Enhanced water filtration performance in electrospun cellulose acetate membranes via TEMPO-mediated cellulose nanocrystal incorporation and hot pressing

Enhanced water filtration performance in electrospun cellulose acetate membranes via TEMPO-mediated cellulose nanocrystal incorporation and hot pressing | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Enhanced water filtration performance in electrospun cellulose acetate membranes via TEMPO-mediated cellulose nanocrystal incorporation and hot pressing Ane Arrizabalaga-Luzuriaga, Stefano Torresi, Ainara Saralegi, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6880184/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 25 Aug, 2025 Read the published version in Journal of Polymers and the Environment → Version 1 posted 11 You are reading this latest preprint version Abstract Access to clean water is increasingly critical due to escalating pollution from industrialization and population growth. This study presents the development of advanced cellulose acetate (CA)-based membranes for water filtration through an integrated approach combining electrospinning, hot pressing, and cellulose nanocrystal (CNC) functionalization. A 12 wt.% CA solution in a 4:1 acetone/acetic acid mixture was electrospun under optimized conditions (1 mL/h, 15 cm, 35–70% relative humidity) to produce uniform, bead-free nanofibrous mats. Subsequent hot pressing at 100 °C and 20 bar yielded denser membranes with enhanced mechanical durability and reduced pore size. Functionalization with CNCs and TEMPO-oxidized CNCs (CNCTEMPO) further improved performance. TEMPO oxidation introduced a carboxyl content of 0.56 ± 0.04 mmol/g, enhancing nanocrystal dispersion and interfacial adhesion within the CA matrix. This reduced the water contact angle from 104° to 37° and filtration time from 100 minutes to under 30 seconds. Filtration tests showed improved rejection of 2.0 μm particles (92%) and efficient methylene blue dye removal (up to 95%) in membranes with 3 wt.% CNCTEMPO. This is the first systematic study examining the synergistic effect of electrospinning, hot pressing, and CNCTEMPO functionalization, offering a promising strategy for fabricating high-performance, multifunctional membranes for sustainable water treatment applications. electrospun cellulose acetate membranes water filtration cellulose nanocrystals TEMPO-mediated oxidation nanocomposites membranes Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Introduction Nowadays, access to pure and sustainable water stands as a critical imperative for both living organisms and the advancement of human society. The world is facing with tough global challenges, considering shortage of freshwater and environmental pollution one of the most important challenges [1]. Over the past few decades, water pollution has surged to the forefront of environmental concerns, propelled by rapid industrialization, burgeoning population, mismanagement of water resources, and inadequate waste disposal practices [2]. The repercussions of increased discharges from municipal and industrial wastewater, intensified agricultural activities, and diminished river dilution capacities pose a growing threat to water quality [3]. By the year 2100, an estimated 5.5 billion individuals globally may face exposure to contaminated water [4]. Wastewater treatment facilities, comprising primary, secondary, and tertiary stages, play a pivotal role in mitigating these challenges [5]. However, the release of diverse harmful pollutants into water bodies, including heavy metals, pharmaceuticals, personal care products, pesticides, and microplastics, continues to imperil the ecological balance [6–8]. Despite advancements in treatment processes, the inefficiency in removing microparticles smaller than 100 μm and harmful pollutants, raises concerns about their potential long-term impact on the environment [9–11]. This scientific article addresses the intricate landscape of water pollution, focusing on the often-overlooked challenge of microparticle removal from wastewater effluents. While conventional wastewater treatment plants exhibit high efficacy in removing larger particles, the escape of smaller microparticles, often laden with harmful pollutants such as heavy metals, persistent organic compounds, and toxic additives, poses a direct route for their entry into the environment [12]. These contaminants can adsorb onto the surface of microparticles, facilitating their persistence and bioaccumulation in aquatic ecosystems. Although the residual fraction of these microparticles may be minor, it can still contribute significantly to long-term environmental pollution, presenting risks to both ecological and human health [12]. Recognizing the limitations of current wastewater treatment methodologies, this study delves into advanced approaches, with a particular emphasis on membrane technologies. Despite their pivotal role in water purification, membrane technologies face technical barriers such as high energy demand and fouling-related performance reduction [13–16]. In this context, the exploration of biopolymers, specifically cellulose and its nanoscale derivatives, cellulose nanocrystals (CNC) and cellulose nanofibers (CNF), emerges as a promising avenue. The unique properties of cellulose, including superhydrophilicity and renewable sourcing, make it an attractive candidate for membrane applications [17–19]. Hydrophilicity is critical in enhancing water permeability and minimizing fouling, as hydrophilic surfaces repel hydrophobic contaminants that typically adhere to and clog membrane pores. By improving hydrophilicity, membranes can sustain filtration efficiency for longer periods, reducing cleaning frequency and operational costs [20, 21]. The electrospinning technique, an advanced method for membrane fabrication, further enhances these properties by producing nanoscale fibers with high surface area and controlled porosity. This method allows for the creation of membranes with tailored thickness and morphology, leading to superior filtration performance. Furthermore, the process offers precise control over fiber diameter and arrangement, enabling the design of membranes that can selectively target contaminants based on size and surface characteristics [22, 23]. This flexibility is crucial in addressing the diverse challenges presented by various wastewater streams, including the effective removal of microparticles and harmful pollutants. Additionally, electrospinning facilitates the incorporation of various functional materials, such as CNCs, which can improve mechanical strength and further enhance hydrophilicity and antifouling characteristics. Overall, electrospinning offers a scalable and efficient approach to developing high-performance membranes suitable for advanced water treatment applications [24]. Thus, this article focuses on the development of cellulose acetate membranes through electrospinning—a cutting-edge processing technique. The membranes are designed to serve as efficient water filters, leveraging the benefits of cellulose while addressing challenges associated with mechanical strength, pore structure control, and layer affinity in hybrid membranes [25, 26]. The study aims to optimize electrospinning parameters and cellulose acetate solution composition to achieve membranes with superior efficiency, which will be further functionalized with CNCs and TEMPO-oxidized CNCs to enhance hydrophilicity and promote selective removal of charged pollutants. Additionally, the membranes will undergo hot pressing to improve their mechanical properties and refine pore characteristics. The comprehensive characterization and evaluation of these membranes will shed light on their potential for size exclusion, adsorption, and antifouling functionalities, particularly in removing PS microparticles within the 0.5-2 μm range and methylene blue dye as a model for charged contaminants. This research aims to contribute valuable insights to the ongoing discourse on water quality and provide innovative solutions to the evolving challenges in wastewater treatment. EXPERIMENTAL Materials Cellulose acetate powder (CA, Mn 50,000 Da), acetone (98%), glacial acetic acid (99%), and polystyrene (PS) particles with diameters of 0.5 and 2 µm were obtained from Sigma-Aldrich, USA. Cellulose nanocrystals, provided by the University of Maine (Lot 2018-FPL-CNC-117, with a sulfur content of 1.0 wt.% as indicated by the supplier), were used as reinforcement. Sodium hypochlorite (15%) and hydrochloric acid (37%, ACS reagent) were provided by Scharlau. The TEMPO reagent (2,2,6,6-tetramethylpiperidine-1-oxyl) (98%), hydrochloric acid, sodium bromide, sodium chloride and sodium hydroxide were purchased from Sigma-Aldrich, while methylene blue was sourced from Panreac Chemical. Electropinning of CA nanofibers CA nanofibers mats were fabricated by electrospinning of different CA solutions. Solutions with concentrations of 8, 10 and 12 wt.% CA were prepared in different volumetric ratios of acetone/acetic acid, specifically 1:2, 1:1, 2:1, 3:1 and 4:1. Each solution was subjected to magnetic stirring for 12 h at room temperature to ensure their homogeneity. The electrospinning process was carried out using Fluidnatek LE-10 equipment. The voltage and flow rate were optimized to achieve the best fiber formation, while maintaining a constant distance of 15 cm between the syringe needle and the flat collector. TEMPO-mediated oxidation of cellulose nanocrystals TEMPO-mediated oxidation of CNCs was carried out according to the procedure described in the literature [19]. Briefly, 0.5 g of CNCs were dispersed in 50 mL of deionized water via sonication for 15 minutes. On the other hand, an aqueous solution containing 14.75 mg TEMPO and 162 mg NaBr in 50 mL of deionized water was prepared under constant stirring and then added dropwise to the CNC dispersion. Subsequently, 3 mL of a NaClO solution (12 wt.%) were gradually added to initiate the oxidation reaction. The pH of the suspension was maintained at 10 by adding 0.5 M NaOH, while the suspension was stirred continuously for 3 hours at room temperature. To conclude the oxidation process, the reaction was quenched with approximately 1 mL of ethanol, and the pH was adjusted to 7 using 0.5 M HCl. The oxidized CNCs (CNC TEMPO ) suspension was then thoroughly cleaned by dialysis using Spectra Por® 6 membranes (MWCO 8000) for 7 days to remove any remaining reagents. Finally, the cleaned CNC TEMPO were freeze-dried for subsequent use. Membrane preparation Six different membranes were prepared from CA nanofiber mats. The first membrane was a 30 mm diameter circular sample taken directly from the electrospun CA nanofiber mat (MCA). The second was a similar membrane but subjected to hot-pressing at 100 °C and 20 bar (MCA-HP). The remaining four membranes were functionalized with CNC or CNC TEMPO . For these, 10 mL aqueous dispersions of CNC and CNC TEMPO at 1 and 3 wt.% were prepared, then filtered through 30 mm diameter circular samples taken from the electrospun CA mat. The amount of CNC and CNC TEMPO deposited on the membranes was measured by weighing the mats before and after the impregnation, allowing for an accurate measurement of the retention of both CNC and CNC TEMPO . Finally, these filtered samples were subsequently dried at room temperature and hot-pressed under the same conditions as before, resulting in the functionalized membranes labelled as MCA-1%CNC TEMPO -HP and MCA-3%CNC TEMPO -HP for those treated with 1 and 3 wt.% CNC TEMPO , respectively, and similarly MCA-1%CNC-HP and MCA-3%CNC-HP for those treated with CNC. Membrane filtration and absorption performance For the particle retention assessment, two aqueous dispersions of PS microparticles with diameters of 2 and 0.5 μm, both at a concentration of 0.05 wt.%, were prepared. A volume of 20 mL from each dispersion was filtered through the various membranes using a vacuum pump at a pressure of 0.2 bar. On the other hand, to evaluate the effectiveness of the membranes in removing charged pollutants, an aqueous methylene blue solution at a concentration of 25 ppm was filtered in static mode through the membranes, utilizing 15 mL of the dye solution. This methodology provided valuable insights into the membranes' filtration capabilities for both particle retention and the removal of charged contaminants. Characterization The viscosity of CA solutions was determined using a Haake Viscotester Rheometer (IQ RV 20) equipped with concentric cylinders (CC25 DIN/Ti), operating under a steady shear rate from 0.2 to 400 s⁻¹. All measurements were performed at room temperature with 15 mL of solution to maintain consistency across samples. For structural analysis, CNCs and CNC TEMPO were characterized by X-ray diffraction (XRD), utilizing a Philips X'Pert PRO diffractometer with CuKα radiation (λ = 0.154 nm) at settings of 30 kV and 20 mA. Data was collected from 2θ = 5° to 70° in 0.02° steps, followed by smoothing and baseline correction to evaluate crystallinity and peak fitting. The crystallinity index (CrI) was calculated according to Segal’s method [27], based on the intensity of the peak at 22.6° and the intensity scattered by the amorphous part of the sample located at 18°. where I 002 is the intensity of crystalline peak (22.6°) and I am is the intensity of amorphous peak (18°). The carboxylic content of CNC TEMPO was determined by conductometric titration using a GLP 31 CRISON conductometer with a CRISON 50 70 glass-platinum cell equipped with a Pt 1000 sensor. For the analysis, 32 mg of CNC TEMPO were dispersed in 154 mL of water via ultrasonication. Then, 2.5 mL of 0.02 M NaCl was added, and the mixture was stirred with a magnetic stirrer. Next, 0.1 M HCl was added until the pH of the solution reached 2.91. The suspension was then titrated with 0.005 M NaOH until a pH of 10.8-11 was achieved. The carboxylic content was calculated based on the conductivity curve, using the following equation [28]: RESULT AND DISCUSSION TEMPO-mediated oxidation of cellulose nanocrystals The carboxyl group content of CNC TEMPO was determined by conductometric titration, as described previously, yielding a value of 0.559 ± 0.037 mmol/g. This moderate carboxylation level indicates that a substantial portion of the hydroxymethyl groups on the CNC surface was converted to carboxyl groups through TEMPO oxidation, enhancing surface reactivity without compromising the structural integrity of the CNCs. Such a carboxyl content is advantageous for applications requiring improved dispersibility, hydrophilicity, and compatibility with other materials, making these modified CNCs suitable for use in filtration to improve pollutant capture via increased surface charge. The chemical structure modification performed on the surface of CNCs by TEMPO was analyzed through FTIR spectroscopy, as shown in Fig. 1. The spectra of CNC and CNC TEMPO display distinct differences related to the oxidation of hydroxyl groups on the CNCs. The FTIR spectrum of unmodified CNC displays several characteristic bands. The broad absorption bands at 3330 and 3280 cm⁻¹ correspond to the stretching vibrations of the hydroxyl (-OH) groups, indicative of the extensive hydrogen bonding within the cellulose structure. The band observed at 2900 cm⁻¹ is attributed to C-H stretching vibrations. Additionally, a band near 1645 cm⁻¹ is associated with absorbed water, while the band at 1429 cm⁻¹ represents the symmetric bending of CH₂ groups. Furthermore, the bands at 1160 and 897 cm⁻¹ correspond to the asymmetric stretching vibration of the C-O-C bonds in β-glycosidic linkages, and the bands at 1060 and 1030 cm⁻¹ are associated with C-O-C stretching at the C6 position of the glucose rings [29–31]. Following TEMPO oxidation, the CNC TEMPO spectrum exhibits notable changes, particularly with the emergence of bands at 1730 cm⁻¹ and 1604 cm⁻¹, which are attributed to the carboxyl groups introduced through oxidation [32, 33]. The band at 1730 cm⁻¹ corresponds to the protonated (COOH) form, whereas the band at 1604 cm⁻¹ is linked to the carboxylate (COO⁻) form, indicating the presence of both protonated and deprotonated carboxyl groups depending on moisture and pH. A slight reduction in the intensity of the -OH stretching bands around 3330 cm⁻¹, along with a reduction in the C-H stretching band at 2900 cm⁻¹, further supports the conversion of hydroxyl groups to carboxyl groups via the TEMPO oxidation process [34, 35]. These FTIR results confirm a successful TEMPO-mediated oxidation, converting surface hydroxyl groups on CNCs to carboxyl groups, as evidenced by the distinct carboxyl-associated bands, which enhance the surface reactivity and potential application versatility of the modified CNCs. The main challenge in chemically modifying the surface of nanocellulose is achieving functionalization without altering its morphology, thereby preserving the crystal’s structural integrity and avoiding any polymorphic changes [19]. To examine whether TEMPO-mediated oxidation affected the crystal structure of CNCs, XRD analysis was conducted. The diffractograms in Fig. 2 display characteristic crystalline peaks at 15.2°, 16.7°, and 22.6°, which correspond to the ( ), ( ) and ( ) crystallographic planes, respectively, indicative of the typical cellulose I structure. The crystallinity index (CrI) of the cellulose nanocrystals was calculated using Segal’s method [27], which considers the peak intensity at 22.6° and the amorphous region intensity around 18°. The CrI was found to be approximately 86.7% for untreated CNCs and 86.2% for TEMPO-oxidized nanocrystals. This minor decrease in crystallinity suggests that the internal structure of the nanocrystals remains largely unaffected by the surface modification. Thus, despite the chemical modifications, the CNCs retain their original crystallinity and structural integrity. Optimization of the electrospinning conditions The viscoelastic properties of CA solutions are crucial in determining their electrospinning behaviour. A minimum polymer concentration is necessary to facilitate chain entanglement; below this threshold, the polymer chains merely overlap without entangling, which is essential for successful electrospinning [36]. The rheological behaviour of the solution is influenced by variations in concentration and plays a significant role in controlling the morphology of the electrospun fibers. Additionally, the choice of solvent or solvent mixture impacts these properties. Thus, solution viscosity emerges as a pivotal parameter affecting fiber formation and diameter [36]. Fig. 3 illustrates the evolution of viscosity with shear rate for CA solutions with varying concentrations and acetone-to-acetic acid ratios. Solutions with three CA concentrations (8, 10, and 12 wt.%) and five solvent ratios of acetone/acetic acid (A:AA: 4:1, 3:1, 2:1, 1:1, and 1:2) were analysed. As can be seen, viscosity increases with CA concentration due to the greater chain entanglement of the polymer chains. Furthermore, for solutions with the same CA concentration, viscosity generally rises with a higher acetic acid content. This trend can be attributed to the hydrogen bonding interactions between the hydroxyl (-OH) groups of CA and acetic acid. In contrast as the acetone content increases, the overall -OH groups decrease, leading to the replacement of hydrogen bonding interactions by other weaker forces, such as dipole-dipole or dispersion interactions, resulting in a lower viscosity of the solutions. Optical microscopy results (Supplementary Information (SI), Fig. S1) indicate that solutions with lower viscosities (e.g., 8 wt.% CA in any solvent ratio) failed to produce fibers due to insufficient entanglement of the polymer chains (Fig. S1a) [36]. Conversely, solutions with higher viscosities that contained elevated acetic acid concentrations also did not yield fibers, primarily due to inadequate solvent evaporation (Fig. S1b). In contrast, solutions with high CA concentrations and acetone contents successfully produced electrospun fibers (Fig. S1c). From the analysis of viscosity and the preliminary optical microscopy images of the morphology of electrospun fibers, it can be inferred that the optimal viscosity for fiber formation from cellulose acetate in acetone and acetic acid solutions should fall within the range of 600-2300 mPa. Solutions outside of this viscosity range tend to produce fibers with defects. More specifically, the optimal viscosity for successful fiber creation is estimated to be between 1100-1900 mPa at a shear rate of 1.71 s⁻¹ (at 1 mL/h flow rate). Solutions with CA concentrations of 10 and 12 wt.% CA demonstrated effective electrospinning within these parameters. In addition to the influence of CA concentration and acetone to acetic acid ratio, the effect of flow rate and relative humidity were also examined by OM and SEM. Thus, fiber diameter was found to vary with flow rate, with higher flow rates producing larger fiber diameters. For instance, a 10 wt.% CA solution in a A:AA (2:1) solvent ratio generated fibers with an average diameter of 608 ± 235 nm at a flow rate of 10 mL/h, but at reduced flow rates of 5 or 3 mL/h, beaded fibers were formed (Fig. S1d). Similarly, a 12 wt.% CA solution in A:AA (2:1) ratio produced fibers with diameters of 480 ± 295 nm and 453 ± 231 nm at 5 and 3 mL/h, respectively, whereas in A:AA (1:1) solvent ratio at 3 mL/h generated fibers of 360 ± 193 nm (Fig. S1e). The relative humidity during electrospinning played also a critical role in solvent evaporation and fiber formation. Under high humidity (60-75%), solvents did not fully evaporate, leading to partial fiber formation as shown in Fig. 4. Thus, both solution composition and electrospinning conditions are essential for producing uniform, bead-free CA fibers. Solutions with higher acetone concentrations and lower flow rates demonstrated better suitability for common laboratory humidity levels (40-75%). Thus, fiber formation was successful with 12 wt.% CA solutions in A:AA (3:1) and A:AA (4:1) at flow rates of 1, 3, and 5 mL/h within the same humidity range. Although fibers were produced under all conditions, the smallest diameters were obtained at a flow rate of 1 mL/h, yielding average fiber diameters of 566 ± 218 nm and 399 ± 221 nm for 12 wt.% CA solutions in 3:1 and 4:1 A:AA, respectively (Fig. 5). Table 1 provides a summary of the properties of the electrospun CA solutions, including concentration, solvent ratios, and electrospinning conditions, as well as diameter values of those analyzed by SEM. Table 1 CA concentration and solvent ratios of the electrospun solutions, process parameters such as flow rate and humidity, and morphological characteristics observed by OM or SEM and diameters of the fibers measured by SEM. CA concentration (wt.%) Solvent ratios (A:AA) SEM/OM observation Humidity (%) Flow rate (mL/h) Diameter (nm) 8 1:2 Only beads, no fiber 40 5 - 1:1 Only beads, no fiber 40 5 - 2:1 Fibers with numerous beads 40 5 - 10 1:2 Fibers with large beads 40 5 - 1:1 Fibers with small beads 40 5 - 2:1 Uniform fibers, no beads 40 10 608 ± 235 Flat fibers with solvent remains and beads 60 5 - Flat fibers with solvent remains and beads 40 5 - Flat fibers with solvent remains and small beads 40 3 - 3:1 Fibers with elongated beads 40-70 5 - 4:1 Fibers with small beads 40-70 5 - 12 1:2 Fibers with large beads 40 5 - 1:1 Flat fibers, no beads 40 3 360 ± 193 Flat fibers with solvent remains and beads 60 5 - 2:1 Homogeneous, bead-free fibers 40 3 453 ± 231 Homogeneous, bead-free fibers 40 5 480 ± 295 Flat fibers with solvent remains 60 5 - 3:1 Smooth and uniform fibers, no beads 40-70 1 566 ± 218 4:1 Homogeneous, uniform, bead-free fibers 40-70 1 399 ± 221 In conclusion, the optimal conditions for producing continuous, bead-free CA nanofibers were identified using a solution of 12 wt.% CA in a 4:1 A:AA ratio. The process parameter included an applied voltage of 10 kV, a flow rate of 1 mL/h, a tip-to-collector distance of 15 cm, and a relative humidity range of 35-70%. Under these conditions, the solution was electrospun for 7 hours onto aluminum foil to create a consistent electrospun mat. Thermal treatment and functionalization of membranes In addition to optimizing the electrospinning conditions, further treatment was applied to improve the structural and mechanical properties of the CA membranes. While the electrospun CA fibers initially exhibited a homogeneous, continuous structure with high porosity, subjecting the membranes to hot pressing at 100 °C resulted in a denser configuration. This heat and pressure treatment induced plastic deformation, transforming the fibers' cross-sections from circular to more ribbon-like shapes (Fig. 6). The hot-pressing process proved essential in enhancing the mechanical durability of the CA fiber mats and reducing pore size. This densification occurred not due to melting but rather due to plastic deformation of the CA fibers, given that the glass transition and melting temperatures of cellulose acetate are 198-205 °C and 224-230 °C, respectively [29]. Consequently, hot pressing promoted increased adhesion among the CA fibers, producing membranes with improved structural integrity suitable for applications requiring more compact, mechanically resilient materials. The thermal treatment of CA membranes provided a compacted structure that enhanced mechanical durability, but for further functionality, the surface morphology was modified through the incorporation of CNCs and CNC TEMPO . Thus, after the impregnation and the thermal treatment, the surface morphology of functionalized CA membranes was investigated using SEM imaging (Fig. 7). In most cases, the CNCs altered the morphology within the fiber interstices, though the underlying fibrous structure remained visible across all functionalized mats [37]. It was observed that the impregnation with a 5 wt.% CNC solution led to a significant loss of fibrous morphology in the CA membrane (Fig. S2). Morphological changes were particularly prominent on the direct contact surface between the membrane and the CNC dispersion, likely due to prolonged interaction time, which allowed more extensive bonding between the CNCs and CA nanofibers. Therefore, the maximum CNC concentration used was limited to 3 wt.% Comparisons between membranes treated with 1 and 3 wt.% CNC concentrations revealed a more pronounced morphological change with the use of 3 wt.% CNC dispersion than with 1 wt.% CNC. This observation suggests that a higher concentration of CNC leads to a greater degree of interaction between the nanocrystals and the cellulose acetate fibers, resulting in enhanced structural integration. The increased amount of nanocrystals likely contributes to the formation of a denser and more interconnected network within the membrane, thereby altering its overall morphology. Additionally, the greater retention of CNC at the higher concentration facilitates more effective surface coverage, which can improve the mechanical and functional properties of the membranes. Regarding the TEMPO-oxidized CNCs, they exhibited an even stronger affinity for CA fibers, resulting in a higher deposition rate. This behaviour was confirmed through SEM observations and weight measurements taken after impregnation (Table 2), which demonstrated a retention rate that was 10-20% higher for TEMPO-oxidized CNCs compared to untreated CNCs. Furthermore, increasing the concentration of the CNC dispersion led to greater retention overall. Table 2 . Retention of nanocrystals impregnated in electrospun CA membranes, expressed in milligrams (mg) for different concentrations of CNC and CNC TEMPO . 1 wt.% CNC 3 wt.% CNC 1 wt.% CNC TEMPO 3 wt.% CNC TEMPO Nanocrystal retention (mg) 5.5 ± 2.5 20.0 ± 7.5 6.7 ± 1.9 22.4 ± 10.6 Surface wettability of membranes The surface hydrophilicity of CA electrospun membranes, together with hot-pressed and functionalized membranes, was analyzed using WCA measurements (Table 3). Although CA is inherently hydrophilic, the MCA membrane exhibited a hydrophobic contact angle of 104 ± 1°. This increased hydrophobicity can be attributed to the rough nanofibrous structure created during the electrospinning process. In contrast, the MCA-HP membrane displayed hydrophilic behaviour, with a WCA of 55 ± 2°. This change in hydrophilicity is due to the transformation of the fibers from a circular shape to a more flattened configuration, as illustrated in Fig. 6 and Fig. 7, allowing for greater contact between the CA membrane and water. Additionally, the surface roughness initially provided by the electrospun nanofibers diminishes, restoring the hydrophilic characteristics of the cellulose acetate. The water droplets filtered through the MCA and MCA-HP membranes in 100 and 5 minutes, respectively. Surface treatments with CNC and TEMPO-oxidized CNCs further enhanced the hydrophilicity of the membranes. The measured WCAs for the treated membranes were 43 ± 4° for MCA 1%CNC-HP, 37 ± 1° for MCA 3%CNC-HP, 44 ± 1° for MCA-1%CNC TEMPO -HP, and 37 ± 2° for MCA-3%CNC TEMPO -HP. Moreover, water droplets were filtered through these membranes within approximately 20-30 seconds, demonstrating a significantly higher flux and anti-fouling capacity compared to the untreated membranes. These results indicate that the incorporation of CNC and TEMPO-oxidized CNC not only modifies the hydrophilic properties of the membranes but also enhances their functional performance, making them suitable for applications that require efficient water management and reduced fouling, such as in filtration and separation processes. Efficiency of CA membranes in filtration The particle size filtration efficiency of electrospun cellulose acetate membranes was evaluated using microparticle analysis performed by UV-Vis spectroscopy, with results summarized in Table 4. Additionally, SEM images of the membranes after filtration of 2.0 μm diameter PS microparticles were captured. As it can be seen in Table 4, the thickness of the electrospun CA membranes was also measured and varied significantly across different treatments, influencing their filtration performance. For instance, MCA membrane exhibited the greatest thickness at 108 ± 8 μm, while MCA-HP membranes showed a reduced thickness of 77 ± 13 μm. Notably, the functionalized membranes with 1% CNC and 3% CNC had thicknesses of 74 ± 44 μm and 90 ± 41 μm, respectively. The analysis revealed that the electrospun CA membrane exhibited limited rejection of both 2.0 μm (Fig. 8a) and 0.5 μm PS particles, with rejection rates of 33 ± 1% and 5.0 ± 1%, respectively. However, the hot-pressing and functionalization treatments applied to the membranes resulted in a reduction in surface area and pore size, as evidenced previously by SEM images, which in turn improved filtration performance. Specifically, the rejection efficiency of the hot-pressed electrospun CA membranes increased to 77 ± 4% for 2.0 μm particles (Fig. 8b) and 75 ± 5% for 0.5 μm particles, maintaining a comparable retention efficiency. It appears that the pore sizes in the membranes are not completely uniform, leading to some pores exceeding 2.0 μm in diameter. Table 4 Membrane thickness and rejection percentages of electrospun CA membranes for PS microparticles of 2.0 μm and 0.5 μm diameter. Membrane Membrane thickness ( μ m) Rejection % of PS 2 μ m 0.5 μ m 2 μ m 0.5 μ m MCA 108 ± 8 113 ± 6 33 ± 1% 5 ± 1% MCA-HP 77 ± 13 44 ± 8 77 ± 4% 75 ± 5% MCA-1%CNC-HP 74 ± 44 50 ± 5 89 ± 5% 10 ± 5% MCA-3%CNC-HP 90 ± 41 61 ± 7 19 ± 4% 40 ± 46% MCA-1%CNC TEMPO -HP 89 ± 35 72 ± 19 89 ± 2% 11 ± 2% MCA-3%CNC TEMPO -HP 99 ± 28 76 ± 8 92 ± 3% 17 ± 10% CA membranes infiltrated with 1 wt% CNC exhibited enhanced rejection of 2.0 μm PS microparticles (Fig. 8c), although rejection efficiency decreased with higher CNC concentrations (Fig. 8d). Additionally, the rejection of 0.5 μm PS microparticles was reduced compared to the hot-pressed membranes. This decrease in efficiency has been attributed to the potential formation of micrometric holes during the hot-pressing process. The incorporation of CNCs significantly increases the stiffness of the membrane due to the reinforcing properties of these nanoparticles, which may lead to increased susceptibility to breakage during subsequent pressing treatments. Consequently, higher CNC content or lower microparticle sizes may compromise filtration performance. In contrast, CA membranes infiltrated with TEMPO oxidized CNC demonstrated the highest rejection of 2.0 μm PS microparticles at 3 wt% CNC TEMPO , achieving a rejection efficiency of 92% (Fig. 8e and 8f). This improvement is likely due to the reduction in pore size resulting from the surface treatments. However, microcracks in the pores were also observed, which may compromise the filtration efficiency for microparticles smaller than 2 μm. Moreover, the functionality of the membranes and their interaction with water pollutants were evaluated through the filtration of an aqueous solution of MB. This solution was utilized to assess the viability of the membranes against charged specific contaminants typically found in wastewater. Following the filtration of the MB solution through the membranes, a visual reduction in the intensity of the methylene blue in the filtrate and noticeable color retention on the membranes (Fig. 9) were observed. The filtered solutions were subsequently analyzed by UV-Vis spectroscopy, with results presented in Table 5. As shown in Table 5, the as-prepared CA membrane, the hot-pressed membranes, and those infiltrated with 1 wt% CNC exhibited comparable filtration efficiencies, indicating that these treatments did not significantly affect the retention efficiency of MB. However, when the CNC content was increased to 3 wt%, the retention efficiency improved due to the electrostatic interactions between the cellulose nanoparticles and methylene blue. These interactions are attributed to the sulphate groups present in the CNCs, which engage with the cationic groups of MB. Conversely, the carboxyl groups on the surface of oxidized CNCs enhance the attraction of cationic methylene blue molecules. As a result, MCA-1%CNC TEMPO -HP membranes achieved an impressive MB adsorption efficiency of 90%, while MCA-3%CNC TEMPO -HP membranes reached a maximum adsorption efficiency of 95%. These findings underscore the effectiveness of these membranes in removing specific contaminants through charge interactions, particularly with carboxyl groups. Table 5 Methylene blue retention efficiency of electrospun cellulose acetate membranes. Membrane Membrane thickness ( μm) MB adsortion (ppm) MB adsortion efficiency MCA 111 ± 31 17 69% MCA-HP 43 ± 21 17 69% MCA-1%CNC-HP 35 ± 11 17 66% MCA-3%CNC-HP 45 ± 15 22 89% MCA-1%CNC TEMPO -HP 53 ± 12 23 90% MCA-3%CNC TEMPO -HP 50 ± 5 24 95% CONCLUSIONS The study demonstrates that cellulose acetate membranes with enhanced water filtration performance can be fabricated through a combination of optimized electrospinning, hot pressing, and nanocrystal functionalization. A 12 wt.% CA solution in a 4:1 acetone/acetic acid mixture was successfully electrospun under controlled conditions, yielding uniform, bead‐free nanofibrous mats. Subsequent hot pressing at 100 °C and 20 bar transformed these mats into compact membranes with improved mechanical integrity, suitable for demanding filtration applications. Functionalization with cellulose nanocrystals and TEMPO-oxidized CNCs proved to be a critical step in enhancing the membrane properties. The TEMPO oxidation process produced a carboxyl content of 0.56 ± 0.04 mmol/g, which facilitated improved dispersion and integration of the nanocrystals within the CA matrix. This modification was reflected in a significant reduction of the water contact angle from 104° in the as-spun membranes to as low as 37° in membranes treated with 3 wt.% CNCTEMPO, thereby increasing the hydrophilicity and promoting faster water permeation. Filtration performance was notably enhanced as a result of these processing steps. While hot pressing alone increased the rejection efficiency to approximately 77% for 2.0 μm particles and 75% for 0.5 μm particles, the additional incorporation of CNCTEMPO further improved the rejection efficiency, reaching up to 92% for 2.0 μm particles. Moreover, the presence of carboxyl groups contributed to enhanced electrostatic interactions with cationic contaminants, resulting in methylene blue removal efficiencies as high as 95%. In summary, the experimental results confirm the initial hypothesis. Membranes functionalized with CNCTEMPO and subjected to hot pressing exhibited a significantly lower water contact angle (down to 37°), enhanced rejection efficiencies (up to 92% for 2.0 μm particles), and improved mechanical properties compared to the as-spun membranes. These findings validate that the incorporation of TEMPO-oxidized cellulose nanocrystals effectively enhances water filtration performance, underscoring the novelty and potential of this approach for sustainable water treatment applications. Future work is anticipated to further explore detailed mechanical characterizations and extended pollutant testing. Declarations Acknowledgements: Financial support from the Spanish Ministry of Science and Innovation and State Research Agency (MCIN/AEI/10.13039/501100011033) in the frame of PID2022-140119OB-I00 project and from the Basque Country Government in the frame of 00028-IDA2019-38 and Grupos Consolidados (IT-1690-22) is gratefully acknowledged. The authors also acknowledge the Macrobehavior-Mesostructure-Nanotechnology SGIker unit of the University of the Basque Country (UPV/EHU). References Shirazi MMA, Bazgir S, Meshkani F (2020) A novel dual-layer, gas-assisted electrospun, nanofibrous SAN4-HIPS membrane for industrial textile wastewater treatment by direct contact membrane distillation (DCMD). J Water Process Eng 36:101315. https://doi.org/10.1016/j.jwpe.2020.101315 Tlili I, Alkanhal TA (2019) Nanotechnology for water purification: Electrospun nanofibrous membrane in water and wastewater treatment. J Water Reuse Desalin 9:232–247. https://doi.org/10.2166/wrd.2019.057 UNESCO (2020) The United Nations world water development report 2020: water and climate change Tozer L (2023) Water pollution ‘timebomb’ threatens global health. Nature. https://doi.org/10.1038/d41586-023-02337-7 Mason SA, Garneau D, Sutton R, et al (2016) Microplastic pollution is widely detected in US municipal wastewater treatment plant effluent. Environ Pollut 218:1045–1054. https://doi.org/10.1016/j.envpol.2016.08.056 Zdarta J, Jesionowski T, Pinelo M, et al (2022) Free and immobilized biocatalysts for removing micropollutants from water and wastewater: Recent progress and challenges. Bioresour Technol 344:126201. https://doi.org/10.1016/j.biortech.2021.126201 Sandin G, Peters GM (2018) Environmental impact of textile reuse and recycling – A review. J Clean Prod 184:353–365. https://doi.org/10.1016/j.jclepro.2018.02.266 Hairom NHH, Soon CF, Mohamed RMSR, et al (2021) A review of nanotechnological applications to detect and control surface water pollution. Environ Technol Innov 24:102032. https://doi.org/10.1016/j.eti.2021.102032 Wang K, Ma Q, Wang SD, et al (2016) Electrospinning of silver nanoparticles loaded highly porous cellulose acetate nanofibrous membrane for treatment of dye wastewater. Appl Phys A Mater Sci Process 122:1–10. https://doi.org/10.1007/s00339-015-9566-5 Hu Y, Gong M, Wang J, Bassi A (2019) Current research trends on microplastic pollution from wastewater systems: a critical review. Rev Environ Sci Biotechnol 18:207–230. https://doi.org/10.1007/s11157-019-09498-w Carr SA, Liu J, Tesoro AG (2016) Transport and fate of microplastic particles in wastewater treatment plants. Water Res 91:174–182. https://doi.org/10.1016/j.watres.2016.01.002 Primpke S, Imhof H, Piehl S, et al (2017) Mikroplastik in der Umwelt. Chemie unserer Zeit 51:402–412. https://doi.org/10.1002/ciuz.201700821 Barry MC, Hristovski K, Westerhoff P (2014) Membrane fouling by vesicles and prevention through ozonation. Environ Sci Technol 48:7349–7356. https://doi.org/10.1021/es500435e Wang YN, Tang CY (2011) Fouling of nanofiltration, reverse osmosis, and ultrafiltration membranes by protein mixtures: The role of inter-foulant-species interaction. Environ Sci Technol 45:6373–6379. https://doi.org/10.1021/es2013177 Kim SR, Getachew BA, Kim JH (2017) In Situ Healing of Compromised Membranes via Polyethylenimine-Functionalized Silica Microparticles. Environ Sci Technol 51:12630–12637. https://doi.org/10.1021/acs.est.7b03436 Ihsanullah (2019) Carbon nanotube membranes for water purification: Developments, challenges, and prospects for the future. Sep Purif Technol 209:307–337. https://doi.org/10.1016/j.seppur.2018.07.043 Anirudhan TS, Rejeena SR (2015) Photocatalytic Degradation of Eosin Yellow Using Poly(pyrrole-co-aniline)-Coated TiO 2 /Nanocellulose Composite under Solar Light Irradiation. J Mater 2015:1–11. https://doi.org/10.1155/2015/636409 Wu CN, Saito T, Yang Q, et al (2014) Increase in the water contact angle of composite film surfaces caused by the assembly of hydrophilic nanocellulose fibrils and nanoclay platelets. ACS Appl Mater Interfaces 6:12707–12712. https://doi.org/10.1021/am502701e Lin N, Bruzzese C, Dufresne A (2012) TEMPO-oxidized nanocellulose participating as crosslinking aid for alginate-based sponges. ACS Appl Mater Interfaces 4:4948–4959. https://doi.org/10.1021/am301325r Zhang R, Liu Y, He M, et al (2016) Antifouling membranes for sustainable water purification: Strategies and mechanisms. Chem Soc Rev 45:5888–5924. https://doi.org/10.1039/c5cs00579e Sun Z, Chen F (2016) Hydrophilicity and antifouling property of membrane materials from cellulose acetate/polyethersulfone in DMAc. Int J Biol Macromol 91:143–150. https://doi.org/10.1016/j.ijbiomac.2016.05.072 Chen H, Huang M, Liu Y, et al (2020) Functionalized electrospun nanofiber membranes for water treatment: A review. Sci Total Environ 739:139944. https://doi.org/10.1016/j.scitotenv.2020.139944 Cui J, Li F, Wang Y, et al (2020) Electrospun nanofiber membranes for wastewater treatment applications. Sep Purif Technol 250:117116. https://doi.org/10.1016/j.seppur.2020.117116 Mokhena TC, Jacobs V, Luyt AS (2015) A review on electrospun bio-based polymers for water treatment. eXPRESS Polym Lett 9:839–880. https://doi.org/0.3144/expresspolymlett.2015.79 Xue J, Xie J, Liu W, Xia Y (2017) Electrospun Nanofibers: New Concepts, Materials, and Applications. Acc Chem Res 50:1976–1987. https://doi.org/10.1021/acs.accounts.7b00218 Gopi S, Balakrishnan P, Pius A, Thomas S (2017) Chitin nanowhisker (ChNW)-functionalized electrospun PVDF membrane for enhanced removal of Indigo carmine. Carbohydr Polym 165:115–122. https://doi.org/10.1016/j.carbpol.2017.02.046 Segal L, Creely JJ, Martin AE, Conrad CM (1959) An Empirical Method for Estimating the Degree of Crystallinity of Native Cellulose Using the X-Ray Diffractometer. Text Res J 29:786–794. https://doi.org/10.1177/004051755902901003 Saito T, Isogai A (2004) TEMPO-mediated oxidation of native cellulose. The effect of oxidation conditions on chemical and crystal structures of the water-insoluble fractions. Biomacromolecules 5:1983–1989. https://doi.org/10.1021/bm0497769 Tang Z, Lin X, Yu M, et al (2024) Recent advances in TEMPO-oxidized cellulose nanofibers: Oxidation mechanism, characterization, properties and applications. Int J Biol Macromol 259:129081. https://doi.org/10.1016/j.ijbiomac.2023.129081 Gwon JG, Lee SY, Doh GH, Kim JH (2010) Characterization of chemically modified wood fibers using FTIR spectroscopy for biocomposites. J Appl Polym Sci 116:3212–3219. https://doi.org/10.1002/app.31746 Široký J, Blackburn RS, Bechtold T, et al (2010) Attenuated total reflectance Fourier-transform Infrared spectroscopy analysis of crystallinity changes in lyocell following continuous treatment with sodium hydroxide. Cellulose 17:103–115. https://doi.org/10.1007/s10570-009-9378-x Fraschini C, Chauve G, Bouchard J (2017) TEMPO-mediated surface oxidation of cellulose nanocrystals (CNCs). Cellulose 24:2775–2790. https://doi.org/10.1007/s10570-017-1319-5 Okita Y, Fujisawa S, Saito T, Isogai A (2011) TEMPO-oxidized cellulose nanofibrils dispersed in organic solvents. Biomacromolecules 12:518–522. https://doi.org/10.1021/bm101255x Cao X, Zhu M, Fan F, et al (2020) All-cellulose composites based on jute cellulose nanowhiskers and electrospun cellulose acetate (CA) fibrous membranes. Cellulose 27:1385–1391. https://doi.org/10.1007/s10570-019-02880-5 Larraza I, Vadillo J, Santamaria-Echart A, et al (2020) The effect of the carboxylation degree on cellulose nanofibers and waterborne polyurethane/cellulose nanofiber nanocomposites properties. Polym Degrad Stab 173:109084. https://doi.org/10.1016/j.polymdegradstab.2020.109084 Majumder S, Matin MA, Sharif A, Arafat MT (2019) Understanding solubility, spinnability and electrospinning behaviour of cellulose acetate using different solvent systems. Bull Mater Sci 42:171. https://doi.org/10.1007/s12034-019-1857-6 Goetz LA, Naseri N, Nair SS, et al (2018) All cellulose electrospun water purification membranes nanotextured using cellulose nanocrystals. Cellulose 25:3011–3023. https://doi.org/10.1007/s10570-018-1751-1 Table Table 3 is available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files SISaralegi.docx Table3Contactangleanddropfiltrationtimeofuntreated.docx Graphicalabstrac.tiff Cite Share Download PDF Status: Published Journal Publication published 25 Aug, 2025 Read the published version in Journal of Polymers and the Environment → Version 1 posted Editorial decision: Revision requested 25 Jun, 2025 Reviews received at journal 25 Jun, 2025 Reviews received at journal 18 Jun, 2025 Reviews received at journal 18 Jun, 2025 Reviewers agreed at journal 18 Jun, 2025 Reviewers agreed at journal 18 Jun, 2025 Reviewers agreed at journal 18 Jun, 2025 Reviewers invited by journal 18 Jun, 2025 Editor assigned by journal 13 Jun, 2025 Submission checks completed at journal 13 Jun, 2025 First submitted to journal 12 Jun, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6880184","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":473368408,"identity":"4775de21-e311-4953-b301-47d0b08943bd","order_by":0,"name":"Ane Arrizabalaga-Luzuriaga","email":"","orcid":"","institution":"University of the Basque Country UPV/EHU","correspondingAuthor":false,"prefix":"","firstName":"Ane","middleName":"","lastName":"Arrizabalaga-Luzuriaga","suffix":""},{"id":473368409,"identity":"fde7aa76-952d-4218-8ef1-72cadc57fb36","order_by":1,"name":"Stefano Torresi","email":"","orcid":"","institution":"University of the Basque Country UPV/EHU","correspondingAuthor":false,"prefix":"","firstName":"Stefano","middleName":"","lastName":"Torresi","suffix":""},{"id":473368410,"identity":"b0ed89b2-b866-43ca-a85b-0874eaa140cd","order_by":2,"name":"Ainara Saralegi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABCElEQVRIiWNgGAWjYDACZgST8QADg4QcgwQJWhhAWowJa0EGQC0MiQ2EtPC38x78XFHDYM8/+/CDAx9+WaT3S/cYMHxsq8OpReIwX7LkmWMMiTPOpRkcnNknkTtzzhkDxplth3Fbc5jHQLKBjSGB4QyDwWHeHoncDTdyDJh52w7g1CF/mMf4Z8M/Bnv5M+wfDv/tkUi3B2n5i8dhBod5zCQb2xgYN5zhMTjM8EMiwUACqIWxjRmnFkOgFsvGPonEjWd4Cg72NkgYzriRVnCw5xxuv8idP2N8s+Gbjb3cGfaND378qZPnn5EMZJThdhgUQOOCsQ1CHyCkHgn8IUHtKBgFo2AUjBgAAMHVVVoiugxFAAAAAElFTkSuQmCC","orcid":"","institution":"University of the Basque Country UPV/EHU","correspondingAuthor":true,"prefix":"","firstName":"Ainara","middleName":"","lastName":"Saralegi","suffix":""},{"id":473368412,"identity":"f2591ed7-c8de-41c2-9e3d-55fa66a2ce47","order_by":3,"name":"Arantxa Eceiza","email":"","orcid":"","institution":"University of the Basque Country UPV/EHU","correspondingAuthor":false,"prefix":"","firstName":"Arantxa","middleName":"","lastName":"Eceiza","suffix":""}],"badges":[],"createdAt":"2025-06-12 12:08:26","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6880184/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6880184/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10924-025-03659-5","type":"published","date":"2025-08-25T15:57:31+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":85018294,"identity":"97b82804-8237-487d-8fe1-091b0974fbaa","added_by":"auto","created_at":"2025-06-20 03:45:13","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1127005,"visible":true,"origin":"","legend":"\u003cp\u003eChemical structure of CNC and TEMPO oxidized CNC (A) and FTIR spectra of CNC and CNC\u003csub\u003eTEMPO \u003c/sub\u003e(B).\u003c/p\u003e","description":"","filename":"fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-6880184/v1/21f7e6b7b25227a0a005f52b.png"},{"id":85018486,"identity":"0ef18f44-9027-4854-9cf5-26ced297ac37","added_by":"auto","created_at":"2025-06-20 03:53:12","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":418812,"visible":true,"origin":"","legend":"\u003cp\u003eX-Ray diffractograms of CNCs and CNC\u003csub\u003eTEMPO\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-6880184/v1/0201947062d169419aa66bc0.png"},{"id":85018292,"identity":"b0d3f4d2-d9bf-4e4f-9f47-35f632630238","added_by":"auto","created_at":"2025-06-20 03:45:12","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":693858,"visible":true,"origin":"","legend":"\u003cp\u003eViscosity evolution of different cellulose acetate solutions as a function of shear rate.\u003c/p\u003e","description":"","filename":"fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-6880184/v1/d4b00f428a75babba93fb5d4.png"},{"id":85018300,"identity":"ecf2f102-9866-48e1-9265-9066ee47d850","added_by":"auto","created_at":"2025-06-20 03:45:13","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":12329629,"visible":true,"origin":"","legend":"\u003cp\u003eOptical microscopy images of a 12 wt.% CA solution in a A:AA (2:1) ratio, electrospun at a flow rate of 5 mL/h, under relative humidity conditions of approximately 40% (A) and 60% (B).\u003c/p\u003e","description":"","filename":"fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-6880184/v1/636d4374e5a10ee5425227a7.png"},{"id":85018487,"identity":"c8514d5f-5b23-4f68-a3d8-08fa841ae926","added_by":"auto","created_at":"2025-06-20 03:53:13","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":6576672,"visible":true,"origin":"","legend":"\u003cp\u003eSEM micrographs and diameter distribution of fibers of 12 wt.% CA in A:AA 3:1 (A) and 4:1 (B) at 1 mL/h flow rate and 40% humidity.\u003c/p\u003e","description":"","filename":"fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-6880184/v1/1525bef1af58e1cf90abab6c.png"},{"id":85018298,"identity":"26366c14-7175-43b2-a257-e6ac417eabaa","added_by":"auto","created_at":"2025-06-20 03:45:13","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":6009223,"visible":true,"origin":"","legend":"\u003cp\u003eSEM micrographs of 12 wt.% CA in 4:1 A:AA before hot-pressing (A) and after the hot-pressing treatment (B).\u003c/p\u003e","description":"","filename":"fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-6880184/v1/14756c17bfc3a09b38452d6d.png"},{"id":85018299,"identity":"4ef1720a-b292-4f34-87e3-31f6552b4e93","added_by":"auto","created_at":"2025-06-20 03:45:13","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":12548726,"visible":true,"origin":"","legend":"\u003cp\u003eSEM micrographs of 12 wt.% CA in 4:1 A:AA after hot pressing: (A)\u0026nbsp; upper surface of electrospun CA fibers with 1 wt.% CNC dispersion impregnation, (B) upper surface of electrospun CA fibers with 3 wt.% CNC dispersion impregnation, (C) upper surface of electrospun CA fibers with 1 wt.% CNC\u003csub\u003eTEMPO\u003c/sub\u003e dispersion impregnation, and (D) upper surface of electrospun CA fibers with 3 wt% CNC\u003csub\u003eTEMPO\u003c/sub\u003e dispersion impregnation.\u003c/p\u003e","description":"","filename":"fig7.png","url":"https://assets-eu.researchsquare.com/files/rs-6880184/v1/d0a9338b2c59f64749eb7862.png"},{"id":85018304,"identity":"4a5cd5ff-6cd1-4a84-b10e-335eb7c8d011","added_by":"auto","created_at":"2025-06-20 03:45:15","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":20072213,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of the electrospun cellulose acetate membranes after filtration of an aqueous dispersion of 2.0 μm diameter PS microparticles: (A) as-prepared electrospun CA membrane, (B) hot-pressed electrospun membrane, (C) hot-pressed membrane functionalized with 1 wt% CNC, (D) hot-pressed membrane functionalized with 3 wt% CNC, (E) hot-pressed membrane functionalized with 1 wt% CNC\u003csub\u003eTEMPO\u003c/sub\u003e, and (F) hot-pressed membrane functionalized with 3 wt% CNC\u003csub\u003eTEMPO\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"fig8.png","url":"https://assets-eu.researchsquare.com/files/rs-6880184/v1/a68f4e6090194779333288d0.png"},{"id":85018296,"identity":"ff1dfd91-7ad4-4f87-a3e2-49d091983a75","added_by":"auto","created_at":"2025-06-20 03:45:13","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":2363490,"visible":true,"origin":"","legend":"\u003cp\u003eImage of the filtrate and membranes collected after the filtration of MB solution through the different cellulose acetate membranes.\u003c/p\u003e","description":"","filename":"fig9.png","url":"https://assets-eu.researchsquare.com/files/rs-6880184/v1/98a2f27817b5a8a42895072b.png"},{"id":90345050,"identity":"9eeac6fa-9014-4ae7-9df4-82d0f580ac7d","added_by":"auto","created_at":"2025-09-01 16:09:48","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":60711864,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6880184/v1/20647bb0-12a7-4d54-bdd0-7debe2d2026c.pdf"},{"id":85018301,"identity":"ab8af160-7ed6-448a-8c2c-14b9748ac024","added_by":"auto","created_at":"2025-06-20 03:45:14","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":24003627,"visible":true,"origin":"","legend":"","description":"","filename":"SISaralegi.docx","url":"https://assets-eu.researchsquare.com/files/rs-6880184/v1/486dfe531e7fa0901c9699f0.docx"},{"id":85018306,"identity":"140e9f55-f954-469e-88a9-554bef06ae9e","added_by":"auto","created_at":"2025-06-20 03:45:15","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":120783,"visible":true,"origin":"","legend":"","description":"","filename":"Table3Contactangleanddropfiltrationtimeofuntreated.docx","url":"https://assets-eu.researchsquare.com/files/rs-6880184/v1/dcf02fe75dc744d7eb0b2756.docx"},{"id":85018295,"identity":"24839bf5-30cb-45e6-8cdd-bf752d24c0e4","added_by":"auto","created_at":"2025-06-20 03:45:13","extension":"tiff","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":1290045,"visible":true,"origin":"","legend":"","description":"","filename":"Graphicalabstrac.tiff","url":"https://assets-eu.researchsquare.com/files/rs-6880184/v1/72d6ee33cdf8b398bb78cbc1.tiff"}],"financialInterests":"No competing interests reported.","formattedTitle":"Enhanced water filtration performance in electrospun cellulose acetate membranes via TEMPO-mediated cellulose nanocrystal incorporation and hot pressing","fulltext":[{"header":"Introduction","content":"\u003cp\u003eNowadays, access to pure and sustainable water stands as a critical imperative for both living organisms and the advancement of human society. The world is facing with tough global challenges, considering shortage of freshwater and environmental pollution one of the most important challenges [1]. Over the past few decades, water pollution has surged to the forefront of environmental concerns, propelled by rapid industrialization, burgeoning population, mismanagement of water resources, and inadequate waste disposal practices [2]. The repercussions of increased discharges from municipal and industrial wastewater, intensified agricultural activities, and diminished river dilution capacities pose a growing threat to water quality [3]. By the year 2100, an estimated 5.5 billion individuals globally may face exposure to contaminated water [4]. Wastewater treatment facilities, comprising primary, secondary, and tertiary stages, play a pivotal role in mitigating these challenges [5]. However, the release of diverse harmful pollutants into water bodies, including heavy metals, pharmaceuticals, personal care products, pesticides, and microplastics, continues to imperil the ecological balance [6\u0026ndash;8]. Despite advancements in treatment processes, the inefficiency in removing microparticles smaller than 100 \u0026mu;m and harmful pollutants, raises concerns about their potential long-term impact on the environment [9\u0026ndash;11].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis scientific article addresses the intricate landscape of water pollution, focusing on the often-overlooked challenge of microparticle removal from wastewater effluents. While conventional wastewater treatment plants exhibit high efficacy in removing larger particles, the escape of smaller microparticles, often laden with harmful pollutants such as heavy metals, persistent organic compounds, and toxic additives, poses a direct route for their entry into the environment [12]. These contaminants can adsorb onto the surface of microparticles, facilitating their persistence and bioaccumulation in aquatic ecosystems. Although the residual fraction of these microparticles may be minor, it can still contribute significantly to long-term environmental pollution, presenting risks to both ecological and human health [12].\u003c/p\u003e\n\u003cp\u003eRecognizing the limitations of current wastewater treatment methodologies, this study delves into advanced approaches, with a particular emphasis on membrane technologies. Despite their pivotal role in water purification, membrane technologies face technical barriers such as high energy demand and fouling-related performance reduction [13\u0026ndash;16]. In this context, the exploration of biopolymers, specifically cellulose and its nanoscale derivatives, cellulose nanocrystals (CNC) and cellulose nanofibers (CNF), emerges as a promising avenue. The unique properties of cellulose, including superhydrophilicity and renewable sourcing, make it an attractive candidate for membrane applications [17\u0026ndash;19]. Hydrophilicity is critical in enhancing water permeability and minimizing fouling, as hydrophilic surfaces repel hydrophobic contaminants that typically adhere to and clog membrane pores. By improving hydrophilicity, membranes can sustain filtration efficiency for longer periods, reducing cleaning frequency and operational costs [20, 21].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe electrospinning technique, an advanced method for membrane fabrication, further enhances these properties by producing nanoscale fibers with high surface area and controlled porosity. This method allows for the creation of membranes with tailored thickness and morphology, leading to superior filtration performance. Furthermore, the process offers precise control over fiber diameter and arrangement, enabling the design of membranes that can selectively target contaminants based on size and surface characteristics [22, 23]. This flexibility is crucial in addressing the diverse challenges presented by various wastewater streams, including the effective removal of microparticles and harmful pollutants. Additionally, electrospinning facilitates the incorporation of various functional materials, such as CNCs, which can improve mechanical strength and further enhance hydrophilicity and antifouling characteristics. Overall, electrospinning offers a scalable and efficient approach to developing high-performance membranes suitable for advanced water treatment applications [24].\u003c/p\u003e\n\u003cp\u003eThus, this article focuses on the development of cellulose acetate membranes through electrospinning\u0026mdash;a cutting-edge processing technique. The membranes are designed to serve as efficient water filters, leveraging the benefits of cellulose while addressing challenges associated with mechanical strength, pore structure control, and layer affinity in hybrid membranes [25, 26]. The study aims to optimize electrospinning parameters and cellulose acetate solution composition to achieve membranes with superior efficiency, which will be further functionalized with CNCs and TEMPO-oxidized CNCs to enhance hydrophilicity and promote selective removal of charged pollutants. Additionally, the membranes will undergo hot pressing to improve their mechanical properties and refine pore characteristics. The comprehensive characterization and evaluation of these membranes will shed light on their potential for size exclusion, adsorption, and antifouling functionalities, particularly in removing PS microparticles within the 0.5-2 \u0026mu;m range and methylene blue dye as a model for charged contaminants. This research aims to contribute valuable insights to the ongoing discourse on water quality and provide innovative solutions to the evolving challenges in wastewater treatment.\u003c/p\u003e"},{"header":"EXPERIMENTAL","content":"\u003cp\u003e\u003cstrong\u003eMaterials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCellulose acetate powder (CA, Mn 50,000 Da), acetone (98%), glacial acetic acid (99%), and polystyrene (PS) particles with diameters of 0.5 and 2 µm were obtained from Sigma-Aldrich, USA. Cellulose nanocrystals, provided by the University of Maine (Lot 2018-FPL-CNC-117, with a sulfur content of 1.0 wt.% as indicated by the supplier), were used as reinforcement. Sodium hypochlorite (15%) and hydrochloric acid (37%, ACS reagent) were provided by Scharlau. The TEMPO reagent (2,2,6,6-tetramethylpiperidine-1-oxyl) (98%), hydrochloric acid, sodium bromide, sodium chloride and sodium hydroxide were purchased from Sigma-Aldrich, while methylene blue was sourced from Panreac Chemical.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eElectropinning of CA nanofibers\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCA nanofibers mats were fabricated by electrospinning of different CA solutions. Solutions with concentrations of 8, 10 and 12 wt.% CA were prepared in different volumetric ratios of acetone/acetic acid, specifically 1:2, 1:1, 2:1, 3:1 and 4:1. Each solution was subjected to magnetic stirring for 12 h at room temperature to ensure their homogeneity. The electrospinning process was carried out using Fluidnatek LE-10 equipment. The voltage and flow rate were optimized to achieve the best fiber formation, while maintaining a constant distance of 15 cm between the syringe needle and the flat collector.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTEMPO-mediated oxidation of cellulose nanocrystals\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTEMPO-mediated oxidation of CNCs was carried out according to the procedure described in the literature [19]. Briefly, 0.5 g of CNCs were dispersed in 50 mL of deionized water via sonication for 15 minutes. On the other hand, an aqueous solution containing 14.75 mg TEMPO and 162 mg NaBr in 50 mL of deionized water was prepared under constant stirring and then added dropwise to the CNC dispersion. Subsequently, 3 mL of a NaClO solution (12 wt.%) were gradually added to initiate the oxidation reaction. The pH of the suspension was maintained at 10 by adding 0.5 M NaOH, while the suspension was stirred continuously for 3 hours at room temperature. To conclude the oxidation process, the reaction was quenched with approximately 1 mL of ethanol, and the pH was adjusted to 7 using 0.5 M HCl. The oxidized CNCs (CNC\u003csub\u003eTEMPO\u003c/sub\u003e) suspension was then thoroughly cleaned by dialysis using Spectra Por®\u0026nbsp;6 membranes (MWCO 8000) for 7 days to remove any remaining reagents. Finally, the cleaned CNC\u003csub\u003eTEMPO\u003c/sub\u003e were freeze-dried for subsequent use.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMembrane preparation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSix different membranes were prepared from CA nanofiber mats. The first membrane was a 30 mm diameter circular sample taken directly from the electrospun CA nanofiber mat (MCA). The second was a similar membrane but subjected to hot-pressing at 100 °C and 20 bar (MCA-HP). The remaining four membranes were functionalized with CNC or CNC\u003csub\u003eTEMPO\u003c/sub\u003e. For these, 10 mL aqueous dispersions of CNC and CNC\u003csub\u003eTEMPO\u003c/sub\u003e at 1 and 3 wt.% were prepared, then filtered through 30 mm diameter circular samples taken from the electrospun CA mat. The amount of CNC and CNC\u003csub\u003eTEMPO\u003c/sub\u003e deposited on the membranes was measured by weighing the mats before and after the impregnation, allowing for an accurate measurement of the retention of both CNC and CNC\u003csub\u003eTEMPO\u003c/sub\u003e. Finally, these filtered samples were subsequently dried at room temperature and hot-pressed under the same conditions as before, resulting in the functionalized membranes labelled as MCA-1%CNC\u003csub\u003eTEMPO\u003c/sub\u003e-HP and MCA-3%CNC\u003csub\u003eTEMPO\u003c/sub\u003e-HP for those treated with 1 and 3 wt.% CNC\u003csub\u003eTEMPO\u003c/sub\u003e, respectively, and similarly MCA-1%CNC-HP and MCA-3%CNC-HP for those treated with CNC.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMembrane filtration and absorption performance\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFor the particle retention assessment, two aqueous dispersions of PS microparticles with diameters of 2 and 0.5 μm, both at a concentration of 0.05 wt.%, were prepared. A volume of 20 mL from each dispersion was filtered through the various membranes using a vacuum pump at a pressure of 0.2 bar. On the other hand, to evaluate the effectiveness of the membranes in removing charged pollutants, an aqueous methylene blue solution at a concentration of 25 ppm was filtered in static mode through the membranes, utilizing 15 mL of the dye solution. This methodology provided valuable insights into the membranes' filtration capabilities for both particle retention and the removal of charged contaminants.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCharacterization\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe viscosity of CA solutions was determined using a Haake Viscotester Rheometer (IQ RV 20) equipped with concentric cylinders (CC25 DIN/Ti), operating under a steady shear rate from 0.2 to 400 s⁻¹. All measurements were performed at room temperature with 15 mL of solution to maintain consistency across samples.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor structural analysis, CNCs and CNC\u003csub\u003eTEMPO\u003c/sub\u003e were characterized by X-ray diffraction (XRD), utilizing a Philips X'Pert PRO diffractometer with CuKα radiation (λ = 0.154 nm) at settings of 30 kV and 20 mA. Data was collected from 2θ = 5° to 70° in 0.02° steps, followed by smoothing and baseline correction to evaluate crystallinity and peak fitting. The crystallinity index (CrI) was calculated according to Segal’s method [27], based on the intensity of the peak at 22.6° and the intensity scattered by the amorphous part of the sample located at 18°.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"383\" height=\"85\"\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ewhere I\u003csub\u003e002\u003c/sub\u003e is the intensity of crystalline peak (22.6°) and I\u003csub\u003eam\u003c/sub\u003e is the intensity of amorphous peak (18°).\u003c/p\u003e\n\u003cp\u003eThe carboxylic content of CNC\u003csub\u003eTEMPO\u003c/sub\u003e was determined by conductometric titration using a GLP 31 CRISON conductometer with a CRISON 50 70 glass-platinum cell equipped with a Pt 1000 sensor. For the analysis, 32 mg of CNC\u003csub\u003eTEMPO\u003c/sub\u003e were dispersed in 154 mL of water via ultrasonication. Then, 2.5 mL of 0.02 M NaCl was added, and the mixture was stirred with a magnetic stirrer. Next, 0.1 M HCl was added until the pH of the solution reached 2.91. The suspension was then titrated with 0.005 M NaOH until a pH of 10.8-11 was achieved. The carboxylic content was calculated based on the conductivity curve, using the following equation [28]:\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"RESULT AND DISCUSSION","content":"\u003cp\u003e\u003cstrong\u003eTEMPO-mediated oxidation of cellulose nanocrystals\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe carboxyl group content of CNC\u003csub\u003eTEMPO\u003c/sub\u003e was determined by conductometric titration, as described previously, yielding a value of 0.559 \u0026plusmn; 0.037 mmol/g. This moderate carboxylation level indicates that a substantial portion of the hydroxymethyl groups on the CNC surface was converted to carboxyl groups through TEMPO oxidation, enhancing surface reactivity without compromising the structural integrity of the CNCs. Such a carboxyl content is advantageous for applications requiring improved dispersibility, hydrophilicity, and compatibility with other materials, making these modified CNCs suitable for use in filtration to improve pollutant capture via increased surface charge.\u003c/p\u003e\n\u003cp\u003eThe chemical structure modification performed on the surface of CNCs by TEMPO was analyzed through FTIR spectroscopy, as shown in Fig. 1. The spectra of CNC and CNC\u003csub\u003eTEMPO\u003c/sub\u003e display distinct differences related to the oxidation of hydroxyl groups on the CNCs. The FTIR spectrum of unmodified CNC displays several characteristic bands. The broad absorption bands at 3330 and 3280 cm⁻\u0026sup1; correspond to the stretching vibrations of the hydroxyl (-OH) groups, indicative of the extensive hydrogen bonding within the cellulose structure. The band observed at 2900 cm⁻\u0026sup1; is attributed to C-H stretching vibrations. Additionally, a band near 1645 cm⁻\u0026sup1; is associated with absorbed water, while the band at 1429 cm⁻\u0026sup1; represents the symmetric bending of CH₂ groups. Furthermore, the bands at 1160 and 897 cm⁻\u0026sup1; correspond to the asymmetric stretching vibration of the C-O-C bonds in \u0026beta;-glycosidic linkages, and the bands at 1060 and 1030 cm⁻\u0026sup1; are associated with C-O-C stretching at the C6 position of the glucose rings [29\u0026ndash;31].\u003c/p\u003e\n\u003cp\u003eFollowing TEMPO oxidation, the CNC\u003csub\u003eTEMPO\u003c/sub\u003e spectrum exhibits notable changes, particularly with the emergence of bands at 1730 cm⁻\u0026sup1; and 1604 cm⁻\u0026sup1;, which are attributed to the carboxyl groups introduced through oxidation [32, 33]. The band at 1730 cm⁻\u0026sup1; corresponds to the protonated (COOH) form, whereas the band at 1604 cm⁻\u0026sup1; is linked to the carboxylate (COO⁻) form, indicating the presence of both protonated and deprotonated carboxyl groups depending on moisture and pH. A slight reduction in the intensity of the -OH stretching bands around 3330 cm⁻\u0026sup1;, along with a reduction in the C-H stretching band at 2900 cm⁻\u0026sup1;, further supports the conversion of hydroxyl groups to carboxyl groups via the TEMPO oxidation process [34, 35]. These FTIR results confirm a successful TEMPO-mediated oxidation, converting surface hydroxyl groups on CNCs to carboxyl groups, as evidenced by the distinct carboxyl-associated bands, which enhance the surface reactivity and potential application versatility of the modified CNCs.\u003c/p\u003e\n\u003cp\u003eThe main challenge in chemically modifying the surface of nanocellulose is achieving functionalization without altering its morphology, thereby preserving the crystal\u0026rsquo;s structural integrity and avoiding any polymorphic changes [19]. To examine whether TEMPO-mediated oxidation affected the crystal structure of CNCs, XRD analysis was conducted. The diffractograms in Fig. 2 display characteristic crystalline peaks at 15.2\u0026deg;, 16.7\u0026deg;, and 22.6\u0026deg;, which correspond to the ( ), ( ) and ( ) crystallographic planes, respectively, indicative of the typical cellulose I structure. The crystallinity index (CrI) of the cellulose nanocrystals was calculated using Segal\u0026rsquo;s method [27], which considers the peak intensity at 22.6\u0026deg; and the amorphous region intensity around 18\u0026deg;. The CrI was found to be approximately 86.7% for untreated CNCs and 86.2% for TEMPO-oxidized nanocrystals. This minor decrease in crystallinity suggests that the internal structure of the nanocrystals remains largely unaffected by the surface modification. Thus, despite the chemical modifications, the CNCs retain their original crystallinity and structural integrity.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOptimization of the electrospinning conditions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe viscoelastic properties of CA solutions are crucial in determining their electrospinning behaviour. A minimum polymer concentration is necessary to facilitate chain entanglement; below this threshold, the polymer chains merely overlap without entangling, which is essential for successful electrospinning [36]. The rheological behaviour of the solution is influenced by variations in concentration and plays a significant role in controlling the morphology of the electrospun fibers. Additionally, the choice of solvent or solvent mixture impacts these properties. Thus, solution viscosity emerges as a pivotal parameter affecting fiber formation and diameter [36].\u003c/p\u003e\n\u003cp\u003eFig. 3 illustrates the evolution of viscosity with shear rate for CA solutions with varying concentrations and acetone-to-acetic acid ratios. Solutions with three CA concentrations (8, 10, and 12 wt.%) and five solvent ratios of acetone/acetic acid (A:AA: 4:1, 3:1, 2:1, 1:1, and 1:2) were analysed. As can be seen, viscosity increases with CA concentration due to the greater chain entanglement of the polymer chains. Furthermore, for solutions with the same CA concentration, viscosity generally rises with a higher acetic acid content. This trend can be attributed to the hydrogen bonding interactions between the hydroxyl (-OH) groups of CA and acetic acid. In contrast as the acetone content increases, the overall -OH groups decrease, leading to the replacement of hydrogen bonding interactions by other weaker forces, such as dipole-dipole or dispersion interactions, resulting in a lower viscosity of the solutions.\u003c/p\u003e\n\u003cp\u003eOptical microscopy results (Supplementary Information (SI), Fig. S1) indicate that solutions with lower viscosities (e.g., 8 wt.% CA in any solvent ratio) failed to produce fibers due to insufficient entanglement of the polymer chains (Fig. S1a) [36]. Conversely, solutions with higher viscosities that contained elevated acetic acid concentrations also did not yield fibers, primarily due to inadequate solvent evaporation (Fig. S1b). In contrast, solutions with high CA concentrations and acetone contents successfully produced electrospun fibers (Fig. S1c).\u003c/p\u003e\n\u003cp\u003eFrom the analysis of viscosity and the preliminary optical microscopy images of the morphology of electrospun fibers, it can be inferred that the optimal viscosity for fiber formation from cellulose acetate in acetone and acetic acid solutions should fall within the range of 600-2300 mPa. Solutions outside of this viscosity range tend to produce fibers with defects. More specifically, the optimal viscosity for successful fiber creation is estimated to be between 1100-1900 mPa at a shear rate of 1.71 s⁻\u0026sup1; (at 1 mL/h flow rate). Solutions with CA concentrations of 10 and 12 wt.% CA demonstrated effective electrospinning within these parameters.\u003c/p\u003e\n\u003cp\u003eIn addition to the influence of CA concentration and acetone to acetic acid ratio, the effect of flow rate and relative humidity were also examined by OM and SEM. Thus, fiber diameter was found to vary with flow rate, with higher flow rates producing larger fiber diameters. For instance, a 10 wt.% CA solution in a A:AA (2:1) solvent ratio generated fibers with an average diameter of 608 \u0026plusmn; 235 nm at a flow rate of 10 mL/h, but at reduced flow rates of 5 or 3 mL/h, beaded fibers were formed (Fig. S1d). Similarly, a 12 wt.% CA solution in A:AA (2:1) ratio produced fibers with diameters of 480 \u0026plusmn; 295 nm and 453 \u0026plusmn; 231 nm at 5 and 3 mL/h, respectively, whereas in A:AA (1:1) solvent ratio at 3 mL/h generated fibers of 360 \u0026plusmn; 193 nm (Fig. S1e).\u003c/p\u003e\n\u003cp\u003eThe relative humidity during electrospinning played also a critical role in solvent evaporation and fiber formation. Under high humidity (60-75%), solvents did not fully evaporate, leading to partial fiber formation as shown in Fig. 4. Thus, both solution composition and electrospinning conditions are essential for producing uniform, bead-free CA fibers.\u003c/p\u003e\n\u003cp\u003eSolutions with higher acetone concentrations and lower flow rates demonstrated better suitability for common laboratory humidity levels (40-75%). Thus, fiber formation was successful with 12 wt.% CA solutions in A:AA (3:1) and A:AA (4:1) at flow rates of 1, 3, and 5 mL/h within the same humidity range. Although fibers were produced under all conditions, the smallest diameters were obtained at a flow rate of 1 mL/h, yielding average fiber diameters of 566 \u0026plusmn; 218 nm and 399 \u0026plusmn; 221 nm for 12 wt.% CA solutions in 3:1 and 4:1 A:AA, respectively (Fig. 5).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 1 provides a summary of the properties of the electrospun CA solutions, including concentration, solvent ratios, and electrospinning conditions, as well as diameter values of those analyzed by SEM.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e1\u003c/strong\u003e CA concentration and solvent ratios of the electrospun solutions, process parameters such as flow rate and humidity, and morphological characteristics observed by OM or SEM and diameters of the fibers measured by SEM.\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"657\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCA concentration (wt.%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 99px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSolvent ratios (A:AA)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSEM/OM observation\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eHumidity\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFlow rate (mL/h)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eDiameter\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(nm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" style=\"width: 100px;\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 99px;\"\u003e\n \u003cp\u003e1:2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eOnly beads, no fiber\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 99px;\"\u003e\n \u003cp\u003e1:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eOnly beads, no fiber\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 99px;\"\u003e\n \u003cp\u003e2:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eFibers with numerous beads\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"8\" style=\"width: 100px;\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 99px;\"\u003e\n \u003cp\u003e1:2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eFibers with large beads\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 99px;\"\u003e\n \u003cp\u003e1:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eFibers with small beads\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" style=\"width: 99px;\"\u003e\n \u003cp\u003e2:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eUniform fibers, no beads\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e608 \u0026plusmn; 235\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eFlat fibers with solvent remains and beads\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eFlat fibers with solvent remains and beads\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eFlat fibers with solvent remains and small beads\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 99px;\"\u003e\n \u003cp\u003e3:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eFibers with elongated beads\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e40-70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 99px;\"\u003e\n \u003cp\u003e4:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eFibers with small beads\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e40-70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"8\" style=\"width: 100px;\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 99px;\"\u003e\n \u003cp\u003e1:2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eFibers with large beads\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 99px;\"\u003e\n \u003cp\u003e1:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eFlat fibers, no beads\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e360 \u0026plusmn; 193\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eFlat fibers with solvent remains and beads\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" style=\"width: 99px;\"\u003e\n \u003cp\u003e2:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eHomogeneous, bead-free fibers\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e453 \u0026plusmn; 231\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eHomogeneous, bead-free fibers\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e480 \u0026plusmn; 295\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eFlat fibers with solvent remains\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 99px;\"\u003e\n \u003cp\u003e3:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eSmooth and uniform fibers, no beads\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e40-70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e566 \u0026plusmn; 218\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 99px;\"\u003e\n \u003cp\u003e4:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 217px;\"\u003e\n \u003cp\u003eHomogeneous, uniform, bead-free fibers\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e40-70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e399 \u0026plusmn; 221\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eIn conclusion, the optimal conditions for producing continuous, bead-free CA nanofibers were identified using a solution of 12 wt.% CA in a 4:1 A:AA ratio. The process parameter included an applied voltage of 10 kV, a flow rate of 1 mL/h, a tip-to-collector distance of 15 cm, and a relative humidity range of 35-70%. Under these conditions, the solution was electrospun for 7 hours onto aluminum foil to create a consistent electrospun mat.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThermal treatment and functionalization of membranes\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn addition to optimizing the electrospinning conditions, further treatment was applied to improve the structural and mechanical properties of the CA membranes. While the electrospun CA fibers initially exhibited a homogeneous, continuous structure with high porosity, subjecting the membranes to hot pressing at 100 \u0026deg;C resulted in a denser configuration. This heat and pressure treatment induced plastic deformation, transforming the fibers\u0026apos; cross-sections from circular to more ribbon-like shapes (Fig. 6).\u003c/p\u003e\n\u003cp\u003eThe hot-pressing process proved essential in enhancing the mechanical durability of the CA fiber mats and reducing pore size. This densification occurred not due to melting but rather due to plastic deformation of the CA fibers, given that the glass transition and melting temperatures of cellulose acetate are 198-205 \u0026deg;C and 224-230 \u0026deg;C, respectively [29]. Consequently, hot pressing promoted increased adhesion among the CA fibers, producing membranes with improved structural integrity suitable for applications requiring more compact, mechanically resilient materials.\u003c/p\u003e\n\u003cp\u003eThe thermal treatment of CA membranes provided a compacted structure that enhanced mechanical durability, but for further functionality, the surface morphology was modified through the incorporation of CNCs and CNC\u003csub\u003eTEMPO\u003c/sub\u003e. Thus, after the impregnation and the thermal treatment, the surface morphology of functionalized CA membranes was investigated using SEM imaging (Fig. 7). In most cases, the CNCs altered the morphology within the fiber interstices, though the underlying fibrous structure remained visible across all functionalized mats [37].\u003c/p\u003e\n\u003cp\u003eIt was observed that the impregnation with a 5 wt.% CNC solution led to a significant loss of fibrous morphology in the CA membrane (Fig. S2). Morphological changes were particularly prominent on the direct contact surface between the membrane and the CNC dispersion, likely due to prolonged interaction time, which allowed more extensive bonding between the CNCs and CA nanofibers. Therefore, the maximum CNC concentration used was limited to 3 wt.%\u003c/p\u003e\n\u003cp\u003eComparisons between membranes treated with 1 and 3 wt.% CNC concentrations revealed a more pronounced morphological change with the use of 3 wt.% CNC dispersion than with 1 wt.% CNC. This observation suggests that a higher concentration of CNC leads to a greater degree of interaction between the nanocrystals and the cellulose acetate fibers, resulting in enhanced structural integration. The increased amount of nanocrystals likely contributes to the formation of a denser and more interconnected network within the membrane, thereby altering its overall morphology. Additionally, the greater retention of CNC at the higher concentration facilitates more effective surface coverage, which can improve the mechanical and functional properties of the membranes. Regarding the TEMPO-oxidized CNCs, they exhibited an even stronger affinity for CA fibers, resulting in a higher deposition rate. This behaviour was confirmed through SEM observations and weight measurements taken after impregnation (Table 2), which demonstrated a retention rate that was 10-20% higher for TEMPO-oxidized CNCs compared to untreated CNCs. Furthermore, increasing the concentration of the CNC dispersion led to greater retention overall.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003cstrong\u003e.\u003c/strong\u003e Retention of nanocrystals impregnated in electrospun CA membranes, expressed in milligrams (mg) for different concentrations of CNC and CNC\u003csub\u003eTEMPO\u003c/sub\u003e.\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 140px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e1 wt.% CNC\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e3 wt.% CNC\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e1 wt.% CNC\u003csub\u003eTEMPO\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e3 wt.% CNC\u003csub\u003eTEMPO\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 140px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNanocrystal retention (mg)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e5.5\u0026nbsp;\u0026plusmn;\u0026nbsp;2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e20.0\u0026nbsp;\u0026plusmn;\u0026nbsp;7.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e6.7\u0026nbsp;\u0026plusmn;\u0026nbsp;1.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e22.4\u0026nbsp;\u0026plusmn;\u0026nbsp;10.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eSurface wettability of membranes\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe surface hydrophilicity of CA electrospun membranes, together with hot-pressed and functionalized membranes, was analyzed using WCA measurements (Table 3). Although CA is inherently hydrophilic, the MCA membrane exhibited a hydrophobic contact angle of 104 \u0026plusmn; 1\u0026deg;. This increased hydrophobicity can be attributed to the rough nanofibrous structure created during the electrospinning process. In contrast, the MCA-HP membrane displayed hydrophilic behaviour, with a WCA of 55 \u0026plusmn; 2\u0026deg;. This change in hydrophilicity is due to the transformation of the fibers from a circular shape to a more flattened configuration, as illustrated in Fig. 6 and Fig. 7, allowing for greater contact between the CA membrane and water. Additionally, the surface roughness initially provided by the electrospun nanofibers diminishes, restoring the hydrophilic characteristics of the cellulose acetate. The water droplets filtered through the MCA and MCA-HP membranes in 100 and 5 minutes, respectively.\u003c/p\u003e\n\u003cp\u003eSurface treatments with CNC and TEMPO-oxidized CNCs further enhanced the hydrophilicity of the membranes. The measured WCAs for the treated membranes were 43 \u0026plusmn; 4\u0026deg; for MCA 1%CNC-HP, 37 \u0026plusmn; 1\u0026deg; for MCA 3%CNC-HP, 44 \u0026plusmn; 1\u0026deg; for MCA-1%CNC\u003csub\u003eTEMPO\u003c/sub\u003e-HP, and 37 \u0026plusmn; 2\u0026deg; for MCA-3%CNC\u003csub\u003eTEMPO\u003c/sub\u003e-HP. Moreover, water droplets were filtered through these membranes within approximately 20-30 seconds, demonstrating a significantly higher flux and anti-fouling capacity compared to the untreated membranes. These results indicate that the incorporation of CNC and TEMPO-oxidized CNC not only modifies the hydrophilic properties of the membranes but also enhances their functional performance, making them suitable for applications that require efficient water management and reduced fouling, such as in filtration and separation processes.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEfficiency of CA membranes in filtration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe particle size filtration efficiency of electrospun cellulose acetate membranes was evaluated using microparticle analysis performed by UV-Vis spectroscopy, with results summarized in Table 4. Additionally, SEM images of the membranes after filtration of 2.0 \u0026mu;m diameter PS microparticles were captured. As it can be seen in Table 4, the thickness of the electrospun CA membranes was also measured and varied significantly across different treatments, influencing their filtration performance. For instance, MCA membrane exhibited the greatest thickness at 108 \u0026plusmn; 8 \u0026mu;m, while MCA-HP membranes showed a reduced thickness of 77 \u0026plusmn; 13 \u0026mu;m. Notably, the functionalized membranes with 1% CNC and 3% CNC had thicknesses of 74 \u0026plusmn; 44 \u0026mu;m and 90 \u0026plusmn; 41 \u0026mu;m, respectively.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe analysis revealed that the electrospun CA membrane exhibited limited rejection of both 2.0 \u0026mu;m (Fig. 8a) and 0.5 \u0026mu;m PS particles, with rejection rates of 33\u0026nbsp;\u0026plusmn; 1% and 5.0\u0026nbsp;\u0026plusmn; 1%, respectively. However, the hot-pressing and functionalization treatments applied to the membranes resulted in a reduction in surface area and pore size, as evidenced previously by SEM images, which in turn improved filtration performance. Specifically, the rejection efficiency of the hot-pressed electrospun CA membranes increased to 77\u0026nbsp;\u0026plusmn; 4% for 2.0 \u0026mu;m particles (Fig. 8b) and 75\u0026nbsp;\u0026plusmn; 5% for 0.5 \u0026mu;m particles, maintaining a comparable retention efficiency. It appears that the pore sizes in the membranes are not completely uniform, leading to some pores exceeding 2.0 \u0026mu;m in diameter.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e4\u003c/strong\u003e Membrane thickness and rejection percentages of electrospun CA membranes for PS microparticles of 2.0 \u0026mu;m and 0.5 \u0026mu;m diameter.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMembrane\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 190px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMembrane thickness (\u003c/strong\u003e\u003cstrong\u003e\u0026mu;\u003c/strong\u003e\u003cstrong\u003em)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 193px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eRejection % of PS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 101px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e2\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e\u0026mu;\u003c/strong\u003e\u003cstrong\u003em\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 89px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.5\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e\u0026mu;\u003c/strong\u003e\u003cstrong\u003em\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 101px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e2\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e\u0026mu;\u003c/strong\u003e\u003cstrong\u003em\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.5\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e\u0026mu;\u003c/strong\u003e\u003cstrong\u003em\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMCA\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e\n \u003cp\u003e108\u0026nbsp;\u0026plusmn; 8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003e\n \u003cp\u003e113\u0026nbsp;\u0026plusmn;\u0026nbsp;6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e\n \u003cp\u003e33\u0026nbsp;\u0026plusmn; 1%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e5\u0026nbsp;\u0026plusmn; 1%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMCA-HP\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e\n \u003cp\u003e77\u0026nbsp;\u0026plusmn;\u0026nbsp;13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003e\n \u003cp\u003e44\u0026nbsp;\u0026plusmn; 8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e\n \u003cp\u003e77\u0026nbsp;\u0026plusmn; 4%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e75\u0026nbsp;\u0026plusmn; 5%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMCA-1%CNC-HP\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e\n \u003cp\u003e74 \u0026plusmn; 44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003e\n \u003cp\u003e50\u0026nbsp;\u0026plusmn; 5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e\n \u003cp\u003e89\u0026nbsp;\u0026plusmn; 5%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e10\u0026nbsp;\u0026plusmn; 5%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMCA-3%CNC-HP\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e\n \u003cp\u003e90 \u0026plusmn; 41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003e\n \u003cp\u003e61\u0026nbsp;\u0026plusmn; 7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e\n \u003cp\u003e19\u0026nbsp;\u0026plusmn; 4%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e40\u0026nbsp;\u0026plusmn; 46%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMCA-1%CNC\u003csub\u003eTEMPO\u003c/sub\u003e-HP\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e\n \u003cp\u003e89 \u0026plusmn; 35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003e\n \u003cp\u003e72\u0026nbsp;\u0026plusmn; 19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e\n \u003cp\u003e89\u0026nbsp;\u0026plusmn; 2%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e11\u0026nbsp;\u0026plusmn; 2%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMCA-3%CNC\u003csub\u003eTEMPO\u003c/sub\u003e-HP\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e\n \u003cp\u003e99\u0026nbsp;\u0026plusmn; 28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 89px;\"\u003e\n \u003cp\u003e76\u0026nbsp;\u0026plusmn; 8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 101px;\"\u003e\n \u003cp\u003e92\u0026nbsp;\u0026plusmn; 3%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e17\u0026nbsp;\u0026plusmn; 10%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eCA membranes infiltrated with 1 wt% CNC exhibited enhanced rejection of 2.0 \u0026mu;m PS microparticles (Fig. 8c), although rejection efficiency decreased with higher CNC concentrations (Fig. 8d). Additionally, the rejection of 0.5 \u0026mu;m PS microparticles was reduced compared to the hot-pressed membranes. This decrease in efficiency has been attributed to the potential formation of micrometric holes during the hot-pressing process. The incorporation of CNCs significantly increases the stiffness of the membrane due to the reinforcing properties of these nanoparticles, which may lead to increased susceptibility to breakage during subsequent pressing treatments. Consequently, higher CNC content or lower microparticle sizes may compromise filtration performance.\u003c/p\u003e\n\u003cp\u003eIn contrast, CA membranes infiltrated with TEMPO oxidized CNC demonstrated the highest rejection of 2.0 \u0026mu;m PS microparticles at 3 wt% CNC\u003csub\u003eTEMPO\u003c/sub\u003e, achieving a rejection efficiency of 92% (Fig. 8e and 8f). This improvement is likely due to the reduction in pore size resulting from the surface treatments. However, microcracks in the pores were also observed, which may compromise the filtration efficiency for microparticles smaller than 2 \u0026mu;m.\u003c/p\u003e\n\u003cp\u003eMoreover, the functionality of the membranes and their interaction with water pollutants were evaluated through the filtration of an aqueous solution of MB. This solution was utilized to assess the viability of the membranes against charged specific contaminants typically found in wastewater. Following the filtration of the MB solution through the membranes, a visual reduction in the intensity of the methylene blue in the filtrate and noticeable color retention on the membranes (Fig. 9) were observed. The filtered solutions were subsequently analyzed by UV-Vis spectroscopy, with results presented in Table 5.\u003c/p\u003e\n\u003cp\u003eAs shown in Table 5, the as-prepared CA membrane, the hot-pressed membranes, and those infiltrated with 1 wt% CNC exhibited comparable filtration efficiencies, indicating that these treatments did not significantly affect the retention efficiency of MB. However, when the CNC content was increased to 3 wt%, the retention efficiency improved due to the electrostatic interactions between the cellulose nanoparticles and methylene blue. These interactions are attributed to the sulphate groups present in the CNCs, which engage with the cationic groups of MB.\u003c/p\u003e\n\u003cp\u003eConversely, the carboxyl groups on the surface of oxidized CNCs enhance the attraction of cationic methylene blue molecules. As a result, MCA-1%CNC\u003csub\u003eTEMPO\u003c/sub\u003e-HP membranes achieved an impressive MB adsorption efficiency of 90%, while MCA-3%CNC\u003csub\u003eTEMPO\u003c/sub\u003e-HP membranes reached a maximum adsorption efficiency of 95%. These findings underscore the effectiveness of these membranes in removing specific contaminants through charge interactions, particularly with carboxyl groups.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e5\u003c/strong\u003e Methylene blue retention efficiency of electrospun cellulose acetate membranes.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 149px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMembrane\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 147px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMembrane thickness (\u003c/strong\u003e\u003cstrong\u003e\u0026mu;m)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 131px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMB adsortion (ppm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 154px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMB adsortion efficiency\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 149px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMCA\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 147px;\"\u003e\n \u003cp\u003e111 \u0026plusmn; 31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 154px;\"\u003e\n \u003cp\u003e69%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 149px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMCA-HP\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 147px;\"\u003e\n \u003cp\u003e43 \u0026plusmn; 21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 154px;\"\u003e\n \u003cp\u003e69%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 149px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMCA-1%CNC-HP\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 147px;\"\u003e\n \u003cp\u003e35 \u0026plusmn; 11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 154px;\"\u003e\n \u003cp\u003e66%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 149px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMCA-3%CNC-HP\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 147px;\"\u003e\n \u003cp\u003e45 \u0026plusmn; 15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 154px;\"\u003e\n \u003cp\u003e89%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 149px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMCA-1%CNC\u003csub\u003eTEMPO\u003c/sub\u003e-HP\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 147px;\"\u003e\n \u003cp\u003e53 \u0026plusmn; 12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 154px;\"\u003e\n \u003cp\u003e90%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 149px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMCA-3%CNC\u003csub\u003eTEMPO\u003c/sub\u003e-HP\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 147px;\"\u003e\n \u003cp\u003e50 \u0026plusmn; 5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 154px;\"\u003e\n \u003cp\u003e95%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"},{"header":"CONCLUSIONS","content":"\u003cp\u003eThe study demonstrates that cellulose acetate membranes with enhanced water filtration performance can be fabricated through a combination of optimized electrospinning, hot pressing, and nanocrystal functionalization. A 12 wt.% CA solution in a 4:1 acetone/acetic acid mixture was successfully electrospun under controlled conditions, yielding uniform, bead‐free nanofibrous mats. Subsequent hot pressing at 100 \u0026deg;C and 20 bar transformed these mats into compact membranes with improved mechanical integrity, suitable for demanding filtration applications.\u003c/p\u003e\n\u003cp\u003eFunctionalization with cellulose nanocrystals and TEMPO-oxidized CNCs proved to be a critical step in enhancing the membrane properties. The TEMPO oxidation process produced a carboxyl content of 0.56 \u0026plusmn; 0.04 mmol/g, which facilitated improved dispersion and integration of the nanocrystals within the CA matrix. This modification was reflected in a significant reduction of the water contact angle from 104\u0026deg; in the as-spun membranes to as low as 37\u0026deg; in membranes treated with 3 wt.% CNCTEMPO, thereby increasing the hydrophilicity and promoting faster water permeation.\u003c/p\u003e\n\u003cp\u003eFiltration performance was notably enhanced as a result of these processing steps. While hot pressing alone increased the rejection efficiency to approximately 77% for 2.0 \u0026mu;m particles and 75% for 0.5 \u0026mu;m particles, the additional incorporation of CNCTEMPO further improved the rejection efficiency, reaching up to 92% for 2.0 \u0026mu;m particles. Moreover, the presence of carboxyl groups contributed to enhanced electrostatic interactions with cationic contaminants, resulting in methylene blue removal efficiencies as high as 95%.\u003c/p\u003e\n\u003cp\u003eIn summary, the experimental results confirm the initial hypothesis. Membranes functionalized with CNCTEMPO and subjected to hot pressing exhibited a significantly lower water contact angle (down to 37\u0026deg;), enhanced rejection efficiencies (up to 92% for 2.0 \u0026mu;m particles), and improved mechanical properties compared to the as-spun membranes. These findings validate that the incorporation of TEMPO-oxidized cellulose nanocrystals effectively enhances water filtration performance, underscoring the novelty and potential of this approach for sustainable water treatment applications. Future work is anticipated to further explore detailed mechanical characterizations and extended pollutant testing.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements:\u0026nbsp;\u003c/strong\u003eFinancial support from the Spanish Ministry of Science and Innovation and State Research Agency (MCIN/AEI/10.13039/501100011033) in the frame of PID2022-140119OB-I00 project and from the Basque Country Government in the frame of 00028-IDA2019-38 and Grupos Consolidados (IT-1690-22) is gratefully acknowledged. The authors also acknowledge the Macrobehavior-Mesostructure-Nanotechnology SGIker unit of the University of the Basque Country (UPV/EHU).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eShirazi MMA, Bazgir S, Meshkani F (2020) A novel dual-layer, gas-assisted electrospun, nanofibrous SAN4-HIPS membrane for industrial textile wastewater treatment by direct contact membrane distillation (DCMD). J Water Process Eng 36:101315. https://doi.org/10.1016/j.jwpe.2020.101315\u003c/li\u003e\n\u003cli\u003eTlili I, Alkanhal TA (2019) Nanotechnology for water purification: Electrospun nanofibrous membrane in water and wastewater treatment. J Water Reuse Desalin 9:232\u0026ndash;247. https://doi.org/10.2166/wrd.2019.057\u003c/li\u003e\n\u003cli\u003eUNESCO (2020) The United Nations world water development report 2020: water and climate change\u003c/li\u003e\n\u003cli\u003eTozer L (2023) Water pollution \u0026lsquo;timebomb\u0026rsquo; threatens global health. Nature. https://doi.org/10.1038/d41586-023-02337-7\u003c/li\u003e\n\u003cli\u003eMason SA, Garneau D, Sutton R, et al (2016) Microplastic pollution is widely detected in US municipal wastewater treatment plant effluent. Environ Pollut 218:1045\u0026ndash;1054. https://doi.org/10.1016/j.envpol.2016.08.056\u003c/li\u003e\n\u003cli\u003eZdarta J, Jesionowski T, Pinelo M, et al (2022) Free and immobilized biocatalysts for removing micropollutants from water and wastewater: Recent progress and challenges. Bioresour Technol 344:126201. https://doi.org/10.1016/j.biortech.2021.126201\u003c/li\u003e\n\u003cli\u003eSandin G, Peters GM (2018) Environmental impact of textile reuse and recycling \u0026ndash; A review. J Clean Prod 184:353\u0026ndash;365. https://doi.org/10.1016/j.jclepro.2018.02.266\u003c/li\u003e\n\u003cli\u003eHairom NHH, Soon CF, Mohamed RMSR, et al (2021) A review of nanotechnological applications to detect and control surface water pollution. Environ Technol Innov 24:102032. https://doi.org/10.1016/j.eti.2021.102032\u003c/li\u003e\n\u003cli\u003eWang K, Ma Q, Wang SD, et al (2016) Electrospinning of silver nanoparticles loaded highly porous cellulose acetate nanofibrous membrane for treatment of dye wastewater. Appl Phys A Mater Sci Process 122:1\u0026ndash;10. https://doi.org/10.1007/s00339-015-9566-5\u003c/li\u003e\n\u003cli\u003eHu Y, Gong M, Wang J, Bassi A (2019) Current research trends on microplastic pollution from wastewater systems: a critical review. Rev Environ Sci Biotechnol 18:207\u0026ndash;230. https://doi.org/10.1007/s11157-019-09498-w\u003c/li\u003e\n\u003cli\u003eCarr SA, Liu J, Tesoro AG (2016) Transport and fate of microplastic particles in wastewater treatment plants. Water Res 91:174\u0026ndash;182. https://doi.org/10.1016/j.watres.2016.01.002\u003c/li\u003e\n\u003cli\u003ePrimpke S, Imhof H, Piehl S, et al (2017) Mikroplastik in der Umwelt. Chemie unserer Zeit 51:402\u0026ndash;412. https://doi.org/10.1002/ciuz.201700821\u003c/li\u003e\n\u003cli\u003eBarry MC, Hristovski K, Westerhoff P (2014) Membrane fouling by vesicles and prevention through ozonation. Environ Sci Technol 48:7349\u0026ndash;7356. https://doi.org/10.1021/es500435e\u003c/li\u003e\n\u003cli\u003eWang YN, Tang CY (2011) Fouling of nanofiltration, reverse osmosis, and ultrafiltration membranes by protein mixtures: The role of inter-foulant-species interaction. Environ Sci Technol 45:6373\u0026ndash;6379. https://doi.org/10.1021/es2013177\u003c/li\u003e\n\u003cli\u003eKim SR, Getachew BA, Kim JH (2017) In Situ Healing of Compromised Membranes via Polyethylenimine-Functionalized Silica Microparticles. Environ Sci Technol 51:12630\u0026ndash;12637. https://doi.org/10.1021/acs.est.7b03436\u003c/li\u003e\n\u003cli\u003eIhsanullah (2019) Carbon nanotube membranes for water purification: Developments, challenges, and prospects for the future. Sep Purif Technol 209:307\u0026ndash;337. https://doi.org/10.1016/j.seppur.2018.07.043\u003c/li\u003e\n\u003cli\u003eAnirudhan TS, Rejeena SR (2015) Photocatalytic Degradation of Eosin Yellow Using Poly(pyrrole-co-aniline)-Coated TiO \u003csub\u003e2\u003c/sub\u003e /Nanocellulose Composite under Solar Light Irradiation. J Mater 2015:1\u0026ndash;11. https://doi.org/10.1155/2015/636409\u003c/li\u003e\n\u003cli\u003eWu CN, Saito T, Yang Q, et al (2014) Increase in the water contact angle of composite film surfaces caused by the assembly of hydrophilic nanocellulose fibrils and nanoclay platelets. ACS Appl Mater Interfaces 6:12707\u0026ndash;12712. https://doi.org/10.1021/am502701e\u003c/li\u003e\n\u003cli\u003eLin N, Bruzzese C, Dufresne A (2012) TEMPO-oxidized nanocellulose participating as crosslinking aid for alginate-based sponges. ACS Appl Mater Interfaces 4:4948\u0026ndash;4959. https://doi.org/10.1021/am301325r\u003c/li\u003e\n\u003cli\u003eZhang R, Liu Y, He M, et al (2016) Antifouling membranes for sustainable water purification: Strategies and mechanisms. Chem Soc Rev 45:5888\u0026ndash;5924. https://doi.org/10.1039/c5cs00579e\u003c/li\u003e\n\u003cli\u003eSun Z, Chen F (2016) Hydrophilicity and antifouling property of membrane materials from cellulose acetate/polyethersulfone in DMAc. Int J Biol Macromol 91:143\u0026ndash;150. https://doi.org/10.1016/j.ijbiomac.2016.05.072\u003c/li\u003e\n\u003cli\u003eChen H, Huang M, Liu Y, et al (2020) Functionalized electrospun nanofiber membranes for water treatment: A review. Sci Total Environ 739:139944. https://doi.org/10.1016/j.scitotenv.2020.139944\u003c/li\u003e\n\u003cli\u003eCui J, Li F, Wang Y, et al (2020) Electrospun nanofiber membranes for wastewater treatment applications. Sep Purif Technol 250:117116. https://doi.org/10.1016/j.seppur.2020.117116\u003c/li\u003e\n\u003cli\u003eMokhena TC, Jacobs V, Luyt AS (2015) A review on electrospun bio-based polymers for water treatment. eXPRESS Polym Lett 9:839\u0026ndash;880. https://doi.org/0.3144/expresspolymlett.2015.79\u003c/li\u003e\n\u003cli\u003eXue J, Xie J, Liu W, Xia Y (2017) Electrospun Nanofibers: New Concepts, Materials, and Applications. Acc Chem Res 50:1976\u0026ndash;1987. https://doi.org/10.1021/acs.accounts.7b00218\u003c/li\u003e\n\u003cli\u003eGopi S, Balakrishnan P, Pius A, Thomas S (2017) Chitin nanowhisker (ChNW)-functionalized electrospun PVDF membrane for enhanced removal of Indigo carmine. Carbohydr Polym 165:115\u0026ndash;122. https://doi.org/10.1016/j.carbpol.2017.02.046\u003c/li\u003e\n\u003cli\u003eSegal L, Creely JJ, Martin AE, Conrad CM (1959) An Empirical Method for Estimating the Degree of Crystallinity of Native Cellulose Using the X-Ray Diffractometer. Text Res J 29:786\u0026ndash;794. https://doi.org/10.1177/004051755902901003\u003c/li\u003e\n\u003cli\u003eSaito T, Isogai A (2004) TEMPO-mediated oxidation of native cellulose. The effect of oxidation conditions on chemical and crystal structures of the water-insoluble fractions. Biomacromolecules 5:1983\u0026ndash;1989. https://doi.org/10.1021/bm0497769\u003c/li\u003e\n\u003cli\u003eTang Z, Lin X, Yu M, et al (2024) Recent advances in TEMPO-oxidized cellulose nanofibers: Oxidation mechanism, characterization, properties and applications. Int J Biol Macromol 259:129081. https://doi.org/10.1016/j.ijbiomac.2023.129081\u003c/li\u003e\n\u003cli\u003eGwon JG, Lee SY, Doh GH, Kim JH (2010) Characterization of chemically modified wood fibers using FTIR spectroscopy for biocomposites. J Appl Polym Sci 116:3212\u0026ndash;3219. https://doi.org/10.1002/app.31746\u003c/li\u003e\n\u003cli\u003e\u0026Scaron;irok\u0026yacute; J, Blackburn RS, Bechtold T, et al (2010) Attenuated total reflectance Fourier-transform Infrared spectroscopy analysis of crystallinity changes in lyocell following continuous treatment with sodium hydroxide. Cellulose 17:103\u0026ndash;115. https://doi.org/10.1007/s10570-009-9378-x\u003c/li\u003e\n\u003cli\u003eFraschini C, Chauve G, Bouchard J (2017) TEMPO-mediated surface oxidation of cellulose nanocrystals (CNCs). Cellulose 24:2775\u0026ndash;2790. https://doi.org/10.1007/s10570-017-1319-5\u003c/li\u003e\n\u003cli\u003eOkita Y, Fujisawa S, Saito T, Isogai A (2011) TEMPO-oxidized cellulose nanofibrils dispersed in organic solvents. Biomacromolecules 12:518\u0026ndash;522. https://doi.org/10.1021/bm101255x\u003c/li\u003e\n\u003cli\u003eCao X, Zhu M, Fan F, et al (2020) All-cellulose composites based on jute cellulose nanowhiskers and electrospun cellulose acetate (CA) fibrous membranes. Cellulose 27:1385\u0026ndash;1391. https://doi.org/10.1007/s10570-019-02880-5\u003c/li\u003e\n\u003cli\u003eLarraza I, Vadillo J, Santamaria-Echart A, et al (2020) The effect of the carboxylation degree on cellulose nanofibers and waterborne polyurethane/cellulose nanofiber nanocomposites properties. Polym Degrad Stab 173:109084. https://doi.org/10.1016/j.polymdegradstab.2020.109084\u003c/li\u003e\n\u003cli\u003eMajumder S, Matin MA, Sharif A, Arafat MT (2019) Understanding solubility, spinnability and electrospinning behaviour of cellulose acetate using different solvent systems. Bull Mater Sci 42:171. https://doi.org/10.1007/s12034-019-1857-6\u003c/li\u003e\n\u003cli\u003eGoetz LA, Naseri N, Nair SS, et al (2018) All cellulose electrospun water purification membranes nanotextured using cellulose nanocrystals. Cellulose 25:3011\u0026ndash;3023. https://doi.org/10.1007/s10570-018-1751-1\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Table","content":"\u003cp\u003eTable 3 is available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymers-and-the-environment","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jooe","sideBox":"Learn more about [Journal of Polymers and the Environment](https://www.springer.com/journal/10924)","snPcode":"10924","submissionUrl":"https://submission.nature.com/new-submission/10924/3","title":"Journal of Polymers and the Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"electrospun cellulose acetate membranes, water filtration, cellulose nanocrystals, TEMPO-mediated oxidation, nanocomposites membranes","lastPublishedDoi":"10.21203/rs.3.rs-6880184/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6880184/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAccess to clean water is increasingly critical due to escalating pollution from industrialization and population growth. This study presents the development of advanced cellulose acetate (CA)-based membranes for water filtration through an integrated approach combining electrospinning, hot pressing, and cellulose nanocrystal (CNC) functionalization. A 12 wt.% CA solution in a 4:1 acetone/acetic acid mixture was electrospun under optimized conditions (1 mL/h, 15 cm, 35–70% relative humidity) to produce uniform, bead-free nanofibrous mats. Subsequent hot pressing at 100 °C and 20 bar yielded denser membranes with enhanced mechanical durability and reduced pore size. Functionalization with CNCs and TEMPO-oxidized CNCs (CNCTEMPO) further improved performance. TEMPO oxidation introduced a carboxyl content of 0.56 ± 0.04 mmol/g, enhancing nanocrystal dispersion and interfacial adhesion within the CA matrix. This reduced the water contact angle from 104° to 37° and filtration time from 100 minutes to under 30 seconds. Filtration tests showed improved rejection of 2.0 μm particles (92%) and efficient methylene blue dye removal (up to 95%) in membranes with 3 wt.% CNCTEMPO. This is the first systematic study examining the synergistic effect of electrospinning, hot pressing, and CNCTEMPO functionalization, offering a promising strategy for fabricating high-performance, multifunctional membranes for sustainable water treatment applications.\u003c/p\u003e","manuscriptTitle":"Enhanced water filtration performance in electrospun cellulose acetate membranes via TEMPO-mediated cellulose nanocrystal incorporation and hot pressing","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-20 03:45:08","doi":"10.21203/rs.3.rs-6880184/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-06-25T12:14:45+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-25T12:13:52+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-19T03:54:08+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-18T14:32:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"218926422383815533641278024876339906537","date":"2025-06-18T14:10:00+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"69763516869395080874835687813491100432","date":"2025-06-18T11:32:05+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"167063571342279536141983780433179261069","date":"2025-06-18T10:41:16+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-06-18T09:32:46+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-13T23:02:12+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-06-13T23:01:35+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Polymers and the Environment","date":"2025-06-12T12:02:52+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymers-and-the-environment","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jooe","sideBox":"Learn more about [Journal of Polymers and the Environment](https://www.springer.com/journal/10924)","snPcode":"10924","submissionUrl":"https://submission.nature.com/new-submission/10924/3","title":"Journal of Polymers and the Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"c4ef6d79-f081-473e-b375-18a7ba21dab0","owner":[],"postedDate":"June 20th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-09-01T16:04:34+00:00","versionOfRecord":{"articleIdentity":"rs-6880184","link":"https://doi.org/10.1007/s10924-025-03659-5","journal":{"identity":"journal-of-polymers-and-the-environment","isVorOnly":false,"title":"Journal of Polymers and the Environment"},"publishedOn":"2025-08-25 15:57:31","publishedOnDateReadable":"August 25th, 2025"},"versionCreatedAt":"2025-06-20 03:45:08","video":"","vorDoi":"10.1007/s10924-025-03659-5","vorDoiUrl":"https://doi.org/10.1007/s10924-025-03659-5","workflowStages":[]},"version":"v1","identity":"rs-6880184","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6880184","identity":"rs-6880184","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}