Enhancing Atmospheric Water Harvesting Applications through the Integration of Green Silica and Zinc Oxide Nanoparticles into Chitosan Biopolymer

Enhancing Atmospheric Water Harvesting Applications through the Integration of Green Silica and Zinc Oxide Nanoparticles into Chitosan Biopolymer | 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 Enhancing Atmospheric Water Harvesting Applications through the Integration of Green Silica and Zinc Oxide Nanoparticles into Chitosan Biopolymer Noor Al-Sadeq, Víctor M. Perez-Puyana, Alberto Romero, Johar Amin Ahmed Abdullah This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6819891/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Global depletion of freshwater resources is exacerbating environmental, social, and economic challenges, underscoring the urgent need for sustainable water sources. Eco-friendly synthesis processes can be implemented not only to enhance water adsorption but also to minimize the environmental impact of its production. In this context, green silica and zinc oxide nanoparticles (SiO₂ NPs and ZnO·NPs) were incorporated in chitosan (CH) to develop a chitosan-silica-zinc oxide nanocomposite (CH/SiO₂@ZnO NC) film to harvest water directly from the air. After experimenting with various concentrations, we found that the optimal performance of the green nanocomposite in the cast chitosan films occurs when it constitutes 15% to 20% by weight of the chitosan polymer. At concentrations exceeding 20%, we observed a deterioration in both functional and mechanical performance. This specific percentage range was chosen based on its effectiveness, which should hopefully address any concerns regarding the evaluation of chitosan concentration. Results reveal that these green nanoparticles were successfully produced to an average size of less than 25 nm, significantly enhancing water adsorption. Based on this study, using a formulation of 2 wt% chitosan with 0.15% each of green SiO2 and ZnO nanoparticles, we determined that a 15% nanocomposite-to-chitosan ratio is essential for achieving nanoscale dimensions and enhancing device durability under variable temperatures. The developed nanocomposites demonstrate a passive auto-water generation process, yielding 0.7–1.2 mL/g at ≤35% relative humidity with no external energy input, showcasing superior functionality when compared to traditional materials. This study highlights a scalable, low-cost AWH solution that combines environmental sustainability with enhanced performance. Chitosan Silica Nanocomposites Zinc Oxide Nanocomposites Water Capture Sustainable Atmospheric Water Harvesting Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1. Introduction The lack of access to clean water is a growing global challenge that threatens human lives and sustainable development. Many countries are facing their worst-ever water crisis, with the situation expected to worsen in the coming years due to factors such as population growth, urbanization, unsustainable water usage, and climate change [1]. As traditional freshwater sources continue to diminish, innovative technological solutions are urgently required to address this escalating crisis [2]. From the advancement of renewable energy systems and breakthroughs in desalination techniques to innovations in smart agriculture and efficient resource management, several cutting-edge technologies are driving global sustainability forward [2]. Among these, Atmospheric Water Harvesting (AWH) distinguishes itself by providing a vital solution for extracting sustainable freshwater from atmospheric humidity, especially critical for water-stressed, landlocked, or ecologically sensitive regions [3, 4]. AWH techniques tap into the nearly inexhaustible water present in the atmosphere, which holds approximately 13,000 km³ of freshwater at any given time. These technologies can be categorized into several types, each with distinct principles, advantages, and limitations [3]. According to Gao et al., study (2023), it can be inferred that Atmospheric Water Harvesting (AWH) technologies can be categorized based on three main techniques: condensation-based systems (multi-process sorption), wet desiccation systems (hygroscopic liquid absorption), and adsorption-based systems (hygroscopic solid adsorption) [4]. Condensation-based systems (multi-process sorption) operate at the air/solid and liquid/solid interfaces where vapor condensation and droplet transport are managed through chemical and topological heterogeneous designs. These systems, which function by cooling moist air below its dew point to condense water vapor, are highly energy-intensive and perform optimally in humid environments. They often require significant energy inputs, such as underground or radiation cooling, to sustain condensation processes [4, 5]. Wet desiccation systems (hygroscopic liquid absorption) rely on hygroscopic materials at the air/liquid interface to absorb moisture from the air. These systems utilize interface thermal management strategies like bulk and sustainable interfacial heating to enhance moisture absorption and desorption rates. However, like their solid counterparts, they face challenges due to the energy required to regenerate the desiccants, thus affecting their efficiency and overall operational sustainability [6]. Adsorption-based systems (hygroscopic solid adsorption), particularly those utilizing Metal-Organic Frameworks (MOFs) at the air/solid interface, excel in capturing water vapor even in low-humidity conditions. These systems benefit from the modification of bonding sites, adjustment of intra/interparticle pores, and regulation of pore volume and water affinity to maximize water capture and retention. Despite their high adsorption capacity, they are limited by high material costs and the substantial energy demand for water release, impacting their economic feasibility [7]. While each method: condensation, adsorption, and wet desiccation, provides innovative solutions for water scarcity, they all present significant challenges related to energy consumption, cost, operational efficiency, and scalability. These issues hinder their widespread adoption, necessitating further research and development to refine these technologies for more sustainable and cost-effective applications across diverse climatic conditions. This backdrop sets the stage for exploring alternative approaches, such as green synthesis, which promises to address some of these fundamental challenges by utilizing sustainable methods and materials [8]. To address pressing challenges in water scarcity, our work introduces the development of a nanocomposite designed specifically for use in atmospheric water harvesting (AWH) systems. This material, comprising chitosan-based green silica and zinc oxide, is engineered to be a cost-effective, environmentally friendly solution that optimizes water capture. Before delving into the specific material development, it is crucial to define green synthesis, a sustainable and environmentally friendly method that uses natural extracts as reducing agents to synthesize nanoparticles. This process minimizes environmental impact and enhances the functional properties of nanoparticles [6, 8]. In this context, green extracts from agricultural waste are selected to enhance the hydrophilicity of nanoparticles, thereby improving the water-capture capabilities of films [9]. For example, The Phoenix dactylifera L . leaf extract, for instance, has been proven through studies to effectively reduce metal ions to form nanoparticles while also fine-tuning the balance between hydrophobicity and hydrophilicity [9]. This dual functionality enhances the sustainability and safety of the process while maintaining the consistency and quality of the nanoparticles produced. In addition, the use of natural phytochemicals can help to produce smaller nanoparticles with a larger surface area, crucial for enhancing water adsorption mechanisms without the need for high temperatures or synthetic chemicals [9]. The control of nanoparticle size within this nanocomposite is a critical factor in water-related applications, significantly impacting the water absorption capacity. Smaller nanoparticles, due to their larger surface area to volume ratio, enhance their interaction with water molecules, which increases the efficiency of water capture [10]. This precise control over size is essential for optimizing the performance of nanocomposites in atmospheric water harvesting (AWH) systems. Additionally, the appropriate sizing of metal oxide nanoparticles, such as zinc oxide, not only helps limit bacterial growth and reduce toxicity but also enhances the material's applicability in water purification [11]. On the other hand, chitosan, a biodegradable polymer derived from chitin, is an abundant, sustainable resource noted for its excellent water management properties [12]. It finds diverse applications in the water industry, evident in forms such as powders, films, and beads. For instance, chitosan nanoparticles in powder form are increasingly utilized in water filtration to enhance the extraction of heavy metals from wastewater [12]. Chitosan films, including biopolymeric membranes, have proven effective in ultrafiltration technologies for removing contaminants and pathogens, ensuring safer drinking water [13]. Additionally, chitosan beads are employed to adsorb dyes from textile industry effluents, demonstrating their utility in managing industrial wastewater. These varied applications underline chitosan's crucial role in promoting sustainable water treatment practices [14]. Incorporating nanoparticles into the chitosan matrix, specifically zinc oxide and silica, has been shown to significantly enhance functional properties such as disinfection and antimicrobial activity, critical for water-related applications [15]. Silica nanoparticles, sourced sustainably from agricultural waste like rice husk, bring dehumidification properties to the composite. This sustainable sourcing is not only effective but also environmentally beneficial, leveraging waste materials for productive use and utilizing silica, which is an abundant natural material [16]. Following the introduction of silica, zinc oxide nanoparticles play a specialized role by adjusting the hydrophilicity and hydrophobicity of the chitosan matrix. These adjustments are essential for efficient interaction with water molecules and enhancing the water capture capabilities of the composites. Furthermore, zinc oxide nanoparticles contribute to strengthening the structural integrity and increasing the durability of the composites and their antimicrobial properties are crucial for maintaining the purity of collected water, ensuring it is safe for use [17]. This study introduces a novel chitosan-silica-zinc oxide nanocomposite films, designed to enhance atmospheric water harvesting (AWH) systems. The primary objective is to develop an environmentally friendly and cost-effective alternative to existing materials such as metal-organic frameworks (MOFs), which, despite their high efficiency, often remain economically unfeasible due to high production costs [18]. The proposed nanocomposite addresses key technical, economic, and environmental challenges, offering notable advantages such as reduced energy consumption and improved efficiency. Specifically, by promoting effective water condensation at higher temperatures, it significantly lowers the dependence on intensive cooling processes, making passive AWH devices more practical and affordable. These advancements enhance the global applicability and commercial viability of AWH systems, providing a sustainable and innovative solution to the ongoing water crisis. 2. Methods 2.1. Materials Chitosan (CH, 98% deacetylation, Mv = 1.61·10 5 g·mol −1 ), Zinc chloride (ZnCl 2 ), gallic acid (C 7 H 6 O 5 ), acetone (CH 3 ) 2 CO, acetic acid CH 3 COOH, sodium hydroxide solution (NaOH), hydrochloric acid (HCl), sulfuric acid (H 2 SO 4 ), polyethylene glycol (PEG) and DPPH (2,2-diphenyl-1-picrylhydrazyl) were obtained from Sigma Aldrich (Germany). Also, banana peels, peanut shell waste and date palm leaves were used for the green nanocomposite preparation. The banana peels and peanut shells were sourced from fresh bananas and peanuts obtained from a local market, while the date palm leaves were collected from fallen leaves of palms in Seville. All other reagents and chemicals used in this study were of an analytical quality. 2.2. Methodology of Fabricating the CH/SiO₂@ZnO NC Films To optimize the formulation of CH/SiO₂@ZnO NC (chitosan-silica-zinc oxide nanocomposite) films, the Minitab Box-Behnken Design of Experiments (DOE) was implemented. This statistical approach is crucial for exploring interactions among variables, particularly in environmental studies utilizing green adsorbents and absorbents [20]. Through this method, 14 experimental runs were conducted, including four central points, focusing on three variables: zinc oxide nanoparticle concentration, silica nanoparticle concentration and chitosan concentration. Consistent film thickness was maintained across all samples, a critical parameter achieved through precise calibration of the casting process. A volume of 45 ± 0.5 mL was poured for all films to ensure uniformity and maintain a thickness of 1.0 ± 0.2 mm. This rigorous control of each sample's thickness facilitated valid comparisons of material properties across different formulations. The DOE thoroughly investigated a range of nanoparticle concentrations, designed to cover the lower (0.3 w/v%), middle (0.4 w/v%) and higher (0.8 w/v%) limits. Similarly, Chitosan concentrations in the DOE spanned from 1 to 3 w/v%. It was observed that concentrations below 2% w/v led to films with poor mechanical strength and uneven nanoparticle distribution, which compromised the structural integrity and functionality of the films. Conversely, at 2% w/v, chitosan provided higher viscosity, which ensured uniform nanoparticle embedding and optimal intermolecular interactions, crucial for a robust and durable film structure. Consequently, a chitosan concentration of 2% w/v was selected as the optimal concentration within the tested range. Therefore, the systems chosen from these runs were Run 7 (System F1), CP4 central point (System F2), and Run 10 (System F3), each utilizing varying nanoparticle concentrations, ranging from the lower (0.3 wt%), through the middle (0.4 wt%), to the higher (0.8 wt%), to evaluate their effects on the films' water adsorption, mechanical properties, and antibacterial effectiveness. These systems are detailed in Table 1 in section 2.2.4. Additionally, polyethylene glycol (PEG) at a concentration of 2% w/v was employed as a plasticizer to enhance film flexibility and durability, while also stabilizing nanoparticle dispersion to prevent agglomeration. Lower concentrations of PEG led to brittle films prone to cracking, further validating the choice of 2% w/v for both PEG and chitosan. This methodical integration of DOE findings and controlled experimentation ensured that the selected chitosan and nanoparticle concentrations maximized the functional potential of the nanocomposites for effective water capture applications, aligning with empirical evidence and scientific validation from previous studies [21]. 2.2.1. Green Extracts Preparation In this study, the green extract was derived from the leaves of banana peels and Phoenix dactylifera L. (date palm). Banana peel extract was selected for its ability to enhance nanoparticle hydrophilicity, thereby improving the films’ functional properties for water capture, as indicated by our literature review [22]. In addition, Banana peel extract can be very effective in the green synthesis of nanomaterials, like the zinc oxide nanomaterials influencing their yield, size, shape, and purity; these nanomaterials exhibit antibacterial activity when varying the extract and precursor concentrations [23, 24]. Phoenix dactylifera L . leaf extract, known for its capacity to store water under desert conditions, was used not only as an efficient reducing agent for metal ions but also to benefit the hydrophobicity/hydrophilicity balance, enhancing both the sustainability and safety of the process [21]. The preparation method for the banana peel extract was adapted from Abdullah et al. (2024), with modifications to enhance its disinfection properties to meet our specific design needs [22]. Fresh bananas were locally sourced and thoroughly washed with distilled water and their peels were sterilized by drying at 90°C for 24 hours. The dried peels were ground into fine powder, mixed with distilled water (1:10 w/v), boiled for 10 minutes, filtered and cooled, yielding the banana peel extract. The preparation method for the Phoenix dactylifera L. leaves was followed exactly as described by Abdullah et al. (2024) [22]. The final extract solution was a combination of banana peel and date palm leaf extracts in a 1:1 v/v ratio. 2.2.2. Green ZnO Nanoparticle Preparation Following the methodology described by Gharbi et al. (2025), 20 mL of the extract, with a concentration of 4 mg/mL, was gradually added to a mixed solution of zinc chloride and zinc acetate. This specific concentration was chosen based on its demonstrated efficacy in the referenced study for achieving the desired chemical reaction [25]. The green ZnO solution was prepared by dissolving 0.545 g of ZnCl₂ and 0.438 g of Zn(CH₃COO)₂ in 20 mL of distilled water. This procedure achieved a concentration of 0.2 M, referring specifically to the molarity of the zinc ions (Zn²⁺) in the solution [25]. To promote the environmentally friendly synthesis of zinc oxide nanoparticles, the diluted green extract (4 mg/mL) was gradually added to the ZnO solution. This approach aligns with green chemistry principles by reducing the need for hazardous chemicals and utilizing a sustainable, plant-based extract to facilitate nanoparticle formation. This method of gradual addition has been well-documented and recognized in several studies and applications for its effectiveness in controlling nucleation, which is crucial for producing nanoparticles with smaller and more uniform sizes [26]. The pH of the mixture was adjusted to 11 by adding 5 M NaOH. This process was repeated multiple times, adding additional extract and zinc solutions until the desired quantity of ZnO nanoparticles was obtained in an economically efficient manner. The solution was subjected to magnetic stirring at 50 °C for 2 hours to promote nanoparticle formation. The resulting precipitate was collected by filtration using Whatman No. 1 filter paper and thoroughly washed with distilled water to remove any impurities. The ZnO nanoparticles were then pretreated by heating at 105 °C overnight, followed by calcination at 300°C for 2 hours to produce the final ZnO nanoparticles [25]. 2.2.3. Green SiO 2 Nanoparticles Preparation To prepare nanosilica from peanut shells and banana peels, the materials were washed with distilled water to remove any impurities and then pre-dried in an oven overnight at 80 ºC. Following that, the dried peanut shells and banana peels were calcinated at 500-700 ºC for 2 hours, resulting in a black powder. The powder was subjected to an acid treatment using 1 M hydrochloric acid (HCl), followed by washing with ethanol and water. After drying at 50 ºC for a day, it was calcined at progressive temperatures: 300 ºC for 2 hours, followed by 600 ºC for an additional hour. The material then underwent a base treatment with 200 mL of 5 M sodium hydroxide (NaOH). The pH was adjusted with 5 N sulfuric acid (H₂SO₄) and further fine-tuned by adding 20 mL of 5 M NaOH and 10 mL of the green extract. These precise pH adjustments are crucial not only for achieving a uniform nanoparticle size but also for preventing agglomeration. Research has demonstrated that pH significantly influences nanoparticle behavior, impacting their scattering properties and the tendency to form compact agglomerates [27]. By optimizing pH levels, our process not only enhances the optical properties, which are important for clearer SEM characterization, but also improves the functional characteristics of the nanoparticles [27]. Finally, the mixture was stirred at 50-60 ºC for 2 hours, filtered, washed, dried overnight and calcinated at 600 ºC. The resulting SiO 2 NPs are considered high purity, as indicated by the uniformity of the SEM images that will be detailed in the results and discussion sections. These images serve as evidence of the consistent particle size and shape, which are characteristic of high-purity materials, making them suitable for various applications. 2.2.4 . Films Synthesis through Casting The films were fabricated using the casting method, enhancing mixture homogeneity, enabling early characterization, and supporting design modifications crucial for atmospheric water harvesting applications [28]. Figure 1. Schematic illustration of the green synthesis and casting process for CH/SiO₂@ZnO NC films, showing the preparation steps including mixing, stirring, sonication and casting into molds. Figure 1 illustrates the green synthesis and casting process of the CH/SiO₂@ZnO NC films, describing the step-by-step method used for film preparation. Chitosan was dissolved in 0.05 M acetic acid and stirred at 600-700 rpm for 1 hour at 60 ºC, followed by 15 minutes of mechanical agitation. The green nanoparticles solution, consisting of SiO 2 and ZnO, was prepared in a similar acetic acid solution with 2% w/v PEG, stirred magnetically for 1 hour at 50 ºC and sonicated for 30 minutes. This solution was combined with the chitosan solution under low-speed mechanical agitation for homogenization, cast into Teflon plates (approximately 12 cm²) and dried in an oven at 50 ± 2 ºC for 16-18 hours. This drying phase ensures that the films achieve a consistent dry state, ensuring that the final nanocomposite films are robust and uniformly formed. At least three films per composition were cast for repeatability. The selected films for further evaluation in this study are presented in Table 1, with simplified identifiers (F1, F2, and F3) for clarity throughout the discussion. Table 1: Composition of Chitosan-Silica-Zinc Oxide Nanocomposite Films Sample ID Component w/v% w/w% F1 (CH85· SiO 2 7.5·ZnO7.5) Chitosan 2.00% 85.0% SiO 2 NP 0.15% 7.50% ZnO NP 0.15% 7.50% F2 (CH80· SiO 2 10·ZnO10) Chitosan 2.00% 80.0% SiO 2 NP 0.20% 10.0% ZnO NP 0.20% 10.0% F3 (CH60· SiO 2 20·ZnO20) Chitosan 2.00% 60.0% SiO 2 NP 0.40% 20.0% ZnO NP 0.40% 20.0% F1 = lowest silica/zinc oxide content (15%), F2 = medium content (20%), F3 = highest content (40%) 2.3. Characterization of SiO₂ NPs, ZnO NPs, and CH /SiO₂@ZnO NC Films 2.3.1. X-ray Diffraction (XRD) X-ray Diffraction (XRD) analysis was used to evaluate the crystalline structure of the synthesized green silica nanoparticles (SiO₂ NPs), green ZnO nanoparticles (ZnO NPs) before incorporation into the chitosan matrix and the fabricated CH/SiO₂@ZnO NC films with varying nanoparticle concentrations. The diffractograms were recorded from 2θ = 5° to 70° using a Bruker D8 Advance A25 diffractometer with a Cu anode. XRD analysis is crucial for confirming the crystalline and estimating the size of nanoparticles. The degree of crystallinity determined via XRD can indicate the structural order within the nanoparticles, which affects their physical stability and porosity [29]. Smaller nanoparticles, often implied by broader XRD peaks due to increased surface area to volume ratio, typically exhibit higher porosity [30]. This increased porosity is essential as it enhances the material’s ability to adsorb water effectively, a key characteristic for materials utilized in water harvesting technologies [10]. The Debye-Scherrer formula, referenced as Equation 1, was applied to determine the crystalline size of the green SiO₂ NPs, green ZnO NPs and the green CH/SiO₂@ZnO NC films [31]. This measurement helps understand their impact on the stability of the chitosan-silica complex and their role in maintaining structural integrity and interaction within this complex. Where 𝐷 is the diffracting domain size, k is a correction factor (0.94), λ is the used wavelength (0.154178 nm), β = FWHM (full width at half maximum) and θ is the position of the main peak. 2.3.2. Fourier-transform infrared spectroscopy (FTIR) Fourier-transform infrared spectroscopy (FTIR) was performed to analyze the chemical bonds of the green CH/SiO₂@ZnO NC films. A Hyperion 1000 spectrophotometer (Bruker) equipped with an ATR diamond sensor was used to obtain infrared spectra between 4000 and 400 cm⁻¹ with a resolution of 4 cm⁻¹ and an acquisition of 200 scans. Baseline correction was conducted by measuring without the sample. FTIR spectroscopy was essential for identifying functional groups present in the chitosan-silica-zinc oxide nanocomposites, particularly hydroxyl groups that enhance hydrophilicity, which is critical for water adsorption in atmospheric water harvesting applications. 2.3.3. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS or EDAX) Scanning Electron Microscopy (SEM, Zeiss EVO microscope, Pleasanton, CA, USA) at 3000X magnification and 10 kV acceleration was used to observe the morphological and microstructural characteristics of the green nanoparticles and the CH/SiO₂@ZnO NC films. Image-J software (Version 1.53q, NIH, Bethesda, MD, USA) was used for particle size distribution analysis. Energy Dispersive X-ray Spectroscopy (EDS or EDAX) was performed during SEM analysis to identify and quantify the elemental composition of carbon (C), nitrogen (N), oxygen (O), silicon (Si), and zinc (Zn) within the nanocomposite matrix. This analysis provided insights into the uniformity and integration of the nanoparticles within the chitosan matrix, which is essential for enhancing water capture performance. Comparative analysis with existing studies highlighted the influence of the elemental composition and dispersion on the functional efficiency of nanocomposites in water harvesting applications [32]. 2.3.4. Water Contact Angle (WCA) In this analysis, a micro-syringe applied a 2 µL droplet of deionized water onto the meticulously leveled film on a 1 cm² surface. Measurements illustrated in Figure 7, as discussed in Section 3.4, represent the WCA on the top surface of the film. It should be noted that the bottom surface measurements, although not depicted, exhibited minimal variation, with differences not exceeding ±2°. This consistency was achieved through rigorous control over the casting and drying procedures, aimed at producing a homogenized single-layer surface across the film. Over a period of 20 seconds at 12 frames per second, WCA measurements were accurately taken from both sides of the droplet. To ensure precision, frames showing discrepancies greater than 2° between measurements were discarded. This procedure was repeated five times per sample to ensure the reliability of our results. These WCA measurements are crucial for understanding the degree of hydrophilicity/hydrophobicity achieved through surface modifications, directly correlating with the material’s potential for effective water adsorption and retention in practical applications [33]. 2.3.5. Confocal Microscopy (CM) The surface roughness of the green CH/SiO₂@ZnO NC films was analyzed using a Confocal-Interferometric Optical Microscope (Sensofar S-NEOX, Sky Tech, Bukit Batok, Singapore) at 100× magnification with an 8 μm amplitude Robust Gaussian filter, adhering to ISO 4287 standards. Roughness parameters included the average roughness (Ra, μm), representing the arithmetic mean of absolute profile height deviations, and the quadratic roughness (Rq, μm), calculated as the root mean square of these deviations. 2.3.6. Thermal Stability The thermal stability of the green CH/SiO₂@ZnO NC films was assessed using Thermogravimetric Analysis (TGA) with an SDT Q600 V20.9 instrument. Approximately 8.5 mg of each sample was analyzed under a nitrogen atmosphere. The temperature was ramped from room temperature to 600 °C at 10 °C/min. The TGA monitored weight changes, providing insights into thermal degradation. The onset of degradation was noted when significant weight loss occurred, indicating thermal decomposition. The analysis ensured consistent and repeatable results under standardized conditions. 2.3.7. Mechanical Properties The mechanical properties of the green CH/SiO₂@ZnO NC films were evaluated using tensile tests, conforming to ISO 527-3:2019 standards [34]. Tests were performed on an MTS Insight 10 machine (Darmstadt, Germany) at a constant rate of 10 mm/min under controlled conditions (22 °C, 30 ± 3% RH). Parameters recorded included Young’s modulus (kPa), maximum stress (kPa) and strain at break (ε max , mm/mm), providing insights into the structural integrity and durability of the films. 2.3.8. Antifungal and Antimicrobial Properties The antifungal and antimicrobial properties of the green CH/SiO₂@ZnO NC films were evaluated by comparing them with pure chitosan films without nanoparticles . The microbial environments to which both the green CH/SiO₂@ZnO NC films and the pure chitosan films without nanoparticles (control films) were exposed are defined by room temperature and normal humidity conditions. The films were kept at room temperature, generally around 20°C to 25°C, with a normal humidity range of 35% to 50%. This setup was designed to test the natural resilience of the films against microbial growth under everyday conditions. Daily visual inspections were conducted to identify any signs of microbial activity, such as discoloration, biofilm formation, or morphological changes on the film surface. Under these conditions, the most likely microbes to colonize chitosan films include fungi such as Aspergillus and Penicillium, and possibly yeast species like Candida, which can form biofilms [35]. While this study focused on water capture applications, the antimicrobial evaluation provided insights into the potential of nanoparticle-incorporated chitosan films. Future studies should include detailed microbial testing to quantify resistance to bacterial and fungal growth . 2.3.9. Water Capture To evaluate the water capture capabilities of our green CH/SiO₂@ZnO NC films, we employed a passive system without external energy input. The membranes were stored under control conditions lacking measurable humidity and temperature control to simulate realistic environmental scenarios. This setup aimed to determine the effectiveness of the films in generating water even at controlled humidity levels, which were maintained at 30 ± 5% on average inside a closed environment. The humidity fluctuations might be due to external conditions when storing the films, when storing the films and opening the closed systems in which the films were kept to measure the water generation and collect the water from the films and store these in closed tubes. The ambient humidity was measured between 35% and 45%. This methodology is also adopted to a similar concept inspired by other studies on MOFs, where they utilized a simple setup involving only two plexiglass boxes and ambient sunlight, without any additional energy inputs [36]. 2.3.10. Statistical Analysis Each sample of the green CH/SiO₂@ZnO NC films was tested thrice for reliability. Statistical analysis was conducted using Origin software, presenting results as mean ± standard deviation (M ± SD) and generating graphs to illustrate correlations among morphological, physicochemical, functional, and mechanical properties. A one-way ANOVA was also performed to assess variance heterogeneity and significant differences at a 95% confidence level (p < 0.05). 3. Results And Discussion 3.1. X-ray Diffraction (XRD) X-ray diffraction (XRD) analysis is essential for evaluating the structural characteristics of nanoparticles (NPs) individually and their interaction within the chitosan matrix, particularly regarding crystallinity and particle size, both of which are crucial for water capture applications. The introduction of silica and zinc oxide nanoparticles into chitosan influences the crystallinity and structural arrangement, affecting the overall performance of the nanocomposite films. As shown in Figure 2, the XRD pattern of green silica nanoparticles (SiO₂ NPs) reveals multiple crystalline phases, including tetragonal, cubic, monoclinic and hexagonal structures, while the green zinc oxide nanoparticles (ZnO NPs) exhibit a sharp hexagonal wurtzite structure, indicative of high crystallinity before incorporation into the chitosan matrix. In addition, Table 2 shows the average crystallite size, crystallinity and phases corresponding to NPs and films. Table 2: Summary of XRD Results for SiO₂ NPs, ZnO NPs and CH/SiO₂@ZnO NC Films Sample ID Average Crystallite Size (nm) Crystallinity (%) Phase SiO₂ NPs 19.5 + 1.2 a 76.2 + 1.4 α Cubic, Monoclinic, Hexagonal, Tetragonal ZnO NPs 26.0 + 1.3 b 75.0 + 1.2 α Hexagonal F1 56.9 + 1.6 c 23.1 + 0.9 γ Monoclinic and Hexagonal F2 67.7 + 1.6 d 29.4 + 0.9 β Monoclinic and Hexagonal F3 71.7 + 2.3 d 23.0 + 0.9 γ Monoclinic and Hexagonal F1 = lowest silica/zinc oxide content (15%), F2 = medium content (20%), F3 = highest content (40%). Different letters indicate statistically significant differences (P≤0.05). Figure 3 displays the XRD patterns of CH/SiO₂@ZnO NC films (F1, F2, and F3), corresponding to low (15%), medium (20%) and high (40%) total concentration of the nanocomposite, respectively. The broad peaks observed in the nanocomposite films indicate a semi-crystalline structure with well-dispersed nanoparticles, essential for enhancing water adsorption capabilities [37]. The presence of both monoclinic and hexagonal phases in the films suggests effective incorporation and interaction of SiO₂ nanoparticles, which exhibit tetragonal, hexagonal, monoclinic, and cubic phases, and ZnO nanoparticles, which are present in the hexagonal phase (as shown in Figure 2). This demonstrates the merging of hexagonal and monoclinic phases within the chitosan matrix [37]. As summarized in Table 2, the average crystallite sizes range from 56.9 nm in F1 to 71.7 nm in F3, reflecting the influence of nanoparticle concentration on crystallinity. The moderate crystallinity of F1, characterized by smaller crystallite sizes, optimally balances water adsorption due to the increased surface area and active sites, enhancing the material’s adsorptive properties. Notably, our crystallite sizes are smaller than or comparable to those reported in similar studies. For instance, Faisal et al. (2021) found that green synthesis of zinc oxide nanoparticles resulted in an average crystallite size of 41.3 nm, whereas Rani et al. (2025) reported sizes ranging from 20-40 nm for silica nanoparticles synthesized using green methods [38, 39]. Furthermore, the correlation between crystallite size and adsorption efficiency observed in our study aligns with, yet appears more pronounced than, findings from previous research, possibly due to our optimized synthesis conditions that utilize extracts from both Phoenix dactylifera L. leaves and banana peels [35, 40]. This structural arrangement not only corroborates but also advances prior research on the role of amorphous and crystalline phases in enhancing moisture capture efficiency in nanocomposite materials [37]. The results confirm that CH/SiO₂@ZnO NC films maintain high crystallinity while exhibiting structural features that optimize their functionality in water capture applications. Higher crystallinity in these films contributes to a more defined and stable structure, enhancing the efficiency of water molecule adsorption due to the regularity and accessibility of adsorptive sites [40, 41]. For example, in agricultural settings, crystalline hydrogels in the form of films can be used to create moisture-retaining barriers around plant roots, significantly enhancing water retention in arid soils [42]. Similarly, in atmospheric water harvesting applications, films with uniform crystalline structures, such as those we are developing, could offer enhanced stability. This stability, particularly noted in films like F1 with uniform crystalline distribution and morphology, ensures that the films maintain their integrity and functional properties under varying environmental conditions. Such characteristics could make them highly effective for capturing and condensing atmospheric moisture, drawing on the principles established for other stable crystalline materials in other studies. 3.2. Fourier-transform infrared spectroscopy (FTIR) Fourier-transform infrared spectroscopy (FTIR) analysis of CH/SiO₂@ZnO NC films (F1, F2, and F3) provides comprehensive insights into molecular interactions and the presence of specific functional groups (Figure 4). The broad and intense absorption bands observed between 2800 and 3600 cm⁻¹ correspond mainly to O–H and C–H stretching vibrations, indicating extensive hydrogen bonding interactions within the chitosan matrix and between chitosan and embedded nanoparticles, in alignment with previous findings [43]. Distinct peaks around 1640 cm⁻¹ and 1550 cm⁻¹ represent N–H bending and amide vibrations associated with the chitosan backbone, confirming the polymeric structure's integrity. Additional peaks near 1080 cm⁻¹ and 800 cm⁻¹ correspond to Si–O–Si stretching vibrations, validating the successful integration of silica nanoparticles [44, 45]. The clear presence of a peak at approximately 500 cm⁻¹ confirms Zn–O stretching vibrations, signifying the effective incorporation of zinc oxide nanoparticles within the films [46]. Formulation F1 displays a notably more pronounced O–H stretching vibration peak, suggesting increased hydrophilicity and superior water adsorption capacity relative to F2 and F3 [47]. This characteristic is primarily attributed to the higher chitosan content, leading to more available hydrophilic hydroxyl groups. While chitosan-related peaks (C–H ~2900 cm⁻¹, N–H ~1550 cm⁻¹) exhibit consistency across formulations, slight intensity variations observed in nanoparticle-associated peaks reflect subtle differences in nanoparticle concentration and their interactions within the polymer matrix. These FTIR observations complement the previously discussed XRD results, which highlight the critical balance between crystalline and amorphous phases. While XRD identifies the presence and proportion of crystalline regions, key contributors to mechanical stability and structural robustness, as noted by Darmenbayeva et al. (2024), FTIR provides insights into the chemical functionalities of both crystalline and amorphous phases [48]. The distinct FTIR signatures of amorphous regions, attributed to the greater mobility of polymer chains, indicate enhanced interactions with water molecules and the availability of active sites crucial for water adsorption, as also observed in Darmenbayeva et al. (2024) [48]. Together, these techniques offer a comprehensive understanding of how structural and chemical properties interact to optimize the material's performance Such a balanced structural interplay is essential for optimizing the water adsorption efficacy of CH/SiO₂@ZnO NC films and aligns well with findings documented in existing literature [48]. 3.3. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS or EDAX) Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) analyses provide comprehensive insights into the morphological characteristics and elemental composition of CH/SiO₂@ZnO NC films, respectively. As shown in Figure 5, SEM images of silica nanoparticles (A) display an aggregated and irregular morphology, while zinc oxide nanoparticles (B) exhibit a well-defined, rod-like structure, consistent with previous studies on metal oxide nanoparticles used in polymer matrices [27]. The SEM images of the CH/SiO₂@ZnO NC films (F1, F2 and F3) reveal varying nanoparticle distributions within the chitosan matrix. Lower nanoparticle concentrations (F1) result in a more uniform dispersion, while higher concentrations (F3) show notable aggregation, which can impact the surface area and porosity, essential for adsorption/desorption processes in water capture applications. This observation aligns with research highlighting that increased nanoparticle loading can lead to agglomeration, affecting functional properties [49]. The particle size distribution of the SiO₂ and ZnO nanoparticles within the films, determined using Image-J software, ranged from 3 ± 1 nm (smallest size observed in sample F1) to 16 ± 3 nm (smallest size observed in sample F3), as shown in Figure 5. This trend aligns qualitatively with the XRD results, where an increase in crystalline particle size was observed with higher nanoparticle concentrations, ranging from an average of 56 nm in F1 to 71 nm in F3. The discrepancy between the particle sizes measured by Image-J (3–16 nm) and those from XRD (56–71 nm) is likely due to differences in measurement techniques: Image-J analysis assesses individual nanoparticles visually identifiable within the films, revealing the smallest nanoparticle sizes which are crucial as they indicate the minimal achievable particle dimensions. Identifying these small sizes is important as they contribute significantly to an increased surface area and enhanced adsorption capabilities, consistent with findings from previous studies [50-52]. On the other hand, XRD provides average crystallite sizes calculated from diffraction patterns, reflecting larger crystallite domains or particle aggregates rather than individual nanoparticles. Thus, both analytical approaches offer complementary insights, and their results should be interpreted accordingly. Figure 6 presents the EDS spectra of the CH/SiO₂@ZnO NC films, indicating the presence of carbon (C), nitrogen (N), oxygen (O), silicon (Si) and zinc (Zn). Results confirm the successful incorporation and dispersion of silica and zinc oxide nanoparticles within the chitosan matrix. These findings are consistent with previous literature, where similar nanocomposites demonstrated enhanced structural integrity and functionality due to the synergistic interaction between chitosan and embedded nanoparticles [52]. The increasing Zn content from F1 to F3 confirms the successful incorporation of Zn nanoparticles into the chitosan matrix, as reflected by the more prominent elemental peaks. However, the expected increase in Si is not observed, suggesting that Si may not have fully integrated or dispersed within the chitosan matrix. Instead, it is likely that Si remains more localized on the surface rather than being embedded within the structure. This surface presence could be beneficial for enhancing moisture trapping during the water adsorption process, as silica nanoparticles’ geometry could have a great influence on the interfacial interactions of water molecules, as emphasized by Rama & Abbas's study (2022) [53]. Overall, The SEM and EDS results emphasize the significance of nanoparticle concentration in determining the morphology and elemental composition of nanocomposite films. According to the observed trends in our study, the highest water adsorption capacity was seen in system F1, which had the lowest concentration of nanoparticles. This suggests that better dispersion, rather than higher chitosan content, played a key role in enhancing adsorption performance. Optimal concentrations, such as those in F1, achieve a balance between uniform dispersion and enhanced surface area, crucial for water harvesting applications. Excessive loading, as observed in F3, results in aggregation, potentially limiting functional performance. These findings highlight the importance of optimizing nanoparticle dosage for enhanced performance, consistent with previous studies on nanomaterial-based systems [50-52]. 3.4. Water Contact Angle (WCA) Water contact angle measurements provide critical insights into the hydrophilic properties of CH/SiO₂@ZnO NC films. As shown in Figure 7, contact angles for the films were measured at 46° (F1), 50° (F2) and 58° (F3), compared to 95° for the pure chitosan film (CH). The lower contact angles observed in the nanocomposite films indicate enhanced hydrophilicity, essential for efficient water adsorption, absorption and condensation in atmospheric water harvesting applications. The enhanced hydrophilicity observed in the CH/SiO₂@ZnO nanocomposite (NC) films is primarily attributed to the zinc oxide nanoparticles, particularly in their hexagonal phase synthesized using the green extract detailed in this study. This method has been shown to significantly improve surface wettability and permeability [54, 55]. Additionally, previous research by Kusworo et al. (2021) demonstrated that green synthesis-derived ZnO nanoparticles effectively enhance surface wettability and water uptake [54]. Moreover, the incorporation of agricultural waste-derived mesoporous silica, from banana peels and peanut shells, also synthesized using the green extract detailed in this study, significantly contributes to the films' improved interaction with water molecules, owing to its high surface area and enhanced thermal conductivity [56, 57]. In fact, it has been mentioned in literature that the strategic use of green synthesis methods enhances the structural and functional properties of nanoparticles, aligning with previous studies highlighting the advantages of environmentally friendly synthesis techniques [58]. Overall, compared to pure chitosan films, which have been reported in the literature to exhibit water contact angles ranging from 74° to 104° depending on the study [20, 59], the CH/SiO₂@ZnO NC films demonstrated significantly lower contact angles. This reduction confirms their improved hydrophilicity and highlights their suitability for water harvesting applications. The observed enhancement in hydrophilicity of the CH/SiO₂@ZnO NC films is crucial for atmospheric water harvesting, as effective interaction with water vapor significantly impacts adsorption and condensation efficiency, which aligns with water contact angles of adsorbents/absorbents that have been used in water harvesting applications such as hydrogels and MOFs [60, 61]. Previous studies on chitosan-based nanocomposite scaffolds and films indicate that adding nanocomposites increases surface roughness, which significantly influences the wetting behavior of surfaces, often enhancing hydrophilicity due to increased surface area and more interaction sites for water vapor adsorption [62]. This topic will be developed in Section 3.5. Moreover, Figure 7 shows that the careful selection and concentration of NC are crucial for achieving desired hydrophilicity in films. System F1, having a lower NC concentration than Systems F2 and F3, demonstrated better hydrophilicity. This suggests that increasing nanoparticle concentrations beyond a specific threshold results in higher water contact angles, despite the associated increase in surface roughness and the nanoparticles’ inherent hydrophilicity. This phenomenon is attributed to physicochemical factors such as surface roughness and nanoparticle agglomeration. Ultimately, optimizing nanoparticle concentration was crucial for achieving moderate hydrophilicity, which was sufficient for effective moisture capture from the air without overly facilitating water penetration, highlighting the importance of balancing nanoparticle concentration with surface properties. 3.5. Confocal Microscopy Figure 8 presents the 3D Confocal Microscopy (CM) surface topography images and roughness measurements of the CH/SiO₂@ZnO NC films (F1, F2 and F3), computed through Image-J software. The roughness values recorded were 0.141 µm for F1 (low nanoparticle content), 0.144 µm for F2 (medium nanoparticle content), and 0.269 µm for F3 (high nanoparticle content), with corresponding root mean square roughness values of 0.172 µm, 0.189 µm, and 0.348 µm, respectively. The data indicate an increase in surface roughness with a higher surface texture complexity with higher nanoparticle concentrations, within the chitosan matrix . This trend is consistent with previous studies, which have shown that an increase in nanoparticle content in similar systems, such as chitosan-based nanocomposite films or scaffolds, enhances surface texture. This enhancement is attributed to nanoparticle agglomeration and uneven distribution [62, 63]. Notably, F1, which exhibited the lowest surface roughness, also showed the highest hydrophilicity, challenging the conventional understanding that increased roughness enhances hydrophilicity. This deviation can be attributed to the unique interactions of nanostructured surfaces, where the integration of nanoparticles influences surface energy and wettability [63, 64]. The complexity of surface interactions at the nanoscale highlights the importance of nanoparticle concentration and dispersion. As demonstrated in similar studies by Du et al. (2022) and Liu et al. (2024), nanomaterials with well-dispersed nanoparticles often display varied hydrophilic or hydrophobic properties based on their surface morphology and the nature of nanoparticle integration [63, 64]. The results emphasize the critical balance between surface roughness, nanoparticle concentration and functional performance in water capture applications. The data provided in the inserted table detail the surface roughness parameters, including average roughness (Ra) and root mean square roughness (Rq), further illustrating the impact of nanoparticle incorporation on surface texture. Enhanced roughness due to nanoparticles increases the surface area for water vapor adsorption, improving water capture efficiency. However, optimal nanoparticle concentration is crucial, as excessive amounts can lead to particle agglomeration, reducing effectiveness by creating blockages and uneven surfaces. Thus, fine-tuning these parameters is essential for maximizing water harvesting efficiency. 3.6. Thermal Stability Figure 9 presents the thermal stability analysis of the CH/SiO₂@ZnO NC films (F1, F2, and F3) and pure chitosan (CH), demonstrating distinct thermal stability profiles based on nanoparticle content. Initially, all samples retain over 85% of their original mass up to approximately 70 °C, attributed to the evaporation of adsorbed water rather than material degradation, a behavior consistent with observations in similar systems of chitosan-based films and hydrogels [65]. This initial mass loss confirms the films' capability for rapid moisture adsorption and release, which is crucial for atmospheric water harvesting applications. As the temperature increases, the incorporation of silica and zinc oxide nanoparticles enhances the thermal stability of the chitosan matrix. F1, featuring the optimal NC concentration as emphasized in this study, exhibited slightly better thermal resistance than F2 and F3. However, all systems showed comparable thermal resistance and significant enhancement over the chitosan-only films. The TGA results in Figure 8 highlight that the CH/SiO₂@ZnO NC films remain stable even beyond 300 °C, while pure chitosan (CH) exhibits a lower thermal stability with rapid degradation after initial water loss. This highlights the significant improvement in thermal resistance achieved by incorporating nanoparticles. Enhanced thermal stability is particularly valuable in atmospheric water harvesting systems, where materials are often exposed to fluctuating temperatures during water collection and evaporation processes [66]. While our study confirms the positive effect of silica and zinc oxide nanoparticles in enhancing the thermal resistance of chitosan-based films, as demonstrated in previous studies, we also note distinctions that may not currently align with existing literature [67]. These differences are crucial for a thorough comparison of properties and highlight the unique aspects of our research, thereby contributing new insights to the field. This improvement in thermal stability ensures that the CH/SiO₂@ZnO NC films maintain their structural integrity during repeated wet and dry cycles, a critical factor for the durability and efficiency of water-harvesting materials. The findings further underscore the importance of nanoparticle incorporation in enhancing the thermal and functional properties of biopolymer-based materials, making them more effective for long-term environmental applications [67, 68]. To explore the specific effects of nanoparticle concentration on these enhancements, a series of tests were conducted across a range of nanoparticle loadings. F1, which features the optimal concentration of nanoparticles, demonstrated superior thermal resistance compared to F2 and F3. This challenges the assumptions mentioned in the literature that higher nanoparticle concentrations in F3 would enhance thermal stability within the composite matrix [69]. Instead, the results indicate that all systems exhibit comparable thermal resistance, significantly surpassing that of chitosan-only films. These findings emphasize the importance of optimizing nanoparticle concentration to achieve the best balance of properties for environmental applications, where materials must withstand cyclical and extreme temperature fluctuations. Such insights are crucial for designing nanocomposite films that meet specific requirements in environmental sustainability. 3.7. Mechanical Properties Figure 10 and Table 3 present the mechanical properties of the CH/SiO₂@ZnO NC films (F1, F2, and F3) and pure chitosan (CH) film as determined by the tensile test. The control sample, pure chitosan (CH) film, establishes a baseline with moderate mechanical properties, while the incorporation of silica and zinc oxide nanoparticles significantly enhances these properties depending on the concentration. Incorporation of a moderate concentration of nanoparticles (system F1) led to noticeable improvements in mechanical parameters, especially in stiffness and strength: Young's Modulus and maximum stress increased by 8.7% and 20%, respectively, although no significant differences in strain at break. Further increases in nanoparticle concentration (system F2) continued this trend, with an increase of 26.3% in the Young’s Modulus and 80% in the maximum stress, with respect to the control system. This indicates that higher nanoparticle concentrations can enhance mechanical strength and stiffness without sacrificing elasticity. However, system F3, which had the highest concentration of nanoparticles, showed significant increases in Young's Modulus (344 %) and maximum stress (247 %) but a decrease in strain at break (reduction of 33 %). This reduction highlights a bending point where further increases in nanoparticle content led to increased rigidity and reduced flexibility, undermining the material’s ability to elongate before breaking. These findings demonstrate that while nanoparticle enhancement can significantly improve the mechanical properties of chitosan-based films, there is a critical balance to be achieved. This trend highlights a balance between enhancing mechanical strength and maintaining elasticity, which is crucial for atmospheric water harvesting applications. Higher nanoparticle concentrations improve film durability and structural integrity, but excessive loading may reduce flexibility. Similarly, lower concentrations, as tested in F1, represent the optimal lower limit, as concentrations below this showed effects ranging from good to less favorable. These findings align with previous studies, such as those by Vafaei et al., who reported similar mechanical behavior in biopolymer-nanoparticle composites, emphasizing the need for optimized nanoparticle content for superior mechanical performance [70]. The CH/SiO₂@ZnO NC films' enhanced mechanical properties make them suitable for atmospheric water harvesting, ensuring robustness under varying environmental conditions and multiple cycles of moisture adsorption and desorption, consistent with previous research findings [71]. Table 3: Mechanical properties of CH/SiO₂@ZnO NC films (F1, F2, and F3) and pure chitosan (CH), including Young’s Modulus, Maximum Stress, and Strain at Break. Sample Young’s Modulus (kPa) Maximum stress (kPa) Strain at break (mm/mm) CH (Control) 3661 ± 35 a 793 ± 27 A 0.27 ± 0.05 α F1 3980 ± 46 b 951 ± 23 B 0.35 ± 0.07 α F2 4624 ± 24 c 1427 ± 37 C 0.35 ± 0.08 α F3 16274 ± 124 d 2755 ± 74 D 0.18 ± 0.05 β F1 = lowest silica/zinc oxide content (15%), F2 = medium content (20%), F3 = highest content (40%). Different letters indicate statistically significant differences (P≤0.05). 3.8. Antifungal and Antimicrobial Properties The incorporation of CH/SiO₂@ZnO NC into chitosan films significantly enhances their antifungal and antimicrobial properties, crucial for maintaining water quality and ensuring the safety of drinking water. As shown in Figure 11, the chitosan-only film (CH) developed visible mold within one week, highlighting its limited antimicrobial effectiveness despite chitosan’s inherent antimicrobial properties, which rely on binding to microbial cell membranes and causing structural disruptions [72]. In contrast, the CH/SiO₂@ZnO NC films (Figure 11) remained free from contamination during the same period, demonstrating superior antimicrobial resistance. This enhanced antimicrobial effect is attributed to the synergistic action of ZnO and silica nanoparticles. ZnO nanoparticles generate reactive oxygen species (ROS), which effectively damage microbial DNA, proteins and lipids, leading to cell death [73, 74]. Additionally, ZnO interacts with microbial cell walls, causing structural disruptions and lysis [72]. Silica nanoparticles stabilize ZnO within the chitosan matrix, prolonging the active antimicrobial phase and ensuring a consistent release of antimicrobial agents [73]. The mesoporous structure of nanosilica further contributes by protecting the biopolymer matrix from microbial degradation [75]. The results in Figure 11 illustrate that, unlike the chitosan-only film, which became contaminated within a week, the CH/SiO₂@ZnO NC films exhibited no microbial growth during the same period. This extended protection is particularly advantageous for atmospheric water harvesting applications, where maintaining water quality is essential. Furthermore, the antimicrobial enhancement complements the thermal and mechanical improvements observed in the nanocomposite films, making them suitable for prolonged use in water harvesting systems. The dual functionality of these films, offering both structural durability and antimicrobial resistance, is essential for ensuring the safety and longevity of drinking water systems, consistent with previous studies that emphasize the role of nanoparticles in enhancing the functional properties of biopolymer films [72-75]. 3.9. Water Capture Figure 12 illustrates the water production capabilities of CH/SiO₂@ZnO NC films (F1, F2, and F3) over a two-week period, highlighting the influence of nanoparticle concentration on passive water harvesting. While pure chitosan films displayed lower water capture efficiency, the CH/SiO₂@ZnO NC films demonstrated significant improvements. Notably, the data reveals that under the established humidity conditions, the maximum water production is reached at 7 days, with F1 achieving the highest water generation rate of approximately 1.2 mL/g/day. This peak is an important aspect of the nanoparticle-enhanced water harvesting process observed in these films. The observed trends indicate that moderate nanoparticle concentrations, such as those in F1 and F2, optimize water capture efficiency by enhancing surface area and water adsorption capabilities. However, F3 shows slightly reduced performance due to potential nanoparticle agglomeration at higher concentrations. Importantly, we also correlated these findings with changes in contact angle, demonstrating that as nanoparticle concentration increases, the contact angle also increases, indicating a reduction in hydrophilicity. This correlation between nanoparticle concentration and hydrophilic properties, supported by both our measurements and literature [76, 77], underscores the importance of balancing nanoparticle content to prevent aggregation and maintain optimal performance. The moderate hydrophilicity of the CH/SiO₂@ZnO NC films, with contact angles between 30° and 60°, further enhanced water condensation, consistent with earlier research findings [78]. Enclosed conditions without airflow played a critical role in maintaining high water retention and absorption rates. Additionally, the films exhibited efficient water adsorption and desorption cycles even at relative humidity levels below 30%, making them suitable for low-humidity environments. This dual correlation of concentration effects with both performance and contact angle measurements enriches the discussion by illustrating how interconnected material properties contribute to overall functionality. Water production rates ranged from 0.7 to 1.2 mL/g/day (Figure 12), with F1 achieving optimal efficiency. This is attributed to its smaller nanoparticle sizes, which enhance the surface area significantly compared to films with larger nanoparticles. Films with a higher surface area, as seen in F1, enabled rapid water generation, initiating within two hours and maintaining short cyclic periods of approximately one hour for adsorption and desorption. This finding illustrates the critical role of nanoparticle size and surface area in optimizing water harvesting efficiency. The comparative analysis of the results demonstrates that CH/SiO₂@ZnO NC films have notable potential for eco-friendly passive water harvesting, aligning with the performance of current solar-based atmospheric water harvesting systems. These systems typically utilize metal nanoparticles to boost evaporation through surface plasmon resonance. Our study extends this concept by showing that green-synthesized nanoparticles can similarly enhance water capture efficiency but without requiring external energy inputs [75]. This comparison not only highlights the efficacy of our nanoparticle-enhanced materials but also underscores their applicability in environmental and energy-efficient technologies 4. Conclusions In conclusion, this study has successfully demonstrated the potential of chitosan-based nanocomposite films processed by canting and embedded with green silica and ZnO nanoparticles to address global water shortages. Our findings underscore the delicate balance required in nanoparticles and chitosan concentration for optimal performance, highlighting the complexity and sensitivity of designing effective nanocomposite films. The observed stability, particularly in films like F1 with uniform crystalline distribution and morphology, directly supports their functional reliability and improved moisture capture efficiency under variable environmental conditions. Results confirm that a critical SiO 2 and ZnO nanoparticle concentration threshold at 15 wt% within a chitosan matrix maintains mechanical durability, increases hydrophilicity, reduces nanoparticle aggregation and roughness and maximizes water capture efficiency, facilitating a passive auto-water generation process reaching to produce 1.2 mL/g of water without external energy input. This stability also provides the rationale behind enhanced durability and consistent performance observed during practical testing. The composition balance is crucial for scalable atmospheric water harvesting (AWH) device design, especially across varied temperature conditions. Notably, these chitosan films not only surpassed the basic functionality by preventing biocontamination, a common challenge in humid environments, but also showed superior disinfection properties compared to standalone chitosan films. Ultimately, this research contributes to the ongoing efforts to develop scalable, low-cost solutions for sustainable water harvesting, combining environmental responsibility with advanced nanotechnology. It paves the way for further investigation into the application-specific designs of nanoparticle-enhanced materials, reinforcing the importance of nanotechnology in solving critical environmental challenges. This study not only advances the field of atmospheric water harvesting but also offers a promising avenue for future technological innovations in water scarcity management. Declarations Author Contributions: For research articles with several authors, a short paragraph specifying their individual contributions must be provided. The following statements should be used: Conceptualization, N. A-S. and J. A.A.A.; methodology, N. A-S. and J. A.A.A.; software, N.A-S. and J.A.A.A.; validation, N. A-S., J.A.A.A. and A.R.; formal analysis, N. A-S, V.P.P. and A.R.; investigation, N.A-S.; resources, A.R.; data curation, N.A-S and V.P.P; writing—original draft preparation, N. A-S and J.A.A.A.; writing—review and editing, V.P.P. and A.R.; visualization, J.A.A.A., V.P.P. and A.R.; supervision, V.P.P. and A.R.; project administration, A.R.; funding acquisition, A.R. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the project “Eco-Friendly Membranes for Moisture Collection” (Project Reference: PR202405209), supported by Innovation Hub Solutions . Data Availability Statement: Data supporting this study are available from the corresponding authors upon reasonable request. Acknowledgments: The authors would like to thank Innovation Hub Solutions for funding the project “Eco-Friendly Membranes for Moisture Collection” (Project Reference: PR202405209). We also acknowledge CITIUS for providing access to the X-Ray, Functional Characterization, and Microscopy services used in this study. Conflicts of Interest: The authors declare no conflicts of interest. AI Declaration : During manuscript preparation, the authors used Grammarly for grammar checks and ChatGPT-4 for initial language refinement. The content was rigorously reviewed, edited, and validated by the authors, who assumed full responsibility for the work’s integrity. References Gleick PH, Cooley H. Freshwater scarcity. Annual Review of Environment and Resources. 2021 Oct 18;46(1):319-48. 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Molecules. 2021 Nov 25;26(23):7136. Safavinia L, Akhgar MR, Tahamipour B, Ahmadi SA. Green synthesis of highly dispersed zinc oxide nanoparticles supported on silica gel matrix by Daphne oleoides extract and their antibacterial activity. Iranian Journal of Biotechnology. 2021 Jan;19(1):e2598. Ugalde-Arbizu M, Aguilera-Correa JJ, San Sebastian E, Páez PL, Nogales E, Esteban J, Gómez-Ruiz S. Antibacterial properties of mesoporous silica nanoparticles modified with fluoroquinolones and copper or silver species. Pharmaceuticals. 2023 Jul 5;16(7):961. Solanki R, Makwana N, Kumar R, Joshi M, Patel A, Bhatia D, Sahoo DK. Nanomedicines as a cutting-edge solution to combat antimicrobial resistance. RSC advances. 2024;14(45):33568-86. Ejeian M, Wang RZ. Adsorption-based atmospheric water harvesting. Joule. 2021 Jul 21;5(7):1678-703. Wei Q, Mukaida M, Ding W, Ishida T. Humidity control in a closed system utilizing conducting polymers. RSC advances. 2018;8(23):12540-6. Miao A, Wei M, Xu F, Wang Y. Influence of membrane hydrophilicity on water permeability: An experimental study bridging simulations. Journal of Membrane Science. 2020 Jun 1;604:118087. Liu Q, Qin C, Solomin E, Chen Q, Wu W, Zhu Q, Mahian O. Research progress on the development of new nano materials for solar-driven sorption-based atmospheric water harvesting and corresponding system applications. Nano Energy. 2023 Oct;115:108660. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6819891","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":475843653,"identity":"e373c212-411d-4ad3-982a-05cceb1d8eba","order_by":0,"name":"Noor Al-Sadeq","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzklEQVRIiWNgGAWjYJACZgY2BgZ+BuYGErVINjCSqsXgALFazNmbD34uKLOzNz5+sE3qBsNhewb29gd4tVj2HEuWnnEuOXHbmcQ26RyGw4kNPGcM8GoxuJFjIM3bxpxgdgCiJYFBIge/w4BajH/zttXbG/c/BGuxZ5B/jt9hQC1mQFsOM26QgNjC2CDBQMBhZ46lWc84dzxxxo2HzdY5BumJbTw5BLQcbz58u6Cs2p6/P/ng7ZwKa3t+9uP4HYZuAgMojkbBKBgFo2AUUAoADfxC5Mg3ogUAAAAASUVORK5CYII=","orcid":"","institution":"Universidad de Sevilla","correspondingAuthor":true,"prefix":"","firstName":"Noor","middleName":"","lastName":"Al-Sadeq","suffix":""},{"id":475843654,"identity":"e0b83712-c407-4563-b88e-365cf6c07d33","order_by":1,"name":"Víctor M. Perez-Puyana","email":"","orcid":"","institution":"Universidad de Sevilla","correspondingAuthor":false,"prefix":"","firstName":"Víctor","middleName":"M.","lastName":"Perez-Puyana","suffix":""},{"id":475843655,"identity":"a2cee90e-bb5b-4ad5-a347-12c6f403f34d","order_by":2,"name":"Alberto Romero","email":"","orcid":"","institution":"Universidad de Sevilla","correspondingAuthor":false,"prefix":"","firstName":"Alberto","middleName":"","lastName":"Romero","suffix":""},{"id":475843656,"identity":"ee7b1843-3a93-41a7-a36e-fcba2deec4db","order_by":3,"name":"Johar Amin Ahmed Abdullah","email":"","orcid":"","institution":"Universidad de Sevilla","correspondingAuthor":false,"prefix":"","firstName":"Johar","middleName":"Amin Ahmed","lastName":"Abdullah","suffix":""}],"badges":[],"createdAt":"2025-06-04 11:23:20","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6819891/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6819891/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":85374618,"identity":"d3c6fcdf-2e31-4b4c-ab59-e29a0168d200","added_by":"auto","created_at":"2025-06-25 08:18:20","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":85547,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eSchematic illustration of the green synthesis and casting process for CH/SiO₂@ZnO NC films, showing the preparation steps including mixing, stirring, sonication and casting into molds.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6819891/v1/f57f4bb580964790eddee20d.png"},{"id":85374512,"identity":"ec62c49d-23f3-4d60-aee3-38cf1bcae7a2","added_by":"auto","created_at":"2025-06-25 08:10:20","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":79946,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eX-ray diffraction (XRD) patterns of (A) green SiO₂ NPs and (B) green ZnO NPs prior to incorporation into the chitosan matrix.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6819891/v1/07d9d92a62439097b275f28d.png"},{"id":85375804,"identity":"3e29e32c-4c5d-4e7d-a4e3-21fbe56b6c26","added_by":"auto","created_at":"2025-06-25 08:26:20","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":96103,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eX-ray diffraction (XRD) patterns of green SiO\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e NPs, green ZnO NPs and \u003c/em\u003eCH/SiO₂@ZnO NC\u003cem\u003e films with varying nanoparticle concentrations: F1, F2, and F3, corresponding to low (15%), medium (20%) and high (40%) silica and zinc oxide content, respectively.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6819891/v1/aa24f1a7bbdcdc7959c9c8e9.png"},{"id":85374515,"identity":"c08b13cf-162a-4520-aa2a-93716cb6c115","added_by":"auto","created_at":"2025-06-25 08:10:20","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":72115,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eFTIR spectra of CH/SiO₂@ZnO NC films (\u003c/em\u003e\u003cem\u003e\u003cstrong\u003eF1\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e, \u003c/em\u003e\u003cem\u003e\u003cstrong\u003eF2\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e, and \u003c/em\u003e\u003cem\u003e\u003cstrong\u003eF3\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e).\u003c/em\u003e\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6819891/v1/785723632b358d0f12d05165.png"},{"id":85374619,"identity":"04b977f6-4da1-4221-a34f-2f02b865f4d4","added_by":"auto","created_at":"2025-06-25 08:18:20","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":181088,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eScanning Electron Microscopy (SEM) images of nanoparticles and chitosan-based nanocomposite films. (A) SiO₂ NPs. (B) ZnO NPs. (F1, F2, F3) SEM images of CH/SiO₂@ZnO \u0026nbsp;NC films with low (F1), medium (F2), and high (F3) silica and zinc oxide content. (C) Histogram distribution showing the nanosize range of F1, F2, and F3.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6819891/v1/dea701c2a921a7d7a6021702.png"},{"id":85374519,"identity":"31fd3afe-d45a-418f-9795-daa221d7b346","added_by":"auto","created_at":"2025-06-25 08:10:20","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":278409,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eEnergy-Dispersive X-ray Spectroscopy (EDS) \u003c/em\u003e\u0026nbsp;\u003cem\u003eCH/SiO₂@ZnO NC films with varying nanoparticle concentrations: (F1) low (15%), and (F3) high (40%) silica and zinc oxide content. The EDS spectrum highlights the elemental composition, showing the presence of carbon (C), nitrogen (N), oxygen (O), silicon (Si) and zinc (Zn).\u003c/em\u003e\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6819891/v1/50d4ce3c9e7f13b91dc794bf.png"},{"id":85374522,"identity":"fe18b045-1442-4f8e-aed4-64b0bf1ab16e","added_by":"auto","created_at":"2025-06-25 08:10:20","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":426041,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eWater Contact angle measurements of chitosan-based films: (CH) pure chitosan film, and the CH/SiO₂@ZnO NC films: (F1) low (15%), and (F3) high (40%) silica and zinc oxide content\u003c/em\u003e\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6819891/v1/6ac809986e2db50fc3fae817.png"},{"id":85374516,"identity":"788b96c3-3f5e-4a10-bd0d-07c9273a34be","added_by":"auto","created_at":"2025-06-25 08:10:20","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":215360,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eConfocal Microscopy 3D surface topography images of CH/SiO₂@ZnO NC films: (F1) low (15%), (F2) medium (20%), and (F3) high (40%) silica and zinc oxide content. The inserted table provides surface roughness parameters, including average roughness (Ra) and root mean square roughness (Rq) for each sample.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6819891/v1/e6349a91fb49b66bffb451df.png"},{"id":85375806,"identity":"2b8e49b0-3ec9-42c6-b096-62e283c1bdd8","added_by":"auto","created_at":"2025-06-25 08:26:20","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":295208,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eThermogravimetric analysis (TGA) curves of CH/SiO₂@ZnO NC films (F1, F2, and F3) and pure chitosan (CH) showing mass loss as a function of temperature.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-6819891/v1/d4021963fcc461720be21747.png"},{"id":85374523,"identity":"bf4da050-5d1f-4967-b050-fca0b94b359a","added_by":"auto","created_at":"2025-06-25 08:10:20","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":369923,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eStress-strain curves of CH/SiO₂@ZnO NC films (F1, F2, and F3) and pure chitosan (CH).\u003c/em\u003e\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-6819891/v1/988b8431a0cb360da9fdf8e1.png"},{"id":85374621,"identity":"76dc6427-8abf-41b9-9e57-ad6cd237a956","added_by":"auto","created_at":"2025-06-25 08:18:20","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":267826,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003ePhotographic comparison of chitosan-only film (CH) and CH/SiO₂@ZnO NC \u0026nbsp;films after one week of exposure.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-6819891/v1/8cdb09e02143d7345be876ed.png"},{"id":85375805,"identity":"71d8eb85-0d8f-4000-bdc8-5d1febe425b3","added_by":"auto","created_at":"2025-06-25 08:26:20","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":58736,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003ePassive water generation rates of CH/SiO₂@ZnO NC films (F1, F2, and F3) over 14 days. These experiments were conducted under conditions of relative humidity (RH) at 30% \u003c/em\u003e\u003cu\u003e\u003cem\u003e+\u003c/em\u003e\u003c/u\u003e\u003cem\u003e 2% room temperature.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-6819891/v1/c0e28be09ea01d61b69a998b.png"},{"id":85659704,"identity":"141e1080-9729-4ee7-ac11-1cd788157362","added_by":"auto","created_at":"2025-06-30 11:24:23","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3627256,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6819891/v1/429e2021-7749-4667-a233-929cd5ca60c8.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Enhancing Atmospheric Water Harvesting Applications through the Integration of Green Silica and Zinc Oxide Nanoparticles into Chitosan Biopolymer","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe lack of access to clean water is a growing global challenge that threatens human lives and sustainable development. Many countries are facing their worst-ever water crisis, with the situation expected to worsen in the coming years due to factors such as population growth, urbanization, unsustainable water usage, and climate change [1]. As traditional freshwater sources continue to diminish, innovative technological solutions are urgently required to address this escalating crisis [2]. From the advancement of renewable energy systems and breakthroughs in desalination techniques to innovations in smart agriculture and efficient resource management, several cutting-edge technologies are driving global sustainability forward [2]. Among these, Atmospheric Water Harvesting (AWH) distinguishes itself by providing a vital solution for extracting sustainable freshwater from atmospheric humidity, especially critical for water-stressed, landlocked, or ecologically sensitive regions [3, 4].\u003c/p\u003e\n\u003cp\u003eAWH techniques tap into the nearly inexhaustible water present in the atmosphere, which holds approximately 13,000 km\u0026sup3; of freshwater at any given time. These technologies can be categorized into several types, each with distinct principles, advantages, and limitations [3]. According to Gao et al., study (2023), it can be inferred that Atmospheric Water Harvesting (AWH) technologies can be categorized based on three main techniques: condensation-based systems (multi-process sorption), wet desiccation systems (hygroscopic liquid absorption), and adsorption-based systems (hygroscopic solid adsorption) [4]. Condensation-based systems (multi-process sorption) operate at the air/solid and liquid/solid interfaces where vapor condensation and droplet transport are managed through chemical and topological heterogeneous designs. These systems, which function by cooling moist air below its dew point to condense water vapor, are highly energy-intensive and perform optimally in humid environments. They often require significant energy inputs, such as underground or radiation cooling, to sustain condensation processes [4, 5]. Wet desiccation systems (hygroscopic liquid absorption) rely on hygroscopic materials at the air/liquid interface to absorb moisture from the air. These systems utilize interface thermal management strategies like bulk and sustainable interfacial heating to enhance moisture absorption and desorption rates. However, like their solid counterparts, they face challenges due to the energy required to regenerate the desiccants, thus affecting their efficiency and overall operational sustainability [6]. Adsorption-based systems (hygroscopic solid adsorption), particularly those utilizing Metal-Organic Frameworks (MOFs) at the air/solid interface, excel in capturing water vapor even in low-humidity conditions. These systems benefit from the modification of bonding sites, adjustment of intra/interparticle pores, and regulation of pore volume and water affinity to maximize water capture and retention. Despite their high adsorption capacity, they are limited by high material costs and the substantial energy demand for water release, impacting their economic feasibility [7]. While each method: condensation, adsorption, and wet desiccation, provides innovative solutions for water scarcity, they all present significant challenges related to energy consumption, cost, operational efficiency, and scalability. These issues hinder their widespread adoption, necessitating further research and development to refine these technologies for more sustainable and cost-effective applications across diverse climatic conditions. This backdrop sets the stage for exploring alternative approaches, such as green synthesis, which promises to address some of these fundamental challenges by utilizing sustainable methods and materials [8].\u0026nbsp;To address pressing challenges in water scarcity, our work introduces the development of a nanocomposite designed specifically for use in atmospheric water harvesting (AWH) systems. This material, comprising chitosan-based green silica and zinc oxide, is engineered to be a cost-effective, environmentally friendly solution that optimizes water capture.\u0026nbsp;Before delving into the specific material development, it is crucial to define green synthesis, a sustainable and environmentally friendly method that uses natural extracts as reducing agents to synthesize nanoparticles. This process minimizes environmental impact and enhances the functional properties of nanoparticles [6, 8]. In this context, green extracts from agricultural waste are selected to enhance the hydrophilicity of nanoparticles, thereby improving the water-capture capabilities of films [9]. For example, The \u003cem\u003ePhoenix dactylifera\u0026nbsp;\u003c/em\u003eL\u003cem\u003e.\u003c/em\u003e leaf extract, for instance, has been proven through studies to effectively reduce metal ions to form nanoparticles while also fine-tuning the balance between hydrophobicity and hydrophilicity [9]. This dual functionality enhances the sustainability and safety of the process while maintaining the consistency and quality of the nanoparticles produced. In addition, the use of natural phytochemicals can help to produce smaller nanoparticles with a larger surface area, crucial for enhancing water adsorption mechanisms without the need for high temperatures or synthetic chemicals [9]. The control of nanoparticle size within this nanocomposite is a critical factor in water-related applications, significantly impacting the water absorption capacity. Smaller nanoparticles, due to their larger surface area to volume ratio, enhance their interaction with water molecules, which increases the efficiency of water capture [10]. This precise control over size is essential for optimizing the performance of nanocomposites in atmospheric water harvesting (AWH) systems. Additionally, the appropriate sizing of metal oxide nanoparticles, such as zinc oxide, not only helps limit bacterial growth and reduce toxicity but also enhances the material\u0026apos;s applicability in water purification [11]. On the other hand, chitosan, a biodegradable polymer derived from chitin, is an abundant, sustainable resource noted for its excellent water management properties [12]. It finds diverse applications in the water industry, evident in forms such as powders, films, and beads. For instance, chitosan nanoparticles in powder form are increasingly utilized in water filtration to enhance the extraction of heavy metals from wastewater [12]. Chitosan films, including biopolymeric membranes, have proven effective in ultrafiltration technologies for removing contaminants and pathogens, ensuring safer drinking water [13]. Additionally, chitosan beads are employed to adsorb dyes from textile industry effluents, demonstrating their utility in managing industrial wastewater. These varied applications underline chitosan\u0026apos;s crucial role in promoting sustainable water treatment practices [14].\u0026nbsp;Incorporating nanoparticles into the chitosan matrix, specifically zinc oxide and silica, has been shown to significantly enhance functional properties such as disinfection and antimicrobial activity, critical for water-related applications [15]. Silica nanoparticles, sourced sustainably from agricultural waste like rice husk, bring dehumidification properties to the composite. This sustainable sourcing is not only effective but also environmentally beneficial, leveraging waste materials for productive use and utilizing silica, which is an abundant natural material [16].\u0026nbsp;Following the introduction of silica, zinc oxide nanoparticles play a specialized role by adjusting the hydrophilicity and hydrophobicity of the chitosan matrix. These adjustments are essential for efficient interaction with water molecules and enhancing the water capture capabilities of the composites. Furthermore, zinc oxide nanoparticles contribute to strengthening the structural integrity and increasing the durability of the composites and their antimicrobial properties are crucial for maintaining the purity of collected water, ensuring it is safe for use [17].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis study introduces a novel chitosan-silica-zinc oxide nanocomposite films, designed to enhance atmospheric water harvesting (AWH) systems. The primary objective is to develop an environmentally friendly and cost-effective alternative to existing materials such as metal-organic frameworks (MOFs), which, despite their high efficiency, often remain economically unfeasible due to high production costs [18]. The proposed nanocomposite addresses key technical, economic, and environmental challenges, offering notable advantages such as reduced energy consumption and improved efficiency. Specifically, by promoting effective water condensation at higher temperatures, it significantly lowers the dependence on intensive cooling processes, making passive AWH devices more practical and affordable. These advancements enhance the global applicability and commercial viability of AWH systems, providing a sustainable and innovative solution to the ongoing water crisis.\u003c/p\u003e"},{"header":"2. Methods","content":"\u003cp\u003e\u003cstrong\u003e2.1. Materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eChitosan (CH, 98% deacetylation, Mv = 1.61\u0026middot;10\u003csup\u003e5\u003c/sup\u003e g\u0026middot;mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e), Zinc chloride (ZnCl\u003csub\u003e2\u003c/sub\u003e), gallic acid (C\u003csub\u003e7\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e), acetone (CH\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003eCO, acetic acid CH\u003csub\u003e3\u003c/sub\u003eCOOH, sodium hydroxide solution (NaOH), hydrochloric acid (HCl), sulfuric acid (H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e), polyethylene glycol (PEG) and DPPH (2,2-diphenyl-1-picrylhydrazyl) were obtained from Sigma Aldrich (Germany). Also, banana peels, peanut shell waste and date palm leaves were used for the green nanocomposite preparation. The banana peels and peanut shells were sourced from fresh bananas and peanuts obtained from a local market, while the date palm leaves were collected from fallen leaves of palms in Seville. All other reagents and chemicals used in this study were of an analytical quality.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.2. Methodology of Fabricating the CH/SiO₂@ZnO NC Films\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo optimize the formulation of CH/SiO₂@ZnO NC (chitosan-silica-zinc oxide nanocomposite) films, the Minitab Box-Behnken Design of Experiments (DOE) was implemented. This statistical approach is crucial for exploring interactions among variables, particularly in environmental studies utilizing green adsorbents and absorbents [20]. Through this method, 14 experimental runs were conducted, including four central points, focusing on three variables: zinc oxide nanoparticle concentration, silica nanoparticle concentration and chitosan concentration.\u0026nbsp;Consistent film thickness was maintained across\u0026nbsp;all samples, a critical parameter achieved through precise calibration of the casting process. A volume of 45 \u0026plusmn; 0.5 mL was poured for all films to ensure uniformity and maintain a thickness of 1.0 \u0026plusmn; 0.2 mm. This rigorous control of each sample\u0026apos;s thickness facilitated valid comparisons of material properties across different formulations. The DOE thoroughly investigated a range of nanoparticle concentrations, designed to cover the lower (0.3 w/v%), middle (0.4 w/v%) and higher (0.8 w/v%) limits. Similarly, Chitosan concentrations in the DOE spanned from 1 to 3 w/v%. It was observed that concentrations below 2% w/v led to films with poor mechanical strength and uneven nanoparticle distribution, which compromised the structural integrity and functionality of the films. Conversely, at 2% w/v, chitosan provided higher viscosity, which ensured uniform nanoparticle embedding and optimal intermolecular interactions, crucial for a robust and durable film structure.\u0026nbsp;Consequently, a chitosan concentration of 2% w/v was selected as the optimal concentration within the tested range. Therefore, the systems chosen from these runs were Run 7 (System F1), CP4 central point (System F2), and Run 10 (System F3), each utilizing varying nanoparticle concentrations, ranging from the lower (0.3 wt%), through the middle (0.4 wt%), to the higher (0.8 wt%), to evaluate their effects on the films\u0026apos; water adsorption, mechanical properties, and antibacterial effectiveness. These systems are detailed in Table 1 in section 2.2.4.\u0026nbsp;Additionally, polyethylene glycol (PEG) at a concentration of 2% w/v was employed as a plasticizer to enhance film flexibility and durability, while also stabilizing nanoparticle dispersion to prevent agglomeration. Lower concentrations of PEG led to brittle films prone to cracking, further validating the choice of 2% w/v for both PEG and chitosan. This methodical integration of DOE findings and controlled experimentation ensured that the selected chitosan and nanoparticle concentrations maximized the functional potential of the nanocomposites for effective water capture applications, aligning with empirical evidence and scientific validation from previous studies [21].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.2.1. Green Extracts Preparation\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn this study, the green extract was derived from the leaves of banana peels and \u003cem\u003ePhoenix dactylifera\u003c/em\u003e L. (date palm). Banana peel extract was selected for its ability to enhance nanoparticle hydrophilicity, thereby improving the films\u0026rsquo; functional properties for water capture, as indicated by our literature review [22]. \u0026nbsp;In addition, Banana peel extract can be very effective in the green synthesis of nanomaterials, like the zinc oxide nanomaterials influencing their yield, size, shape, and purity; these nanomaterials exhibit antibacterial activity when varying the extract and precursor concentrations [23, 24].\u003cem\u003e\u0026nbsp;Phoenix dactylifera\u0026nbsp;\u003c/em\u003eL\u003cem\u003e.\u003c/em\u003e leaf extract, known for its capacity to store water under desert conditions, was used not only as an efficient reducing agent for metal ions but also to benefit the hydrophobicity/hydrophilicity balance, enhancing both the sustainability and safety of the process [21]. The preparation method for the banana peel extract was adapted from\u0026nbsp;Abdullah\u0026nbsp;et al. (2024), with modifications to enhance its disinfection properties to meet our specific design needs [22]. Fresh bananas were locally sourced and thoroughly washed with distilled water and their peels were sterilized by drying at 90\u0026deg;C for 24 hours. The dried peels were ground into fine powder, mixed with distilled water (1:10 w/v), boiled for 10 minutes, filtered and cooled, yielding the banana peel extract. The preparation method for the \u003cem\u003ePhoenix dactylifera\u003c/em\u003e L. leaves was followed exactly as described by Abdullah et al. (2024) [22]. The final extract solution was a combination of banana peel and date palm leaf extracts in a 1:1 v/v ratio.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.2.2. Green ZnO Nanoparticle Preparation\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFollowing the methodology described by Gharbi et al. (2025), 20 mL of the extract, with a concentration of 4 mg/mL, was gradually added to a mixed solution of zinc chloride and zinc acetate. This specific concentration was chosen based on its demonstrated efficacy in the referenced study for achieving the desired chemical reaction [25]. The green ZnO solution was prepared by dissolving 0.545 g of ZnCl₂ and 0.438 g of Zn(CH₃COO)₂ in 20 mL of distilled water. This procedure achieved a concentration of 0.2 M, referring specifically to the molarity of the zinc ions (Zn\u0026sup2;⁺) in the solution [25]. To promote the environmentally friendly synthesis of zinc oxide nanoparticles, the diluted green extract (4 mg/mL) was gradually added to the ZnO solution. This approach aligns with green chemistry principles by reducing the need for hazardous chemicals and utilizing a sustainable, plant-based extract to facilitate nanoparticle formation. This method of gradual addition has been well-documented and recognized in several studies and applications for its effectiveness in controlling nucleation, which is crucial for producing nanoparticles with smaller and more uniform sizes [26]. The pH of the mixture was adjusted to 11 by adding 5 M NaOH. This process was repeated multiple times, adding additional extract and zinc solutions until the desired quantity of ZnO nanoparticles was obtained in an economically efficient manner. The solution was subjected to magnetic stirring at 50 \u0026deg;C for 2 hours to promote nanoparticle formation. The resulting precipitate was collected by filtration using Whatman No. 1 filter paper and thoroughly washed with distilled water to remove any impurities. The ZnO nanoparticles were then pretreated by heating at 105 \u0026deg;C overnight, followed by calcination at 300\u0026deg;C for 2 hours to produce the final ZnO nanoparticles [25].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.2.3. Green SiO\u003csub\u003e2\u003c/sub\u003e Nanoparticles Preparation\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo prepare nanosilica from peanut shells and banana peels, the materials were washed with distilled water to remove any impurities and then pre-dried in an oven overnight at 80 \u0026ordm;C. Following that, the dried peanut shells and banana peels were calcinated at 500-700 \u0026ordm;C for 2 hours, resulting in a black powder.\u0026nbsp;The powder was subjected to an acid treatment using 1 M hydrochloric acid (HCl), followed by washing with ethanol and water. After drying at 50 \u0026ordm;C for a day, it was calcined at progressive temperatures: 300 \u0026ordm;C for 2 hours, followed by 600 \u0026ordm;C for an additional hour. The material then underwent a base treatment with 200 mL of 5 M sodium hydroxide (NaOH). The pH was adjusted with 5 N sulfuric acid (H₂SO₄) and further fine-tuned by adding 20 mL of 5 M NaOH and 10 mL of the green extract. These precise pH adjustments are crucial not only for achieving a uniform nanoparticle size but also for preventing agglomeration. Research has demonstrated that pH significantly influences nanoparticle behavior, impacting their scattering properties and the tendency to form compact agglomerates [27]. By optimizing pH levels, our process not only enhances the optical properties, which are important for clearer SEM characterization, but also improves the functional characteristics of the nanoparticles [27]. Finally, the mixture was stirred at 50-60 \u0026ordm;C for 2 hours, filtered, washed, dried overnight and calcinated at 600 \u0026ordm;C. The resulting SiO\u003csub\u003e2\u003c/sub\u003e NPs are considered high purity, as indicated by the uniformity of the SEM images that will be detailed in the results and discussion sections. These images serve as evidence of the consistent particle size and shape, which are characteristic of high-purity materials, making them suitable for various applications.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.2.4\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e. Films Synthesis through Casting\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe films were fabricated using the casting method, enhancing mixture homogeneity, enabling early characterization, and supporting design modifications crucial for atmospheric water harvesting applications [28].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003cimg src=\"data:image/png;base64,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\" alt=\"image\" width=\"125\" height=\"43\"\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eFigure 1.\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cem\u003eSchematic illustration of the green synthesis and casting process for CH/SiO₂@ZnO NC films, showing the preparation steps including mixing, stirring, sonication and casting into molds.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eFigure 1 illustrates the green synthesis and casting process of the CH/SiO₂@ZnO NC films, describing the step-by-step method used for film preparation. Chitosan was dissolved in 0.05 M acetic acid and stirred at 600-700 rpm for 1 hour at 60 \u0026ordm;C, followed by 15 minutes of mechanical agitation. The green nanoparticles solution, consisting of SiO\u003csub\u003e2\u003c/sub\u003e and ZnO, was prepared in a similar acetic acid solution with 2% w/v PEG, stirred magnetically for 1 hour at 50 \u0026ordm;C and sonicated for 30 minutes. This solution was combined with the chitosan solution under low-speed mechanical agitation for homogenization, cast into Teflon plates (approximately 12 cm\u0026sup2;) and dried in an oven at 50 \u0026plusmn; 2 \u0026ordm;C for 16-18 hours. This drying phase ensures that the films achieve a consistent dry state, ensuring that the final nanocomposite films are robust and uniformly formed.\u0026nbsp;At least three films per composition were cast for repeatability. The selected films for further evaluation in this study are presented in Table 1, with simplified identifiers (F1, F2, and F3) for clarity throughout the discussion.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eTable 1:\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cem\u003eComposition of Chitosan-Silica-Zinc Oxide Nanocomposite Films\u003c/em\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"566\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 219px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSample ID\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 140px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eComponent\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ew/v%\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ew/w%\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" style=\"width: 219px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eF1 (CH85\u0026middot;\u003c/strong\u003e\u003cstrong\u003eSiO\u003csub\u003e2\u003c/sub\u003e7.5\u0026middot;ZnO7.5)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 140px;\"\u003e\n \u003cp\u003eChitosan\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e2.00%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e85.0%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 140px;\"\u003e\n \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e NP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.15%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e7.50%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 140px;\"\u003e\n \u003cp\u003eZnO NP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.15%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e7.50%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" style=\"width: 219px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eF2 (CH80\u0026middot;\u003c/strong\u003e\u003cstrong\u003eSiO\u003csub\u003e2\u003c/sub\u003e10\u0026middot;ZnO10)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 140px;\"\u003e\n \u003cp\u003eChitosan\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e2.00%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e80.0%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 140px;\"\u003e\n \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e NP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.20%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e10.0%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 140px;\"\u003e\n \u003cp\u003eZnO NP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.20%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e10.0%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" style=\"width: 219px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eF3 (CH60\u0026middot;\u003c/strong\u003e\u003cstrong\u003eSiO\u003csub\u003e2\u003c/sub\u003e20\u0026middot;ZnO20)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 140px;\"\u003e\n \u003cp\u003eChitosan\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e2.00%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e60.0%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 140px;\"\u003e\n \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e NP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.40%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e20.0%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 140px;\"\u003e\n \u003cp\u003eZnO NP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.40%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e20.0%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eF1 = lowest silica/zinc oxide content (15%), F2 = medium content (20%), F3 = highest content (40%)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.3. Characterization of\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eSiO₂ NPs, ZnO NPs, and\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eCH\u003c/strong\u003e\u003cstrong\u003e/SiO₂@ZnO NC Films\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.3.1. X-ray Diffraction (XRD)\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eX-ray Diffraction (XRD) analysis was used to evaluate the crystalline structure of the synthesized green silica nanoparticles (SiO₂ NPs), green ZnO nanoparticles (ZnO NPs) before incorporation into the chitosan matrix and the fabricated CH/SiO₂@ZnO NC films with varying nanoparticle concentrations. The diffractograms were recorded from 2\u0026theta; = 5\u0026deg; to 70\u0026deg; using a Bruker D8 Advance A25 diffractometer with a Cu anode. XRD analysis is crucial for confirming the crystalline and estimating the size of nanoparticles. The degree of crystallinity determined via XRD can indicate the structural order within the nanoparticles, which affects their physical stability and porosity [29]. Smaller nanoparticles, often implied by broader XRD peaks due to increased surface area to volume ratio, typically exhibit higher porosity [30]. This increased porosity is essential as it enhances the material\u0026rsquo;s ability to adsorb water effectively, a key characteristic for materials utilized in water harvesting technologies [10].\u0026nbsp;The Debye-Scherrer formula, referenced as Equation 1, was applied to determine the crystalline size of the green SiO₂ NPs, green ZnO NPs and the green CH/SiO₂@ZnO NC films\u0026nbsp;[31]. This measurement helps understand their impact on the stability of the chitosan-silica complex and their role in maintaining structural integrity and interaction within this complex.\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"125\" height=\"43\"\u003e\u003c/p\u003e\n\u003cp\u003eWhere 𝐷 is the diffracting domain size, \u003cem\u003ek\u003c/em\u003e is a correction factor (0.94), \u003cem\u003e\u0026lambda;\u003c/em\u003e is the used wavelength (0.154178 nm), \u0026beta; = FWHM (full width at half maximum) and \u003cem\u003e\u0026theta;\u003c/em\u003e is the position of the main peak.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.3.2. Fourier-transform infrared spectroscopy (FTIR)\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFourier-transform infrared spectroscopy (FTIR) was performed to analyze the chemical bonds of the green CH/SiO₂@ZnO NC films. A Hyperion 1000 spectrophotometer (Bruker) equipped with an ATR diamond sensor was used to obtain infrared spectra between 4000 and 400 cm⁻\u0026sup1; with a resolution of 4 cm⁻\u0026sup1; and an acquisition of 200 scans. Baseline correction was conducted by measuring without the sample. FTIR spectroscopy was essential for identifying functional groups present in the chitosan-silica-zinc oxide nanocomposites, particularly hydroxyl groups that enhance hydrophilicity, which is critical for water adsorption in atmospheric water harvesting applications.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.3.3. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS or EDAX)\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eScanning Electron Microscopy (SEM, Zeiss EVO microscope, Pleasanton, CA, USA) at 3000X magnification and 10 kV acceleration was used to observe the morphological and microstructural characteristics of the green nanoparticles and the CH/SiO₂@ZnO NC films. Image-J software (Version 1.53q, NIH, Bethesda, MD, USA) was used for particle size distribution analysis. Energy Dispersive X-ray Spectroscopy (EDS or EDAX) was performed during SEM analysis to identify and quantify the elemental composition of carbon (C), nitrogen (N), oxygen (O), silicon (Si), and zinc (Zn) within the nanocomposite matrix. This analysis provided insights into the uniformity and integration of the nanoparticles within the chitosan matrix, which is essential for enhancing water capture performance. Comparative analysis with existing studies highlighted the influence of the elemental composition and dispersion on the functional efficiency of nanocomposites in water harvesting applications [32].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.3.4. Water Contact Angle (WCA)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn this analysis, a micro-syringe applied a 2 \u0026micro;L droplet of deionized water onto the meticulously leveled film on a 1 cm\u0026sup2; surface. Measurements illustrated in Figure 7, as discussed in Section 3.4, represent the WCA on the top surface of the film. It should be noted that the bottom surface measurements, although not depicted, exhibited minimal variation, with differences not exceeding \u0026plusmn;2\u0026deg;. This consistency was achieved through rigorous control over the casting and drying procedures, aimed at producing a homogenized single-layer surface across the film. Over a period of 20 seconds at 12 frames per second, WCA measurements were accurately taken from both sides of the droplet. To ensure precision, frames showing discrepancies greater than 2\u0026deg; between measurements were discarded. This procedure was repeated five times per sample to ensure the reliability of our results. These WCA measurements are crucial for understanding the degree of hydrophilicity/hydrophobicity achieved through surface modifications, directly correlating with the material\u0026rsquo;s potential for effective water adsorption and retention in practical applications [33].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.3.5. Confocal Microscopy (CM)\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe surface roughness of the green CH/SiO₂@ZnO NC films was analyzed using a Confocal-Interferometric Optical Microscope (Sensofar S-NEOX, Sky Tech, Bukit Batok, Singapore) at 100\u0026times; magnification with an 8 \u0026mu;m amplitude Robust Gaussian filter, adhering to ISO 4287 standards. Roughness parameters included the average roughness (Ra, \u0026mu;m), representing the arithmetic mean of absolute profile height deviations, and the quadratic roughness (Rq, \u0026mu;m), calculated as the root mean square of these deviations.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.3.6. Thermal Stability\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe thermal stability of the green CH/SiO₂@ZnO NC films was assessed using Thermogravimetric Analysis (TGA) with an SDT Q600 V20.9 instrument. Approximately 8.5 mg of each sample was analyzed under a nitrogen atmosphere. The temperature was ramped from room temperature to 600 \u0026deg;C at 10 \u0026deg;C/min. The TGA monitored weight changes, providing insights into thermal degradation. The onset of degradation was noted when significant weight loss occurred, indicating thermal decomposition. The analysis ensured consistent and repeatable results under standardized conditions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.3.7. Mechanical Properties\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe mechanical properties of the green CH/SiO₂@ZnO NC films were evaluated using tensile tests, conforming to ISO 527-3:2019 standards [34]. Tests were performed on an MTS Insight 10 machine (Darmstadt, Germany) at a constant rate of 10 mm/min under controlled conditions (22 \u0026deg;C, 30 \u0026plusmn; 3% RH). Parameters recorded included Young\u0026rsquo;s modulus (kPa), maximum stress (kPa) and strain at break (\u0026epsilon;\u003csub\u003emax\u003c/sub\u003e, mm/mm), providing insights into the structural integrity and durability of the films.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.3.8.\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003eAntifungal and Antimicrobial Properties\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe antifungal and antimicrobial properties of the green CH/SiO₂@ZnO NC films were evaluated by comparing them with pure chitosan films without nanoparticles \u0026nbsp;.\u0026nbsp;The microbial environments to which both the green CH/SiO₂@ZnO NC films and the pure chitosan films without nanoparticles (control films) were exposed are defined by room temperature and normal humidity conditions. The films were kept at room temperature, generally around 20\u0026deg;C to 25\u0026deg;C, with a normal humidity range of 35% to 50%. This setup was designed to test the natural resilience of the films against microbial growth under everyday conditions. Daily visual inspections were conducted to identify any signs of microbial activity, such as discoloration, biofilm formation, or morphological changes on the film surface. Under these conditions, the most likely microbes to colonize chitosan films include fungi such as Aspergillus and Penicillium, and possibly yeast species like Candida, which can form biofilms [35]. While this study focused on water capture applications, the antimicrobial evaluation provided insights into the potential of nanoparticle-incorporated chitosan films. Future studies should include detailed microbial testing to quantify resistance to bacterial and fungal growth .\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.3.9. Water Capture\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo evaluate the water capture capabilities of our green CH/SiO₂@ZnO NC films, we employed a passive system without external energy input. The membranes were stored under control conditions lacking measurable humidity and temperature control to simulate realistic environmental scenarios. This setup aimed to determine the effectiveness of the films in generating water even at controlled humidity levels, which were maintained at 30 \u0026plusmn; 5% on average inside a closed environment. The humidity fluctuations might be due to external conditions when storing the films, when storing the films and opening the closed systems in which the films were kept to measure the water generation and collect the water from the films and store these in closed tubes. The ambient humidity was measured between 35% and 45%. This methodology is also adopted to a similar concept inspired by other studies on MOFs, where they utilized a simple setup involving only two plexiglass boxes and ambient sunlight, without any additional energy inputs [36].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.3.10. Statistical Analysis\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEach sample of the green CH/SiO₂@ZnO NC films was tested thrice for reliability. Statistical analysis was conducted using Origin software, presenting results as mean \u0026plusmn; standard deviation (M \u0026plusmn; SD) and generating graphs to illustrate correlations among morphological, physicochemical, functional, and mechanical properties. A one-way ANOVA was also performed to assess variance heterogeneity and significant differences at a 95% confidence level (p \u0026lt; 0.05).\u003c/p\u003e"},{"header":"3. Results And Discussion","content":"\u003cp\u003e\u003cstrong\u003e3.1. X-ray Diffraction (XRD)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eX-ray diffraction (XRD) analysis is essential for evaluating the structural characteristics of nanoparticles (NPs) individually and their interaction within the chitosan matrix, particularly regarding crystallinity and particle size, both of which are crucial for water capture applications. The introduction of silica and zinc oxide nanoparticles into chitosan influences the crystallinity and structural arrangement, affecting the overall performance of the nanocomposite films. As shown in Figure 2, the XRD pattern of green silica nanoparticles (SiO₂ NPs) reveals multiple crystalline phases, including tetragonal, cubic, monoclinic and hexagonal structures, while the green zinc oxide nanoparticles (ZnO NPs) exhibit a sharp hexagonal wurtzite structure, indicative of high crystallinity before incorporation into the chitosan matrix. In addition, Table 2 shows the average crystallite size, crystallinity and phases corresponding to NPs and films.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eTable 2:\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cem\u003eSummary of XRD Results for SiO₂ NPs, ZnO NPs and\u0026nbsp;\u003c/em\u003eCH/SiO₂@ZnO \u003cem\u003eNC Films\u003c/em\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eSample ID\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eAverage Crystallite Size (nm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eCrystallinity (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhase\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eSiO₂ NPs\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e19.5 \u003cu\u003e+\u003c/u\u003e 1.2\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e76.2 \u003cu\u003e+\u003c/u\u003e 1.4\u003csup\u003e\u0026alpha;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCubic, Monoclinic, Hexagonal, Tetragonal\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eZnO NPs\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e26.0 \u003cu\u003e+\u003c/u\u003e 1.3\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e75.0 \u003cu\u003e+\u003c/u\u003e 1.2\u003csup\u003e\u0026alpha;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eHexagonal\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eF1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e56.9 \u003cu\u003e+\u003c/u\u003e 1.6\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e23.1 \u003cu\u003e+\u003c/u\u003e 0.9\u003csup\u003e\u0026gamma;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMonoclinic and Hexagonal\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eF2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e67.7 \u003cu\u003e+\u003c/u\u003e 1.6\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e29.4 \u003cu\u003e+\u003c/u\u003e 0.9\u003csup\u003e\u0026beta;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMonoclinic and Hexagonal\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eF3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e71.7 \u003cu\u003e+\u003c/u\u003e 2.3\u003csup\u003ed\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e23.0 \u003cu\u003e+\u003c/u\u003e 0.9\u003csup\u003e\u0026gamma;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMonoclinic and Hexagonal\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cem\u003eF1 = lowest silica/zinc oxide content (15%), F2 = medium content (20%), F3 = highest content (40%). Different letters indicate statistically significant differences (P\u0026le;0.05).\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eFigure 3 displays the XRD patterns of CH/SiO₂@ZnO NC films (F1, F2, and F3), corresponding to low (15%), medium (20%) and high (40%) total concentration of the nanocomposite, respectively. The broad peaks observed in the nanocomposite films indicate a semi-crystalline structure with well-dispersed nanoparticles, essential for enhancing water adsorption capabilities [37]. The presence of both monoclinic and hexagonal phases in the films suggests effective incorporation and interaction of SiO₂ nanoparticles, which exhibit tetragonal, hexagonal, monoclinic, and cubic phases, and ZnO nanoparticles, which are present in the hexagonal phase (as shown in Figure 2). This demonstrates the merging of hexagonal and monoclinic phases within the chitosan matrix [37].\u003c/p\u003e\n\u003cp\u003eAs summarized in Table 2, the average crystallite sizes range from 56.9 nm in F1 to 71.7 nm in F3, reflecting the influence of nanoparticle concentration on crystallinity. The moderate crystallinity of F1, characterized by smaller crystallite sizes, optimally balances water adsorption due to the increased surface area and active sites, enhancing the material\u0026rsquo;s adsorptive properties. Notably, our crystallite sizes are smaller than or comparable to those reported in similar studies. For instance, Faisal et al. (2021) found that green synthesis of zinc oxide nanoparticles resulted in an average crystallite size of 41.3 nm, whereas Rani et al. (2025) reported sizes ranging from 20-40 nm for silica nanoparticles synthesized using green methods [38, 39]. Furthermore, the correlation between crystallite size and adsorption efficiency observed in our study aligns with, yet appears more pronounced than, findings from previous research, possibly due to our optimized synthesis conditions that utilize extracts from both\u0026nbsp;\u003cem\u003ePhoenix dactylifera\u003c/em\u003e L. leaves and banana peels [35, 40]. This structural arrangement not only corroborates but also advances prior research on the role of amorphous and crystalline phases in enhancing moisture capture efficiency in nanocomposite materials [37]. The results confirm that CH/SiO₂@ZnO NC films maintain high crystallinity while exhibiting structural features that optimize their functionality in water capture applications. Higher crystallinity in these films contributes to a more defined and stable structure, enhancing the efficiency of water molecule adsorption due to the regularity and accessibility of adsorptive sites [40, 41]. For example, in agricultural settings, crystalline hydrogels in the form of films can be used to create moisture-retaining barriers around plant roots, significantly enhancing water retention in arid soils [42]. Similarly, in atmospheric water harvesting applications, films with uniform crystalline structures, such as those we are developing, could offer enhanced stability. This stability, particularly noted in films like F1 with uniform crystalline distribution and morphology, ensures that the films maintain their integrity and functional properties under varying environmental conditions. Such characteristics could make them highly effective for capturing and condensing atmospheric moisture, drawing on the principles established for other stable crystalline materials in other studies.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2. Fourier-transform infrared spectroscopy (FTIR)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFourier-transform infrared spectroscopy (FTIR) analysis of CH/SiO₂@ZnO NC films (F1, F2, and F3) provides comprehensive insights into molecular interactions and the presence of specific functional groups (Figure 4). The broad and intense absorption bands observed between 2800 and 3600 cm⁻\u0026sup1; correspond mainly to O\u0026ndash;H and C\u0026ndash;H stretching vibrations, indicating extensive hydrogen bonding interactions within the chitosan matrix and between chitosan and embedded nanoparticles, in alignment with previous findings [43]. Distinct peaks around 1640 cm⁻\u0026sup1; and 1550 cm⁻\u0026sup1; represent N\u0026ndash;H bending and amide vibrations associated with the chitosan backbone, confirming the polymeric structure\u0026apos;s integrity. Additional peaks near 1080 cm⁻\u0026sup1; and 800 cm⁻\u0026sup1; correspond to Si\u0026ndash;O\u0026ndash;Si stretching vibrations, validating the successful integration of silica nanoparticles [44, 45]. The clear presence of a peak at approximately 500 cm⁻\u0026sup1; confirms Zn\u0026ndash;O stretching vibrations, signifying the effective incorporation of zinc oxide nanoparticles within the films [46].\u003c/p\u003e\n\u003cp\u003eFormulation F1 displays a notably more pronounced O\u0026ndash;H stretching vibration peak, suggesting increased hydrophilicity and superior water adsorption capacity relative to F2 and F3 [47]. This characteristic is primarily attributed to the higher chitosan content, leading to more available hydrophilic hydroxyl groups. While chitosan-related peaks (C\u0026ndash;H ~2900 cm⁻\u0026sup1;, N\u0026ndash;H ~1550 cm⁻\u0026sup1;) exhibit consistency across formulations, slight intensity variations observed in nanoparticle-associated peaks reflect subtle differences in nanoparticle concentration and their interactions within the polymer matrix. These FTIR observations complement the previously discussed XRD results, which highlight the critical balance between crystalline and amorphous phases. While XRD identifies the presence and proportion of crystalline regions, key contributors to mechanical stability and structural robustness, as noted by Darmenbayeva et al. (2024), FTIR provides insights into the chemical functionalities of both crystalline and amorphous phases [48]. The distinct FTIR signatures of amorphous regions, attributed to the greater mobility of polymer chains, indicate enhanced interactions with water molecules and the availability of active sites crucial for water adsorption, as also observed in Darmenbayeva et al. (2024) [48]. Together, these techniques offer a comprehensive understanding of how structural and chemical properties interact to optimize the material\u0026apos;s performance Such a balanced structural interplay is essential for optimizing the water adsorption efficacy of CH/SiO₂@ZnO NC films and aligns well with findings documented in existing literature [48].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.3. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS or EDAX)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eScanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) analyses provide comprehensive insights into the morphological characteristics and elemental composition of CH/SiO₂@ZnO NC films, respectively. As shown in Figure 5, SEM images of silica nanoparticles (A) display an aggregated and irregular morphology, while zinc oxide nanoparticles (B) exhibit a well-defined, rod-like structure, consistent with previous studies on metal oxide nanoparticles used in polymer matrices [27]. The SEM images of the CH/SiO₂@ZnO NC films (F1, F2 and F3) reveal varying nanoparticle distributions within the chitosan matrix. Lower nanoparticle concentrations (F1) result in a more uniform dispersion, while higher concentrations (F3) show notable aggregation, which can impact the surface area and porosity, essential for adsorption/desorption processes in water capture applications. This observation aligns with research highlighting that increased nanoparticle loading can lead to agglomeration, affecting functional properties [49].\u0026nbsp;The particle size distribution of the SiO₂ and ZnO nanoparticles within the films, determined using Image-J software, ranged from 3 \u0026plusmn; 1 nm (smallest size observed in sample F1) to 16 \u0026plusmn; 3 nm (smallest size observed in sample F3), as shown in Figure 5. This trend aligns qualitatively with the XRD results, where an increase in crystalline particle size was observed with higher nanoparticle concentrations, ranging from an average of 56 nm in F1 to 71 nm in F3. The discrepancy between the particle sizes measured by Image-J (3\u0026ndash;16 nm) and those from XRD (56\u0026ndash;71 nm) is likely due to differences in measurement techniques: Image-J analysis assesses individual nanoparticles visually identifiable within the films, revealing the smallest nanoparticle sizes which are crucial as they indicate the minimal achievable particle dimensions. Identifying these small sizes is important as they contribute significantly to an increased surface area and enhanced adsorption capabilities, consistent with findings from previous studies [50-52]. On the other hand, XRD provides average crystallite sizes calculated from diffraction patterns, reflecting larger crystallite domains or particle aggregates rather than individual nanoparticles. Thus, both analytical approaches offer complementary insights, and their results should be interpreted accordingly.\u0026nbsp;Figure 6 presents the EDS spectra of the CH/SiO₂@ZnO NC films, indicating the presence of carbon (C), nitrogen (N), oxygen (O), silicon (Si) and zinc (Zn). Results confirm the successful incorporation and dispersion of silica and zinc oxide nanoparticles within the chitosan matrix. These findings are consistent with previous literature, where similar nanocomposites demonstrated enhanced structural integrity and functionality due to the synergistic interaction between chitosan and embedded nanoparticles [52].\u0026nbsp;The increasing Zn content from F1 to F3 confirms the successful incorporation of Zn nanoparticles into the chitosan matrix, as reflected by the more prominent elemental peaks. However, the expected increase in Si is not observed, suggesting that Si may not have fully integrated or dispersed within the chitosan matrix. Instead, it is likely that Si remains more localized on the surface rather than being embedded within the structure. This surface presence could be beneficial for enhancing moisture trapping during the water adsorption process, as silica nanoparticles\u0026rsquo; geometry could have a great influence on the interfacial interactions of water molecules, as emphasized by Rama \u0026amp; Abbas\u0026apos;s study (2022) [53]. Overall,\u0026nbsp;The SEM and EDS results emphasize the significance of nanoparticle concentration in determining the morphology and elemental composition of nanocomposite films. According to the observed trends in our study, the highest water adsorption capacity was seen in system F1, which had the lowest concentration of nanoparticles. This suggests that better dispersion, rather than higher chitosan content, played a key role in enhancing adsorption performance. Optimal concentrations, such as those in F1, achieve a balance between uniform dispersion and enhanced surface area, crucial for water harvesting applications. Excessive loading, as observed in F3, results in aggregation, potentially limiting functional performance. These findings highlight the importance of optimizing nanoparticle dosage for enhanced performance, consistent with previous studies on nanomaterial-based systems [50-52].\u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.4. Water Contact Angle (WCA)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWater contact angle measurements provide critical insights into the hydrophilic properties of CH/SiO₂@ZnO NC films. As shown in Figure 7, contact angles for the films were measured at 46\u0026deg; (F1), 50\u0026deg; (F2) and 58\u0026deg; (F3), compared to 95\u0026deg; for the pure chitosan film (CH). The lower contact angles observed in the nanocomposite films indicate enhanced hydrophilicity, essential for efficient water adsorption, absorption and condensation in atmospheric water harvesting applications.\u0026nbsp;The enhanced hydrophilicity observed in the CH/SiO₂@ZnO nanocomposite (NC) films is primarily attributed to the zinc oxide nanoparticles, particularly in their hexagonal phase synthesized using the green extract detailed in this study. This method has been shown to\u0026nbsp;significantly improve surface wettability and permeability [54, 55]. Additionally, previous research by Kusworo et al. (2021) demonstrated that green synthesis-derived ZnO nanoparticles effectively\u0026nbsp;enhance surface wettability and water uptake [54]. Moreover, the incorporation of agricultural waste-derived mesoporous silica, from banana peels and peanut shells, also synthesized using the green extract detailed in this study, significantly contributes to the films\u0026apos; improved interaction with water molecules, owing to its high surface area and enhanced thermal conductivity [56, 57]. In fact, it has been mentioned in literature that\u0026nbsp;the strategic use of green synthesis methods enhances the structural and functional properties of nanoparticles, aligning with previous studies highlighting the advantages of environmentally friendly synthesis techniques [58].\u003c/p\u003e\n\u003cp\u003eOverall,\u0026nbsp;compared to pure chitosan films, which have been reported in the literature to exhibit water contact angles ranging from 74\u0026deg; to 104\u0026deg; depending on the study [20, 59], the CH/SiO₂@ZnO NC films demonstrated significantly lower contact angles. This reduction confirms their improved hydrophilicity and highlights their suitability for water harvesting applications.\u0026nbsp;The observed enhancement in hydrophilicity of the CH/SiO₂@ZnO NC films is crucial for atmospheric water harvesting, as effective interaction with water vapor significantly impacts adsorption and condensation efficiency, which aligns with water contact angles of adsorbents/absorbents that have been used in water harvesting applications such as hydrogels and MOFs [60, 61]. Previous studies on chitosan-based nanocomposite scaffolds and films indicate that adding nanocomposites increases surface roughness, which significantly influences the wetting behavior of surfaces, often enhancing hydrophilicity due to increased surface area and more interaction sites for water vapor adsorption [62]. This topic will be developed in Section 3.5. Moreover, Figure 7 shows that the careful selection and concentration of NC are crucial for achieving desired hydrophilicity in films. System F1, having a lower NC concentration than Systems F2 and F3, demonstrated better hydrophilicity. This suggests that increasing nanoparticle concentrations beyond a specific threshold results in higher water contact angles, despite the associated increase in surface roughness and the nanoparticles\u0026rsquo; inherent hydrophilicity. This phenomenon is attributed to physicochemical factors such as surface roughness and nanoparticle agglomeration. Ultimately, optimizing nanoparticle concentration was crucial for achieving moderate hydrophilicity, which was sufficient for effective moisture capture from the air without overly facilitating water penetration, highlighting the importance of balancing nanoparticle concentration with surface properties.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.5. Confocal Microscopy\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 8 presents the 3D Confocal Microscopy (CM) surface topography images and roughness measurements of the CH/SiO₂@ZnO NC films (F1, F2 and F3), computed through Image-J software. The roughness values recorded were 0.141 \u0026micro;m for F1 (low nanoparticle content), 0.144 \u0026micro;m for F2 (medium nanoparticle content), and 0.269 \u0026micro;m for F3 (high nanoparticle content), with corresponding root mean square roughness values of 0.172 \u0026micro;m, 0.189 \u0026micro;m, and 0.348 \u0026micro;m, respectively. The data indicate an increase in surface roughness with a higher surface texture complexity with higher nanoparticle concentrations, within the chitosan matrix\u003cem\u003e.\u0026nbsp;\u003c/em\u003eThis trend is consistent with previous studies, which have shown that an increase in nanoparticle content in similar systems, such as chitosan-based nanocomposite films or scaffolds, enhances surface texture. This enhancement is attributed to nanoparticle agglomeration and uneven distribution [62, 63]. Notably, F1, which exhibited the lowest surface roughness, also showed the highest hydrophilicity, challenging the conventional understanding that increased roughness enhances hydrophilicity. This deviation can be attributed to the unique interactions of nanostructured surfaces, where the integration of nanoparticles influences surface energy and wettability [63, 64]. The complexity of surface interactions at the nanoscale highlights the importance of nanoparticle concentration and dispersion. As demonstrated in similar studies by Du et al. (2022) and Liu et al. (2024), nanomaterials with well-dispersed nanoparticles often display varied hydrophilic or hydrophobic properties based on their surface morphology and the nature of nanoparticle integration [63, 64]. The results emphasize the critical balance between surface roughness, nanoparticle concentration and functional performance in water capture applications. The data provided in the inserted table detail the surface roughness parameters, including average roughness (Ra) and root mean square roughness (Rq), further illustrating the impact of nanoparticle incorporation on surface texture. Enhanced roughness due to nanoparticles increases the surface area for water vapor adsorption, improving water capture efficiency. However, optimal nanoparticle concentration is crucial, as excessive amounts can lead to particle agglomeration, reducing effectiveness by creating blockages and uneven surfaces. Thus, fine-tuning these parameters is essential for maximizing water harvesting efficiency.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.6. Thermal Stability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 9\u0026nbsp;presents the thermal stability analysis of the CH/SiO₂@ZnO NC films (F1, F2, and F3) and pure chitosan (CH), demonstrating distinct thermal stability profiles based on nanoparticle content. Initially, all samples retain over 85% of their original mass up to approximately 70 \u0026deg;C, attributed to the evaporation of adsorbed water rather than material degradation, a behavior consistent with observations in similar systems of chitosan-based films and hydrogels [65]. This initial mass loss confirms the films\u0026apos; capability for rapid moisture adsorption and release, which is crucial for atmospheric water harvesting applications. As the temperature increases, the incorporation of silica and zinc oxide nanoparticles enhances the thermal stability of the chitosan matrix. F1, featuring the optimal NC concentration as emphasized in this study, exhibited slightly better thermal resistance than F2 and F3. However, all systems showed comparable thermal resistance and significant enhancement over the chitosan-only films.\u003c/p\u003e\n\u003cp\u003eThe TGA results in Figure 8 highlight that the CH/SiO₂@ZnO NC films remain stable even beyond 300 \u0026deg;C, while pure chitosan (CH) exhibits a lower thermal stability with rapid degradation after initial water loss. This highlights the significant improvement in thermal resistance achieved by incorporating nanoparticles. Enhanced thermal stability is particularly valuable in atmospheric water harvesting systems, where materials are often exposed to fluctuating temperatures during water collection and evaporation processes [66]. While our study confirms the positive effect of silica and zinc oxide nanoparticles in enhancing the thermal resistance of chitosan-based films, as demonstrated in previous studies, we also note distinctions that may not currently align with existing literature [67]. These differences are crucial for a thorough comparison of properties and highlight the unique aspects of our research, thereby contributing new insights to the field.\u0026nbsp;This improvement in thermal stability ensures that the CH/SiO₂@ZnO NC films maintain their structural integrity during repeated wet and dry cycles, a critical factor for the durability and efficiency of water-harvesting materials. The findings further underscore the importance of nanoparticle incorporation in enhancing the thermal and functional properties of biopolymer-based materials, making them more effective for long-term environmental applications\u0026nbsp;[67, 68]. To explore the specific effects of nanoparticle concentration on these enhancements, a series of tests were conducted across a range of nanoparticle loadings. F1, which features the optimal concentration of nanoparticles, demonstrated superior thermal resistance compared to F2 and F3. This challenges the assumptions mentioned in the literature that higher nanoparticle concentrations in F3 would enhance thermal stability within the composite matrix [69]. Instead, the results indicate that all systems exhibit comparable thermal resistance, significantly surpassing that of chitosan-only films. These findings emphasize the importance of optimizing nanoparticle concentration to achieve the best balance of properties for environmental applications, where materials must withstand cyclical and extreme temperature fluctuations. Such insights are crucial for designing nanocomposite films that meet specific requirements in environmental sustainability.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.7. Mechanical Properties\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 10 and Table 3 present the mechanical properties of the CH/SiO₂@ZnO NC films (F1, F2, and F3) and pure chitosan (CH) film as determined by the tensile test. The control sample, pure chitosan (CH) film, establishes a baseline with moderate mechanical properties, while the incorporation of silica and zinc oxide nanoparticles significantly enhances these properties depending on the concentration. Incorporation of a moderate concentration of nanoparticles (system F1) led to noticeable improvements in mechanical parameters, especially in stiffness and strength: Young\u0026apos;s Modulus and maximum stress increased by 8.7% and 20%, respectively, although no significant differences in strain at break. Further increases in nanoparticle concentration (system F2) continued this trend, with an increase of 26.3% in the Young\u0026rsquo;s Modulus and 80% in the maximum stress, with respect to the control system. This indicates that higher nanoparticle concentrations can enhance mechanical strength and stiffness without sacrificing elasticity. However, system F3, which had the highest concentration of nanoparticles, showed significant increases in Young\u0026apos;s Modulus (344 %) and maximum stress (247 %) but a decrease in strain at break (reduction of 33 %). This reduction highlights a bending point where further increases in nanoparticle content led to increased rigidity and reduced flexibility, undermining the material\u0026rsquo;s ability to elongate before breaking. These findings demonstrate that while nanoparticle enhancement can significantly improve the mechanical properties of chitosan-based films, there is a critical balance to be achieved.\u003c/p\u003e\n\u003cp\u003eThis trend highlights a balance between enhancing mechanical strength and maintaining elasticity, which is crucial for atmospheric water harvesting applications. Higher nanoparticle concentrations improve film durability and structural integrity, but excessive loading may reduce flexibility. Similarly, lower concentrations, as tested in F1, represent the optimal lower limit, as concentrations below this showed effects ranging from good to less favorable. These findings align with previous studies, such as those by Vafaei et al., who reported similar mechanical behavior in biopolymer-nanoparticle composites, emphasizing the need for optimized nanoparticle content for superior mechanical performance [70].\u0026nbsp;The CH/SiO₂@ZnO NC films\u0026apos; enhanced mechanical properties make them suitable for atmospheric water harvesting, ensuring robustness under varying environmental conditions and multiple cycles of moisture adsorption and desorption, consistent with previous research findings\u0026nbsp;[71].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eTable 3:\u003c/em\u003e\u003c/strong\u003e\u003cem\u003e\u0026nbsp;Mechanical properties of CH/SiO₂@ZnO NC films (F1, F2, and F3) and pure chitosan (CH), including Young\u0026rsquo;s Modulus, Maximum Stress, and Strain at Break.\u003c/em\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSample\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 147px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eYoung\u0026rsquo;s Modulus (kPa)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 130px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMaximum stress\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(kPa)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 177px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eStrain at break (mm/mm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCH (Control)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 147px;\"\u003e\n \u003cp\u003e3661 \u0026plusmn; 35\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 130px;\"\u003e\n \u003cp\u003e793 \u0026plusmn; 27\u003csup\u003eA\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 177px;\"\u003e\n \u003cp\u003e0.27 \u0026plusmn; 0.05\u003csup\u003e\u0026alpha;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eF1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3980 \u0026plusmn; 46\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e951 \u0026plusmn; 23\u003csup\u003eB\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.35 \u0026plusmn; 0.07\u003csup\u003e\u0026alpha;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eF2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4624 \u0026plusmn; 24\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1427 \u0026plusmn; 37\u003csup\u003eC\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.35 \u0026plusmn; 0.08\u003csup\u003e\u0026alpha;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eF3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e16274 \u0026plusmn; 124\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2755 \u0026plusmn; 74\u003csup\u003eD\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.18 \u0026plusmn; 0.05\u003csup\u003e\u0026beta;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cem\u003eF1 = lowest silica/zinc oxide content (15%), F2 = medium content (20%), F3 = highest content (40%). Different letters indicate statistically significant differences (P\u0026le;0.05).\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.8.\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eAntifungal and Antimicrobial Properties\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe incorporation of CH/SiO₂@ZnO NC into chitosan films significantly enhances their antifungal and antimicrobial properties, crucial for maintaining water quality and ensuring the safety of drinking water. As shown in Figure 11, the chitosan-only film (CH) developed visible mold within one week, highlighting its limited antimicrobial effectiveness despite chitosan\u0026rsquo;s inherent antimicrobial properties, which rely on binding to microbial cell membranes and causing structural disruptions [72].\u0026nbsp;In contrast, the CH/SiO₂@ZnO NC films (Figure 11) remained free from contamination during the same period, demonstrating superior antimicrobial resistance.\u003c/p\u003e\n\u003cp\u003eThis enhanced antimicrobial effect is attributed to the synergistic action of ZnO and silica nanoparticles. ZnO nanoparticles generate reactive oxygen species (ROS), which effectively damage microbial DNA, proteins and lipids, leading to cell death [73, 74].\u0026nbsp;Additionally, ZnO interacts with microbial cell walls, causing structural disruptions and lysis [72]. Silica nanoparticles stabilize ZnO within the chitosan matrix, prolonging the active antimicrobial phase and ensuring a consistent release of antimicrobial agents [73]. The mesoporous structure of nanosilica further contributes by protecting the biopolymer matrix from microbial degradation\u0026nbsp;[75].\u0026nbsp;The results in Figure 11 illustrate that, unlike the chitosan-only film, which became contaminated within a week, the CH/SiO₂@ZnO NC films exhibited no microbial growth during the same period. This extended protection is particularly advantageous for atmospheric water harvesting applications, where maintaining water quality is essential. Furthermore, the antimicrobial enhancement complements the thermal and mechanical improvements observed in the nanocomposite films, making them suitable for prolonged use in water harvesting systems. The dual functionality of these films, offering both structural durability and antimicrobial resistance, is essential for ensuring the safety and longevity of drinking water systems, consistent with previous studies that emphasize the role of nanoparticles in enhancing the functional properties of biopolymer films [72-75].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.9. Water Capture\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 12 illustrates the water production capabilities of CH/SiO₂@ZnO NC films (F1, F2, and F3) over a two-week period, highlighting the influence of nanoparticle concentration on passive water harvesting. While pure chitosan films displayed lower water capture efficiency, the CH/SiO₂@ZnO NC films demonstrated significant improvements. Notably, the data reveals that under the established humidity conditions, the maximum water production is reached at 7 days, with F1 achieving the highest water generation rate of approximately 1.2 mL/g/day. This peak is an important aspect of the nanoparticle-enhanced water harvesting process observed in these films.\u003c/p\u003e\n\u003cp\u003eThe observed trends indicate that moderate nanoparticle concentrations, such as those in F1 and F2, optimize water capture efficiency by enhancing surface area and water adsorption capabilities. However, F3 shows slightly reduced performance due to potential nanoparticle agglomeration at higher concentrations. Importantly, we also correlated these findings with changes in contact angle, demonstrating that as nanoparticle concentration increases, the contact angle also increases, indicating a reduction in hydrophilicity. This correlation between nanoparticle concentration and hydrophilic properties, supported by both our measurements and literature [76, 77], underscores the importance of balancing nanoparticle content to prevent aggregation and maintain optimal performance. The moderate hydrophilicity of the CH/SiO₂@ZnO NC films, with contact angles between 30\u0026deg; and 60\u0026deg;, further enhanced water condensation, consistent with earlier research findings [78]. Enclosed conditions without airflow played a critical role in maintaining high water retention and absorption rates. Additionally, the films exhibited efficient water adsorption and desorption cycles even at relative humidity levels below 30%, making them suitable for low-humidity environments. This dual correlation of concentration effects with both performance and contact angle measurements enriches the discussion by illustrating how interconnected material properties contribute to overall functionality.\u003c/p\u003e\n\u003cp\u003eWater production rates ranged from 0.7 to 1.2 mL/g/day (Figure 12), with F1 achieving optimal efficiency. This is attributed to its smaller nanoparticle sizes, which enhance the surface area significantly compared to films with larger nanoparticles. Films with a higher surface area, as seen in F1, enabled rapid water generation, initiating within two hours and maintaining short cyclic periods of approximately one hour for adsorption and desorption. This finding illustrates the critical role of nanoparticle size and surface area in optimizing water harvesting efficiency.\u003c/p\u003e\n\u003cp\u003eThe comparative analysis of the results demonstrates that CH/SiO₂@ZnO NC films have notable potential for eco-friendly passive water harvesting, aligning with the performance of current solar-based atmospheric water harvesting systems. These systems typically utilize metal nanoparticles to boost evaporation through surface plasmon resonance. Our study extends this concept by showing that green-synthesized nanoparticles can similarly enhance water capture efficiency but without requiring external energy inputs [75]. This comparison not only highlights the efficacy of our nanoparticle-enhanced materials but also underscores their applicability in environmental and energy-efficient technologies\u003c/p\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn conclusion, this study has successfully demonstrated the potential of chitosan-based nanocomposite films processed by canting and embedded with green silica and ZnO nanoparticles to address global water shortages. Our findings underscore the delicate balance required in nanoparticles and chitosan concentration for optimal performance, highlighting the complexity and sensitivity of designing effective nanocomposite films.\u0026nbsp;The observed stability, particularly in films like F1 with uniform crystalline distribution and morphology, directly supports their functional reliability and improved moisture capture efficiency under variable environmental conditions.\u0026nbsp;Results confirm that a critical SiO\u003csub\u003e2\u003c/sub\u003e and ZnO nanoparticle concentration threshold at 15 wt% within a chitosan matrix maintains mechanical durability, increases hydrophilicity, reduces nanoparticle aggregation and roughness and maximizes water capture efficiency, facilitating a passive auto-water generation process reaching to produce 1.2 mL/g of water without external energy input. This stability also provides the rationale behind enhanced durability and consistent performance observed during practical testing. The composition balance is crucial for scalable atmospheric water harvesting (AWH) device design, especially across varied temperature conditions. Notably, these chitosan films not only surpassed the basic functionality by preventing biocontamination, a common challenge in humid environments, but also showed superior disinfection properties compared to standalone chitosan films. Ultimately, this research contributes to the ongoing efforts to develop scalable, low-cost solutions for sustainable water harvesting, combining environmental responsibility with advanced nanotechnology. It paves the way for further investigation into the application-specific designs of nanoparticle-enhanced materials, reinforcing the importance of nanotechnology in solving critical environmental challenges. This study not only advances the field of atmospheric water harvesting but also offers a promising avenue for future technological innovations in water scarcity management.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions:\u003c/strong\u003e For research articles with several authors, a short paragraph specifying their individual contributions must be provided. The following statements should be used: Conceptualization, N. A-S. and J. A.A.A.; methodology, N. A-S. and J. A.A.A.; software, N.A-S. and J.A.A.A.; validation, N. A-S., J.A.A.A. and A.R.; formal analysis, N. A-S, V.P.P. and A.R.; investigation, N.A-S.; resources, A.R.; data curation, N.A-S and V.P.P; writing\u0026mdash;original draft preparation, N. A-S and J.A.A.A.; writing\u0026mdash;review and editing, V.P.P. and A.R.; visualization, J.A.A.A., V.P.P. and A.R.; supervision, V.P.P. and A.R.; project administration, A.R.; funding acquisition, A.R. All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e This research was funded by the project \u003cem\u003e\u0026ldquo;Eco-Friendly Membranes for Moisture Collection\u0026rdquo;\u003c/em\u003e (Project Reference: PR202405209), supported by \u003cstrong\u003eInnovation Hub Solutions\u003c/strong\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement:\u003c/strong\u003e Data supporting this study are available from the corresponding authors upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments:\u003c/strong\u003e The authors would like to thank \u003cstrong\u003eInnovation Hub Solutions\u003c/strong\u003e for funding the project \u003cem\u003e\u0026ldquo;Eco-Friendly Membranes for Moisture Collection\u0026rdquo;\u003c/em\u003e (Project Reference: PR202405209). We also acknowledge \u003cstrong\u003eCITIUS\u003c/strong\u003e for providing access to the X-Ray, Functional Characterization, and Microscopy services used in this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest:\u003c/strong\u003e The authors declare no conflicts of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAI Declaration :\u0026nbsp;\u003c/strong\u003eDuring manuscript preparation, the authors used Grammarly for grammar checks and ChatGPT-4 for initial language refinement. The content was rigorously reviewed, edited, and validated by the authors, who assumed full responsibility for the work\u0026rsquo;s integrity.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eGleick PH, Cooley H. Freshwater scarcity. Annual Review of Environment and Resources. 2021 Oct 18;46(1):319-48. Triple Threat How disease, climate risks, and unsafe water, sanitation and hygiene create a deadly combination for children. 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Nano Energy. 2023 Oct;115:108660.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Chitosan, Silica Nanocomposites, Zinc Oxide Nanocomposites, Water Capture, Sustainable Atmospheric Water Harvesting","lastPublishedDoi":"10.21203/rs.3.rs-6819891/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6819891/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Global depletion of freshwater resources is exacerbating environmental, social, and economic challenges, underscoring the urgent need for sustainable water sources. Eco-friendly synthesis processes can be implemented not only to enhance water adsorption but also to minimize the environmental impact of its production. In this context, green silica and zinc oxide nanoparticles (SiO₂ NPs and ZnO·NPs) were incorporated in chitosan (CH) to develop a chitosan-silica-zinc oxide nanocomposite (CH/SiO₂@ZnO NC) film to harvest water directly from the air. After experimenting with various concentrations, we found that the optimal performance of the green nanocomposite in the cast chitosan films occurs when it constitutes 15% to 20% by weight of the chitosan polymer. At concentrations exceeding 20%, we observed a deterioration in both functional and mechanical performance. This specific percentage range was chosen based on its effectiveness, which should hopefully address any concerns regarding the evaluation of chitosan concentration. Results reveal that these green nanoparticles were successfully produced to an average size of less than 25 nm, significantly enhancing water adsorption. Based on this study, using a formulation of 2 wt% chitosan with 0.15% each of green SiO2 and ZnO nanoparticles, we determined that a 15% nanocomposite-to-chitosan ratio is essential for achieving nanoscale dimensions and enhancing device durability under variable temperatures. The developed nanocomposites demonstrate a passive auto-water generation process, yielding 0.7–1.2 mL/g at ≤35% relative humidity with no external energy input, showcasing superior functionality when compared to traditional materials. This study highlights a scalable, low-cost AWH solution that combines environmental sustainability with enhanced performance.","manuscriptTitle":"Enhancing Atmospheric Water Harvesting Applications through the Integration of Green Silica and Zinc Oxide Nanoparticles into Chitosan Biopolymer","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-25 08:10:15","doi":"10.21203/rs.3.rs-6819891/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a1806112-3353-4e23-b3d0-c162d5f76356","owner":[],"postedDate":"June 25th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-06-30T11:24:04+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-25 08:10:15","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6819891","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6819891","identity":"rs-6819891","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}