Innovative PVC/Fe(OH) 3 Ion Exchange Membranes for Efficient Arsenic Removal: Synthesis, Performance, and pH-Dependent Behavior

Innovative PVC/Fe(OH) 3 Ion Exchange Membranes for Efficient Arsenic Removal: Synthesis, Performance, and pH-Dependent Behavior | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Innovative PVC/Fe(OH) 3 Ion Exchange Membranes for Efficient Arsenic Removal: Synthesis, Performance, and pH-Dependent Behavior Alireza Hamidi, Azizeh Javadi, Seyed Mohsen Hosseini, Atefeh Hamidi, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7068769/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Arsenic removal from aqueous systems is of increasing concern due to its high toxicity and association with serious health risks, including cardiovascular diseases, hypertension, and various forms of cancer. Ion exchange membranes serve as active separation interfaces in electrochemical systems, such as electrodialysis, offering a cost-effective and efficient strategy for the selective removal of arsenic from aqueous solutions. The focus of this research is on diverse membranes for cation-selective exchange that were developed and modified with Fe(OH) 3 nanoparticles using the solution casting technique, based on polyvinyl chloride (PVC). This study investigated the effect of varying nanoparticle concentrations on the electrochemical properties of the membrane, with particular emphasis on its efficacy in arsenic removal. Additionally, the influence of filler additives, casting solution composition, pH levels, and electrolyte concentration on the membrane’s electrochemical behavior was systematically evaluated. The incorporation of Fe(OH) 3 nanoparticles into the membrane matrix resulted in notable enhancements in membrane potential, ion transport efficiency, and ionic sensitivity. Furthermore, the presence of these nanoparticles significantly increased the ionic flux across the membrane, from 9.28 × 10 5 to 12.6 × 10 5 mol·m -2 ·s -1 . The modified membranes exhibited enhanced transport efficiency and ion selectivity at pH = 7 compared to other pH conditions. The results further revealed that the membrane's electrical resistance initially decreased significantly with increasing electrolyte pH, followed by a subsequent increase at higher pH levels. The membranes exhibited lower selectivity toward divalent ions in comparison to monovalent ions. Moreover, membranes modified with Fe(OH) 3 nanoparticles displayed superior electrochemical performance relative to the unmodified counterparts. Mixed matrix membrane Electrodialysis Membrane Ion exchange Arsenic removal Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Synopsis This research underscores the environmental relevance of PVC/Fe(OH) 3 nanocomposite membranes, offering an advanced and cost-effective approach for arsenic remediation in water systems, thereby supporting public health and ecological sustainability. 1. Introduction The over-extraction of groundwater and the declining water levels in wells have resulted in a notable rise in the concentration of various elements, particularly heavy metals. Consequently, numerous water sources have become contaminated with these metals. The most frequently encountered heavy metals include arsenic, iron, chromium, manganese, nickel, cadmium, and lead [ 1 ]. The Environmental Protection Agency (EPA) has set a maximum permissible threshold of 10 micrograms per liter for arsenic in drinking water due to its potential health hazards. Recently, the contamination of groundwater with arsenic has emerged as a major health issue, contributing to conditions such as cardiovascular diseases, hypertension, internal cancers, skin lesions, and even skin cancer. As a result, there has been a growing interest among scientists and researchers in developing effective methods for arsenic removal. Techniques for extracting arsenic from groundwater include settling or precipitation, ion exchange resins, adsorption using activated alumina and iron oxides/hydroxides, reverse osmosis, and electrodialysis [ 2 ]. Research into the effectiveness of electrodialysis membranes and ion exchange reveals significant potential for removing ions from polluted water. Ionic groups are bonded to the polymer chain in ion exchange membranes, enabling the displacement of opposing ions driven by an electric field [ 3 – 6 ]. A variety of research efforts have focused on enhancing the physicochemical properties of Ion Exchange Membranes (IEMs). These approaches involve changing the types of different polymer matrices, incorporating functional groups, blending multiple polymers, incorporating inorganic additives or fillers like metal oxides and nanoparticles, adjusting cross-link density, and modifying the surface[ 3 , 7 – 14 ]. This study used cation-exchange membranes, Fe(OH) 3 nanoparticles, and PVC to develop a mixed composite structure through the casting method. The functional group agent, cation-exchange resin particles, was used alongside Tetrahydrofuran (THF) as the solvent. The study explored how the addition of Fe(OH) 3 Nanoparticles and different conditions of electrolyte (including concentration, pH, and type) influenced the electrochemical characteristics of membranes. The ideal concentration of Fe(OH) 3 in the casting solution had been investigated and documented in prior studies. Given that modified ion exchange membranes have not yet been applied for arsenic removal from drinking water, this study seeks to address this gap by using modified ion exchange membranes to remove the element. Furthermore, the study identifies the optimal membrane composition based on the percentage of iron hydroxide nanoparticles for this application [ 3 , 4 , 15 ]. The results hold particular importance for electromembrane applications, with an emphasis on the electrodialysis technique used in water treatment and recycling. 2. Materials and Methodology 2.1. Components Tetrahydrofuran (THF) was utilized as the solvent (Merck Inc., Germany). Ferric hydroxide (Fe(OH) 3 ), a reddish-brown particle with a Specific Surface Area (SSA) of 30–50 m 2 /g and a mean size of 20–40 nanometers (nm), was used as an inorganic filler and supplied by Sigma-Aldrich. Amberlyst® 15, the cation-exchange with highly acidic-functional resin in the H + form with an ion-exchange capacity greater than 1.7 meq/g (dry basis), a bulk density of 0.6 g/cm 3 , and a particle size distribution ranging from 0.355 to 1.18 mm (over 90%), was obtained from Merck Inc. (Germany) and incorporated into the membrane fabrication process. Additional chemicals used in the experiments were procured from Merck Inc., and purified water was applied exclusively during. Polyvinyl chloride (PVC, grade 7054), having a density of 490 kg/m 3 and a viscosity of about 105 cm 3 /g, served as the membrane matrix and was provided by Bandar Imam Petrochemical Company (BIPC) in Iran. 2.2. Development of Ion Exchange Membranes Composite cation-exchange membranes based on PVC were prepared via the solution casting technique. THF was employed as the solvent, and cation-exchange resin powder served as the functional component. Initially, the resin particles were dehydrated in an oven (Gilson Co.) at 45°C for 24 hours. Subsequently, the dried resin was ground using a planetary ball mill (Fritsch Premium Pulverisette 5) and sieved to obtain particles within the desired size range. For membrane fabrication, resin particles with a size range of 37–44 µm were selected. The preparation involved dispersing the polymer matrix PVC in THF at a polymer-to-solvent ratio of 1:20 (w/v). This step was conducted in a sealed glass vessel equipped with a motorized stirrer and maintained under continuous stirring for 6 hours. Following this, a predetermined amount of Fe(OH) 3 was introduced as an inorganic additive. Subsequently, the ground resin particles were incorporated into the polymer solution to serve as functional group carriers, maintaining a resin-to-polymer ratio of 1:1 (w/w). Table 1 summarizes the preparation parameters for six membrane samples, each formulated with varying weight percentages of Fe(OH) 3 nanoparticles in the overall solution. The mixtures were thoroughly stirred at 25°C to promote uniform dispersion of the nanoparticles. To further improve dispersion and disrupt potential agglomerates, the solutions were subjected to ultrasonication for one hour using an ultrasonic device. Following sonication, the mixture was further stirred for 30 minutes. It was then poured onto a clean, dried glass plate at room temperature for casting. The membrane was left to dry at 25°C before being soaked in pure water to eliminate any remaining THF solvent. In the final, the membranes underwent pretreatment in a solution of 0.5M NaCl. The thickness of the membrane was determined using an electronic caliper, yielding approximately 60–70 µm for a range of thicknesses. Table 1 The composition of the PVC/Fe(OH) 3 composite membranes Membrane Code Nanoparticles content wt.% Matrix content wt.% M1 0 100 M2 0.5 99.5 M3 1 99 M4 2 98 M5 4 96 M6 8 92 2.3. Test Cell Specifications The properties associated with the electrical-chemical performance of the membrane were evaluated using a custom-designed experimental cell [ 3 , 4 , 10 ]. The test cell consisted of two cylindrical chambers made of Pyrex glass, with the membrane mounted between them. Each chamber was sealed on one side with a platinum (Pt) electrode secured by a Teflon support, while the opposite side was in direct contact with the membrane surface. 2.4. Membrane Characterization 2.4.1. Morphology The performance of the fabricated membranes is strongly influenced by their matrix, predominantly the organization of ionic domains within them [ 16 ]. Field Emission Scanning Electron Microscopy (FE-SEM, AUT Foundation, model MIRA3TESCAN-XMU) was implemented to assess the surface Physical configuration of the prepared membranes. Single Particle Inductively Coupled Plasma Mass Spectrometry (SP-ICP-MS) is one of the methods that functions similarly to conventional ICP-MS but operates in "single particle" mode. In this method, nanoparticles suspended in an aqueous solution are introduced into the plasma, where a portion of the nanoparticles is atomized. The individual atoms are ionized, forming a cloud of ions. This ion cloud subsequently passes through a mass analyzer and reaches the detector, producing a rapid and intense pulse signal. The frequency of these pulse signals correlates with the nanoparticle quantity and concentration, while the signal intensity is connected to the mass or nanoparticle size of NPs [ 17 ]. SP-ICP-MS analysis was conducted using a NexION 2000 ICP-MS, PerkinElmer Co., equipped with the Nano Application Module within Syngistix Software. 2.4.2. Strength and Durability Properties A stress test was conducted using an all-purpose testing apparatus with model CMT 4204 of Shenzhen Sans Testing Machine Company in Shenzhen, China. The specimen had an initial gauge A dimension of 30 mm in length, 10 mm in width, and a depth measuring 0.07 mm. The tester crossbeam speed was adjusted to 1 mm/min at room temperature. Tensile parameters, including elongation at break and tensile strength, were determined by analyzing the stress-strain curves. 2.4.3. Membrane Potential, Ion Transport Number, and Selective Permeability The membrane potential is influenced by the distribution of ions across the membrane pores and the ion movement within the membrane relative to the external environment. It represents the combined effect of the diffusion potential and the Donnan potential [ 18 – 20 ]. The equilibrated membrane, which had different electrolyte solution concentrations on both sides, was utilized to assess this parameter. To reduce the impact of boundary layer turbulence, magnetic stirrers were used in both compartments throughout the experiment. The voltage across the membrane was recorded with a standard calomel electrode, an auto multimeter, and the interconnection of the two compartments. The potential of the membrane ( \(\:{E}_{Measure}\) ) was determined by applying the Nernst equation [ 3 , 16 , 18 , 20 – 22 ]. 2.4.4. Permeability and Ionic Flux Dynamics A testing chamber was employed to measure ionic permeability and flux. A 0.1M AsCl 3 solution was applied to the right region of the chamber, while a 0.01M AsCl 3 solution was added to the opposite region. Reliable platinum electrodes were employed to apply direct current (DC) electrical voltage was applied across the chamber with a constant optimal voltage (V). The diffusion constant and flow of cations in the membrane phase are determined based on our previous work, considering the pH measured in the cathodic section with a Digital pH meter (Jenway, Model: 3510). As a result, cations migrated across the membrane layer toward the cathode area. Consequently, ions of hydroxide generated during the process accumulate in the cathodic region, leading to an enhancement in the pH of that area [ 23 – 25 ]. 2.4.5. Electrical Resistance The electrical resistivity of the stabilized membrane ( \(\:r=\left({R}_{m}A\right)\) ) was evaluated in a 0.5M NaCl solution at room temperature with an AC bridge operating at a frequency corresponding to 1.600 Hz. The membrane resistance ( \(\:{R}_{m}\) = \(\:{R}_{1}\) − \(\:{R}_{2}\) ) was evaluated by subtracting the solution's electrical resistance ( \(\:{R}_{2}\) ) from the total resistance of the cell ( \(\:{R}_{1}\) ) [ 3 , 4 , 16 ]. 2.5. Adsorption of Arsenite and Arsenate on Iron Hydroxide Surfaces Iron and aluminum are instrumental in the progression of oxide adsorbents. The typical method for producing base-metal hydroxides involves drying at elevated temperatures. Regardless of their water capacity, hydrated materials tend to rapidly return to an oxidized or hydroxide state. Oxide adsorbents feature a significant number of OH groups on their surfaces, which play a crucial role in defining their adsorption characteristics. The polarity nature of the Interface, combined with potential Protonation or deprotonation of the hydroxyl groups, makes oxide adsorbents effective for the purification of ionic compounds, including phosphates, arsenates, fluorides, and heavy metal species. Granular Iron (III) hydroxide, also known as ferric hydroxide, has garnered interest as a highly effective adsorbent for arsenates, phosphates, and various other ions. There are different products available that feature crystal structures based on α-FeOOH (Goethite) and β-FeOOH (Akaganeite). The SSA of these materials ranges from 352 to 652 m 2 /g, comparable to that of aluminum oxide, with particle sizes typically in the range of 2.3 to 3 nm. The pH of the treated water plays a critical role in determining the ion adsorption capacity of oxide-based adsorbents, as it directly influences their surface charge characteristics. By modulating the pH, the efficiency of ion removal can be optimized. Both ferric hydroxide and aluminum oxide exhibit a positive surface charge at pH values above 8, suggesting that anion adsorption is most effective within the neutral pH range. Moreover, increasing the pH facilitates desorption of the anions, thereby enhancing the regeneration of the adsorbent [ 1 ]. Oxide adsorbents, such as ferric hydroxide and aluminum oxide, possess specific crystal structures where negative charges interact with oxygen or hydroxide ions, effectively neutralizing each other. In contrast, positive charges engage with metal ions. To maintain charge balance, these ions are arranged systematically on the surface. In aqueous solutions, protons neutralize the negative charges on the oxygen surface, while hydroxide ions counteract the positive charges on the iron surface. Consequently, the surfaces of oxide adsorbents become coated with OH groups. These groups are essential in the adsorption or release of protons, contingent upon the pH. The equations indicate that the surface acquires a positive charge under acidic conditions and a negative charge under basic conditions. Within these pH ranges, there are specific values where the total positive and negative charges balance out, resulting in an average surface charge of zero. This condition is termed the point of zero charge (pzc). Understanding the surface of the adsorption of ionic species and the impact of pH on these processes makes the pH pzc a vital parameter for adsorbents. Generally, it can be anticipated that the adsorption of ionic species on charged surfaces is significantly affected by electrostatic attractions and repulsive forces [ 1 ]. When using anion A2-groups, OH groups are replaced. If we substitute the conditions of the research, we will have [ 26 ]: \(\:\equiv\:Fe-OH+\:{HAsO}_{4}^{2-}\:\leftrightarrow\:\:\equiv\:Fe-\:{OAs{O}_{3}H}^{-}+\:{OH}^{-}\) (R-1) The complex outer sphere model posits that ions can attach to surface sites while retaining their hydrated water molecules. This suggests that water molecules act as a barrier between the ions and the adsorption sites. Consequently, the separation to the interface is greater compared to the more intricate inner spherical structure, resulting in a weaker adsorption strength. The region where the outer sphere complex forms is also regarded as a Component of the inner layer in the two-layer model. Outside the beta layer, there exists a repulsion layer that neutralizes any residual surface charge by incorporating additional counter ions (ions with an opposite charge to the surface layers). In the repulsion layer, the concentration of counter ions diminishes as the distance from the surface increases. This continues until the concentration of cations in the liquid phase matches that of the anions. The surface potential varies with Proximity to the interface, as proposed in several intricate surface models. Research utilizing Extended X-ray Absorption Fine Structure (EXAFS) data indicates arsenic (V) creates a bidentate complex with two ligands bidentate complex within the core (inner adsorption site) [ 27 ]. It has been noted that the adsorption mechanism of different soluble arsenic species onto Fe(II) or Fe(III) hydroxide surfaces involves electrostatic attraction, which facilitates the formation of complexes on the adsorbent surface. This finding supports the Uptake of arsenic onto iron oxide at pH levels above pzc . 2.6. Solution Preparation An AsCl 3 solution, a colorless liquid, was used for the cell preparation. For the solution synthesis, arsenic (III) oxide was reacted with hydrogen chloride, followed by distillation to produce arsenic chloride (AsCl 3 ) according to the following reaction: \(\:{As}_{2}{O}_{3}+\:6\text{H}\text{C}\text{l}\:\to\:\:2As{Cl}_{3}+\:3{H}_{2}O\) (R-2) A solution of 0.1M AsCl 3 was positioned on the right of the cell as the concentrated solution, while a 0.01M solution was applied to the opposite side as the dilute solution. Since both solutions are aqueous, the following reaction may take place, in which the hydrolysis of AsCl 3 produces arsenous acid and hydrochloric acid: \(\:\text{A}\text{s}{Cl}_{3}+\:3{H}_{2}O\:\to\:\:As({OH)}_{3}+\:3HCl\) (R-3) All experiments involving the membranes were conducted using NaCl solutions at Concentration levels of 0.1M and 0.01M. However, for the characterization of the membranes in a bivalent ionic solution, NaCl was used as the monovalent ionic solution, while BaCl 2 served as the bivalent ionic solution [ 28 ]. 3. Results and Discussion 3.1. Morphology FE-SEM was implemented to assess the distribution of the PVC membrane matrix containing resin and filler additive particles. Figure 1 presents images of both the neat PVC membrane and the PVC/Fe(OH) 3 composite membrane containing 4% Fe(OH) 3 (M5), captured from both side and top views at various magnifications. The images demonstrate that the membrane's surface is encompassed with a uniform spread of ferric hydroxide additives and resin. This finding implies that sonication contributes significantly to enhancing the consistency of particle distribution, leading to a more uniform phase in the membranes. The visuals indicate that the membranes exhibit a fairly uniform texture. The even dispersion of particles throughout the membrane structure facilitates the creation of high-conductivity zones and establishes effective routes for counter-ion movement. Moreover, a greater number of conductive Regions on the membrane's exterior reinforces the even electrical field surrounding the membrane, thereby reducing charge separation effects. Additionally, the equal spread of particles in the polymer-based solutions enhances the thickness of the pouring solution, leading to a reduction in the solvent rate of evaporation caused by preventing particle aggregation. This, in turn, enhances the interaction between polymer chains and particle surfaces, ultimately leading to improved membrane selectivity. 3.2. Effect of Fe(OH) 3 Nanoparticles on the Fabricated Membranes Properties Figures 2 depict the membrane potential, transport number, perm-selectivity, surface-area electrical resistivity, permeability, and the flux of both the neat PVC membrane and the PVC/Fe(OH) 3 composite membranes. The findings distinctly demonstrate that incorporating Fe(OH) 3 nanoparticles into the PVC matrix improves all these parameters. This enhancement is due to the adsorptive characteristics of the nanoparticles, which boost the membrane's electric charge distribution and increase the accessibility of functional groups for ion exchange within the membrane structure. The membrane modified with 4 wt.% Fe(OH)₃ nanoparticles (M5) exhibited superior electrochemical performance compared to the unmodified membrane (M1) and other composite membranes (M2, M3, M4, and M6), as evidenced by enhanced membrane potential (Fig. 2 a), ion transport number (Fig. 2 b), and ion selectivity (Fig. 2 c). This improved performance is primarily attributed to the high arsenic adsorption capacity of Fe(OH)₃ nanoparticles. Specifically, the membrane potential increased from 45.5 mV (M1) to 53 mV (M5), the transport number rose from 0.89 to 0.98, and arsenic selectivity improved from 0.8334 to 0.9434. These findings identify membrane M5 as the optimal formulation, demonstrating the most favorable electrochemical and separation properties. Figure 2 d presents a comparative analysis of the electrical resistance between samples M1 and M5. The results indicate that sample M5 exhibits significantly lower electrical resistance than sample M1. This reduction is likely due to the favorable interfacial interactions and adhesion properties of the incorporated Fe(OH) 3 nanoparticles, which facilitate ion transport across the membrane–solution interface and thereby enhance overall membrane conductivity. The Fe(OH) 3 -modified membrane demonstrated improved electrical performance compared to the unmodified counterpart lacking nanoparticle incorporation. As illustrated in Figs. 2 e and 2 f, increasing the Fe(OH) 3 content from 0 to 4 wt.% resulted in notable enhancements in both ion adsorption and membrane permeability, primarily attributed to the magnetic properties of Fe(OH) 3 nanoparticles. These magnetic characteristics not only strengthen ion interactions at the membrane surface but also promote a more uniform distribution of nanoparticles within the membrane matrix, as confirmed by SEM analysis. However, further increasing the Fe(OH) 3 concentration to 8 wt.% led to excessive adsorption and particle aggregation, causing pore blockage and subsequently reducing both ionic permeability and selectivity. Figures 2 e and 2 f demonstrate that ion permeability and flux progressively increase from membrane M1 to M5 in parallel with rising nanoparticle content. This enhancement is closely linked to the high arsenic adsorption capacity and strong ion affinity of Fe(OH) 3 nanoparticles, which facilitate efficient ion exchange and transport. Conversely, the membrane with 8 wt.% nanoparticles (M6) exhibited a decline in both parameters, likely due to reduced transport pathways resulting from nanoparticle overloading. Moreover, the incorporation of Fe(OH) 3 nanoparticles into the casting solution significantly improved sodium ion permeability and transport rate, which is attributed to the interfacial adhesion properties of the nanoparticles that enhance ion mobility across the membrane–solution interface. Among all tested samples, the membrane containing 4 wt.% Fe(OH) 3 (M5) demonstrated the highest ionic flux and permeability, confirming its superior electrochemical and transport performance. 3.3. Impact of pH on the Fabricated Membranes' Properties The influence of pH on membrane electrochemical potential (Fig. 3 a), transport number (Fig. 3 b), and perm-selectivity (Fig. 3 c) was investigated for both the unmodified PVC membrane (M1) and the membrane incorporating 4 wt.% Fe(OH) 3 nanoparticles (M5), the latter having exhibited the best performance across these parameters. The results indicate that both membranes achieved optimal electrochemical behavior, which is characterized by enhanced membrane potential, ion transport number, and perm-selectivity, at neutral pH (pH = 7), compared to other tested pH conditions. This enhancement can be ascribed to variations in the dissociation of ionizable functional groups, and the filler charge concentration additives at different pH levels influence the charged characteristics of the membrane matrix. At the ideal electrolyte pH, the increased separation of ion-exchangeable active groups and the improved electric charge density within the membrane structure result in a marked enhancement of ion transfer between the membrane phase and the solution. Figure 3 d demonstrates how pH influences the electrical resistivity of both the neat membrane (M1) and the modified membrane with 4 wt.% nanoparticles (M5). The findings reveal that both membranes show reduced electrical resistivity at neutral pH in comparison to other pH levels. This suggests that the electrical resistance of the membranes increases as the pH deviates from neutrality (pH 7), regardless of whether the deviation is toward more acidic or more alkaline conditions. These variations in membrane conductance can be attributed to the pH-dependent dissociation behavior of the membrane’s active sites under different electrolyte conditions. 3.4. Arsenic Removal Efficiency of Fabricated Membrane The findings of the SP-ICP-MS test revealed the arsenic concentrations in both the prototype wastewater and the treated effluent after filtration through a membrane embedded with Fe(OH) 3 nanoparticles. The initial arsenic concentration in the untreated wastewater was measured at 308.4 ppm. Following treatment with the Fe(OH) 3 -modified membrane (M5), the arsenic concentration was significantly reduced to 3.4 ppm. This corresponds to a remarkable removal efficiency of 98.89%, indicating the effectiveness of Fe(OH) 3 nanoparticles in capturing arsenic ions. As discussed in Section 2.5 with reference to reactions R-3 through R-9, this substantial reduction is attributed to the strong adsorption capacity of Fe(OH) 3 for arsenic species, leading to a pronounced decline in arsenic levels in the treated effluent. 3.5. Mechanical Properties of Fabricated Membrane To determine the structural integrity of the fabricated membranes, stress testing was implemented, and the resulting curves are shown in Fig. 4 . A summary of the tensile properties is also listed in the Table. As indicated in Table 3, the M3 membrane shows the highest peak force among the membranes tested. Additionally, within the PVC-Fe(OH) 3 membranes, M5 demonstrates the greatest elongation at break, suggesting improved toughness and making it the optimized sample. The M3 sample shows significant tensile strength and elongation at break, resulting in high toughness. Moreover, when comparing the tensile properties of the unmodified membrane (M1) with those of membranes M4, M6, and M2, it was observed that the peak force (N), peak stress (MPa), break extension (mm), and break strain (%) of the unmodified membrane were greater than those of the PVC-Fe(OH) 3 membranes. The addition of nanoparticles to the membranes, along with their efficient scattering and distribution throughout the structure, appears to have enhanced the performance of certain samples, such as M3 and M5. However, in the case of membrane M6, the high concentration of nanoparticles has negatively affected its structural integrity, leading to a marked decrease in both breaking strength and strain at rupture. 3.6. Membrane Behavior in Divalent Ion Solutions The elimination of ions or concentration of solutions presents a considerable challenge due to the scaling of divalent ions from the membrane surface, which occurs as a result of hydroxide formation. Figure 5 illustrates the performance of samples M1 and M5 in this regard. The findings reveal that both neat and composite membranes demonstrate reduced membrane potential (Fig. 5 a), ion transport ratio (Fig. 5 b), and selectivity (Fig. 5 c) when exposed to bivalent ionic solution (BaCl 2 ) in comparison to a monovalent ionic solution (NaCl). This phenomenon can be attributed to the more intense connections established between divalent ions and the ion-exchange functional sites, which reduce the electrochemical properties of the membrane. Bivalent ions demonstrate a greater electrostatic attraction to the bound opposite charge sites on the membrane, making their dissociation more challenging. Additionally, the greater ionic radius and hydration size of bivalent ions, in comparison to monovalent ions, may also play a role in decreasing the membrane voltage, ion transport ratio, and selective permeability. Declarations Acknowledgements The authors gratefully acknowledge the financial support provided by Amirkabir University of Technology (Tehran Polytechnic) for the conduct of this research. Conflict of Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References Worch, E., Adsorption technology in water treatment . Vol. 10. 2012: de Gruyter Berlin. PROTECTION, E., ENVIRONMENTAL PROTECTION AGENCY (EPA). 2003. Hosseini, S.M., et al., Electrochemical characterization of mixed matrix heterogeneous cation exchange membranes modified by simultaneous using ilmenite-co-iron oxide nanoparticles . 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Długołęcki, P., et al., Current status of ion exchange membranes for power generation from salinity gradients . Journal of Membrane Science, 2008. 319(1–2): p. 214–222. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 29 Jul, 2025 Reviews received at journal 29 Jul, 2025 Reviews received at journal 23 Jul, 2025 Reviewers agreed at journal 20 Jul, 2025 Reviewers agreed at journal 20 Jul, 2025 Reviewers invited by journal 20 Jul, 2025 Editor assigned by journal 17 Jul, 2025 Submission checks completed at journal 17 Jul, 2025 First submitted to journal 07 Jul, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7068769","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":488307800,"identity":"61f0e1cb-6c99-4009-a5a2-d43a81eb3d54","order_by":0,"name":"Alireza Hamidi","email":"","orcid":"","institution":"Amir Kabir University of Technology (Tehran Polytechnic)","correspondingAuthor":false,"prefix":"","firstName":"Alireza","middleName":"","lastName":"Hamidi","suffix":""},{"id":488307801,"identity":"42d2a8a6-a3c0-41c0-b73b-355191382c15","order_by":1,"name":"Azizeh Javadi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAy0lEQVRIiWNgGAWjYFCCA0DMJiEH4/IQrcWYgYGZaC0gwMaQ2ADVQhjwNx5+JvGjzCK9f0b+AYYfNQwy5g0EtEgcOGYm2XNOInfGjWQGxp5jDDwyBwhZc+CAsQFvm0RuA1ALA28DA48EIR3yB45/NvzbJpEuD7LlLzFaDA6cMXwMtCXBAKiFmShbDA+cKXwsc07CcOOZxwaHZY5JENYid+P4hoNvyurk5Y4nPnz4psbGnqAWYJAh2EAmYQ3AiGkgQtEoGAWjYBSMbAAApfs8NQ2srR4AAAAASUVORK5CYII=","orcid":"","institution":"Amir Kabir University of Technology (Tehran Polytechnic)","correspondingAuthor":true,"prefix":"","firstName":"Azizeh","middleName":"","lastName":"Javadi","suffix":""},{"id":488307802,"identity":"8b944716-8de8-42ed-a24b-5cff0e551241","order_by":2,"name":"Seyed Mohsen Hosseini","email":"","orcid":"","institution":"Arak University","correspondingAuthor":false,"prefix":"","firstName":"Seyed","middleName":"Mohsen","lastName":"Hosseini","suffix":""},{"id":488307803,"identity":"b9eb9f0c-195c-4c4a-a583-bb0e8504d7da","order_by":3,"name":"Atefeh Hamidi","email":"","orcid":"","institution":"Amir Kabir University of Technology (Tehran Polytechnic)","correspondingAuthor":false,"prefix":"","firstName":"Atefeh","middleName":"","lastName":"Hamidi","suffix":""},{"id":488307804,"identity":"9d043d3f-7ab9-402f-ac5d-f696cacb07a7","order_by":4,"name":"Arash Tayyebi","email":"","orcid":"","institution":"University of North Dakota, Grand Forks","correspondingAuthor":false,"prefix":"","firstName":"Arash","middleName":"","lastName":"Tayyebi","suffix":""}],"badges":[],"createdAt":"2025-07-07 21:23:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7068769/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7068769/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":87387032,"identity":"1c853a06-c75a-44aa-aa6c-31c6f312db30","added_by":"auto","created_at":"2025-07-23 09:04:06","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":32951764,"visible":true,"origin":"","legend":"\u003cp\u003eFE-SEM images of the prepared membranes: (a) and (b) Depict the Lateral view and Planar view of the neat PVC membrane (M1), respectively, while (c) and (d) represent the Lateral view and Planar view of the PVC/Fe(OH)\u003csub\u003e3\u003c/sub\u003e composite membrane (M5), respectively\u003c/p\u003e","description":"","filename":"image1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7068769/v1/d4a10b69d768d9150628e267.jpg"},{"id":87387021,"identity":"12000b6d-2485-4513-a742-ee4e30751139","added_by":"auto","created_at":"2025-07-23 09:04:06","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":3675087,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanoparticles on (a) membrane potential, (b) transport number, (c) perm-selectivity, (d) surface-area electrical resistivity, (e) permeability and (f) flux of the neat PVC (M1) and membranes containing 0.5, 1, 2, 4, and 8 wt.% Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanoparticles (M2 to M6) at pH = 7\u003c/p\u003e","description":"","filename":"image2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7068769/v1/5589d490f44e0d098be80914.jpg"},{"id":87388582,"identity":"50acfd0f-e41e-4e9b-a2cf-3918061322d5","added_by":"auto","created_at":"2025-07-23 09:12:06","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":4964322,"visible":true,"origin":"","legend":"\u003cp\u003eImpact of electrolyte pH on (a) membrane electrochemical potential, (b) membrane transport number, (c) perm-selectivity, and (d) surface-area Electrical Resistivity of the neat PVC membrane (M1) and the membrane with 4 wt.% Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanoparticles (M5)\u003c/p\u003e","description":"","filename":"image3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7068769/v1/e25560e987f6d85efcc5e458.jpg"},{"id":87387023,"identity":"1a1c921c-dddf-426a-9e64-e5be8c53ec89","added_by":"auto","created_at":"2025-07-23 09:04:06","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1603700,"visible":true,"origin":"","legend":"\u003cp\u003eStress versus strain curves for the prepared membranes\u003c/p\u003e","description":"","filename":"image4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7068769/v1/71014ec5457950f88ebc890f.jpg"},{"id":87388761,"identity":"84bcf65e-1c55-47ea-90f0-473851b7cd02","added_by":"auto","created_at":"2025-07-23 09:20:06","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":3585877,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of (a) membrane electrochemical potential, (b) membrane transport number, and (c) perm-selectivity of M1 and M5 in monovalent and bivalent ionic solutions\u003c/p\u003e","description":"","filename":"image5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7068769/v1/fadbf656588cdd966e137c7f.jpg"},{"id":87467492,"identity":"c0d09fb1-b4cf-4227-9864-2f64d9d90bc5","added_by":"auto","created_at":"2025-07-24 08:10:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":47584328,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7068769/v1/ecba9662-2312-4c61-ad87-36e0a5885ed6.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Innovative PVC/Fe(OH) 3 Ion Exchange Membranes for Efficient Arsenic Removal: Synthesis, Performance, and pH-Dependent Behavior","fulltext":[{"header":"Synopsis","content":"\u003cp\u003eThis research underscores the environmental relevance of PVC/Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanocomposite membranes, offering an advanced and cost-effective approach for arsenic remediation in water systems, thereby supporting public health and ecological sustainability.\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"1. Introduction","content":"\u003cp\u003eThe over-extraction of groundwater and the declining water levels in wells have resulted in a notable rise in the concentration of various elements, particularly heavy metals. Consequently, numerous water sources have become contaminated with these metals. The most frequently encountered heavy metals include arsenic, iron, chromium, manganese, nickel, cadmium, and lead [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe Environmental Protection Agency (EPA) has set a maximum permissible threshold of 10 micrograms per liter for arsenic in drinking water due to its potential health hazards. Recently, the contamination of groundwater with arsenic has emerged as a major health issue, contributing to conditions such as cardiovascular diseases, hypertension, internal cancers, skin lesions, and even skin cancer. As a result, there has been a growing interest among scientists and researchers in developing effective methods for arsenic removal. Techniques for extracting arsenic from groundwater include settling or precipitation, ion exchange resins, adsorption using activated alumina and iron oxides/hydroxides, reverse osmosis, and electrodialysis [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Research into the effectiveness of electrodialysis membranes and ion exchange reveals significant potential for removing ions from polluted water. Ionic groups are bonded to the polymer chain in ion exchange membranes, enabling the displacement of opposing ions driven by an electric field [\u003cspan additionalcitationids=\"CR4 CR5\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. A variety of research efforts have focused on enhancing the physicochemical properties of Ion Exchange Membranes (IEMs). These approaches involve changing the types of different polymer matrices, incorporating functional groups, blending multiple polymers, incorporating inorganic additives or fillers like metal oxides and nanoparticles, adjusting cross-link density, and modifying the surface[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan additionalcitationids=\"CR8 CR9 CR10 CR11 CR12 CR13\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThis study used cation-exchange membranes, Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanoparticles, and PVC to develop a mixed composite structure through the casting method. The functional group agent, cation-exchange resin particles, was used alongside Tetrahydrofuran (THF) as the solvent. The study explored how the addition of Fe(OH)\u003csub\u003e3\u003c/sub\u003e Nanoparticles and different conditions of electrolyte (including concentration, pH, and type) influenced the electrochemical characteristics of membranes. The ideal concentration of Fe(OH)\u003csub\u003e3\u003c/sub\u003e in the casting solution had been investigated and documented in prior studies. Given that modified ion exchange membranes have not yet been applied for arsenic removal from drinking water, this study seeks to address this gap by using modified ion exchange membranes to remove the element. Furthermore, the study identifies the optimal membrane composition based on the percentage of iron hydroxide nanoparticles for this application [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The results hold particular importance for electromembrane applications, with an emphasis on the electrodialysis technique used in water treatment and recycling.\u003c/p\u003e"},{"header":"2. Materials and Methodology","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003e2.1. Components\u003c/h2\u003e\n\u003cp\u003eTetrahydrofuran (THF) was utilized as the solvent (Merck Inc., Germany). Ferric hydroxide (Fe(OH)\u003csub\u003e3\u003c/sub\u003e), a reddish-brown particle with a Specific Surface Area (SSA) of 30\u0026ndash;50 m\u003csup\u003e2\u003c/sup\u003e/g and a mean size of 20\u0026ndash;40 nanometers (nm), was used as an inorganic filler and supplied by Sigma-Aldrich. Amberlyst\u0026reg; 15, the cation-exchange with highly acidic-functional resin in the H\u003csup\u003e+\u003c/sup\u003e form with an ion-exchange capacity greater than 1.7 meq/g (dry basis), a bulk density of 0.6 g/cm\u003csup\u003e3\u003c/sup\u003e, and a particle size distribution ranging from 0.355 to 1.18 mm (over 90%), was obtained from Merck Inc. (Germany) and incorporated into the membrane fabrication process. Additional chemicals used in the experiments were procured from Merck Inc., and purified water was applied exclusively during. Polyvinyl chloride (PVC, grade 7054), having a density of 490 kg/m\u003csup\u003e3\u003c/sup\u003e and a viscosity of about 105 cm\u003csup\u003e3\u003c/sup\u003e/g, served as the membrane matrix and was provided by Bandar Imam Petrochemical Company (BIPC) in Iran.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n\u003ch2\u003e2.2. Development of Ion Exchange Membranes\u003c/h2\u003e\n\u003cp\u003eComposite cation-exchange membranes based on PVC were prepared via the solution casting technique. THF was employed as the solvent, and cation-exchange resin powder served as the functional component. Initially, the resin particles were dehydrated in an oven (Gilson Co.) at 45\u0026deg;C for 24 hours. Subsequently, the dried resin was ground using a planetary ball mill (Fritsch Premium Pulverisette 5) and sieved to obtain particles within the desired size range.\u003c/p\u003e\n\u003cp\u003eFor membrane fabrication, resin particles with a size range of 37\u0026ndash;44 \u0026micro;m were selected. The preparation involved dispersing the polymer matrix PVC in THF at a polymer-to-solvent ratio of 1:20 (w/v). This step was conducted in a sealed glass vessel equipped with a motorized stirrer and maintained under continuous stirring for 6 hours. Following this, a predetermined amount of Fe(OH)\u003csub\u003e3\u003c/sub\u003e was introduced as an inorganic additive. Subsequently, the ground resin particles were incorporated into the polymer solution to serve as functional group carriers, maintaining a resin-to-polymer ratio of 1:1 (w/w).\u003c/p\u003e\n\u003cp\u003eTable\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e summarizes the preparation parameters for six membrane samples, each formulated with varying weight percentages of Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanoparticles in the overall solution. The mixtures were thoroughly stirred at 25\u0026deg;C to promote uniform dispersion of the nanoparticles. To further improve dispersion and disrupt potential agglomerates, the solutions were subjected to ultrasonication for one hour using an ultrasonic device. Following sonication, the mixture was further stirred for 30 minutes. It was then poured onto a clean, dried glass plate at room temperature for casting. The membrane was left to dry at 25\u0026deg;C before being soaked in pure water to eliminate any remaining THF solvent. In the final, the membranes underwent pretreatment in a solution of 0.5M NaCl. The thickness of the membrane was determined using an electronic caliper, yielding approximately 60\u0026ndash;70 \u0026micro;m for a range of thicknesses.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eThe composition of the PVC/Fe(OH)\u003csub\u003e3\u003c/sub\u003e composite membranes\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMembrane Code\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eNanoparticles content wt.%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMatrix content wt.%\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eM1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e100\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eM2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e99.5\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eM3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e99\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eM4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e98\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eM5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e96\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eM6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e92\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n\u003ch2\u003e2.3. Test Cell Specifications\u003c/h2\u003e\n\u003cp\u003eThe properties associated with the electrical-chemical performance of the membrane were evaluated using a custom-designed experimental cell [\u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e10\u003c/span\u003e]. The test cell consisted of two cylindrical chambers made of Pyrex glass, with the membrane mounted between them. Each chamber was sealed on one side with a platinum (Pt) electrode secured by a Teflon support, while the opposite side was in direct contact with the membrane surface.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n\u003ch2\u003e2.4. Membrane Characterization\u003c/h2\u003e\n\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.1. Morphology\u003c/h2\u003e\n\u003cp\u003eThe performance of the fabricated membranes is strongly influenced by their matrix, predominantly the organization of ionic domains within them [\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e]. Field Emission Scanning Electron Microscopy (FE-SEM, AUT Foundation, model MIRA3TESCAN-XMU) was implemented to assess the surface Physical configuration of the prepared membranes. Single Particle Inductively Coupled Plasma Mass Spectrometry (SP-ICP-MS) is one of the methods that functions similarly to conventional ICP-MS but operates in \"single particle\" mode. In this method, nanoparticles suspended in an aqueous solution are introduced into the plasma, where a portion of the nanoparticles is atomized. The individual atoms are ionized, forming a cloud of ions. This ion cloud subsequently passes through a mass analyzer and reaches the detector, producing a rapid and intense pulse signal. The frequency of these pulse signals correlates with the nanoparticle quantity and concentration, while the signal intensity is connected to the mass or nanoparticle size of NPs [\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e]. SP-ICP-MS analysis was conducted using a NexION 2000 ICP-MS, PerkinElmer Co., equipped with the Nano Application Module within Syngistix Software.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.2. Strength and Durability Properties\u003c/h2\u003e\n\u003cp\u003eA stress test was conducted using an all-purpose testing apparatus with model CMT 4204 of Shenzhen Sans Testing Machine Company in Shenzhen, China. The specimen had an initial gauge A dimension of 30 mm in length, 10 mm in width, and a depth measuring 0.07 mm. The tester crossbeam speed was adjusted to 1 mm/min at room temperature. Tensile parameters, including elongation at break and tensile strength, were determined by analyzing the stress-strain curves.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.3. Membrane Potential, Ion Transport Number, and Selective Permeability\u003c/h2\u003e\n\u003cp\u003eThe membrane potential is influenced by the distribution of ions across the membrane pores and the ion movement within the membrane relative to the external environment. It represents the combined effect of the diffusion potential and the Donnan potential [\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e]. The equilibrated membrane, which had different electrolyte solution concentrations on both sides, was utilized to assess this parameter. To reduce the impact of boundary layer turbulence, magnetic stirrers were used in both compartments throughout the experiment. The voltage across the membrane was recorded with a standard calomel electrode, an auto multimeter, and the interconnection of the two compartments. The potential of the membrane (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{E}_{Measure}\\)\u003c/span\u003e\u003c/span\u003e) was determined by applying the Nernst equation [\u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.4. Permeability and Ionic Flux Dynamics\u003c/h2\u003e\n\u003cp\u003eA testing chamber was employed to measure ionic permeability and flux. A 0.1M AsCl\u003csub\u003e3\u003c/sub\u003e solution was applied to the right region of the chamber, while a 0.01M AsCl\u003csub\u003e3\u003c/sub\u003e solution was added to the opposite region. Reliable platinum electrodes were employed to apply direct current (DC) electrical voltage was applied across the chamber with a constant optimal voltage (V). The diffusion constant and flow of cations in the membrane phase are determined based on our previous work, considering the pH measured in the cathodic section with a Digital pH meter (Jenway, Model: 3510). As a result, cations migrated across the membrane layer toward the cathode area. Consequently, ions of hydroxide generated during the process accumulate in the cathodic region, leading to an enhancement in the pH of that area [\u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.5. Electrical Resistance\u003c/h2\u003e\n\u003cp\u003eThe electrical resistivity of the stabilized membrane (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:r=\\left({R}_{m}A\\right)\\)\u003c/span\u003e\u003c/span\u003e) was evaluated in a 0.5M NaCl solution at room temperature with an AC bridge operating at a frequency corresponding to 1.600 Hz. The membrane resistance (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{R}_{m}\\)\u003c/span\u003e\u003c/span\u003e = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{R}_{1}\\)\u003c/span\u003e\u003c/span\u003e\u0026minus;\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{R}_{2}\\)\u003c/span\u003e\u003c/span\u003e) was evaluated by subtracting the solution's electrical resistance (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{R}_{2}\\)\u003c/span\u003e\u003c/span\u003e) from the total resistance of the cell (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{R}_{1}\\)\u003c/span\u003e\u003c/span\u003e) [\u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n\u003ch2\u003e2.5. Adsorption of Arsenite and Arsenate on Iron Hydroxide Surfaces\u003c/h2\u003e\n\u003cp\u003eIron and aluminum are instrumental in the progression of oxide adsorbents. The typical method for producing base-metal hydroxides involves drying at elevated temperatures. Regardless of their water capacity, hydrated materials tend to rapidly return to an oxidized or hydroxide state. Oxide adsorbents feature a significant number of OH groups on their surfaces, which play a crucial role in defining their adsorption characteristics. The polarity nature of the Interface, combined with potential Protonation or deprotonation of the hydroxyl groups, makes oxide adsorbents effective for the purification of ionic compounds, including phosphates, arsenates, fluorides, and heavy metal species. Granular Iron (III) hydroxide, also known as ferric hydroxide, has garnered interest as a highly effective adsorbent for arsenates, phosphates, and various other ions. There are different products available that feature crystal structures based on \u0026alpha;-FeOOH (Goethite) and \u0026beta;-FeOOH (Akaganeite). The SSA of these materials ranges from 352 to 652 m\u003csup\u003e2\u003c/sup\u003e/g, comparable to that of aluminum oxide, with particle sizes typically in the range of 2.3 to 3 nm. The pH of the treated water plays a critical role in determining the ion adsorption capacity of oxide-based adsorbents, as it directly influences their surface charge characteristics. By modulating the pH, the efficiency of ion removal can be optimized. Both ferric hydroxide and aluminum oxide exhibit a positive surface charge at pH values above 8, suggesting that anion adsorption is most effective within the neutral pH range. Moreover, increasing the pH facilitates desorption of the anions, thereby enhancing the regeneration of the adsorbent [\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eOxide adsorbents, such as ferric hydroxide and aluminum oxide, possess specific crystal structures where negative charges interact with oxygen or hydroxide ions, effectively neutralizing each other. In contrast, positive charges engage with metal ions. To maintain charge balance, these ions are arranged systematically on the surface. In aqueous solutions, protons neutralize the negative charges on the oxygen surface, while hydroxide ions counteract the positive charges on the iron surface. Consequently, the surfaces of oxide adsorbents become coated with OH groups. These groups are essential in the adsorption or release of protons, contingent upon the pH. The equations indicate that the surface acquires a positive charge under acidic conditions and a negative charge under basic conditions. Within these pH ranges, there are specific values where the total positive and negative charges balance out, resulting in an average surface charge of zero. This condition is termed the point of zero charge (pzc). Understanding the surface of the adsorption of ionic species and the impact of pH on these processes makes the pH pzc a vital parameter for adsorbents. Generally, it can be anticipated that the adsorption of ionic species on charged surfaces is significantly affected by electrostatic attractions and repulsive forces [\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eWhen using anion A2-groups, OH groups are replaced. If we substitute the conditions of the research, we will have [\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]:\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Taba\" border=\"1\"\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\equiv\\:Fe-OH+\\:{HAsO}_{4}^{2-}\\:\\leftrightarrow\\:\\:\\equiv\\:Fe-\\:{OAs{O}_{3}H}^{-}+\\:{OH}^{-}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e(R-1)\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eThe complex outer sphere model posits that ions can attach to surface sites while retaining their hydrated water molecules. This suggests that water molecules act as a barrier between the ions and the adsorption sites. Consequently, the separation to the interface is greater compared to the more intricate inner spherical structure, resulting in a weaker adsorption strength. The region where the outer sphere complex forms is also regarded as a Component of the inner layer in the two-layer model. Outside the beta layer, there exists a repulsion layer that neutralizes any residual surface charge by incorporating additional counter ions (ions with an opposite charge to the surface layers). In the repulsion layer, the concentration of counter ions diminishes as the distance from the surface increases. This continues until the concentration of cations in the liquid phase matches that of the anions.\u003c/p\u003e\n\u003cp\u003eThe surface potential varies with Proximity to the interface, as proposed in several intricate surface models. Research utilizing Extended X-ray Absorption Fine Structure (EXAFS) data indicates arsenic (V) creates a bidentate complex with two ligands bidentate complex within the core (inner adsorption site) [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e]. It has been noted that the adsorption mechanism of different soluble arsenic species onto Fe(II) or Fe(III) hydroxide surfaces involves electrostatic attraction, which facilitates the formation of complexes on the adsorbent surface. This finding supports the Uptake of arsenic onto iron oxide at pH levels above \u003cem\u003epzc\u003c/em\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n\u003ch2\u003e2.6. Solution Preparation\u003c/h2\u003e\n\u003cp\u003eAn AsCl\u003csub\u003e3\u003c/sub\u003e solution, a colorless liquid, was used for the cell preparation. For the solution synthesis, arsenic (III) oxide was reacted with hydrogen chloride, followed by distillation to produce arsenic chloride (AsCl\u003csub\u003e3\u003c/sub\u003e) according to the following reaction:\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tabb\" border=\"1\"\u003e\n\u003ctbody\u003e\n\u003ctr style=\"height: 35.7455px;\"\u003e\n\u003ctd style=\"height: 35.7455px;\" align=\"left\"\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{As}_{2}{O}_{3}+\\:6\\text{H}\\text{C}\\text{l}\\:\\to\\:\\:2As{Cl}_{3}+\\:3{H}_{2}O\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35.7455px;\" align=\"left\"\u003e\n\u003cp\u003e(R-2)\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003eA solution of 0.1M AsCl\u003csub\u003e3\u003c/sub\u003e was positioned on the right of the cell as the concentrated solution, while a 0.01M solution was applied to the opposite side as the dilute solution. Since both solutions are aqueous, the following reaction may take place, in which the hydrolysis of AsCl\u003csub\u003e3\u003c/sub\u003e produces arsenous acid and hydrochloric acid:\u003c/div\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tabc\" border=\"1\"\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{A}\\text{s}{Cl}_{3}+\\:3{H}_{2}O\\:\\to\\:\\:As({OH)}_{3}+\\:3HCl\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e(R-3)\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eAll experiments involving the membranes were conducted using NaCl solutions at Concentration levels of 0.1M and 0.01M. However, for the characterization of the membranes in a bivalent ionic solution, NaCl was used as the monovalent ionic solution, while BaCl\u003csub\u003e2\u003c/sub\u003e served as the bivalent ionic solution [\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003e3.1. Morphology\u003c/h2\u003e\u003cp\u003eFE-SEM was implemented to assess the distribution of the PVC membrane matrix containing resin and filler additive particles. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents images of both the neat PVC membrane and the PVC/Fe(OH)\u003csub\u003e3\u003c/sub\u003e composite membrane containing 4% Fe(OH)\u003csub\u003e3\u003c/sub\u003e (M5), captured from both side and top views at various magnifications. The images demonstrate that the membrane's surface is encompassed with a uniform spread of ferric hydroxide additives and resin. This finding implies that sonication contributes significantly to enhancing the consistency of particle distribution, leading to a more uniform phase in the membranes.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe visuals indicate that the membranes exhibit a fairly uniform texture. The even dispersion of particles throughout the membrane structure facilitates the creation of high-conductivity zones and establishes effective routes for counter-ion movement. Moreover, a greater number of conductive Regions on the membrane's exterior reinforces the even electrical field surrounding the membrane, thereby reducing charge separation effects. Additionally, the equal spread of particles in the polymer-based solutions enhances the thickness of the pouring solution, leading to a reduction in the solvent rate of evaporation caused by preventing particle aggregation. This, in turn, enhances the interaction between polymer chains and particle surfaces, ultimately leading to improved membrane selectivity.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\u003ch2\u003e3.2. Effect of Fe(OH)\u003csub\u003e3\u003c/sub\u003e Nanoparticles on the Fabricated Membranes Properties\u003c/h2\u003e\u003cp\u003eFigures \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e depict the membrane potential, transport number, perm-selectivity, surface-area electrical resistivity, permeability, and the flux of both the neat PVC membrane and the PVC/Fe(OH)\u003csub\u003e3\u003c/sub\u003e composite membranes. The findings distinctly demonstrate that incorporating Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanoparticles into the PVC matrix improves all these parameters. This enhancement is due to the adsorptive characteristics of the nanoparticles, which boost the membrane's electric charge distribution and increase the accessibility of functional groups for ion exchange within the membrane structure. The membrane modified with 4 wt.% Fe(OH)₃ nanoparticles (M5) exhibited superior electrochemical performance compared to the unmodified membrane (M1) and other composite membranes (M2, M3, M4, and M6), as evidenced by enhanced membrane potential (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea), ion transport number (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb), and ion selectivity (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). This improved performance is primarily attributed to the high arsenic adsorption capacity of Fe(OH)₃ nanoparticles. Specifically, the membrane potential increased from 45.5 mV (M1) to 53 mV (M5), the transport number rose from 0.89 to 0.98, and arsenic selectivity improved from 0.8334 to 0.9434. These findings identify membrane M5 as the optimal formulation, demonstrating the most favorable electrochemical and separation properties.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed presents a comparative analysis of the electrical resistance between samples M1 and M5. The results indicate that sample M5 exhibits significantly lower electrical resistance than sample M1. This reduction is likely due to the favorable interfacial interactions and adhesion properties of the incorporated Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanoparticles, which facilitate ion transport across the membrane\u0026ndash;solution interface and thereby enhance overall membrane conductivity. The Fe(OH)\u003csub\u003e3\u003c/sub\u003e-modified membrane demonstrated improved electrical performance compared to the unmodified counterpart lacking nanoparticle incorporation.\u003c/p\u003e\u003cp\u003eAs illustrated in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef, increasing the Fe(OH)\u003csub\u003e3\u003c/sub\u003e content from 0 to 4 wt.% resulted in notable enhancements in both ion adsorption and membrane permeability, primarily attributed to the magnetic properties of Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanoparticles. These magnetic characteristics not only strengthen ion interactions at the membrane surface but also promote a more uniform distribution of nanoparticles within the membrane matrix, as confirmed by SEM analysis. However, further increasing the Fe(OH)\u003csub\u003e3\u003c/sub\u003e concentration to 8 wt.% led to excessive adsorption and particle aggregation, causing pore blockage and subsequently reducing both ionic permeability and selectivity.\u003c/p\u003e\u003cp\u003eFigures \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef demonstrate that ion permeability and flux progressively increase from membrane M1 to M5 in parallel with rising nanoparticle content. This enhancement is closely linked to the high arsenic adsorption capacity and strong ion affinity of Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanoparticles, which facilitate efficient ion exchange and transport. Conversely, the membrane with 8 wt.% nanoparticles (M6) exhibited a decline in both parameters, likely due to reduced transport pathways resulting from nanoparticle overloading.\u003c/p\u003e\u003cp\u003eMoreover, the incorporation of Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanoparticles into the casting solution significantly improved sodium ion permeability and transport rate, which is attributed to the interfacial adhesion properties of the nanoparticles that enhance ion mobility across the membrane\u0026ndash;solution interface. Among all tested samples, the membrane containing 4 wt.% Fe(OH)\u003csub\u003e3\u003c/sub\u003e (M5) demonstrated the highest ionic flux and permeability, confirming its superior electrochemical and transport performance.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003e3.3. Impact of pH on the Fabricated Membranes' Properties\u003c/h2\u003e\u003cp\u003eThe influence of pH on membrane electrochemical potential (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea), transport number (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb), and perm-selectivity (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec) was investigated for both the unmodified PVC membrane (M1) and the membrane incorporating 4 wt.% Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanoparticles (M5), the latter having exhibited the best performance across these parameters. The results indicate that both membranes achieved optimal electrochemical behavior, which is characterized by enhanced membrane potential, ion transport number, and perm-selectivity, at neutral pH (pH\u0026thinsp;=\u0026thinsp;7), compared to other tested pH conditions.\u003c/p\u003e\u003cp\u003eThis enhancement can be ascribed to variations in the dissociation of ionizable functional groups, and the filler charge concentration additives at different pH levels influence the charged characteristics of the membrane matrix. At the ideal electrolyte pH, the increased separation of ion-exchangeable active groups and the improved electric charge density within the membrane structure result in a marked enhancement of ion transfer between the membrane phase and the solution.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed demonstrates how pH influences the electrical resistivity of both the neat membrane (M1) and the modified membrane with 4 wt.% nanoparticles (M5). The findings reveal that both membranes show reduced electrical resistivity at neutral pH in comparison to other pH levels. This suggests that the electrical resistance of the membranes increases as the pH deviates from neutrality (pH 7), regardless of whether the deviation is toward more acidic or more alkaline conditions. These variations in membrane conductance can be attributed to the pH-dependent dissociation behavior of the membrane\u0026rsquo;s active sites under different electrolyte conditions.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\u003ch2\u003e3.4. Arsenic Removal Efficiency of Fabricated Membrane\u003c/h2\u003e\u003cp\u003eThe findings of the SP-ICP-MS test revealed the arsenic concentrations in both the prototype wastewater and the treated effluent after filtration through a membrane embedded with Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanoparticles. The initial arsenic concentration in the untreated wastewater was measured at 308.4 ppm. Following treatment with the Fe(OH)\u003csub\u003e3\u003c/sub\u003e-modified membrane (M5), the arsenic concentration was significantly reduced to 3.4 ppm. This corresponds to a remarkable removal efficiency of 98.89%, indicating the effectiveness of Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanoparticles in capturing arsenic ions. As discussed in Section \u003cspan refid=\"Sec12\" class=\"InternalRef\"\u003e2.5\u003c/span\u003e with reference to reactions R-3 through R-9, this substantial reduction is attributed to the strong adsorption capacity of Fe(OH)\u003csub\u003e3\u003c/sub\u003e for arsenic species, leading to a pronounced decline in arsenic levels in the treated effluent.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\u003ch2\u003e3.5. Mechanical Properties of Fabricated Membrane\u003c/h2\u003e\u003cp\u003eTo determine the structural integrity of the fabricated membranes, stress testing was implemented, and the resulting curves are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. A summary of the tensile properties is also listed in the Table. As indicated in Table\u0026nbsp;3, the M3 membrane shows the highest peak force among the membranes tested. Additionally, within the PVC-Fe(OH)\u003csub\u003e3\u003c/sub\u003e membranes, M5 demonstrates the greatest elongation at break, suggesting improved toughness and making it the optimized sample. The M3 sample shows significant tensile strength and elongation at break, resulting in high toughness. Moreover, when comparing the tensile properties of the unmodified membrane (M1) with those of membranes M4, M6, and M2, it was observed that the peak force (N), peak stress (MPa), break extension (mm), and break strain (%) of the unmodified membrane were greater than those of the PVC-Fe(OH)\u003csub\u003e3\u003c/sub\u003e membranes. The addition of nanoparticles to the membranes, along with their efficient scattering and distribution throughout the structure, appears to have enhanced the performance of certain samples, such as M3 and M5. However, in the case of membrane M6, the high concentration of nanoparticles has negatively affected its structural integrity, leading to a marked decrease in both breaking strength and strain at rupture.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec20\" class=\"Section2\"\u003e\u003ch2\u003e3.6. Membrane Behavior in Divalent Ion Solutions\u003c/h2\u003e\u003cp\u003eThe elimination of ions or concentration of solutions presents a considerable challenge due to the scaling of divalent ions from the membrane surface, which occurs as a result of hydroxide formation. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e illustrates the performance of samples M1 and M5 in this regard. The findings reveal that both neat and composite membranes demonstrate reduced membrane potential (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea), ion transport ratio (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb), and selectivity (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec) when exposed to bivalent ionic solution (BaCl\u003csub\u003e2\u003c/sub\u003e) in comparison to a monovalent ionic solution (NaCl).\u003c/p\u003e\u003cp\u003eThis phenomenon can be attributed to the more intense connections established between divalent ions and the ion-exchange functional sites, which reduce the electrochemical properties of the membrane. Bivalent ions demonstrate a greater electrostatic attraction to the bound opposite charge sites on the membrane, making their dissociation more challenging. Additionally, the greater ionic radius and hydration size of bivalent ions, in comparison to monovalent ions, may also play a role in decreasing the membrane voltage, ion transport ratio, and selective permeability.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors gratefully acknowledge the financial support provided by Amirkabir University of Technology (Tehran Polytechnic) for the conduct of this research.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWorch, E., \u003cem\u003eAdsorption technology in water treatment\u003c/em\u003e. Vol. 10. 2012: de Gruyter Berlin.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePROTECTION, E., \u003cem\u003eENVIRONMENTAL PROTECTION AGENCY (EPA).\u003c/em\u003e 2003.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHosseini, S.M., et al., \u003cem\u003eElectrochemical characterization of mixed matrix heterogeneous cation exchange membranes modified by simultaneous using ilmenite-co-iron oxide nanoparticles\u003c/em\u003e. Korean Journal of Chemical Engineering, 2015. 32: p. 429\u0026ndash;435.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHosseini, S., et al., \u003cem\u003ePreparation and electrochemical characterization of polyvinylchloride/FeTiO 3-co-Fe 3 O 4 nanoparticles mixed matrix ion exchange membranes: Investigation of concentration and pH effects\u003c/em\u003e. Korean Journal of Chemical Engineering, 2015. 32: p. 1827\u0026ndash;1834.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBaker, R.W., \u003cem\u003eMembrane technology and applications\u003c/em\u003e. 2023: John Wiley \u0026amp; Sons.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSafarpour, M., A. Safikhani, and V. Vatanpour, \u003cem\u003ePolyvinyl chloride-based membranes: A review on fabrication techniques, applications and future perspectives\u003c/em\u003e. Separation and Purification Technology, 2021. 279: p. 119678.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGohil, G., V. Binsu, and V.K. Shahi, \u003cem\u003ePreparation and characterization of mono-valent ion selective polypyrrole composite ion-exchange membranes\u003c/em\u003e. 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Journal of Membrane Science, 2005. 263(1\u0026ndash;2): p. 137\u0026ndash;145.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHosseini, S., et al., \u003cem\u003ePreparation and characterization of PVC based heterogeneous ion exchange membrane coated with Ag nanoparticles by (thermal-plasma) treatment assisted surface modification\u003c/em\u003e. Journal of Industrial and Engineering Chemistry, 2013. 19(3): p. 854\u0026ndash;862.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDaraei, P., et al., \u003cem\u003eNovel polyethersulfone nanocomposite membrane prepared by PANI/Fe3O4 nanoparticles with enhanced performance for Cu (II) removal from water\u003c/em\u003e. Journal of Membrane Science, 2012. 415: p. 250\u0026ndash;259.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNoah, N.M., \u003cem\u003eCurrent status and advancement of nanomaterials within polymeric membranes for water purification\u003c/em\u003e. ACS Applied Nano Materials, 2023.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSalehi, E., et al., \u003cem\u003eSurface modification of sulfonated polyvinylchloride cation-exchange membranes by using chitosan polymer containing Fe 3 O 4 nanoparticles\u003c/em\u003e. Journal of Solid State Electrochemistry, 2016. 20: p. 371\u0026ndash;377.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLi, X., et al., \u003cem\u003eElectrochemical properties of sulfonated PEEK used for ion exchange membranes\u003c/em\u003e. Journal of Membrane Science, 2005. 254(1\u0026ndash;2): p. 147\u0026ndash;155.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLiu, H., et al., \u003cem\u003eSingle particle ICP-MS combined with filtration membrane for accurate determination of silver nanoparticles in the real aqueous environment\u003c/em\u003e. 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Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2004. 251(1\u0026ndash;3): p. 133\u0026ndash;140.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTanaka, Y., \u003cem\u003eBipolar membrane electrodialysis.\u003c/em\u003e Membrane science and technology, 2007. 12: p. 405\u0026ndash;436.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNagarale, R., et al., \u003cem\u003eStudies on electrochemical characterization of polycarbonate and polysulfone based heterogeneous cation-exchange membranes\u003c/em\u003e. Reactive and Functional Polymers, 2004. 61(1): p. 131\u0026ndash;138.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNagarale, R., V.K. Shahi, and R. Rangarajan, \u003cem\u003ePreparation of polyvinyl alcohol\u0026ndash;silica hybrid heterogeneous anion-exchange membranes by sol\u0026ndash;gel method and their characterization\u003c/em\u003e. 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Randall, \u003cem\u003eSurface complexation of arsenic (V) to iron (III)(hydr) oxides: structural mechanism from ab initio molecular geometries and EXAFS spectroscopy\u003c/em\u003e. Geochimica et Cosmochimica Acta, 2003. 67(22): p. 4223\u0026ndash;4230.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDługołęcki, P., et al., \u003cem\u003eCurrent status of ion exchange membranes for power generation from salinity gradients\u003c/em\u003e. Journal of Membrane Science, 2008. 319(1\u0026ndash;2): p. 214\u0026ndash;222.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Mixed matrix membrane, Electrodialysis, Membrane, Ion exchange, Arsenic removal","lastPublishedDoi":"10.21203/rs.3.rs-7068769/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7068769/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eArsenic removal from aqueous systems is of increasing concern due to its high toxicity and association with serious health risks, including cardiovascular diseases, hypertension, and various forms of cancer. Ion exchange membranes serve as active separation interfaces in electrochemical systems, such as electrodialysis, offering a cost-effective and efficient strategy for the selective removal of arsenic from aqueous solutions. The focus of this research is on diverse membranes for cation-selective exchange that were developed and modified with Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanoparticles using the solution casting technique, based on polyvinyl chloride (PVC). This study investigated the effect of varying nanoparticle concentrations on the electrochemical properties of the membrane, with particular emphasis on its efficacy in arsenic removal. Additionally, the influence of filler additives, casting solution composition, pH levels, and electrolyte concentration on the membrane\u0026rsquo;s electrochemical behavior was systematically evaluated. The incorporation of Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanoparticles into the membrane matrix resulted in notable enhancements in membrane potential, ion transport efficiency, and ionic sensitivity. Furthermore, the presence of these nanoparticles significantly increased the ionic flux across the membrane, from 9.28 \u0026times; 10\u003csup\u003e5\u003c/sup\u003e to 12.6 \u0026times; 10\u003csup\u003e5\u003c/sup\u003e mol\u0026middot;m\u003csup\u003e-2\u003c/sup\u003e\u0026middot;s\u003csup\u003e-1\u003c/sup\u003e. The modified membranes exhibited enhanced transport efficiency and ion selectivity at pH\u0026thinsp;=\u0026thinsp;7 compared to other pH conditions. The results further revealed that the membrane's electrical resistance initially decreased significantly with increasing electrolyte pH, followed by a subsequent increase at higher pH levels. The membranes exhibited lower selectivity toward divalent ions in comparison to monovalent ions. Moreover, membranes modified with Fe(OH)\u003csub\u003e3\u003c/sub\u003e nanoparticles displayed superior electrochemical performance relative to the unmodified counterparts.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e","manuscriptTitle":"Innovative PVC/Fe(OH) 3 Ion Exchange Membranes for Efficient Arsenic Removal: Synthesis, Performance, and pH-Dependent Behavior","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-23 09:04:01","doi":"10.21203/rs.3.rs-7068769/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-29T23:52:33+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-29T12:07:29+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-23T06:45:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"163663943362163538739696827340315619159","date":"2025-07-20T23:39:26+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"180143248157622898686266400056137521014","date":"2025-07-20T23:04:17+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-20T23:02:44+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-17T07:41:58+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-17T07:39:44+00:00","index":"","fulltext":""},{"type":"submitted","content":"Ionics","date":"2025-07-07T21:14:51+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"2a78ffba-c4ed-450e-8013-41a8bb460750","owner":[],"postedDate":"July 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-08-25T08:39:22+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-23 09:04:01","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7068769","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7068769","identity":"rs-7068769","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}