids, as confirmed by FTIR.This aids in the bonding between the conjugates of AgNP-flavonoids and clay layers and enhances their stability, all in one step, which plays an important role in the synthesis of Ag-Nanoclay composites.
This was discussed in the FTIR and SEM results sections.Similar results were found in the literature in which using green-seen synthesis of AgNPs resulted in the functionalization of AgNPs using bio-compounds in plant extracts.Chandrasekaran et al (2016) produced latex-functionalized AgNPs using Carica papaya latex extract [64], while Heidari et al (2018) used T. vulgaris extract to produce bio-functionalized T. vulgaris AgNPs [65], and Pandian et al, (2021) were able to produce quercetin-functionalized silver nanoparticles [66].
The bio-functionalized silver nanoparticles synthesized in this study was successfully bonded to the surface of nanoclay to produce Ag-Nanoclay.
According to FTIR analysis results and SEM images of the prepared Ag-Nanoclay nanocomposite, the proposed mechanism for the formation of Ag-Nanoclay is shown in figure 5.
Additionally, a scanning electron microscope was used to examine the effect of the addition of Ag-Nanoclay nanocomposites on the PVDF membrane cross section and surface in terms of porosity.
The cross-sectional SEM images of the different membranes (figure 6) show that the pore structure along the sections did not change significantly with the addition of Ag-Nanoclay in terms of pore shape and size.However, the upper surfaces of the membranes (figure 7) prove that the addition of Ag-Nanoclay to PVDF increased the pore size for both nanoparticle loadings (1 wt% and 3 wt%), with average pore size of 28.4 nm, 88.5 nm and 158.5 nm for PVDF, PVDF-1%Ag-Nanoclay, and PVDF-3%Ag-Nanoclay respectively.
Ag-Nanoclay was not detected in the cross-section and upper surface SEM images; however, it can be seen clearly in the lower surface images, which means that during the membrane casting, the Ag-Nanoclay precipitates down to the lower part of the membranes because of its higher density compared to PVDF.Similar results have been reported by Sirinupong et al, 2018 [67].The size of Ag-Nanoclay particles in the PVDF-3 wt% Ag-Nanoclay has an average size of 553.5 nm, which is higher than those in PVDF-1 wt%Ag-Nanoclay which has an average size of 213.4 nm, and it is noted that both loaded PVDF membranes show some degree of agglomeration.In addition, figures 8(b) and (c) show that some AgNPs were coated, which proves that the proposed mechanism of functionalization of AgNPs with flavonoids is valid.However, the coating was not achieved for all AgNPs, which may indicate that not all the formed AgNPs were bonded to nanoclay similarly, and some nanoparticles which were not coated tend to agglomerate, especially at high loading (3 wt%) Atomic force microscopy was used to examine the effect of Ag-Nanoclay on the morphology of the membranes (figure 9).The surface roughness of PVDF exhibited Ag-Nanoclay loading.However, it was higher for the 1 wt% loading than for 3 wt%.This indicates that at 1 wt% Ag-Nanoclay loading, there are some nanoparticles on the surface of the PVDF surface, causing an increase in roughness; however, at higher loading (3 wt%), agglomeration of the Ag-Nanoclay nanocomposite is expected to occur, causing less Ag-Nanoclay to be present at the surface.This result is in agreement with Hadavand et al 2019 [68], who found that the roughness of epoxy polysulfide nanocomposites increased upon the addition of nanoclay (1 wt% and 3 wt%), and then decreased again at higher loading (5 wt%) owing to the agglomeration of nanoclay at high loading percentages.The effect of the Ag-Nanoclay nanocomposites on the hydrophilicity of the surface was also examined.As shown in figure 10, the addition of Ag-Nanoclay had no significant effect at 1 wt%.However, it increased the contact angle at 3 wt% loading, which indicated that it changed the surface by decreasing its hydrophilicity, but the membrane surface was still hydrophilic.This change in hydrophilicity may be due to the hydrophobic nature of quercetin and isorhamnetin, which increased upon the addition of Ag-Nanoclay for both bonds the silver nanoparticles with the nanoclay surface, decreasing its hydrophilicity, especially at a high loading content (3 wt%).
Table 2 shows the effect of the addition of Ag-Nanoclay to the PVDF membranes on the porosity.It is known that the presence of nanoparticles results in an unstable ternary system during phase inversion, leading to rapid demixing; consequently, the porosity increases [69].This can be seen clearly at a higher loading of Ag-Nanoclay nanocomposite because at 1 wt%, it appears that the porosity of loaded PVDF is almost similar to that of pure PVDF.However, at 3 wt%, the porosity increased slightly.

Flux and rejection of PVDF membranes
The impact of Ag-Nanoclay on the water flux through the PVDF membranes was investigated, as depicted in figure 11.The study reveals that the addition of Ag-Nanoclay did not significantly affect the water flux.This is because various opposite factors influence the water flux, such as pore size and the presence of Ag-Nanoclay.Although the pore size increased due to the addition of Ag-Nanoclay, which could have increased the water flux (as shown in figure 7), the presence of Ag-Nanoclay created physical barriers that hindered water flux due to agglomeration.The physical barriers increased the resistance to water permeating the membrane, while simultaneously decreasing the hydrophilicity of the PVDF membrane, which reduced the attraction for water molecules to pass through the membranes, consequently reducing the water flux.Some previous studies showed increased pure water flux [67][68][69], while others showed decreased water flux [70] upon the addition of nanoclay or nanosilver to the polymer membrane.It was also found in the literature that opposite factors acted against each other.Monsef et al (2019) found that at low nanoparticle loading, a decrease in porosity decreased the water flux, on the other hand at higher nanoparticle loading, the enhancement in hydrophilicity overcame the porosity, resulting in an enhancement in water flux [70].Similar results were found when testing water containing 0.5 g L −1 BSA (figure 12).The presence of Ag-Nanoclay did not significantly affect the water flux, which indicates that the presence of Ag-Nanoclay within the PVDF polymeric membrane did not negatively affect the osmotic pressure difference in a way that would reduce the membrane efficiency; this also suggests that Ag-Nanoclay and PVDF have an acceptable degree of compatibility within the polymer matrix.
Figure 13 illustrates the BSA rejection % outcomes, indicating that incorporating Ag-Nanoclay did not significantly elevate the BSA rejection, which aligns with the expectation.As previously mentioned, Ag-Nanoclay acts as a barrier against BSA's passage through the membrane cross-section, increasing BSA rejection %.However, adding Ag-Nanoclay increases the pore size, which leads to a reduction in BSA rejection%.
Based on the previous results, it can be concluded that including Ag-Nanoclay nanocomposites in PVDF membranes does not negatively affect PVDF membranes' flux and rejection performance.However, the added value of their inclusion was tested by examining the mechanical and antibacterial properties of the PVDF-Ag-Nanoclay nanocomposite membranes compared to those of the PVDF membranes.The better mechanical and antibacterial properties would suggest that the prepared membranes have a longer shelf life because of their better resistance to applied pressure during filtration and biofouling resulting from water filtration over time without jeopardizing the acceptable flux and rejection rates of PVDF membranes.

Tensile properties
To examine the mechanical properties, tensile tests were performed on the PVDF and PVDF-Ag-Nanoclay membranes.As seen in figure 14, the stress-strain diagram shows an enhancement of tensile strength, which increased by 67% upon adding 1 wt% Ag-Nanoclay due to the effect of nanoclay strength.However, it decreased by 50% when the Ag-Nanoclay loading increased to 3 wt%.This is attributed to the degree of Ag-Nanoclay agglomeration that occurs at 3 wt% and to the increase in pore size, which is expected to negatively affect mechanical properties [71].Both loadings (1 wt% and 3 wt%) caused a reduction in elongation, which was expected because of the poor ductility of the nanoclay.Furthermore, the Ag-Nnanoclay demonstrated significant antibacterial activity against S. aureus at concentrations of 500 ppm and 600 ppm, with inhibition percentages of 84.37% and 85.21%, respectively.The AgNPs linked to the nanoclay exhibited a spherical shape and a high surface-to-volume ratio.This characteristic facilitates their connection to bacterial cell walls, thereby increasing the efficiency of antibacterial activity [72].
Several studies have confirmed these findings.Roy et al (2017) successfully synthesized a novel silver-loaded montmorillonite using acid and concluded that the novel silver-loaded montmorillonite exhibited antibacterial  activity [73].In another study, AgNPs were intercalated with a highly biocompatible halloysite nanoclay using a green method with curcumin as the reducing agent.The antibacterial activity of the mixture of AgNPs and curcumin in the halloysite nanoclay was investigated using a disk diffusion test.The results demonstrated the effective antibacterial activity of the mixture against both gram-positive (B.cereus) and gram-negative (E.coli) bacteria [74].

Antibacterial activity for membrane
To examine the antibacterial activity of the Ag-Nanoclay nanocomposite as an antifouling agent, the antibacterial activity of the PVDF membranes with and without the Ag-Nanoclay nanocomposites was investigated.According to the results in tables 3 and 4, the PVDF-Ag-Nanoclay membranes (1 wt% and 3 wt%) exhibited high antibacterial activity against both gram-negative (E.coli) and gram-positive (S. aureus) bacteria, suggesting their potential as anti-biofouling membranes.Similar results have been reported previously.In a study on a nanocomposite of palygorskite/silver nanoparticles that was synthesized using a polydopamine coating strategy and embedded into the layer of a polyamide reverse osmosis membrane, the prepared nanocomposite membrane exhibited high antibacterial activity against E. coli [75].Another study used carrageenan, AgNPs as an antimicrobial nanofiller, and an organically modified clay mineral to prepare antimicrobial bionanocomposite films.The antibacterial efficiency results demonstrated that the nanocomposite film exhibited highly effective antimicrobial activity against both gram-positive (Listeria monocytogenes) and gram-negative (E.coli) bacteria [76].Gabriel et al (2017) synthesized AgNPs on chitosan/montmorillonite nanocomposite films using a photochemical (UV irradiation) method.The growth of E. coli and Bacillus subtilis was inhibited by all nanocomposite-AgNP films, as indicated by their antibacterial activity [77].

Conclusions
Ag-Nanoclay nanocomposites were successfully synthesized using Paronychia argentea plant.UV-vis spectroscopy confirmed this, showing a broad peak around 450 nm related to AgNPs.Green synthesis allows for the bonding between AgNPs and functional groups in plant extracts, such as flavonoids.FTIR and XRD analyses confirmed this bonding.The clay layers were bonded to the conjugates of AgNP-flavonoids, distributed nonhomogenously on their surfaces, with sizes ranging from 20 to 60 nm.
PVDF membranes were prepared using the phase inversion method, incorporating the synthesized Ag-Nanoclay nanocomposite at 1 wt% and 3 wt%.SEM images showed that the addition of Ag-Nanoclay increased the pore size for both nanoparticle loadings.The particles in PVDF-3 wt%Ag-Nanoclay were larger than those in PVDF-1 wt%Ag-Nanoclay, and both the loaded PVDF membranes showed some degree of agglomeration.Atomic force microscopy showed that at 1 wt% Ag-Nanoclay loading, there were some nanoparticles on the PVDF surface, causing an increase in roughness.However, at a higher loading (3 wt%), the roughness was lower than that of the 1 wt% membrane, but still higher than that of the pure PVDF membrane due to agglomeration of the Ag-Nanoclay nanocomposite, causing a lower percentage of Ag-Nanoclay to be present at the surface.
Contact angle measurements showed that adding Ag-Nanoclay had no significant effect at 1 wt%, but it increased the contact angle at 3 wt% loading.This was related to the hydrophobic nature of the flavonoids, bonding silver nanoparticles with the nanoclay surface and decreasing their hydrophilicity.The porosity increased slightly with the addition of Ag-Nanoclay.
The study found that adding Ag-Nanoclay did not significantly affect the water flux through PVDF membranes in tests with distilled water and 0.5 g L −1 BSA water, nor did it increase the BSA rejection significantly.The lack of significant effects was due to the opposite impact of the pore size increase, porosity enhancement, hydrophilicity decrease, and physical barriers resulting from Ag-Nanoclay within the PVDF membranes.However, the addition of Ag-Nanoclay had an apparent effect on the mechanical properties of the membranes.The 1 wt% loading increased the tensile strength by 67%, while the 3 wt% decreased it by 50%.Both loading percentages decreased the ductility of PVDF membranes.This indicates that 1 wt% is a good choice for enhancing the tensile strength, which indicates the ability to withstand higher pressures during filtration.Additionally, both PDVF nanocomposite membranes showed very high sterilization rates (>99%) against E. coli and S. aureus, indicating that the addition of Ag-Nanoclay enhanced the anti-biofouling properties of PVDF membranes.
The addition of Ag-Nanoclay nanocomposite to PVDF membranes improves their mechanical and antibacterial properties, leading to a longer shelf life.This is due to their ability to withstand applied pressure during filtration and prevent biofouling that may occur over time without affecting the acceptable flux and rejection rates of PVDF membranes.As a result, Ag-Nanoclay nanocomposite is an excellent potential nanofiller for different types of membranes to be used in applications that require tolerance to high pressure and high fouling.

5. 4 .
Antibacterial activity 5.4.1.Antibacterial efficiency for synthesized Ag-Nanoclay This test was performed to determine the antibacterial activity of the Ag-Nanoclay.According to the results shown in figure15, the AgNnanoclay exhibited high antibacterial activity against E. coli.The most effective concentrations were 500 and 600 ppm, showing 99.9% inhibition rates.

Figure 12 .
Figure 12.Water flux rate in the presence of BSA.

Table 1 .
The percent conversion of Ag + ions to AgNPs.