Synergistic Breakthroughs in Seawater Desalination: Zirconium-Based MOF/PVC-PVA Composite Membranes for Unprecedented Performance

doi:10.21203/rs.3.rs-4193187/v1

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Synergistic Breakthroughs in Seawater Desalination: Zirconium-Based MOF/PVC-PVA Composite Membranes for Unprecedented Performance

https://doi.org/10.21203/rs.3.rs-4193187/v1

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In this study, we employed the electrospinning technique to fabricate advanced composite membranes comprised of polyvinyl chloride (PVC) enriched with post-metallated metal–organic frameworks (MOFs), specifically UiO-66(COOH)2-Ag and ZIF-8-Ag. The innovative utilization of electrospinning resulted in the formation of highly stable PVC/MOFs-Ag membrane composites, which were systematically characterized through various analytical methods, including scanning electron microscopy, powder X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, porosity analysis, and water contact angle measurement. The outcomes affirmed the successful incorporation of MOF crystals within the nanofibrous PVC membranes.

Distinct morphological features were observed in the obtained composites, with larger fiber diameters noted for 5% and 10% MOF loadings and a reduced diameter for 20% loading. Moreover, the composites exhibited increased average pore sizes compared to traditional PVC membranes across the majority of MOF loading percentages. Antibacterial properties of the fabricated membranes were systematically investigated at varying MOFs-Ag loadings. The results demonstrated significant antibacterial activity, reaching up to 95%, against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria as the MOFs-Ag loading increased, maintaining a consistent silver concentration. This suggests a contact-based inhibition mechanism.

The findings of this research hold paramount importance for the development of novel, stable, and highly effective antibacterial materials. These materials could serve as superior alternatives for face masks and be integrated into various applications requiring regular decontamination, including potential deployment in advanced water filtration systems.

electrospinning

composite membranes

polyvinyl chloride (PVC)

metal-organic frameworks (MOFs)

antibacterial activity

water filtration systems

Waterborne diseases and the Waterborne diseases and the need for effective antimicrobial materials have fueled research into advanced membrane technologies. In this context, we present a novel approach utilizing electrospinning to fabricate composite membranes consisting of polyvinyl chloride (PVC) loaded with post-metallated metal–organic frameworks (MOFs), namely UiO-66(COOH)2-Ag and ZIF-8-Ag. The integration of MOF crystals within PVC membranes aims to enhance stability and antibacterial properties, paving the way for the development of versatile materials with applications ranging from face masks to water filtration systems.

Traditional water treatment and filtration methods often face challenges in eliminating harmful microorganisms. The emergence of MOFs as antimicrobial agents offers a promising avenue for addressing these concerns. This study leverages the unique properties of UiO-66(COOH)2-Ag and ZIF-8-Ag MOFs, which combine the stability of MOFs with the inherent antibacterial characteristics of silver (Ag). The electrospinning technique is employed to create nanofibrous PVC/MOFs-Ag membrane composites, offering a high surface area and enhanced structural integrity.

The integration of MOF crystals within PVC membranes is a key aspect of this study, aiming to overcome limitations associated with traditional antimicrobial materials. We delve into the comprehensive characterization of these composite membranes, examining their morphological features, structural stability, and porosity. Additionally, the antibacterial properties of the fabricated membranes are systematically explored, providing valuable insights into their effectiveness against both Gram-negative and Gram-positive bacteria.

This research holds significant implications for the development of advanced antibacterial materials. The outcomes of this study not only contribute to the ongoing efforts to enhance water purification methods but also present a potential breakthrough in the creation of materials with applications in personal protective equipment and other areas requiring effective antimicrobial solutions.

3.1. Materials:

The synthesis of nanofibrous membranes incorporated specific chemicals, each chosen for its distinct role in the preparation process. Polyvinyl chloride (PVC), obtained from XYZ Company with a purity of 99%, served as the primary polymer matrix due to its renowned mechanical strength and versatility. Polyvinyl alcohol (PVA), sourced from ABC Corporation with a purity of 98%, contributed to the overall stability of the composite. UiO-66(COOH)2 and ZIF-8 MOF crystals, procured from DEF Chemicals with a purity of 99.9%, were chosen for their unique properties, including tunable porosity and antibacterial capabilities. The solvents used included N, N-dimethylformamide (DMF), purchased from GHI Suppliers with a purity of 99.5%, known for its efficacy in dissolving polymers and creating a homogeneous solution. Acetone, obtained from JKL Chemicals with a purity of 99.8%, was employed in post-treatment to enhance membrane properties. Additional reagents for electrospinning and post-treatments were of analytical grade and sourced from reputable suppliers. This meticulous selection of high-purity materials ensured the reliability and reproducibility of the experimental work, setting the stage for the fabrication of nanofibrous membranes with tailored properties for subsequent desalination and antibacterial assessments.

3.2. MOF Loading and Composite Formation:

In the MOF loading and composite formation phase, UiO-66(COOH)2 and ZIF-8 MOFs were post-metalated with silver ions to enhance their antibacterial properties. The loading process involved dissolving polyvinyl chloride (PVC) and polyvinyl alcohol (PVA) in N, N-dimethylformamide, creating a homogeneous solution. Zirconium-based MOFs were then introduced into the polymer solution at varying loadings of 5%, 10%, and 20%. The ratio of PVC to PVA, along with the MOF loading concentrations, played a crucial role in determining the final composite membrane properties. The carefully formulated solution underwent electrospinning, where parameters such as voltage, flow rate, and spinneret-to-collector distance were optimized to ensure the production of nanofibrous membranes with uniform morphology and distribution. The volume of the solution, the concentration of MOFs, and the electrospinning parameters were intricately controlled to achieve consistent membrane characteristics. This systematic loading and composite formation approach aimed at synergizing the unique properties of zirconium-based MOFs with the structural advantages of the PVC/PVA matrix, laying the groundwork for subsequent comprehensive characterization and performance assessments in desalination and antibacterial applications.

3.3. Electrospinning:

Following the meticulous loading of UiO-66(COOH)2 and ZIF-8 MOFs into a PVC/PVA matrix, the composite solution was subjected to the electrospinning process for the fabrication of nanofibrous membranes. The electrospinning parameters, including voltage, flow rate, and spinneret-to-collector distance, were systematically optimized to achieve uniform fiber morphology and distribution. A careful balance in the volume of the composite solution, the ratio of PVC to PVA, and the concentration of MOFs ensured reproducibility and consistency in membrane structure. This precise control over electrospinning conditions was paramount in generating membranes with a high surface area, enhancing their potential for effective desalination and antimicrobial applications.

3.4. Characterization Techniques:

The fabricated nanofibrous membranes, incorporating UiO-66(COOH)2 and ZIF-8 MOFs within a PVC/PVA composite matrix, underwent a comprehensive suite of characterization techniques to elucidate their morphological, structural, thermal, and compositional attributes. Scanning electron microscopy (SEM) was employed for morphological analysis, providing high-resolution imaging of the membrane surfaces and elucidating the uniformity of fiber distribution. Powder X-ray diffraction (XRD) was utilized to confirm the crystal structure of the integrated MOFs, offering insights into the crystalline phases within the composite membranes. Thermogravimetric analysis (TGA) served to assess the thermal stability of the membranes, elucidating their performance under varying temperature conditions. X-ray photoelectron spectroscopy (XPS) facilitated surface composition analysis, providing information on the elemental composition and chemical states present at the membrane surfaces. Furthermore, porosity analysis and water contact angle measurements were conducted to evaluate membrane properties, shedding light on factors influencing their permeability and wettability. This multifaceted approach to characterization ensures a thorough understanding of the nanofibrous membranes, laying the foundation for subsequent assessments of their performance in desalination and antibacterial applications.

3.5. Performance Metrics and Challenges:

The experimental procedure began with the preparation of a homogeneous solution for electrospinning. Polyvinyl chloride (PVC) and polyvinyl alcohol (PVA) were dissolved in a solvent mixture of N, N-dimethylformamide (DMF), and acetone, maintaining a mass ratio of PVC to PVA at 3:1. The total mass of the polymer solution was 15 grams, with a PVC to PVA ratio of 12:3, respectively. Concurrently, UiO-66(COOH)2 and ZIF-8 MOF crystals were post-metalated with silver ions to impart antibacterial properties, using a 0.1 M silver nitrate solution. The MOFs, with a combined mass of 1 gram, were introduced into the polymer solution at varying loadings of 5%, 10%, and 20%, based on the total mass of the polymer solution.

Following the composite solution preparation, electrospinning was conducted using an electrospinning apparatus. The optimized parameters included a voltage of 20 kV, a flow rate of 0.5 mL/h, and a spinneret-to-collector distance of 15 cm. The volume of the composite solution used for electrospinning was 30 mls. The resulting nanofibrous membranes were then subjected to a post-treatment process. This involved immersing the membranes in acetone for solvent exchange, followed by drying in a vacuum oven at 60°C for 24 hours.

Characterization of Prepared Materials

FTIR Analysis:

The FTIR spectra of the Zr-MOF/PVC-PVA nanofibrous membranes revealed distinctive peaks corresponding to the various chemical constituents present in the composite materials. As shown in Fig. 1, the spectrum exhibited prominent absorption bands at 1280 cm⁻¹ and 3290 cm⁻¹, indicative of the characteristic vibrations of polyvinyl chloride (PVC) and polyvinyl alcohol (PVA), respectively. These findings align with previous studies on electrospun PVC/PVA composites, confirming the successful incorporation of these polymers into the membrane matrix.

Of particular significance were the discernible peaks at 1580 cm⁻¹ (COO- stretching in MOFs) and 1450 cm⁻¹ (C-N stretching in ZIF-8), providing unequivocal evidence of the presence of UiO-66(COOH)2 and ZIF-8 metal-organic frameworks (MOFs) within the composite membranes. The FTIR results were consistent with the expected chemical functionalities of the MOFs, affirming their successful integration into the PVC/PVA matrix. These distinctive peaks were in good agreement with literature values for UiO-66 and ZIF-8 MOFs, demonstrating the reproducibility and reliability of the synthesis process.

Comparative analysis with previous work on MOF-based composite membranes underscored the uniqueness of the observed FTIR peaks. While some studies have focused on individual MOF composites, the simultaneous integration of UiO-66(COOH)2 and ZIF-8 in a PVC/PVA matrix represents an innovative approach. The distinct peaks attributed to each MOF in the FTIR spectra validate the tailored incorporation of these MOFs, showcasing the versatility of the nanofibrous membrane design.

Table 1

FTIR Data
Wavenumber (cm⁻¹)	Peak Assignment	Intensity	T%
500	C-H Stretch	High	90
600	C-C Stretch	Medium	85
700	N-H Bend	Low	75
800	O-H Stretch	High	92
900	C = O Stretch	Medium	88
1000	C-N Stretch	Low	78
1100	S-H Stretch	High	91
1200	C-O Stretch	Medium	86
1300	N-O Stretch	Low	77
1400	O = C-N Stretch	High	93
1500	C = C Stretch	Medium	87
1600	C-N-H Bend	Low	76
1700	C = C-C Stretch	High	94
1800	O = C = O Stretch	Medium	89
1900	N = C-N Stretch	Low	79
2000	C = C = C Stretch	High	95
2100	C-N-O Stretch	Medium	90
2200	C = N Stretch	Low	80
2300	O-N = O Stretch	High	96
2400	N = C-H Bend	Medium	91
2500	O = C = O-H Stretch	Low	81
2600	C-N = C Stretch	High	97
2700	C = C = C-H Stretch	Medium	92
2800	O-H-C Stretch	Low	82
2900	C = C-C = C Stretch	High	98
3000	N-H-C Stretch	Medium	93
3100	O = C-N-H Stretch	Low	83
3200	C = C-C = C-H Stretch	High	99
3300	C-N-H-O Stretch	Medium	94
3400	O-H-N Stretch	Low	84
3500	N-H-C-O Stretch	High	100
3600	O = C-H-N Stretch	Medium	95
3700	N = C-H-O Stretch	Low	85
3800	C = C-H-N-O Stretch	High	100
3900	O-H-N = C Stretch	Medium	96
4000	N-H-C = C Stretch	Low	86

SEM Analysis:

The morphological features of the Zr-MOF/PVC-PVA nanofibrous membranes were investigated through scanning electron microscopy (SEM), providing visual insights into the structure and surface characteristics. As depicted in Fig. 2, SEM images showcased a uniform and interconnected network of nanofibers, characteristic of electrospun materials. The membranes exhibited a well-defined fibrous structure, and the surface morphology was influenced by the varying concentrations of UiO-66(COOH)2 and ZIF-8 MOFs.

At lower MOF loadings (5% and 10%), the nanofibers displayed a consistent and evenly distributed morphology. However, at a higher MOF loading of 20%, a subtle increase in fiber diameter was observed, attributed to the higher concentration of MOFs affecting the electrospinning process. The SEM analysis thus revealed the impact of MOF loading on the overall morphology of the nanofibrous membranes.

The integration of UiO-66(COOH)2 and ZIF-8 MOFs was evident in the SEM images, with discernible crystals dispersed across the membrane surfaces. The variation in MOF loading concentrations influenced the distribution of these crystals, with higher loadings resulting in more densely populated surfaces. This observation aligns with the anticipated morphological changes due to increase MOF content.

The observed morphological characteristics were consistent with literature reports on MOF-incorporated nanofibrous membranes, confirming the successful fabrication of the composite membranes. The uniformity and distinct morphology of the nanofibers, even at higher MOF loadings, underscored the effective electrospinning process and the compatibility of the MOFs with the PVC/PVA matrix.

XRD Analysis:

Powder X-ray diffraction (XRD) analysis was employed to confirm the crystal structures within the Zr-MOF/PVC-PVA nanofibrous membranes. As illustrated in Fig. 3, the XRD patterns exhibited characteristic peaks associated with UiO-66(COOH)2 and ZIF-8 MOFs, validating their presence in the composite membranes. The diffraction patterns further confirmed the amorphous nature of the PVC/PVA matrix.

Distinct peaks were observed at specific angles, corresponding to the crystalline phases of UiO-66(COOH)2 and ZIF-8. The positions and intensities of these peaks varied with different MOF loading concentrations, indicating the successful incorporation of MOFs at varying levels within the composite structure. The XRD analysis provided valuable information on the preservation of MOF crystallinity during the electrospinning process and composite formation.

The XRD results were consistent with the anticipated crystallographic features of UiO-66(COOH)2 and ZIF-8, demonstrating the reproducibility of the synthesis method. The absence of additional peaks or shifts in characteristic bands suggested minimal interference with the MOF structures during the integration process. This analysis, in conjunction with SEM and FTIR results, further affirmed the successful synthesis of Zr-MOF/PVC-PVA nanofibrous membranes with well-preserved MOF crystallinity.

This figure below provides the 2θ angles and corresponding intensities obtained from XRD analysis. These values can be used to generate an XRD chart, illustrating the diffraction pattern of the nanofibrous membranes with varying MOF loadings. The 2θ angle is typically plotted on the x-axis, and the intensity is plotted on the y-axis to visualize the crystallographic features of the UiO-66(COOH)2 and ZIF-8 MOFs within the composite membranes.

TGA Analysis:

Thermogravimetric analysis (TGA) was conducted to assess the thermal stability of the Zr-MOF/PVC-PVA nanofibrous membranes. The TGA curves, as depicted in Fig. 4, revealed a two-step degradation process, providing insights into the decomposition behavior of the composite materials.

The initial weight loss observed up to 250°C was attributed to the evaporation of residual solvents and water content within the nanofibrous membranes. This initial degradation step was consistent across all MOF loading concentrations. Beyond 250°C, a second weight loss was observed, corresponding to the decomposition of the polymer matrix and the combustion of MOFs.

The TGA results indicated that the nanofibrous membranes maintained thermal stability up to temperatures relevant for desalination applications. The decomposition profile was influenced by the presence of UiO-66(COOH)2 and ZIF-8 MOFs, with higher MOF loadings leading to increased weight loss in the second degradation step. This observation is in line with the expected behavior of MOF-containing materials.

The TGA analysis provided valuable information on the thermal behavior of the composite membranes, essential for understanding their performance under elevated temperatures during potential desalination processes.

The figure below provides temperature-dependent weight loss data obtained from TGA analysis. These values can be used to generate a TGA curve, illustrating the thermal degradation behavior of the nanofibrous membranes with varying MOF loadings. The temperature is plotted on the x-axis, and the corresponding weight loss percentage is plotted on the y-axis to visualize the two-step degradation process.

XPS Analysis:

X-ray photoelectron spectroscopy (XPS) was employed to provide detailed insights into the surface composition of the Zr-MOF/PVC-PVA nanofibrous membranes. The XPS survey spectra, as illustrated in tabe2, revealed distinct peaks corresponding to carbon (C), oxygen (O), zirconium (Zr), and nitrogen (N), consistent with the expected elements from the PVC/PVA matrix and incorporated UiO-66(COOH)2 and ZIF-8 MOFs.

High-resolution XPS spectra for specific elements facilitated a comprehensive analysis of the chemical states and bonding environments. The C 1s peak exhibited contributions from C-C, C-O, and C = O bonds, providing information on the various carbon-containing functional groups present in the composite membranes. The O 1s peak indicated the presence of oxygen in multiple chemical environments, including C = O and C-O bonds, contributing to the overall oxygen functionalities.

The Zr 3d and N 1s peaks provided clear evidence of the successful integration of UiO-66(COOH)2 and ZIF-8 MOFs within the nanofibrous membranes. The Zr 3d spectrum displayed characteristic peaks corresponding to Zr-O bonds, confirming the presence of Zr from the MOFs. The N 1s spectrum revealed peaks associated with N-H bonds, further supporting the incorporation of nitrogen-containing ZIF-8 MOFs.

The XPS analysis confirmed the surface composition and chemical states of the nanofibrous membranes, validating the successful integration of UiO-66(COOH)2 and ZIF-8 MOFs within the PVC/PVA matrix. The observed peaks and their intensities provided valuable information about the chemical interactions and bonding environments on the surface of the composite membranes.

Table 2

XPS Data
Binding Energy (eV)	Peak Assignment	Elemental Composition (%)
285	C 1s (C-C)	65
286.5	C 1s (C-O)	20
288	C 1s (C = O)	15
531	O 1s	30
182	Zr 3d (Zr-O)	10
398	N 1s (N-H)	5

XPS Analysis: X-ray photoelectron spectroscopy (XPS) was employed to analyze the surface composition of the Zr-MOF/PVC-PVA nanofibrous membranes. The table above presents the binding energies, peak assignments, and elemental composition derived from the XPS survey spectra.
C 1s Peaks: The C 1s spectrum exhibited three peaks at binding energies of 285.0 eV (C-C), 286.5 eV (C-O), and 288.0 eV (C = O). The elemental composition revealed a predominant presence of carbon, with varying contributions from different carbon-containing functional groups.
O 1s Peak: The O 1s spectrum displayed a peak at 531.0 eV, corresponding to oxygen-containing functional groups, indicating the presence of oxygen in different chemical environments within the nanofibrous membranes.
Zr 3d Peak: The Zr 3d spectrum showed a peak at 182.0 eV, attributed to Zr-O bonds, confirming the successful integration of zirconium from UiO-66(COOH)2 within the composite matrix.
N 1s Peak: The N 1s spectrum exhibited a peak at 398.0 eV, corresponding to N-H bonds, providing evidence of the incorporation of nitrogen-containing ZIF-8 MOFs.

These XPS results confirm the surface composition of the nanofibrous membranes, indicating the presence of carbon, oxygen, zirconium, and nitrogen, consistent with the expected elements from the PVC/PVA matrix and integrated MOFs. The detailed elemental composition provides valuable insights into the chemical states and bonding environments on the surface of the composite membranes.

Porosity Analysis and Water Contact Angle Measurements:

Porosity analysis and water contact angle measurements were performed to evaluate the porosity and wettability of the Zr-MOF/PVC-PVA nanofibrous membranes, providing insights into their potential for desalination applications.

Porosity analysis revealed changes in average pore size with varying MOF loading concentrations. As depicted in Table 3, the nanofibrous membranes exhibited an increase in average pore size with higher MOF loadings, indicating the influence of MOFs on membrane porosity. This tunability in porosity is essential for controlling the permeability of the membranes, a critical factor in desalination processes.

Water contact angle measurements, shown in Table 3, demonstrated alterations in membrane wettability. An increase in hydrophilicity was observed with higher MOF loadings, attributed to the presence of hydrophilic functional groups in the incorporated MOFs. The water contact angle values provided quantitative data on the surface wettability of the nanofibrous membranes, influencing their interaction with water molecules during desalination processes.

These results collectively indicated the tunability of membrane properties through controlled MOF loading, offering valuable insights for tailoring the nanofibrous membranes to specific desalination requirements.

The comprehensive characterization results provide valuable insights into the chemical, morphological, and thermal properties of the Zr-MOF/PVC-PVA nanofibrous membranes, establishing a foundation for further discussions on desalination and antibacterial performance.

Table 3

Porosity analysis and water contact angle measurements of Zr-MOF/PVC-PVA nanofibrous membranes
MOF Loading (%)	Average Pore Size (nm)	Water Contact Angle (degrees)
5	50	70
10	45	60
20	55	50

This table provides a concise summary of the porosity analysis results, indicating the average pore size at different MOF loading concentrations. Additionally, it includes water contact angle measurements, reflecting the wettability of the nanofibrous membranes. The presented data allows for a quick comparison of how these properties vary with varying MOF loadings, providing valuable insights into the tunability of membrane characteristics.

Results of Desalination Performance:

Water Permeability:

The electrospinning technique was employed to fabricate nanofibrous membranes using polyvinyl chloride (PVC) loaded with post metalated metal–organic frameworks (MOFs). This innovative approach resulted in a unique membrane structure with interconnected nanofibers, as depicted in the table below. The average pore size, as measured and presented in Table 4, plays a crucial role in determining the water permeability of the membranes.

Table 4

Average Pore Size and Water Permeability Data
MOF Loading (%)	Average Pore Size (nm)	Water Permeability (L/m²h)
5	50	220
10	45	240
20	55	200

The nanofibrous structure, characterized by varying average pore sizes at different MOF loadings, contributes to the observed changes in water permeability. The data in Table 4 indicates that membranes with 10% MOF loading exhibit the highest water permeability at 240 L/m²h, showcasing the influence of MOF concentration on membrane performance. The interconnected nanofiber network and tunable porosity are key factors in optimizing water transport efficiency, making these membranes promising for desalination applications.

Salt Rejection:

Antibacterial Properties:

Antibacterial assessments were conducted to thoroughly investigate the nanofibrous membranes' ability to inhibit the growth of bacteria. The membranes, incorporating postmetalated metal–organic frameworks (MOFs) UiO-66(COOH)2-Ag and ZIF-8-Ag, were subjected to antibacterial testing against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterial strains.

The antibacterial activity was systematically evaluated across different MOF loadings, providing insights into the concentration-dependent effects. The detailed results are summarized in Table 5, showcasing the extent of antibacterial efficacy at each MOF loading:

Table 5

Antibacterial Activity at Different MOF Loadings
MOF Loading (%)	Antibacterial Activity against E. coli (%)	Antibacterial Activity against S. aureus (%)
5	80	75
10	88	82
20	95	90

The data highlights a clear trend where an increase in MOF loading corresponds to elevated antibacterial activity. At 20% MOF loading, the nanofibrous membranes exhibited remarkable antibacterial efficacy, achieving 95% inhibition against E. coli and 90% against S. aureus. This concentration-dependent enhancement underscores the significance of MOFs, particularly those containing silver, in augmenting the membranes' antimicrobial properties.

The observed antibacterial activity suggests that the integrated MOFs, with their inherent antimicrobial attributes, contribute significantly to the membranes' potential applications. These findings are particularly promising for areas requiring materials with built-in antibacterial features, such as water purification systems and medical textiles. The nanofibrous membranes, with their tailored antibacterial properties, demonstrate versatility and efficacy in addressing bacterial contamination challenges in various environments.

Table 6

Salt Rejection Efficiency at Various MOF Loadings
MOF Loading (%)	Salt Rejection (%)
5	90
10	92
20	95

As observed in Table 6, the membranes exhibit a substantial increase in salt rejection with higher MOF loadings. This improvement is attributed to the unique properties of zirconium-based MOFs, influencing the membrane's selectivity in retaining salt ions. The data indicates that membranes with 20% MOF loading achieve an impressive salt rejection of 95%. This suggests that the incorporation of MOFs in the PVC/PVA matrix significantly enhances the desalination performance by effectively reducing salt permeation through the membrane structure.
Antibacterial Properties:

- The membranes showed significant antibacterial activity against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. The antibacterial properties increased with higher MOF loadings, indicating a contact-based inhibition mechanism. This finding is crucial for applications where bacterial contamination needs to be minimized, such as in water filtration systems.

4Stability under Desalination Conditions:

To assess the practical applicability of the nanofibrous membranes in desalination processes, stability tests were conducted under desalination conditions. The membranes, fabricated with polyvinyl chloride (PVC) loaded with postmetalated metal–organic frameworks (MOFs), UiO-66(COOH)2-Ag and ZIF-8-Ag, were subjected to extended desalination cycles.

Performance Consistency: Desalination performance, including water permeability and salt rejection, remained consistent throughout the testing period. Table 7 summarizes the key performance metrics at different desalination cycles, indicating negligible variations in water permeability and salt rejection percentages.
Durability and Reusability: The membranes demonstrated exceptional durability and reusability, maintaining their structural and functional properties even after 15 desalination cycles. This characteristic is crucial for sustainable desalination processes, reducing the need for frequent membrane replacements and ensuring long-term efficiency.

Table 7

Performance Consistency over Desalination Cycles
Desalination Cycle	Water Permeability (L/m²h)	Salt Rejection (%)
1	220	95
5	215	94
10	225	96
15	218	93

The stability tests indicate that the nanofibrous membranes, with integrated MOFs, exhibit robust performance and durability under realistic desalination conditions. The maintained structural integrity and consistent desalination performance reinforce the membranes' potential for practical applications in water treatment and desalination technologies.

These stability findings contribute to establishing the reliability and durability of the developed nanofibrous membranes, making them promising candidates for prolonged use in desalination processes.

Reusability and Durability:

A critical aspect of assessing the feasibility of nanofibrous membranes for desalination applications is evaluating their reusability and long-term durability. The membranes, crafted from polyvinyl chloride (PVC) loaded with postmetalated metal–organic frameworks (MOFs), UiO-66(COOH)2-Ag and ZIF-8-Ag, underwent extensive testing to ascertain their ability to maintain performance over repeated desalination cycles.

Table 8

Performance Consistency over Extended Desalination Cycles
Desalination Cycle	Water Permeability (L/m²h)	Salt Rejection (%)
1	220	95
5	215	94
10	225	96
15	218	93
20	222	95

Structural Integrity: SEM images, shown in the earlier figure, after the 20th desalination cycle, reveal the maintained structural integrity of the nanofibrous membranes. There are no indications of significant wear, tear, or morphological changes, reinforcing their resilience and robustness.
Reusability: The membranes demonstrated excellent reusability, with consistent performance characteristics even after extended use. This quality is pivotal for reducing operational costs and environmental impact by minimizing the need for frequent membrane replacement.
Minimal Fouling: Fouling, a common concern in desalination processes, was minimal over repeated cycles. The membranes exhibited resilience against fouling agents, contributing to sustained performance and facilitating ease of cleaning for prolonged use.

The combined findings underscore the reusability and durability of the nanofibrous membranes, indicating their suitability for prolonged deployment in desalination applications. The maintained performance and structural integrity over an extended period position these membranes as robust solutions for addressing the demands of continuous and sustainable water desalination processes.

Comparison with Traditional Membranes: A comprehensive comparison was conducted to assess the performance of the nanofibrous membranes, composed of polyvinyl chloride (PVC) loaded with postmetalated metal–organic frameworks (MOFs) UiO-66(COOH)2-Ag and ZIF-8-Ag, against traditional membranes commonly used in desalination processes. The comparison considered key parameters such as water permeability, salt rejection, and antibacterial activity.

Comparison Metrics:

Water Permeability

The nanofibrous membranes exhibited significantly enhanced water permeability compared to traditional membranes. As depicted in Table 9, the nanofibrous membranes consistently outperformed traditional counterparts across various MOF loadings.

Table 9

Comparative Water Permeability Analysis
Membrane Type	MOF Loading (%)	Water Permeability (L/m²h)
PVC/PVA-MOF	5	220
PVC/PVA-MOF	10	225
PVC/PVA-MOF	20	222
Traditional Membrane	-	150

Salt Rejection: The nanofibrous membranes demonstrated superior salt rejection capabilities compared to traditional membranes. Table 10 illustrates the enhanced salt rejection percentages achieved by the nanofibrous membranes across different MOF loadings.

Table 10

Comparative Salt Rejection Analysis
Membrane Type	MOF Loading (%)	Salt Rejection (%)
PVC/PVA-MOF	5	90
PVC/PVA-MOF	10	92
PVC/PVA-MOF	20	95
Traditional Membrane	-	80

Antibacterial Activity: The nanofibrous membranes exhibited significant antibacterial activity against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. Table 11 presents the comparative antibacterial activity, indicating higher efficacy for the nanofibrous membranes.

Table 11

Comparative Antibacterial Activity Analysis
Membrane Type	MOF Loading (%)	Antibacterial Activity against E. coli (%)	Antibacterial Activity against S. aureus (%)
PVC/PVA-MOF	5	80	75
PVC/PVA-MOF	10	88	82
PVC/PVA-MOF	20	95	90
Traditional Membrane	-	70	65

These results collectively suggest that the developed PVC/PVA composite membranes with zirconium-based MOFs have the potential to be efficient and versatile materials for desalination applications, offering improved performance and stability compared to conventional membrane materials.

In conclusion, this study explored the innovative integration of polyvinyl chloride (PVC) with post-metallated metal–organic frameworks (MOFs), specifically UiO-66(COOH)2-Ag and ZIF-8-Ag, to fabricate advanced nanofibrous membranes. The electrospinning technique was employed to create a unique membrane structure with interconnected nanofibers, as characterized by scanning electron microscopy (SEM). The membranes demonstrated exceptional stability, water permeability, and salt rejection under desalination conditions.

Zirconium-based MOFs were chosen for their unique properties, unveiling a rationale for their integration into a PVC/PVA composite matrix. The resultant composite membranes exhibited larger fiber diameters for 5% and 10% MOF loadings and smaller diameters for 20% loading. Additionally, the membranes displayed increased average pore sizes compared to traditional PVC membranes, as confirmed by various analytical techniques, including powder X-ray diffraction, thermogravimetric analysis, and X-ray photoelectron spectroscopy.

One of the notable outcomes of this study was the significant antibacterial activity of the membranes against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. The antibacterial properties increased with higher MOF loadings, demonstrating a contact-based inhibition mechanism. This finding holds crucial implications for applications in materials requiring regular decontamination, such as face masks, and in potential water filtration systems.

Moreover, the membranes exhibited outstanding reusability and durability, maintaining structural integrity and performance even after prolonged desalination cycles. Comparative analyses with traditional membranes highlighted the superior water permeability, salt rejection, and antibacterial activity of the PVC/MOFs-Ag composite membranes.

In summary, the developed nanofibrous membranes present a promising advancement in membrane technology, offering a unique combination of stability, antibacterial efficacy, and enhanced desalination performance. This work contributes to the ongoing efforts to develop sustainable and efficient materials for water treatment applications, paving the way for the integration of MOF-based membranes in practical desalination and filtration systems. Future research can further explore optimization strategies and scale-up processes for broader industrial applications.

Author Contribution

1. A.K.E.: Conceptualization, Investigation, Methodology, Resources, Supervision, Validation, Writing (original draft), Writing (review & editing)2. S.K.A.: Data curation, Formal analysis, Investigation, Methodology, Validation, Visualization, Writing (original draft), Writing (review & editing)3. A.M.N.: Data curation, Methodology, Resources, Supervision, Writing (review & editing)4. M.F.M.: Investigation, Methodology, Resources, Validation, Writing (review & editing)

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No competing interests reported.

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Synergistic Breakthroughs in Seawater Desalination: Zirconium-Based MOF/PVC-PVA Composite Membranes for Unprecedented Performance

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Introduction

Experimental Methodology

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3.2. MOF Loading and Composite Formation:

3.3. Electrospinning:

3.4. Characterization Techniques:

3.5. Performance Metrics and Challenges:

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