Evaluation of biobased materials in the development of polymeric membranes for water capture and purification

Evaluation of biobased materials in the development of polymeric membranes for water capture and purification Noor Al-Sadeq a,b,* , Víctor M. Perez-Puyana a , Mohammad H. Hashem b , Mohammad S. Harb b , Alberto Romero a a Departamento de Ingeniería Química, Facultad de Química, Universidad de Sevilla, 41012 Sevilla, Spain b Department of Chemical Engineering, Faculty of Engineering and Architecture, American University of Beirut, Beirut 1107 2020, Lebanon ARTICLE INFO Keywords: Chitosan Electrospinning Biobased membranes Water capture Sustainable water management ABSTRACT The current study addresses the pressing issue of unsustainable water management, particularly in regions experiencing high water stress. It focuses on examining the viability of polymeric membranes composed of biobased materials, mainly chitosan, for various sustainable water management solutions. The membranes evaluated in the study were blends of PVC with either chitosan-silica or charcoal-silica, designed to enhance their functionality and performance. Scanning Electron Microscopy was used to analyze the fiber morphologies of the different membrane compositions. All tested membranes demonstrated robust mechanical properties. Notably, the PVC-Chitosan-Silica (8:2:4) membrane also showed good mechanical properties, combined with superior thermal stability. It excelled in functional tests, achieving water capture efficiencies up to 1.2 ml/g and lead removal rates as high as 92 %. Furthermore, this membrane displayed a lower mass loss at elevated temperatures, suggesting enhanced durability under thermal stress. These results underline the effective combination of chitosan and silica in improving the mechanical strength and thermal stability of polymeric membranes, making the PVC-Chitosan-Silica (8:2:4) particularly effective for advanced water management applications. The study illustrates the unique capabilities of chitosan and silica, advocating for their further exploration and optimization in future sustainable water treatment technologies, which could potentially lead to groundbreaking advancements in the field. 1. Introduction Water stress, intensified by climate change, population growth, and urbanization, is a critical global issue leading to the depletion of the Earth's freshwater resources [1]. According to the United Nations, nearly 703 million people lack access to clean water, and >1.5 billion suffer from inadequate sanitation services, highlighting the need for sustainable water management solutions [2,3]. Intensive agriculture and industrial activities further compound these challenges, emphasizing the necessity for innovative and sustainable practices focusing on water conservation and pollution prevention [4,5]. Traditional methods such as desalination and wastewater recycling are crucial for conserving freshwater sources but come with significant environmental and sustainability challenges. Alternatively, atmospheric water harvesting (AWH) directly addresses water scarcity, capturing water from the air and providing it especially valuable in arid regions devoid of natural freshwater sources. Although atmospheric water harvesting seems ideal for lessening water scarcity, most devices rely heavily on ambient humidity and temperature conditions. This reliance creates operational difficulties in arid zones like deserts, where low humidity necessitates high energy consumption, increasing costs and exacerbating environmental and sustainability issues [6]. Recent advancements in passive adsorption-based technologies have shown potential for efficient water extraction in these conditions, although they are often limited by high costs and operational complexities [7,8]. Amid these technological explorations, chitosan has emerged as a pivotal material in water purification and harvesting due to its adaptable properties derived from chitin in shrimp shells. For water purification, the hydrophilic nature of chitosan can be specifically enhanced or alternatively adjusted to develop hydrophobic properties through copolymeric designs and co-assembly, optimizing its efficacy in contaminant removal [9]. In water harvesting applications, modifications to chitosan's surface properties and design are crafted through co-assembly with materials like silica xerogel to maximize moisture capture. Previous * Corresponding author at: Departamento de Ingeniería Química, Universidad de Sevilla, 41011 Sevilla, Spain. E-mail address: [email protected] (N. Al-Sadeq). Contents lists available at ScienceDirect International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac https://doi.org/10.1016/j.ijbiomac.2025.139791 Received 19 June 2024; Received in revised form 23 December 2024; Accepted 10 January 2025 International Journal of Biological Macromolecules 297 (2025) 139791 Available online 14 January 2025 0141-8130/© 2025 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/bync-nd/4.0/ ). studies have shown this combination to be an effective material for water harvesting [10]. Building on the existing body of research, our study focuses on the potential of membrane technology for integrated water capture and treatment. Notable developments in this area include using chitosan/TiO 2 and alginate-based composite membranes, which have shown significant capabilities in removing contaminants and exhibiting photocatalytic and antimicrobial properties [11,12]. These advancements are exemplified by the work of Ghosh et al. (2023), which demonstrates the efficient use of titanium dioxide nanoparticle-coated meshes for fog capture and pollutant degradation [13]. This research sets a benchmark for dual-function water solutions, highlighting the feasibility and efficiency of integrating water capture with treatment through advanced membrane technologies. Moreover, integrating chitosan with materials like charcoal and silica, known for their pollutant adsorption and moisture capture capabilities, enhances the overall performance of the membranes. The inclusion of eco-friendly PVC, noted for its effective trapping of water droplets and excellent electrospinning properties, further supports the development of high-efficiency water harvesting systems [14,15]. This preliminary study explores the feasibility of creating a dual bio-membrane technology suitable for water harvesting and treatment by combining biowaste materials and processes. The objective is to initially assess and optimize the selection of operational process parameters, designing adsorption-based biomembranes that utilize cost-effective and high-performing materials effectively, aligning with Sustainable Development Goals and advancing the field of water resource management [16]. 2. Experimental 2.1. Materials PVC (CAS# 9002-86-2, MW: 85 g/mol) was supplied from Sigma Aldrich. It was selected for its robust mechanical properties, ensuring durability and stability of nanofibers during electrospinning and subsequent environmental exposure [14]. Chitosan (CAS# 9012-76-4, MW: 100,000–300,000 Da, DD: 75–85 %) was obtained for its biodegradability, thermal stability, and efficacy in water affinity and heavy metal removal, making it suitable for eco-friendly water purification systems [17]. Silica (CAS# 7631-86-9, MW: 60 g/mol) was supplied by Acros Organics, China. It was chosen for its dehumidification properties and its role in enhancing the sustainability of the materials [18]. Charcoal (CAS# 68647-86-9) from coconut shells was provided by REDA Chemicals Industry. It is noted for its high adsorption/absorption capacity, contributing significantly to the membranes' effectiveness in water purification [19]. Dimethylformamide (DMF, ≥99.5 %, MW: 73.09 g/mol) and Tetrahydrofuran (THF, ≥99.8 %, MW: 72.1 g/mol) were sourced from Fisher Scientific's analytical grade Fisher Chemicals. These solvents were chosen based on their ability to effectively dissolve PVC for the electrospinning process [17,20]. Glacial acetic acid (CH3COOH) 99.5 % and sodium hydroxide solution (NaOH) (CAS# 1310-73-2, MW: 40 g/ mol) were also obtained from Fisher Scientific. Acetic acid was used to prepare the chitosan solution, while NaOH was used to adjust the pH of the silica solution, ensuring proper dispersion of the materials. 2.2. Membranes fabrication 2.2.1. Sample preparation Table 1 outlines the specific quantities and weight percentages of materials used in the study, designed to maximize the use of biowaste and enhance sustainability within the electrospinning experimental design. The selection of materials was based on existing literature and refined through trial and error [17,20]. This approach includes a 15 % weight concentration of PVC, aimed at enhancing sustainability. PVC was prepared in a 5 ml solvent system of DMF/THF (50/50 volume ratio) at 50 ◦C and stirred at 300 rpm, a protocol also stated in the literature for electrospinning of PVC [21]. Chitosan was dissolved in 5 ml of 99.5 % acetic acid, while silica gel was mechanically milled to a fine powder and dispersed in 5 ml of distilled water. The pH of the silica suspension was adjusted to 8.5 using sodium hydroxide to ensure optimal dispersion. In systems 1 and 2, the PVC-Charcoal-Silica (8:2:1) and PVC-Chitosan-Silica (8:2:1), the concentration of PVC and chitosan were kept constant at 15 % and 3 % w/v, respectively, with silica maintained at 2 % w/v. These systems were designed to assess the comparative performance of charcoal and chitosan in terms of lead removal and water harvesting. System 3, PVC-Chitosan-Silica (8:2:4), focused on incrementally increasing the silica content to evaluate the threshold at which silica begins to affect the electrospinning process and fiber quality adversely. The increase was tested up to the point where silica content caused clogging, establishing 8 % w/v as the operational limit for the inclusion of silica in the PVC matrix. This observation aligns with general electrospinning principles that highlight the importance of polymer solution concentration on the viscosity/elasticity (rheology) and surface tension, which crucially affects the morphology of the nanofibers [22,23]. 2.2.2. Electrospinning DOE A Fluidnatek LE-10 (Bioinica, Spain) laboratory-scale electrospinning machine was used to obtain the electrospun PVC-ChitosanSilica and PVC-Charcoal-Silica solutions. The voltage was adjusted to 15 kV, while the collector voltage was −2 kV. Additionally, the rotation speed was set to 500 rpm, and the distance between the needle and collector comprised 15 cm [22]. During the creation of samples, the rotation was essential to maintain the fiber's even distribution on the collector. The rotation has been recommended in previous studies for the establishment of uniform membrane thickness and increases the degree of homogeneity of fiber arrangement compared to their static alternatives [21]. The flow rate was controlled at 6 ml/h, significantly exceeding the general range of 0.12 ml/h to1 ml/h enrolled for PVC [22]. This has been noticed by trial and error to increase the size of pores to enhance the water molecules affinity of the biomembranes. In addition, previous studies showed a high correlation between increasing pore size and rate of water capture [23]. A two-hour spinning duration was employed to fabricate thinner membranes that optimize humidity management. To guarantee the consistency of processing conditions, the temperature and relative humidity were maintained at 25 ◦C and 30 %, respectively. Following electrospinning, solvent evaporation was carried out at room temperature with low humidity to ensure the solvent removal. These conditions were selected to avoid variations in fiber formation due to environmental factors and align with the best practices highlighted in the literature [21–23]. Table 1 Evaluated systems including components, quantities and percentages. Sample name PVC (g)/5 ml Chitosan (g)/5 ml Charcoal (g)/5 ml Silica (g)/5 ml Total weight (g)/5 ml PVC (w/v %) Chitosan (w/v %) Charcoal (w/v %) Silica (w/v %) Total (w/v %) PVC-Charcoal-Silica (8:2:1) 2.25 –0.45 0.30 3.00 15 % –3 % 2 % 20 % PVC-Chitosan-Silica (8:2:1) 2.25 0.45 –0.30 3.00 15 % 3 % –2 % 20 % PVC-Chitosan-Silica (8:2:4) 2.25 0.45 –1.20 4.00 15 % 3 % –8 % 26 % N. Al-Sadeq et al. International Journal of Biological Macromolecules 297 (2025) 139791 2 2.3. Characterization of electrospun membranes 2.3.1. Morphological characterization 2.3.1.1. Fiber diameter and membrane morphology. Fiber diameter and membrane morphology were analyzed using a Scanning Electron Microscope (SEM) by a Zeiss EVO equipment (Zeiss, Germany). Samples were observed at a 10 kV acceleration voltage and at a magnification between 500×and 1000×. A thin layer of gold was applied to the surface of the samples to give them conductive properties. SEM images of the electrospun biomembranes were captured at magnifications indicating resolutions of 10 μ m. A digital processing software (Image J) was used to determine the mean fiber diameter and the porosity of the samples. 2.3.1.2. Pore structure. Capillary flow porometry (CFP) was utilized to evaluate the pore structure of the PVC-Chitosan-Silica and PVCCharcoal-Silica membranes using an instrument from Porous Materials Inc. (Serial No. 11152015-3260). A ‘Wet Up/Calc. Dry, Linear’ test measured the flow through the pores at varying pressures after they were saturated with Galwick, a wetting fluid with a surface tension of 15.9 dynes/cm. This fluid was selected based on its recommended use in similar studies, highlighting its efficacy in accurately measuring pore sizes and distributions due to its optimal wetting properties [24]. The test measured the differential pressure required to initiate and sustain the flow of a fluid through various pore sizes. As the pressure was steadily incremented, the flow rates were recorded for both the wetting fluid (Wet Flow) and air (Dry Flow). The bubble point pressure, suggesting the required pressure to push air through the largest saturated pore, and its diameter were determined. The average pressures and diameters at stable flow provided the mean flow pore characteristics. The mean pore diameter was statistically determined using Eq. (1): DM =∑(Di ×Qi) ∑Qi (1) DM stands for the mean pore diameter, Di for the diameter at each pressure increment, and Qi for the volumetric gas flow rate through the pores at that increment. The result is a volume-weighted average pore diameter indicative of the prevalent pore sizes in the PVC-ChitosanSilica and PVC-Charcoal-Silica membranes. 2.3.2. Fourier-transform infrared spectroscopy (FTIR) The chemical bonds of each system were analyzed by Fouriertransform infrared spectroscopy (FTIR) using a Hyperion 1000 spectrophotometer (Bruker). Samples were introduced into an ATR diamond sensor to obtain their corresponding infrared profiles, ranging from 4000 to 400 cm −1 with a resolution of 4 cm −1 and an acquisition of 200 scans, as conducted in previous studies [25,26]. Baseline correction was performed by measuring without the sample. In conjunction with FTIR, Energy Dispersive X-ray Spectroscopy (EDS or EDAX) was employed during Scanning Electron Microscopy (SEM) evaluations to identify and quantify elemental compositions (C, N, Si and Cl). This dual approach not only allowed for the characterization of the membrane's chemical structure but also confirmed the presence and interaction of components such as chitosan, charcoal, silica and PVC within the fabricated membranes. 2.3.3. X-ray diffractometry (XRD) and thermogravimetric analysis (TGA) 2.3.3.1. X-ray diffractometry (XRD). X-ray Diffraction (XRD) was utilized to investigate the phase composition of PVC-Charcoal-Silica and PVC-Chitosan-Silica blends using a Bruker D8 Advance A25 diffractometer. This technique elucidates the crystalline structures within the fibers, highlighting the interactions among chitosan, silica, charcoal, and PVC in the composites [27]. XRD is crucial for detecting phase transitions in polymers like PVC and chitosan when combined with additives such as silica gel and charcoal. The ability to detect crystallinity is essential for assessing whether blends of various amorphous components can transition to a crystalline phase, significantly impacting surface areas relevant to absorption and adsorption mechanisms in various engineering applications [28]. Generally, an increased degree of crystallinity enhances a material's stability, thereby improving its physical and chemical properties, as documented in previous studies [29]. Thus, XRD is instrumental in optimizing the functional design of these electrospun membranes. 2.3.3.2. Thermogravimetric analysis (TGA). For assessing the thermal stability of both PVC-Charcoal-Silica and PVC-Chitosan-Silica electrospun membranes, SDT Q600 V20.9 instrument was employed to carry out a Thermogravimetric Analysis (TGA). The analysis was conducted with samples weighing approximately 8.5 mg, heated from room temperature to 600 ◦C at a rate of 10 ◦C/min in a nitrogen atmosphere. The TGA method provided insights into the membranes' thermal degradation by monitoring weight changes. This comprehensive thermal analysis compares the stability and degradation properties of two different composite membranes, which is crucial for optimizing their performance in water harvesting and water/wastewater treatment applications. Being thermally stable is critically important, as these membranes must withstand hot air flows in water harvesting and condensationbased applications and hot water in treatment processes [30,31]. 2.3.4. Mechanical characterization The mechanical properties of the PVC-Chitosan-Silica and PVCCharcoal-Silica membranes were rigorously evaluated using a RSAIII rheometer (TA Instruments, USA). This device facilitated both static and dynamic tensile testing to assess the comprehensive mechanical profile of the membranes. 2.3.4.1. Static tensile tests. Static tensile tests were conducted in continuous deformation mode following a modified version of the protocol described in ISO 527-3:2019, which is specifically designed for determining the tensile properties of plastic films [32]. These specific conditions were chosen to assess the membranes' ability to withstand increasing the applied load: their tensile strength, elongation, and point of failure. Stress-strain curves from these tests were analyzed to calculate Young's modulus (E), maximum stress ( σ max ), and strain at break ( ε max ). Multiple samples, each meticulously prepared, were tested under controlled room temperature conditions at a strain rate of 1 mm/min to ensure reliability and repeatability of results. Data analysis was performed using the TA Orchestrator software to ensure precision in capturing and interpreting test data. 2.3.4.2. Dynamic mechanical analysis. After conducting static testing, we explored the dynamic mechanical properties by performing strain sweep tests. These tests involved applying strains ranging from 0.01 to 2 % at a frequency of 1 Hz to determine the linear viscoelastic range of the materials. At a strain below the critical strain, we conducted frequency sweep tests from 0.1 to 20 Hz at room temperature. This phase of testing helped us measure the elastic modulus (E ′ ) and the viscous modulus (E ″ ), giving us detailed insights into how these moduli change with strain and frequency. In addition, E ′ 1 and tan δ1 at 1 Hz were calculated, providing a standardized basis for comparing the systems. 2.3.5. Static water contact angles Utilizing the optical contact angle (OCA 15EC from DataPhysics, Germany) we assessed the hydrophilicity and hydrophobicity of “Sol 2” membrane samples with a “t0 thickness 100.” At a controlled rate of 1 μ l per second, 3 μ l of distilled water were applied onto each membrane. The system captured droplet images, calculating both left and right contact angles. This process was repeated for multiple iterations to N. Al-Sadeq et al. International Journal of Biological Macromolecules 297 (2025) 139791 3 ensure measurement accuracy. The averaged angles provided a quantified static water contact angle for each membrane, indicating its wettability. To obtain the Average Contact Angle (ACA), Eq. (2) was used: ACA =1 N∑N i=1(CALi +CARi 2)(2) where CALi and CARi are the contact angles measured on the left and right sides of the water droplet for the i-th iteration. N is the total number of iterations conducted. 2.4. Water capture The experimental protocol for water harvesting was conducted using a small humidity chamber, as illustrated in Fig. S1. Humidity chambers are recognized as effective tools for evaluating water capture, consistent with previous research [33]. This chamber was equipped with a compartment for water and salt to generate humidity, covered by a mesh where the membrane samples were positioned. The experiment tested water harvesting across three humidity levels: 32 %, 54 %, and 86 %, achieved by dissolving precise amounts of salts tailored for each range: •167 g of Magnesium Chloride Hexahydrate (MgCl 2 ⋅6H 2 O) was dissolved in 100 ml of water to achieve 32 % RH at 25 ◦C. •125 g of Magnesium Nitrate Hexahydrate ((MgNO 3 ) 2 ⋅6H 2 O) was dissolved in 100 ml of water to achieve 54 % RH at 25 ◦C. •34.2 g of Potassium Chloride (KCl) was dissolved in 100 ml of water to achieve 86 % RH at 25 ◦C. Each membrane sample, of equal weight, was placed on a mesh above which 10 ml of the corresponding salt solution was added for each specified humidity level. The entire assembly was heated in an oven at 50 ◦C for 30 min and then cooled in a refrigerator at 7 ◦C for another 30 min to induce condensation, resulting in a total duration of 1 h. Subsequently, the water droplets on the membrane's surface were measured in ml/g. This protocol was replicated three times to verify the consistency and reliability of the results. Water collection was quantified as ml/mg on the surface of each membrane, a methodology that is similar to previously utilized in studies concerning water harvesting with PVCcontaining nanofibers [15]. 2.5. Heavy metals removal Lead removal trials were conducted to conduct a preliminary investigation into the potential efficacy of our biomembranes as adsorbents for heavy metal removal. Lead nitrate was used to prepare solutions at concentrations of 10, 30, and 100 ppm. For each concentration, three containers were prepared, each containing 15 ml of solution. The synthetic lead solutions were then treated with our sample membranes. The weight of the biomembrane samples used for treatment was fixed at 50 mg. The contact time used for treatment (Ct) was ranged between 30 and 120 min. This is the amount of time during which the membranes are kept in the lead solutions to test their heavy metal removal capabilities. The initial and final lead concentrations were evaluated using atomic absorption spectrometry with calibrated samples. The spectrometric analysis was performed using an iCE 3000 model AA05170902 v1.30 spectrometer (Thermo Fisher Scientific, USA), set to flame instrument mode, equipped with a CETAC 260 autosampler, and operating without dilution. The lead adsorption capacities were calculated through Eq. (3), and the lead removal rates were calculated through Eq. (4) [34]. Qf(%) = (Ci −Cf) (Ci)×100 (3) R(Pb)(%) = (Ci −Cf) (Ci)×100 (4) where Qf, Ci, Cf, and R(Pb)% are the lead adsorption capacity, lead initial concentration, lead final concentration and lead removal rate, respectively. 2.6. Statistical analysis An average of several replicates per measurement of each sample were conducted. Statistical analysis was performed using one-way ANOVA (p <0.05). The mean and standard deviation of each measurement were calculated. OriginPro 8.5 (OriginLab, Northampton, MA) was used for the graphical presentation of the quantitative data. 3. Results and discussion 3.1. Characterization of electrospun membranes 3.1.1. Morphological properties 3.1.1.1. Fiber diameter and membrane morphology. SEM micrographs from the three distinct membrane systems can be observed in Fig. 1. Based on these images, fiber diameter and porosity are illustrated in Table 2. As can be observed, System 2, PVC-Chitosan-Silica (8:2:1) (Fig. 1B) displays small fiber diameters along with the highest porosity. These characteristics suggest that the fibers are arranged with relatively more space between them, indicative of a loosely packed structure. Such a configuration is beneficial for applications requiring a high surface area, such as adsorption and absorption, a finding supported by the study conducted by Hermosillo et al. [35]. In contrast, the PVC-Chitosan-Silica composition of (8:2:4) displays larger fibers and reduced porosity, as detailed in Table 2 and observed in Fig. 1C. The notable increase in silica and chitosan content directly influences these morphological changes. The silica fibers, approximately 95 μ m in size as specified, contribute to the formation of larger fibers by affecting the viscosity of the solution and the distribution of particles within the matrix. Additionally, the chitosan used has a particle size of about 200 μ m, which tends to agglomerate due to its polymeric nature, leading to an overall increase in particle size in the solution. Particle size and distribution in the polymer structure substantially impact material morphology. Specifically, silica and chitosan present larger fibers due to lower porosity, which depends on smaller gaps between particles. Therefore, the fabricated composites are impacted by a detailed correlation between the material composition and a particular size of particles. In fact, the use of silica and chitosan in desired proportions to influence the material's physical properties for optimal performance have been emphasized in Eddya et al., study [36]. These results, in correlation to Eddya et al. [36] study, address the necessity of reducing the material's particle size and increasing its surface area. Other studies in the literature have demonstrated that optimizing the structure of granular and powdered materials such as charcoal and silica, through methods including electrospinning, can lead to a proportionally optimized structure with enhanced morphological characteristics. When these materials are mixed with polymers like PVC and chitosan, the resultant composites often exhibit improved physical properties [36,37]. In this logic, our results reveal that the PVCCharcoal-Silica (8:2:1) is associated with a balanced structure that could be beneficial for various applications. Fiber formation was more evident, as indicated in Fig. 1A. Table 2 indicates that the charcoal used had larger particles compared to silica, likely due to its smaller area. 3.1.1.2. Pore structure. Fig. 2 shows the pore size distribution for the PVC-Charcoal-Silica and PVC-Chitosan-Silica membranes. The PVCN. Al-Sadeq et al. International Journal of Biological Macromolecules 297 (2025) 139791 4 Charcoal-Silica (8:2:1) membrane predominantly features a pore size distribution around 3.2 μ m, serving as an intermediate between the other two configurations. The charcoal component likely enhances adsorption and absorption through chemical properties independent of pore size, suggesting that material composition plays a critical role in adsorptive performance [19]. The PVC-Chitosan-Silica (8:2:1) primarily features small pores around 2 μ m, making up over 70 % of the total pores. In contrast, the modified PVC-Chitosan-Silica (8:2:4) displays larger pores at 6.6 μ m, which are beneficial for atmospheric water harvesting as they prevent clogging and facilitate moisture capture and release [38,39]. While larger pores generally suggest a lower specific surface area, The interplay between pore size, porosity, and surface area is complex. The effectiveness of the PVC-Charcoal-Silica membrane in heavy metals adsorption highlights the importance of considering all aspects of material design, including chemical enhancements and particle size adjustments [37,39]. Future studies will include BET-specific surface area measurements to elucidate further how these structural Fig. 1. SEM images of (A) PVC-Charcoal-Silica (8:2:1), (B) PVC-Chitosan-Silica (8:2:1) and (C) PVC-Chitosan-Silica (8:2:4). Table 2 Fiber diameter and porosity of the PVC-Charcoal-Silica (8:2:1), PVC-ChitosanSilica (8:2:1) and PVC-Chitosan-Silica (8:2:4). Systems Fiber diameter ( μ m) Porosity (%) PVC-Charcoal-Silica (8:2:1) 2.6 ±0.5 50 ±5 PVC-Chitosan-Silica (8:2:1) 1.6 ±0.7 59 ±8 PVC-Chitosan-Silica (8:2:4) 4.2 ±0.9 35 ±8 Fig. 2. Pore size distribution (%) vs average diameter (microns) of the PVCCharcoal-Silica (8:2:1), PVC-Chitosan-Silica (8:2:1) and PVC-ChitosanSilica (8:2:4). N. Al-Sadeq et al. International Journal of Biological Macromolecules 297 (2025) 139791 5 properties impact adsorption capabilities. 3.1.2. Fourier-transform infrared spectroscopy (FTIR) Table 3 (elemental analysis) shows the presence of specific atoms and their proportions within the fabricated membranes. It can be clearly indicated from this analysis that electrospinning has been successfully employed. Additionally, Fig. 3 shows the FTIR spectra of systems A, B, and C. The C – H stretching at 2900 cm −1 emphasizes PVC's significant presence in all systems. The C – – O stretching at 1730 cm −1 and the C – Cl stretching at 616 cm −1 further confirm the PVC uniform influence in all systems. Those spectra observations align with other studies related to isotherms and kinetic modeling of PVC as a recycled polymer [33]. The PVC-Charcoal-Silica (8:2:1), illustrated in Fig. 3A, lacks chitosan, shown by the absence of N – H and C – O stretching peaks. Charcoal's presence is subtly indicated by broad features around 1600 cm −1 , likely from C – – C stretching, adding spectral complexity despite its lower concentration relative to PVC and silica. The PVC-Chitosan-Silica (8:2:1), illustrated in Fig. 3B, shows chitosan's influence with peaks around 3300 cm −1 for N – H stretching and 1000–1150 cm −1 for C – O stretching, though less dominant than PVC peaks. Silica's role is indicated by sharp peaks near 1100 cm −1 for Si-O-Si stretching and 800 cm −1 for Si – O bending. The PVC-Chitosan-Silica (8:2:4), illustrated in Fig. 3C, exhibits increased silica content, highlighted by sharper peaks around 997 cm −1 and enhanced amide spectral features around 1500–1650 cm −1 , suggesting a higher chitosan content than in the PVC-ChitosanSilica (8:2:1), yet still overlaid with PVC peaks. Those findings align with studies related to chitosan, silica, and charcoal properties in literature studies [40–42]. 3.1.3. X-ray diffractometry (XRD)and thermogravimetric analysis (TGA) 3.1.3.1. X-ray diffractometry (XRD). Fig. 4A presents the X-ray diffraction (XRD) patterns of electrospun films composed of polyvinyl chloride (PVC) blended with charcoal-silica. The PVC-Charcoal-Silica films (composition ratio 8:2:1) display obvious peaks at 26◦and 37◦, with the most intense peak observed at 26◦. However, PVC-ChitosanSilica films exhibit broad diffraction peaks, indicative of an amorphous structure. This observation suggests partial crystallization, corroborating previous studies on polymer blends with PVC [43]. The incorporation of charcoal and silica into the PVC matrix appears to promote this semi-crystalline phase transition despite the inherently amorphous nature of the individual components. This phenomenon is noteworthy, as enhancing the crystallinity of materials generally considered to be amorphous could offer significant advantages in water treatment applications. Enhanced crystallinity has been associated with improved performance of adsorbent materials, which is critical for effective water purification [34]. However, the influence of increased crystallinity on water vapor adsorption remains complex and depends on several factors, including polymer type and the specifics of the nanocomposite blend. Studies suggest that while some polymers may exhibit reduced water vapor sorption with increased crystallinity [44], others, like metal-organic frameworks (MOFs), show enhanced water capture capabilities [45]. Therefore, although the PVC-Charcoal-Silica blend demonstrates a transition to a semi-crystalline state, the implications for water capture and treatment efficiency cannot be conclusively determined from this preliminary data alone. Further investigations are necessary to validate these findings and explore the potential applications of these materials in water management technologies. Table 3 Elemental composition of the PVC-Charcoal-Silica and PVC-Chitosan-Silica blends. PVC-Charcoal-Silica blend PVC-Chitosan-Silica blend Element Weight (%) Element Weight (%) C 55 C 51 N 0 N 4 Si 1 Si 2 Cl 44 Cl 43 Fig. 3. FTIR spectra of (A) PVC-Charcoal-Silica (8:2:1), (B) PVC-Chitosan-Silica (8:2:1) and (C) PVC-Chitosan-Silica (8:2:4). N. Al-Sadeq et al. International Journal of Biological Macromolecules 297 (2025) 139791 6 3.1.3.2. Thermogravimetric analysis (TGA). Fig. 4B compares the thermal stability of three tested PVC-biobased blends. At 595 ◦C, the PVCChitosan-Silica (8:2:4) showed the least mass loss at 69 %, indicating greater thermal stability compared to the PVC-Chitosan-Silica (8:2:1) and the PVC-Charcoal-Silica (8:2:1), which experienced 88 % and 84 % mass loss, respectively. Adding higher silica content improved the thermal stability, which is in line with previous studies such as Abasalizadeh et al. [46], which demonstrated that the inclusion of PVC composites with higher silica content obtained higher thermal stability. Additionally, it can be concluded that the PVC-chitosan composite has improved thermal stability compared to the PVC-charcoal composite, which is also in line with studies in literature, such as the study of Ergun [47], who reported that chitosan-based materials exhibit greater thermal stability than those with activated carbon. Overall, at 250 to 257 ◦C, the PVC-Chitosan-Silica and PVC-Charcoal-Silica membranes showed minimal mass loss (3 % to 5 %), indicating their capability to maintain structural integrity under moderate thermal conditions. 3.1.4. Mechanical analysis The stress-strain curves presented in Fig. 5 show the mechanical behavior of PVC-Charcoal-Silica and PVC-Chitosan-Silica membranes under tensile load. Fig. 6 presents a comprehensive dynamic mechanical analysis of PVC-Charcoal-Silica and PVC-Chitosan-Silica membranes. Table 4 illustrates the main parameters used to assess the mechanical properties of the different tested biomembranes. 3.1.4.1. Tensile tests. It can be inferred from the tensile tests that PVCChitosan-Silica (8:2:4) is the stiffest material, showing the highest Young's Modulus (E) of 792 kPa (±30 kPa), and also sustains the highest maximum stress ( σ max ) of 491 kPa (±31 kPa). On the other hand, the PVC-Charcoal-Silica (8:2:1) showed the highest strain at break ( ε max ), reaching 265 % (±13 %). This indicates that the PVC-Charcoal-Silica (8:2:1) exhibits more elongation than the other two systems and enhances mechanical properties, as shown in Fig. 8. Relating these findings to studies in the literature, such as the study by Alonso-Gonz´ alez et al. [48], it can be inferred that PVC-Chitosan-Silica (8:2:4), with its good stiffness and robustness, can be suitable for applications in the water industry, but it also had a greater critical deformation. Despite being preliminary findings, the results are positive in terms of stiffness, approaching values that can be further optimized by exploring plasticization strategies similar to those used in the study by Alonso-Gonz´ alez et al. [48]. In that study, the use of specific types of biodegradable plastics, such as sorbitol, significantly improved the tensile strength and flexibility of bioplastics. In addition, studies by Nagalakshmi et al. and Du et al. [49,50] suggest that further research into its long-term durability under fluctuating pressures could prove beneficial. On the other hand, comparing the tensile testing results of PVC-Charcoal-Silica (8:2:1) with similar scenarios in the literature, its high elasticity and moderate stiffness make it highly suitable for environments requiring small thickness and high elongation at break. These properties are generally associated with longer lifetimes and align well with porous membranes made from polymeric nanocomposites, which are suitable for various water treatment applications [51]. 3.1.4.2. Dynamic mechanical analysis (DMA). By observing Fig. 6A, the three systems, PVC-Charcoal-Silica (8:2:1), PVC-Chitosan-Silica (8:2:1), and PVC-Chitosan-Silica (8:2:4), demonstrate that their storage modulus (E ′ ) is consistently greater than their loss modulus (E ″ ) across all tested strains. This confirms that the developed membranes have a viscoelastic but fundamentally solid behavior. The storage modulus for each system begins high and generally maintains a robust profile up to a certain strain point beyond which a notable decrease is observed. This point of initial decrease is what defines the critical strain for each material, marking the onset of more significant plastic deformation, signaling the onset of material breakdown. The critical strains ( ε cr ) for PVC-CharcoalSilica (8:2:1), PVC-Chitosan-Silica (8:2:1), and PVC-Chitosan-Silica (8:2:4) were all found to be <1 %. It can be indicated that the PVCChitosan-Silica (8:2:4) exhibits the largest linear viscoelastic range and a greater critical deformation. This aligns with the results from the tensile tests, as it has significantly higher values for elongation at break (Fig. 5). Therefore, this system with the highest resilience and stability, making it ideal for applications that demand the highest structural integrity under extended stress making it ideal for applications requiring durability and effective energy management, such as stable water treatment as deduced from Nagalakshmi et al. and Du et al. studies [49,50]. By observing Fig. 6A, the relationship between the storage modulus and loss modulus of the three systems versus frequency can be interpreted. Specifically, by interpreting E' (kPa) and tan δ, measured at a frequency of 1 Hz for all three systems, as shown in Table 4. These properties indicate the varying mechanical behaviors of the three systems. The PVC-Chitosan-Silica systems, particularly the PVC-ChitosanSilica (8:2:4), outperform the others in terms of storage modulus, demonstrating the highest stiffness and structural integrity as indicated by static tensile tests. Overall, the mechanical analysis underscores the potential of PVC-Charcoal-Silica membranes, which demonstrate high strain at break and lower critical deformation, suggesting their suitability for applications requiring durability and flexibility. Additionally, Fig. 4. (A) Crystallinity determination of the PVC-Charcoal-Silica (8:2:1) and (B) TGA of the PVC-Charcoal-Silica (8:2:1), PVC-Chitosan-Silica (8:2:1) and PVC-Chitosan-Silica (8:2:4). N. Al-Sadeq et al. International Journal of Biological Macromolecules 297 (2025) 139791 7 improvements to PVC-Chitosan-Silica membranes have enhanced their stiffness, making them particularly suitable for water and wastewater treatment applications where robust mechanical properties are crucial due to the demands of loads and pressures. These characteristics may be less critical in water harvesting applications, where water capture efficiency and thermal stability often take precedence. [52]. 3.1.5. Static water contact angle Fig. 7 presents the average water contact angles for three distinct membrane systems, providing insights into how material compositions influence their hydrophobic properties. For the PVC-Chitosan-Silica (8:2:1) system, with a lower content of chitosan and silica, the average contact angle is approximately 109.6◦. Meanwhile, the PVCChitosan-Silica (8:2:4) system, which has a higher silica content, exhibits an increased contact angle of 130.0◦. This observation suggests that adding more silica might affect electrospinning, potentially hindering fiber formation and leading to a more solid material structure that enhances hydrophobicity. Such effects of increased solid content on fiber morphology have been well documented in previous studies [22]. The FTIR results in Fig. 3C corroborate this hypothesis. The sharper Si-O-Si stretching peaks around 997 cm −1 for the PVC-Chitosan-Silica (8:2:4) indicate a substantial presence of silica, aligning with the increased hydrophobicity as reflected by the higher contact angle. Similarly, the PVC-Charcoal-Silica system, shown in Fig. 7A, exhibits a moderate contact angle of 116.6◦. Although this system lacks chitosan, the presence of charcoal adds complexity to the spectral features around 1600 cm −1 , likely from C – – C stretching, influencing its hydrophobic properties. These systems' varied hydrophilicity, as detailed in our FTIR and contact angle results, falls within a range that Zhou et al. [53] suggest has potential for optimization to achieve an ideal balance for water capture applications. This is further exemplified by the study on PVC-PVP nanofibers, where a high contact angle of 130.25◦indicates a hydrophobic surface [15]. Surfaces with higher contact angles typically exhibit low surface energy and high surface roughness, which are beneficial for increasing water harvesting capacity. Our findings align with these studies, demonstrating that our membranes can achieve comparable efficiency and effectiveness in water harvesting applications with strategic modifications. 3.2. Water capture Table 5 outlines the differences in water harvesting capacity under varying humidity conditions, keeping other factors such as membrane weight, temperature, and time constant as detailed in the methodology. Fig. S2 shows the water droplets collected on each membrane type, with the PVC-chitosan-silica (8:2:4) membrane showing the highest water capture, as indicated in the table. At 86 % RH, this translates to 0.7 to 1.2 ml/g of membrane material, achieved passively. Even at a lower humidity of 32 %, the results indicate a water capture of 0.1 to 0.3 ml/g. These findings echo results from previous studies involving PVC-PVP nanofibers, which reported high water harvesting capabilities despite a similar hydrophobic contact angle of 130◦, comparable to that of the PVC-chitosan-silica (8:2:4) [15]. This comparison underscores that a membrane's capacity to retain water droplets, significantly influenced by its surface texture and thickness, is more vital than hydrophilicity for water harvesting efficiency. Despite the hydrophobic nature of the PVCchitosan-silica (8:2:4) membrane, indicated by a water contact angle of 130◦, its superior performance can be attributed to the increased silica content, which enhances its ability to hold water on a thicker, more textured surface. This challenges the conventional emphasis on hydrophilicity as the primary beneficial characteristic for such applications and calls for further investigation in future studies. Additionally, the experimental setup revealed that water desorption began as temperatures exceeded the dew point (7 ◦C), facilitating continuous water capture and regeneration of the membrane surface for subsequent cycles, emphasizing the importance of temperature fluctuations on water harvesting dynamics [54]. 3.3. Heavy metals removal As illustrated in Fig. 8, preliminary lead removal testing revealed the promising heavy metal removal capabilities of PVC-based Fig. 5. Membrane strain-controlled transient tensile tests of the PVC-Charcoal-Silica (8:2:1), PVC-Chitosan-Silica (8:2:1) and PVC-Chitosan-Silica (8:2:4). N. Al-Sadeq et al. International Journal of Biological Macromolecules 297 (2025) 139791 8 biomembranes across various lead concentrations and contact times. The PVC-Charcoal-Silica (8:2:1) membrane shown in (Fig. 8A) exhibited an adsorption capacity (Qf) of approximately 2 mg/g at 10 ppm and 6.7 mg/g at 30 ppm. The active charcoal component of this membrane features a porous structure that is highly conducive to adsorption, facilitating the swift uptake of lead ions. This characteristic has been corroborated by extensive literature, which confirms the efficacy of porous materials in enhancing adsorption dynamics. [55]. Notably, the adsorption reaction reached equilibrium within 30 min, as no significant change in Qf was observed between 30 and 60 min. This equilibrium behavior indicates that the adsorption sites on the membrane are effectively saturated, crucial for understanding the kinetics of lead ion capture. The rapid kinetics highlight the membrane's efficiency in adsorbing lead ions at lower concentrations [56]. This aligns with findings from previous studies that demonstrate the effectiveness of activated carbon from biomaterials in removing heavy metals from dilute solutions, commonly recommended for industrial-scale water and wastewater treatment. However, the PVC-Chitosan-Silica (8:2:1) system in (Fig. 8B), despite demonstrating high removal rates and adsorption capacities at elevated concentrations (e.g., 92 % removal at 100 ppm within 120 min), required nearly double the contact time to achieve comparable results to the PVC-Charcoal-Silica (8:2:1) membrane. This indicates that the chitosan in this membrane interacts differently with lead ions, potentially forming stronger or more numerous chemical bonds compared to charcoal. This also highlights a trade-off in performance, where faster kinetics in one system might be offset by higher capacity and efficiency in another, especially at higher contaminant levels. The influence of increasing silica content was evident in the PVCChitosan-Silica (8:2:4) membrane (Fig. 8C), which showed a performance trend similar to the PVC-Charcoal-Silica (8:2:1) membrane. However, at 30 ppm and a contact time of 60 min, the PVC-ChitosanSilica (8:2:4) membrane outperformed, achieving a notably higher adsorption capacity and removal rate. This enhancement is likely due to the increased surface area provided by the added silica, which facilitates more extensive lead ion interaction sites. This suggests that the Fig. 6. Dynamic mechanical analysis of the PVC-Charcoal-Silica (8:2:1), PVCChitosan-Silica (8:2:1) and PVC-Chitosan-Silica (8:2:4): (A) Strain sweep tests and (B) Frequency sweep tests. Table 4 Mechanical properties of the PVC-Charcoal-Silica (8:2:1), PVC-Chitosan-Silica (8:2:1) and PVC-Chitosan-Silica (8:2:4). System Young's modulus (kPa) Maximum stress (kPa) Strain of break (%) E ′ 1 (kPa) tan δ 1 (−) ε cr (−) PVC-Charcoal-Silica (8:2:1) 188 ±41 267 ±22 265 ±13 901 ±12 0.04 ±0.01 0.05 PVC-Chitosan-Silica (8:2:1) 253 ±23 259 ±20 142 ±11 1921 ±11 0.02 ±0.01 0.05 PVC-Chitosan-Silica (8:2:4) 792 ±30 491 ±31 150 ±17 7728 ±21 0.04 ±0.03 0.09 E ′ 1 (kPa): storage modulus at frequency 1 Hz, tan δ 1 : loss tangent at frequency 1 Hz, ε cr : critical strain. Fig. 7. Static water contact angle of (A) PVC-Charcoal-Silica (8:2:1), (B) PVC-Chitosan-Silica (8:2:1) and (C) PVC-Chitosan-Silica (8:2:4). Table 5 Water collected by PVC-Charcoal-Silica (8:2:1), PVC-Chitosan-Silica (8:2:1), and PVC-Chitosan-Silica (8:2:4). Humidity conditions Water harvested (ml/g) RH (%) PVC-CharcoalSilica (8:2:1) PVC-ChitosanSilica (8:2:1) PVC-ChitosanSilica (8:2:4) 32 % 0.12 ±0.07 0.15 ±0.13 0.30 ±0.32 54 % 0.31 ±0.11 0.41 ±0.17 0.70 ±0.71 86 % 0.71 ±0.52 1.00 ±0.63 1.20 ±0.91 N. Al-Sadeq et al. International Journal of Biological Macromolecules 297 (2025) 139791 9