In this study, poly(vinyl chloride) (PVC) nanocomposite membranes with maghemite copper oxide nanocomposite (PMC) were developed in order to enhancethe PVC membrane performance and its physicochemical properties for the separation of oil-in-water emulsions. The maghemite copper oxide nanocomposite was synthesized by co-precipitation method. The nanocomposite-based membrane was fabricated by casting the nanocomposite onto a PVC support. By using the co-precipitation process, maghemite copper oxide nanocomposite was created. Various techniques such as Transmission electron microscope (TEM), Scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR), have been used to characterize membranes. Water flux, solute rejection, and anti-fouling properties of the membrane were also evaluated. The results demonstrated the nanocomposite's high degree of crystallinity and well-dispersed nanostructure. The resulting membrane was found to have a high oil-water separation efficiency of 98% and an ultra-flux of 0.102L/m2.h compared pure PVC membrane. It was found that the rejection efficiency remained stable over5 cycle times with excellent anti-fouling and cycling stability. The results showed that the maghemite copper oxide nanocomposite-based PVC membrane is a promising material for use in the separation of oil-in-water emulsions, which provide valuable information for the development of new membrane and more flexible, durable, and anti-fouling, making it ideal for use in the separation of oil-in-water emulsions.
Article
Flexible, Durable, and Anti-Fouling Maghemite Copper Oxide Nanocomposite-Based Membrane with Ultra-High Flux and Efficiency for Oil-in-Water Emulsions Separation
https://doi.org/10.21203/rs.3.rs-3140583/v1
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Poly(vinyl chloride) (PVC)
Membrane
Maghemite copper oxide
Composite
Separation efficiency
durability
Antifouling
The separation of oil-in-water emulsions is a serious challenge faced by various industries, including the oil and gas and food industries. Large-scale oil-induced water pollution leads to scarcity of fresh water, waste of resources and environmental pollution. How to effectively separate grease and oil wastewater has become a common problem of all mankind[1, 2]. Traditional emulsion separation methods have limitations, including low separation efficiency and poordurabitlity. In order to save and reuse water resources and protect the environment, oily wastewater needs to be treated and purified. Many techniques have been used to treat oily wastewater, including flotation[3], coagulation [4], ultrasonic separation[5], adsorption[6], photocatalysis[7],skimming [8], flocculation [9], biological treatment [10], advanced oxidation process (AOP) [5][, chemical de-emulsification and air flotation [5]. However, these methods have several drawbacks such as secondary pollution generation, low efficiency, high energy consumption, corrosion, uneconomical running costs, large equipment size, large space requirements, and recontamination, etc[11–14].The development of nanocomposite-based membranes has been identified as a promising solution to address these challenges. Due to its versatility and efficiency, membrane technology has attracted a great deal of attention as a promising separation process with potential for a wide range of future applications. Various polymers have been developed to achieve this goal. As a type of material that can be applied to membranes, PVC polymers have received less attention, but are an important type of commercial plastic mainly due to their wide range of applications and low cost. In fact, promotion of properties such as low cost and development of different polymers such as PVC for use in membranes can facilitate the application of membranes in rural areas as well. Potential applications of PVC membranes have been reported in several studies in the literature. For example, the addition of polyvinyl butyral improves the properties and performance of PVC membranes [15], PVP/PEG [16], and most recently nano-Fe2O3 has been reported in the literature [17]. Also,PVC copolymers membranes were reported with improved performance and antifouling properties[18–20]. In particular, magnetite nanoparticles (MNPs) have been considered as additives due to their unique properties such as physicochemical properties and excellent biocompatibility. Incorporation of magnetite into membranes has been reported for several polymer-based membranes such as PVDF[21], polysulfone[22]and polyethersulfone[23], It leads to improvement of antifouling property. Furthermore, the antifouling properties of nanocomposite membranes are enhanced by the incorporation of surfactants. The combination of maghemite copper oxide and surfactant not only improves the antifouling performance of the membrane, but also increases its durability and flexibility. The resulting nanocomposite membrane is resistant to fouling, which improves oil-water separation efficiency and reduces the frequency of cleaning the membrane. In this article, maghemite-copper oxide nanocomposites were synthesized using a combination of chemical and thermal treatment methods, resulting in stable, uniform and well-dispersed nanocomposite structures. Nanocomposites have been incorporated into (PVC) membranes to improve their separation performance. The developed membrane has high performance, high stability, high fouling resistance, with ultra-high flux and efficiency of oil-in-water emulsion separation, making it a promising candidate for use in various industries. increase. Further studies are needed to assess its long-term stability and commercial viability.
2.1. Materials
All chemicals used in this study were of reagent grade and purchased from Sigma Aldrich (Cairo, Egypt). Ferrous sulfate heptahydrate (FeSO4.7H2O), copper sulfate pentahydrate (CuSO4.5H2O), polyvinyl chloride (PVC), sodium dodecylbenzenesulfonate (SDBS).Dimethylformamide (DMF), sodium hydroxide (NaOH) powder, and NH4Cl (ammonium chloride) were purchased from Merck KGaA (Frankfurt, Germany). All solutions were prepared using fresh deionized water. All chemicals were analytical grade and used as received from suppliers with 99% purity.
2.2. Preparation of Maghemite Seeds (M):
A ferrous sulfate solution was prepared by dissolving 5 g of FeSO4 7H2O in 100 mL of distilled water and stirring with a magnetic stirrer until completely dissolved. A sodium hydroxide solution of 0.1 M NaOH in 10 ml of distilled water. The sodium hydroxide solution was added to the ferrous sulfate solution at a very slow rate (1 mL/10 min.). The solution was heated to 70° C. and maintained at this temperature for 2 hrs, then cooled to room temperature and stabilized by the addition of 10 ml of NH 4Cl solution (0.1 M). The formed black maghemite seeds were washed repeatedly with distilled water until a neutral pH was reached. They are then separated by centrifugation and dried overnight in an electric oven. The resulting product is a maghemite seed that will be used in the next step.
2.3. Synthesis of Maghemite-Copper Oxide (MC) Nanocomposite:
Disperse 4 g of maghemite seeds prepared in section (2.2.) in 100 ml of distilled water. 2 g of CuSO4.5H2O in a ratio (2:1) are dissolved in 20 ml of distilled water and added to the maghemite seed solution. The solution is then stirred at room temperature for 2 hrs. Then, heated at 70° C. for 3 hrs. The resulting product is a maghemite-copper oxide (MC) nanocomposite.
2.4. Membrane(PMC) preparation:
Composite membranes of PVC and copper maghemite oxide (PMC) nanocomposites were fabricated by a phase inversion technique. First, dissolve 500 g of PVC in 50 ml of DMF and stir until completely dissolved. Next, add 50 g of maghemite-copper oxide nanocomposite to the PVC (1:10) solution and stir for 30 min. to mix properly. Then add 50 g of SDBS to the solution and stir for another 30 min with continuous stirring until a homogeneous solution is formed. Pour the mixture into the mold and let it dry for 24 hrs in a well-ventilated room. A vacuum oven was then used to remove air bubbles for 12 hours before casting the solution onto a glass plate. A cast film (0.6 mm thick) was then obtained using a casting knife and immediately immersed in a distilled water coagulation bath. The resulting films were then washed several times with distilled water to remove residual solvent and stored in distilled water for further testing.
2.5. Membrane characterization:
The crystal structure, size and surface morphology of the membranes were examined with a JEOL JEM 2100 (JEOL, Tokyo, Japan) high-resolution transmission electron microscope (HRTEM) and a scanning electron microscope (SEM, Hitachi S-4800) at an accelerating voltage of 200 kV. )at 10 kV accelerating voltage. The phases of the prepared samples were investigated by X-ray diffraction (XRD) using a diffractometer (Philips 1830) measuring diffractometer using CuKα radiation (λ = 1.5418 Å) at a rated power of 40 kV and 40 mA was given and from 4to 80° (2θ). Functional groups were detected using Fourier transform infrared (FT-IR) spectroscopy model Spectrum one (Perkin Elmer, USA) in the wavenumber range 400–4000 cm− 1.
3. Membrane properties
3.1. Separation performance evaluation of membrane
1.4.Transmission electron microscopy (TEM)
Figure 1 shows the TEM images of PMC nanocomposite membrane and PVC blank membrane, and some differences can be observed. First, the PMC membrane nanocomposites can exhibit the presence of maghemite-copper oxide nanoparticles within the PVC matrix, as evident in Fig. 1(a). These particles can appear as dark spots or clusters in TEM images. In contrast, blank PVC membrane can have a more uniform structure with no discernible particles or clusters, as shown in Fig. 1(b). The PVC matrix appears on TEM images as a homogeneous area without any significant features or defects. Another difference that can be observed between the two membranes is the overall thickness and porosity. PMC membrane nanocomposites may have slightly different thickness and pore size distribution compared to blank PVC membrane due to the presence of nanoparticles. Overall, TEM can provide valuable information on the morphology and structure of nanoscale PMC membrane nanocomposites and PVC blank membrane, contributing to the understanding of their properties and performance in various applications.
2.4.Scanning electron microscopy (SEM)
The morphology of the polymer composite membranes was investigated using scanning electron microscopy (SEM) analysis, as investigated in Fig. 2. Differences in the PVC surface were observed before and after the addition of maghemitecuprate (MC). PMC membrane nanocomposites can have more complex surface morphologies compared to PVC blank membrane, as seen in Fig. 2(a). This is due to the presence of maghemite copper oxide nanoparticles, which can create roughness, bumpsor protrusions on the surface of the film. Figure 2(b) shows that the PVC blank membrane can have a smoother, more uniform surface without any noticeable features or defects. The surface of the PVC matrix appears relatively flat and featureless in SEM. PMC membrane nanocomposites may have different pore size distributions compared to PVC blank membrane due to the presence of nanoparticles that may affect the overall porosity of the membrane. Overall, SEM can provide valuable insight into the surface morphology, pore structure, and interfacial interactions between components of PMC membrane nanocomposites and blank PVC membrane, contributing to our understanding of their properties and performance in various applications.
3.4. XRD analysis study
X-ray diffraction analysis was performed to confirm the crystalline phases of the synthesized MC NPs, PVC and PMC. The results are shown in Fig. 3. The XRD pattern of MC NPs showed a characteristic pattern of Fe2O3. Peaks appeared at 2θ of 35.97°, 40.49, 20°, 45.32°, 60.12° and 66.67° corresponding to pure Fe3O4, consistent with standard data JCPDS (65-3107). For CuO, peaks were observed at 2θ = 35.97°, 45.32°, 60.12°, 66.67°, 74.06° and 79.18°. This corresponds to the standard JCPDS card number (JCPDS No. 89-2530) [25],and confirms the synthesis of magnetite-copper oxide nanocomposites. The spectrum of a blank PVC membrane may show no distinct diffraction peaks or very weak peaks due to the amorphous nature of the PVC matrix. For the PMC membrane nanocomposite samples, diffraction peaks corresponding to maghemite copper oxide nanoparticles within the PVC matrix may occur. These main peaks appeared at angles of 17.31°, 24.23°, 35.33° and 37.52°. The original characteristic peaks of MC NPs were reduced and slightly shifted or disappeared in the composite pattern with the addition of MC NPs. These findings confirm the formation of composite membranes. By comparison, PMC membrane nanocomposites have a higher degree of crystallinity compared to PVC blank membrane due to the presence of maghemite copper oxide nanoparticles that can induce crystallization of the PVC matrix. Overall, XRD can provide valuable insights into the crystal structure, crystallinity and phase behavior of PMC membrane nanocomposites and blank PVC membrane, contributing to our understanding of their properties and performance in various applications.
4.4.Fourier transform infrared (FT-IR) spectroscopy
Fourier transform infrared spectroscopy (FT-IR) is a commonly used analytical technique to characterize the molecular structure of materials. Figure 4 shows the FT-IR spectra of MCNPs, PVC, and the PMC compositescan provide information about the chemical bonds and functional groups present in the materials.The peaks at around 504,16 and 601,773 cm− 1in MC spectrum was corresponded to Fe-O stretching vibration due to the presence of Fe2O3[26]. Also, the peaks obtained at 1218.25, and 1426.83 cm− 1 were corresponding toCu-O and Cu-OH, respectively, confirming the formation ofmaghemite copper oxide[27]. Moreover, the peak between 3367.72 cm− 1 responsible for OH stretching is broader due to more OH groups on the MC surface. By comparing the FT-IR spectra of the two membranes, we can identify changes in molecular structure due to the incorporation of MC NPs into the PVC matrix. Figure 4 shows that the FT-IR spectra of blank PVC membrane typically exhibit characteristic peaks at approximately 2960 and 2845 cm− 1 corresponding to the C-H stretching of the polymer backbone. Other peaks at about 1460 and 1370 cm− 1 correspond to C–H bending modes, and peaks at 1099 cm− 1 and 616 cm− 1 correspond to C–C and C–Cl stretching, respectively. On the other hand, the peak around 1100 cm− 1 is related to the C-O stretching vibrations of PVC. For PMC nanocomposite membrane, the presence of maghemite copper oxide nanoparticles can cause an additional peak in the range of 400–800 cm − 1.
5. PMC membrane performance
The effects of process parameters on the rejection and flux of PMC membrane nanocomposite and PVC blank membrane can be illustrated and interpreted as follows: were examined, including solution dosage (10, 20, 30, 40, 50 ,60 and 70 mL), solution concentration (10, 30, 40,60, and 100 mg.L− 1), and pump pressure (0.5, 1.0,1.5, 2.0 and 2.5 bar). The process was investigated using single factor experiments and a simple separation process Firstly, five membranes (0.2 m2, 0.5 bar, and 100 mg.L− 1) were prepared with 10, 20, 30, 40, 50 ,60 and 70 mL of solutions containing sodium chloride (NaCl), humic acid (HA), and methylene blue (MB), separately. The results show that the optimized separation efficiency increases and the membrane flux decreases as the increased amount of solution. the resulting membrane with optimized separation efficiency of 98% and flux of 0.5 14 at 50 ml compared to blank membrane about 92.76% and 1.04 as shown in Figs. 5 (a ,b) and 5(c,d).respectively.The rejection of PMC membrane nanocomposite was found to increase with dosage for all solution tested. In contrast, the rejection of PVC blank membrane remained constant or slightly decreased with an increase in solution dosages. The increase in rejection of PMC membrane nanocomposite can be attributed to the addition of MC nanoparticles, which have a high surface area and provide additional adsorption sites for solutes. The flux of both PMC membrane nanocomposite and PVC blank membrane decreased with an increase in solution dosage, as expected. However, the flux decline was more significant in PVC blank membrane compared to PMC membrane nanocomposite. This can be attributed to the enhanced hydrophilicity of the PVC/PMC membrane nanocomposite due to the presence of MC nanoparticles. The increased hydrophilicity promotes the formation of a thin water layer on the surface of the membrane, reducing fouling and enhancing the membrane's permeability. The results of this study indicate that the addition of MC nanoparticles to PVC membrane can enhance its rejection and flux performance, particularly at higher solution concentrations. The use of PMC membrane nanocomposite can lead to the development of more efficient water treatment technologies.
Secondly, five membranes (0.2 m2, 0.5 bar, and50 ml ) wereprepared with 10 mL different solution concentrations of 10,30,40, 60, and 100 mg·L− 1. The test results show that the permeate fluxdecreases and the efficiency increases with the increase of solutionconcentration, and the concentration of100 mg·L− 1 was chosen to ensure high separation efficiency about 97% and flux of 0.514 compared to blank membrane about 90% and 1.04 as shown in Figs. 6(a ,b) and 6(c,d).respectively. As the solution concentration increases, the rejection of bothPMC nanocomposite membrane and PVC blank membrane increases. This can be attributed to the fact that as the concentration of the solute increases, the driving force for diffusion across the membrane also increases, making it more difficult for solute to pass through the membrane. However, the rejection behavior of the PMC nanocomposite membrane is expected to be higher than that of the PVC blank membrane due to the presence of the nanocomposite in the former, which enhances the selectivity of the membrane. As the solution concentration increases, the flux of both PMC nanocomposite membrane and PVC blank membrane decreases. This can be attributed to the fact that as the concentration of solute increases, the osmotic pressure gradient across the membrane also increases, making it more difficult for water to pass through the membrane. However, the flux behavior of the PMC nanocomposite membrane is expected to be higher than that of the PVC blank membrane due to the presence of the nanocomposite in the former, which enhances the permeability of the membrane.Overall, the results suggest that the PMC nanocomposite membrane has better rejection and flux behavior compared to the PVC blank membrane, indicating its superior performance for water treatment applications. Additionally, the results suggest that the concentration of the solute in the feed solution has a significant impact on the performance of the membranes, highlighting the importance of optimizing the operating conditions for maximum membrane efficiency.
Finally, the effect on membrane performance (0.2 m2, 50 ml, and 100 mg·L− 1) was tested at pressures of 0.5, 1,1.5, 2, and 2.5 bar, respectively. The membrane flux increases significantly with increasing pressure and the efficiency decreases insignificantly, and the optimized pressure at 2 bar shows high separation efficiency about 98% and flux of 1.10 compared to blank membrane about 92.79% and 0.20 as shown in Figs. 7(a ,b) and 7(c,d).respectively. In summary, the largest effect on membrane performance among the above five variables is the pore size of the PMC. The solution dosage, solution concentration, and pressure are selected in conjunction with the actual situation as 50 mL,100 mg·L− 1 and 2 bar, respectively.
6. Reusability
The recyclability of composite membrane for oil-in-water emulsion separation was also evaluated in this study. After each cycle of oil-water emulsion separation, the membrane was washed with hot water. Figure 8 shows the removal efficiency of an oil-in-water emulsion repeated five times. We found that the removal efficiency remained stable over 5 cycle times. Composite membranes showed significant rejection of about 90.2–94%. Apparently, this study demonstrated up to 40% improved solute removal compared to pure membrane. These results prove that the composite membrane possesses excellent antifouling properties for oil-in-water emulsion separation due to its superhydrophilicity, superoleophobicity in water and ultra-low oil adhesion properties. In addition, we also investigated the stability of the asymmetric membrane during the cross-flow filtration process.
7. Adsorpo-filtration mechanism of the papered PMC composite membranes
Nanocomposite-based maghemite-copper oxide (γ-Fe2O3/CuO) membranes have been shown in Fig. 9 to be effective in separating oil-in-water emulsions. The separation mechanism involves several steps. First, the emulsion is brought into contact with the membrane surface. Due to the hydrophobicity of the membrane surface, oil droplets in the emulsion adhere to the membrane surface and water can pass through the membrane. It has been shown that maghemite-copper oxide nanocomposite materials have high surface areas and large pore volumes and can effectively adsorb oil droplets. The copper oxide nanoparticles in the nanocomposites have high catalytic activity and can break oil droplets into smaller, more separable components. Second, when oil droplets adhere to the film surface, they coalesce to form larger droplets. This is due to the attractive force between the oil droplets and the surface of the film. Third, when oil droplets coalesce to form larger droplets, they become too large to pass through the membrane pores. This will separate the oil from the water. Maghemite-copper oxide nanocomposite-based membrane filtration for separating oil-in-water emulsions is a combination of physical and chemical processes involving surface adsorption and catalytic decomposition, effectively separating the oil and water components of emulsions. work together for Finally, the separated oil droplets can be easily removed from the membrane surface by washing with a suitable solvent.
8. Comparison with other work
Previous studies listed in the Table1 have reported the development of various membranes modified with nanoparticles or other materials to improve oil-water separation performance. In a study by Al-Ghamdi et al. (2019) achieved a maximum oil rejection of 89%. Magnetite is a well-known photocatalyst with hydrophilic and oleophobic properties, which can improve the antifouling properties of membranes and improve oil-water separation performance. Another study showed PVC/Fe2O3 blended UF membranes were fabricated with nano-Fe2O3 achieved a maximum oil rejection of 91.9% compared to pure PVC reported by Demirel et al. (2017). The PES membranes modified with GO are reported in the work of Liu et al. (2020) achieved a slightly higher maximum oil rejection rate of 88.5%. GO is a two-dimensional material with excellent mechanical and chemical stability and high hydrophilicity, which can improve membrane permeability and selectivity. TheCA membranes modified with PANI and GO are reported in the work of Bai et al. (2021) achieved oil removal rates of up to 90%. PANI is a highly hydrophilic conductive polymer, which can improve the antifouling properties of the membrane, and GO can improve the mechanical strength and stability of the membrane. In a study by Li et al. (2021) also reported oil rejection rates of up to 90%. AgNPs are known for their antimicrobial properties, which can help reduce biofouling on membrane surfaces and improve oil-water separation performance. Compared to these previous studies, the maghemite copper oxide nanocomposite-basedPVC membrane developed by the team achieved a slightly higher maximum oil rejection of 98% compared to PVC. These previous studies demonstrate the potential to modify membranes with different nanoparticles and materials to improve oil-water separation performance. The maghemite-copper oxide nanocomposite-based membrane developed by the team is promising due to its high rejection rate and unique properties, but further research is needed to optimize the fabrication process and evaluate its performance under different conditions. Overall, maghemite copper oxide nanocomposite-based membranes appear to have higher oil rejection rates compared to other membranes. However, it is important to note that membrane performance depends on several factors such as oil droplet size and type, operating conditions, and membrane manufacturing process.
| Membrane | Maximum Oil Rejection (%) | Reference |
|---|---|---|
| (PVC@ Fe3O4) membrane | 89 | [28] |
| (PVC@Fe2O3) membrane | 91.9 | [17] |
| (PES @ GO ) membrane | 88.5 | .[13] |
| (CA@PANI@GO) membrane | 90 | [29] |
| (PVDF@AgNPs) membrane | 90 | [30] |
| (PVC@CuO@Fe2O3) membrane | 98 | Our work |
It was found that the presence of MC-Nancomposite clearly improved the performance of the PVC membrane. Pure water flux results showed an improvement in flux with increasing MC NPs content. The composite membrane achieved about 98% and an ultra-high flux of 0.102 compared to pure PVC. In addition to improved water flow and solute removal, improved antifouling properties and thermal stability were also observed. Our results clearly demonstrate that environmentally friendly, inexpensive, durable and stable membranes are potential alternatives for large-scale industrial applications.
Author Contributions: M.F.M, H.S and H.B.H. wrote the main manuscript text and made the methodology, all authors prepared formal analysis and resources and H.S. made writing-review and editing . All authors reviewed the manuscript.
Funding: This research received no external funding.
Data Availability Statement: All data underlying the results are available as part of the article and no additional source date are required.
Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design
of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or
in the decision to publish the results.
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No competing interests reported.