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

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.