Application of magnetic nanomodified CoFe₂O₄/polyvinylidene chloride thin film as a high-performance filtration system for wastewater treatment

1. Introduction

Water pollution, a pervasive and intricate problem, jeopardizes ecosystems, human well-being, and the planet’s overall health. From rivers and lakes to oceans and groundwater, the contamination of water bodies with harmful substances renders them unusable for many purposes. Water pollution, particularly from hazardous chemicals, poses a major threat to modern society [1]. Heavy metal contamination is a critical component of this problem [2], as these metal ions in wastewater can negatively impact both human and animal health. Growing ecological and public health concerns surround heavy metals due to their increased use across diverse sectors, including industry, agriculture, households, and technology [3]. Addressing water contamination demands a collaborative effort from individuals, governments, and industry. We can conserve this critical resource for current and future generations by advocating responsible water management and implementing sustainable practices [4]. The contamination of wastewater with heavy metals poses significant environmental and health risks, necessitating effective remediation strategies. Heavy metals, such as chromium (Cr), cadmium (Cd), lead (Pb), and copper (Cu), are toxic even at low concentrations and can accumulate in living organisms, leading to various health issues [5-8]. The conventional approaches for the removal of heavy metals, such as ion exchange and chemical precipitation, often fall short in terms of efficiency and sustainability [9-12].

Cost-effective solutions like thin-film technologies and nanocomposites are gaining traction, with polymers frequently serving as suitable substrates [13]. With 35 million tons produced annually worldwide, polyvinyl chloride (PVC) is a thermoplastic polymer that has been broadly used and has several advantages, such as weather durability, flame retardancy, acoustic and thermal insulation, low maintenance requirements, ease of installation, and visual attractiveness. However, its high chlorine content presents environmental challenges, especially during recycling, due to the numerous chlorine atoms bound within its structure [14-16]. Therefore, reusing PVC waste is essential, making landfill disposal the least preferred method. Chemical modification of PVC, such as the addition of sulfonic groups, can enhance its surface characteristics and create a uniform distribution of active sites, improving its performance as a dye adsorbent. Such modifications enable the creation of novel materials from waste polymers, expanding their potential applications beyond those of the original polymer. Dehydrochlorination and conjugated double bond formation in PVC can be achieved through nucleophilic substitution and elimination reactions [17]. Adsorption, a process where contaminants bind to an adsorbent’s surface, is a key method for heavy metal removal. Typical adsorbents include graphene oxide [18], activated carbon [19], modified chitosan [20], and magnetite [21]. Fe₃O₄ and MxFe₂O₄ nanoparticles (NPs) are examples of NP adsorbents that are garnering more attention because of their special qualities, which include their high surface area, peculiar shape, and incredibly small size. These characteristics all help to accelerate the kinetics of metal ion adsorption from wastewater [22].

Ferrites, represented by the formula MxFe₂O₄ (where Mx can be a variety of metals like Co, Ni, Zn, or Mg), are a class of magnetic nanoadsorbents of particular interest. Particularly noteworthy are the mechanical hardness, good chemical stability, and mild saturation magnetization of cobalt ferrite (CoFe₂O₄) [23]. It also exhibits superior magnetic responsiveness compared to other ferrites of similar size [24]. Recent advancements in nanotechnology have opened new avenues for enhancing the adsorption properties of materials used in wastewater treatment. Among various nanomaterials, iron oxide NPs, particularly cobalt ferrite (CoFe₂O₄) and manganese ferrite (MnFe₂O₄), have garnered attention due to their magnetic properties, which facilitate easy separation from aqueous solutions [23]. This study focuses on CoFe₂O₄ due to its superior stability, higher saturation magnetization, and enhanced adsorption capacity compared to MnFe₂O₄. CoFe₂O₄ has been shown to effectively adsorb heavy metals owing to its high surface area and the active sites that promote the binding of metal ions [23].

Previous studies have demonstrated the efficacy of nanomodified polymers in enhancing adsorption performance. For instance, the incorporation of iron oxide NPs into various polymer matrices has resulted in significant enhancements in heavy metal removal efficiency [24]. However, the specific impacts of CoFe₂O₄ on the adsorption capacity of PVC have not been extensively explored. This research aims to investigate the potential of CoFe₂O₄-modified PVC as an effective adsorbent for heavy metal remediation in wastewater. By evaluating its adsorption performance and stability, this study seeks to contribute valuable insights into the development of sustainable materials for environmental applications. The contamination of water with heavy metals is a critical environmental issue, necessitating effective purification methods. This study investigates the use of nanomodified PVC to enhance the adsorption and removal of heavy metals from wastewater. The integration of magnetic CoFe₂O₄ NPs into PVC matrices represents a novel method to improve the adsorption capacity and facilitate magnetic separation of heavy metals. The modified PVC exhibited an ion exchange capacity of ∼1.25 mmol/g, significantly outperforming the unmodified version. Removal efficiency improved with increased concentrations of CoFe₂O₄ NPs, demonstrating the effectiveness of the modification. While the modification process increased costs by 10%, it led to a fourfold increase in adsorption efficiency, presenting a favorable cost-to-benefit ratio. The nanomodified PVC maintained consistent performance over five reuse cycles, highlighting its potential for sustainable applications. Filtration experiments indicated that magnetically controlled separation is a viable method, allowing for efficient heavy metal removal under varying magnetic field strengths. This research underscores the potential of nanomodified PVC as an innovative and cost-effective solution for heavy metal remediation in wastewater, paving the way for improved water purification technologies.

2. Materials and Methods

2.7. Filtration test under magnetic field

This study used two types of contaminated water: one with 100 ppm lead chloride and the other with 100 ppm cadmium chloride. For the filtration test, a lead chloride solution was placed in the chamber of an american petroleum institute (API) filter press (as shown in Figure 1). Nitrogen gas at 20 psi was used to pressurize the solution, forcing it through filter paper. As the solution passed through, some heavy metal was adsorbed by the membrane, and the resulting filtrate was collected in test tubes. This collection process was repeated 15 times.

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Figure 1.

Filtration of polluted water through nanomembrane and collection of output filtrate.

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Filtrate samples were collected in varying volumes: 5 cc for the first 10 samples, 10 cc for the next 5, 20 cc for the 16^th, 30 cc for the 17^th, and 50 cc for the 18th. The filtrate began to appear cloudy in the later stages, suggesting a decline in the membrane’s absorption capacity, likely due to pore blockage by lead and saturation of the membrane’s active sites. For each filtrate sample, both the cumulative volume and the cumulative lead concentration (measured using ICP spectrometry) were recorded. A graph was then generated plotting the cumulative lead concentration (ppm) against the cumulative filtrate volume (mL). The same filtration procedure was repeated using a 100 ppm cadmium chloride solution, and a similar graph was constructed plotting cumulative strontium concentration against filtrate volume. These filtration tests were conducted for both lead chloride and cadmium chloride solutions under three different magnetic field strengths: 0 T, 0.2 T, and 0.4 T. The research experiments were accomplished at the Natural and Health Sciences Research Center.

3. Results and Discussion

The produced thin films’ morphology was examined using scanning electron microscopy (SEM) (Figure 2). Microparticles of various sizes are present in the thick, granular structure of the original PVC (Figure 2a). The SEM picture of cobalt ferrite nanoparticles that have been calcined at 600°C has been displayed in Figure 2(b). Because of their weak surface interactions (such as van der Waals forces) and magnetic nature, these nanoparticles, which have an average size of 74 ± 1.6 nm, seem agglomerated. There is also noticeable porosity on the surface of the ferrite nanoparticle. Because the nucleation and crystal development of the cobalt ferrite nanoparticles occurred simultaneously, the co-precipitation approach with NaOH as a precipitating agent produced a more uniform distribution of the particles. After being nanomodified, the PVC’s morphology underwent significant alteration (Figures 2c and d). Lamellar zones, which are characterized by tiny flakes and a structure that appears to be porous but has distinct regions, appeared. Figures 2(e-h) displays elemental mapping that verifies the nanoparticles’ elemental makeup. Only cobalt (22.35 w%), iron (39.22 w%), and oxygen (38.44 w%) were detected by energy-dispersive X-ray spectroscopy (EDS) (Figures 2d and i), confirming the lack of contaminants. With an average pore width of 6.7 nm, the PVC’s surface area increased from 0.3 m²/g to 89 m²/g after this nanomodification [14], putting the nanomodified PVC in the mesoporous category, which is advantageous for adsorption. After measuring the thickness of the film at various locations, the average thickness was found to be 170±15 μm.

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Figure 2.

(a) Microscopic examinations of the studied materials. Following calcination at 600°C, the cobalt ferrite NPs’ size (averaging 74±1.6 nm) and propensity to clump together due to magnetic forces are seen in (b), a SEM image. SEM and TEM pictures of the resultant PVC/CoFe₂O₄ membrane are shown in (c and d). Images (e–h) display elemental mapping that verifies the nanoparticles’ elemental makeup. Lastly, an EDS spectrum from (d and i) confirms that only cobalt (22.35 weight percent), iron (39.22 weight percent), and oxygen (38.44 weight percent) are present; no other elements were found.

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Figure 3 shows the PVC Fourier transform infrared (FTIR) spectrum. C=C stretching is indicated by a band at 1600 cm⁻¹, while phenyl ring vibrations are found in the 1600-1500 cm⁻¹ range. Between 1450 cm⁻¹ and 1350 cm⁻¹, the asymmetric and symmetric bending modes of CH₃ are detected, respectively. CH₂ symmetric stretching is represented by a peak at 2966 cm⁻¹, while CH₂ bending also manifests at approximately 1450 cm⁻¹. The vibrational modes found in the octahedral and tetrahedral locations of the CoFe₂O₄ structure, respectively, are characterized by the peaks seen at about 420 and 590 cm⁻¹. Stretching and bending vibrations of adsorbed water are indicated by the bands in the 3500-3000 cm⁻¹ and 1600-1650 cm⁻¹ ranges, respectively. The presence of hydroxyl groups on the metal oxide surface is shown by a signal at 1385 cm⁻¹.A peak at 690 cm⁻¹ indicates the C-Cl bond axial deformation, which verified the chlorine content of the PVC both before and after alteration. As the concentration of CoFe₂O₄ NPs in the PVC thin film increases (from 0.2 (MPVC1) to 0.8 (MPVC4)), several changes may be observed in the FTIR spectra. Increased CoFe₂O₄ concentration may lead to shifts in the characteristic peaks of PVC due to interactions between the NPs and the polymer matrix. For example, the C=C stretching peak at 1600 cm⁻¹ might shift slightly due to the influence of the NPs. The peaks characteristic of CoFe₂O₄, particularly those around 420 cm⁻¹ and 590 cm⁻¹, would likely become more pronounced as the concentration of CoFe₂O₄ increases. This would indicate a higher presence of the NPs within the PVC matrix. As CoFe₂O₄ concentration rises, the band at 1385 cm⁻¹ related to hydroxyl groups may also change in intensity. This could suggest a higher number of hydroxyl groups interacting with the NPs, affecting adsorption characteristics. The bands in the 3500-3000 cm⁻¹ range associated with adsorbed water may increase in intensity, indicating greater water retention within the film as more CoFe₂O₄ is incorporated. An increase in CoFe₂O₄ content might lead to a decrease in the intensity of certain PVC peaks, reflecting a competitive interaction where the NPs affect the vibrational modes of the polymer. The Payne cup method was used to measure the water vapor flux [27]. When evaluated at 300 K and pH 5.0, the nanomodified PVC displayed a much greater ion exchange capacity of 1.274 ± 0.08 mmol·g⁻¹ [14], surpassing previously reported values [14,27]. The ion exchange capacity of pure PVC was determined to be 0.044 ± 0.02 mmol·g⁻¹.

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Figure 3.

FTIR spectra of PVC, CoFe₂O₄ NPs, and nanomodified PVC/CoFe₂O₄ thin films.

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The X-ray diffraction (XRD) patterns of CoFe₂O₄ samples that were calcined at 600°C have been displayed in Figure 4(a). The joint committee on powder diffraction standards (JCPDS) database’s standard values (80–2377) agree with the diffraction pattern. Peaks located at 30.19°, 35.86°, 43.55°, 53.70°, 56.15°, 63.25°, and 75.22° were associated with the CoFe₂O₄ NPs’ (220), (311), (222), (400), (422), (511), (440), and (533) planes. The clear, broad diffraction peaks seen at the (220), (311), (400), and (440) planes verify the creation of a pure spinel phase. The magnetization curve of room-temperature CoFe₂O₄ NPs has been displayed as a function of an applied magnetic field up to 15 kOe in Figure 4(b).

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Figure 4.

(a) A single-phase spinel structure is indicated of CoFe₂O₄ NPs. (b) displays the saturation magnetization hysteresis loop for CoFe₂O₄ NPs. In agreement with SEM findings, (c) DLS data of CoFe₂O₄ NPs at 25°C shows an average particle size of 75.82±5.74 nm. (d) The prepared CoFe₂O₄ NPs’ zeta potential analysis.

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Magnetization continued to rise even at the maximum field, suggesting that a higher field would be needed for full saturation. Plotting magnetization against 1/H and extrapolating to an infinite magnetic field (y-intercept) allowed for the estimation of the saturation magnetization (Ms). The bulk value of 74.08 emu/g published in the literature is higher than the resulting Ms value of 70.15 emu/g [28]. The dynamic light scattering (DLS) measurements for the cobalt ferrite NPs at 25°C have been shown in Figure 4(c). According to the DLS analysis, the particle size is roughly 75.82 ± 5.74 nm, which is in line with the average size seen in the SEM pictures. A suitably low zeta potential (-20.6 ± 5.9 mV) was demonstrated by the cobalt ferrite nanoparticles (Figure 4d) to inhibit rapid aggregation and preserve a stable, dispersed dispersion.

In selecting the polymer matrix, PVC was chosen over alternatives such as polyvinyl alcohol (PVA) and chitosan for several reasons. PVC exhibits excellent chemical resistance and stability under various environmental conditions, making it suitable for long-term applications in wastewater treatment. PVC has superior mechanical strength and durability compared to PVA and chitosan, which can be important for practical applications where structural integrity is required. PVC is widely available and cost-effective, making it an attractive option for large-scale applications in environmental remediation. PVC can be easily modified to enhance its adsorption capacity, allowing for the incorporation of functional nanoparticles like CoFe₂O₄, which can significantly improve its performance in heavy metal removal. While PVA and chitosan have their merits, such as biodegradability and inherent adsorption properties, their limitations in stability and cost-effectiveness make PVC a more viable choice for this study [29]. To assess the adsorption capacity of the CoFe₂O₄/PVC thin films with varying compositions, heavy metal adsorption experiments were conducted. To containers holding the thin films, 1 L of a 100 ppm heavy metal solution was added. The experiments were performed at a pH between 5.5 and 6.5 and a temperature of 25°C. ICP-OES was used to measure the concentrations of metals. Eq. (1) was used to determine the removal effectiveness (R%) for the thin films. The findings have been shown in Figure 5(a), which displays the adsorption efficiency after 60 min. The system may reach a saturation point where additional CoFe₂O₄ does not significantly increase adsorption capacity. Once the active sites are fully occupied, further additions may have little effect.

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Figure 5.

(a) The adsorption efficiency of heavy metal removal (R%) after 1 h. (b) Adsorption quantity at equilibrium Qe.

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The results (Figure 5a) show a significant improvement in heavy metal removal with the nanomodified PVC thin films compared to the unmodified PVC. For Fe, Cr, Co, Mn, and Ni, removal increased from 19-30% with PVC to 94-100% with the nanomodified films. Similarly, Pb, Cu, Cd, and Zn removal increased from 9-27% with PVC to over 88% with the nanomodified films. This enhanced performance is attributed to the incorporation of magnetic CoFe₂O₄ NPs, which are known to improve the mechanical, barrier, magnetic, and thermal properties of polymers [30]. The removal percentage (R%) also increases with greater adsorbent mass due to the availability of more active sites [14,30]. Qe (quantity of metal adsorbed per gram of adsorbent) values, determined using Eq. (2), have been presented in Figure 5(b). The addition of chitosan to the polymer thin film increased the adsorption capacity compared to the 100% polymer thin film (with mean values of 18.05 and 10.60, respectively, and standard deviations of 37.15 and 19.08). As shown in Figure 5(b), from the lowest adsorption group (Pb and Zn) to the medium group (Cu, Ni, Mn, and Cd) and finally to the highest adsorption group (Co, Cr, and Fe), the quantity of adsorption rises as the concentration of CoFe₂O₄ NPs in the nanomodified PVC increases. The performance of the suggested adsorbent was examined using several adsorption/desorption cycles to determine its appropriateness for a circular economy and long-term use. To extract and recover the bound heavy metals, the thin films were cleaned using a variety of solutions (fresh water, NaCl, citric acid, and EDTA) following each adsorption phase. A contact time of 30 min was found to be sufficient for effective heavy metal recovery. Table 1 summarizes the adsorption and desorption percentages achieved across several cycles. Notably, 0.25 M citric acid proved particularly effective in desorbing iron and chromium, enabling both the reuse of these recovered pollutants and the recycling of the adsorbent for multiple cycles.

Without sacrificing its capacity to extract heavy metals from water, a suggested adsorbent recycling method permits pollutant recovery and recurrent adsorbent reuse. The best solution for releasing deposited heavy metals following the adsorption phase was found to be citric acid (0.25 M). ICP-OES, the same technique used to measure heavy metal intake, was utilized to quantify the desorbed contaminants. The thin films were cleaned with citric acid after heavy metal adsorption to get rid of the bound metals and make them suitable for reuse. It was discovered that a 30-min contact time was adequate for recovering heavy metals. This cycle (adsorption, washing, and analysis) was repeated four times to test the reusability of the nanomodified PVC thin films (Figure 6). The results indicate that these films exhibit excellent stability when used to remove iron.

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Figure 6.

(a) Nanomodified PVC/CoFe₂O₄ thin film for Fe metal is recyclable. (b) SEM of the thin film following the fifth treatment cycle.

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The findings presented by Wan Ngah et al. [31], Ahmad et al. [32], Goci et al. [33], and Mojiri et al. [34] agree with the findings of this investigation. By increasing the specific surface area and active sites in the PVC polymer, nanomodifying it enhances the effectiveness of heavy metal removal. In addition to providing steady recyclability and a four-fold boost in efficiency over unmodified PVC, the nanoparticle modification procedure raises the PVC thin film’s cost by 10%.

3.1. Filtration test

The use of a magnetic field in the study serves several important purposes, and it’s essential to provide clarity on this aspect. The magnetic field aids in the efficient separation of the nanomodified PVC from the treated water after the adsorption process. This enables easier recovery of the adsorbent material. The magnetic properties of CoFe₂O₄ NPs may enhance the adsorption process by aligning the particles and potentially increasing the surface area available for interaction with heavy metals. Utilizing a magnetic field can simplify the filtration process, making it easier to remove the adsorbent from the solution without the need for complex mechanical filtration systems. Filtration tests were conducted using PbCl₂ and CdCl₂ solutions, and the results were recorded. Figure 7(a) plots the cumulative concentration of Pb²⁺ ions (ppm) in the output filtrate against the cumulative filtrate volume (mL). Figure 7(b) shows the same relationship for Cd²⁺ ions. Three trend lines—0 T, 0.2 T, and 0.4 T—representing varying magnetic field intensities are included in both figures. The presence of iron oxide within the magnetic membrane enhances absorption efficiency when a magnetic field is applied. This enhancement is attributed to the condensation of ferrite particles within the membrane under the influence of the magnetic field. This condensation decreases the membrane’s permeability, which in turn leads to increased adsorption. Using Eq. 1 (not provided in the source text) and an initial concentration (C₀) of 100 mg/L for both Pb²⁺ and Cd²⁺, the sorption efficiencies were calculated for each magnetic field strength (0 T, 0.2 T, and 0.4 T). The ion concentration at a cumulative filtrate volume of 200 ml (Ct) was used in the calculation. Table 2 summarizes the obtained sorption efficiencies for Pb²⁺ and Cd²⁺. The proposed mechanism suggests that when the membrane’s permeability is reduced (due to the magnetic field), the heavy metal ions have more contact time with the ferrite particles. They can’t just flow straight through as easily. This increased contact time allows for more interaction between the ions and the ferrite, giving the membrane more opportunity to adsorb the heavy metals. Figure 7(c) presents the TEM image of the thin film following the filtration test, confirming the film’s stability.

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Figure 7.

Output (a) Pb²⁺ and (b) Cd²⁺ ions cumulative concentration in ppm versus output filtrate cumulative volume in ml. (c) TEM image of the thin film after the filtration test.

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Table 2. Sorption efficiencies for Pb²⁺ and Cd²⁺ in the presence of three magnetic fields.

Ions	0T	0.2T	0.4T
Pb	42%	63%	68%
Cd	62%	75%	85%

The magnetic properties of CoFe₂O₄ facilitate simple adsorbent recovery and reuse, a key benefit in wastewater treatment. Studies have shown that these composites retain their adsorption capacity across numerous cycles, making them economically attractive for large-scale applications. The combination of cost-effective PVC with CoFe₂O₄ creates an affordable method for removing heavy metals from wastewater, a crucial factor for industries seeking efficient and budget-friendly treatment options. When a magnetic field is applied to the CoFe₂O₄-modified PVC membrane, the iron oxide NPs align and condense within the membrane structure. This alignment is particularly effective at higher magnetic field strengths (0.2 T and 0.4 T). The condensation of ferrite particles reduces the overall permeability of the membrane. This change means that the fluid flow through the membrane is impeded, slowing down the passage of the solution containing heavy metal ions. As the permeability decreases, the heavy metal ions (Pb²⁺ and Cd²⁺) encounter a longer residence time within the membrane. Instead of flowing through rapidly, they are retained longer in the vicinity of the ferrite particles. The prolonged contact time allows for more frequent interactions between the heavy metal ions and the ferrite particles. This interaction is crucial, as it provides more opportunities for adsorption to occur. The increased surface area available for adsorption, combined with the affinity of the ferrite for the metal ions, leads to higher adsorption rates. The cumulative concentration of Pb²⁺ and Cd²⁺ ions in the output filtrate, plotted against cumulative filtrate volume, shows a marked decrease in ion concentration at higher magnetic field strengths. This indicates that more ions are being adsorbed by the membrane when the magnetic field is applied, as reflected in the calculated sorption efficiencies. The stability of the thin film post-filtration, as confirmed by the TEM image (Figure 7c), indicates that the structural integrity of the membrane is maintained even after prolonged exposure to heavy metal solutions. This stability is essential for practical uses in wastewater treatment. In summary, the proposed mechanism illustrates how the application of a magnetic field enhances the adsorption efficiency of heavy metals by increasing contact time and interaction between the ions and the modified membrane, ultimately leading to improved filtration performance [35]. Here are some potential limitations of the study on nanomodified PVC for heavy metal remediation. The experiments might have been conducted under controlled lab conditions that do not fully replicate real-world wastewater scenarios, affecting the generalizability of the results. While the modified PVC performed well over five reuse cycles, the durability and efficiency beyond this limit were not examined, which could impact its long-term viability. The feasibility of scaling the modification process for industrial applications was not addressed, which is crucial for real-world implementation.

4. Conclusions

This study demonstrates that nanomodified PVC, enhanced with CoFe₂O₄ NPs, is a highly effective adsorbent for the removal of heavy metals from wastewater. Those NPs significantly enhanced the adsorption capacity and surface properties of the PVC matrix. The treated thin films achieved substantial removal rates for heavy metals, including Fe, Cr, Cd, Cu, and Pb, while effectively removing Ni, Co, Cd, and Mn within the same timeframe. A 0.25 M citric acid wash was identified as the most efficient method for desorbing bound ions, allowing for the successful reuse and recycling of the adsorbent across multiple cycles. The nanomodified PVC showed excellent stability and performance, maintaining effectiveness over five reuse cycles. Interestingly, while higher initial heavy metal concentrations generally reduced overall adsorption, the relative efficiency for Pb adsorption exceeded that of Cd, highlighting the superior performance of the nanomembrane for certain ions. Despite a marginal increase in material costs due to nanomodification, the significant improvements in adsorption efficiency position nanomodified PVC as a promising and sustainable option for addressing heavy metal contamination in wastewater treatment.