Sustainable Atmospheric Water Harvesting Nanocomposite Films Based on Green-Synthesized Oxide–Chitosan

This study focuses on sustainable atmospheric water harvesting (AWH) using film-containing green nanomaterials. Particular emphasis is given to chitosan as a sustainable biopolymer matrix due to its intrinsic hydrophilicity, biodegradability, film-forming ability and abundance of amino and hydroxyl functional groups that favor water adsorption and nanoparticle interaction. ZnO, SiO2 and Fe-Zn-SiO2 nanoparticles with abundant hydroxyl groups were synthesized from plant-based materials such as biomass from peanut and banana wastes, as well as plant extracts. Nanocomposite membranes containing nanoparticles with a high specific surface area and moisture-sensitive behavior were successfully developed. Results showed that bilayer films outperformed monolayer systems in water harvesting performance. In particular, the bilayer film composed of Chitosan/G-ZnO (10 wt.%) on the top layer and Chitosan/G-SiO2 (10 wt.%) in the bottom layer displayed outstanding hydrophilic properties with water contact angles reduced to 42–43°. The material demonstrated an equilibrium adsorption capacity for water at 0.90 g/g and a passive yield of 1.5–2.2 mL/g per day. The improved adsorption behavior was attributed to the synergistic effect between the hydroxyl-rich oxide nanoparticles, the intrinsic water affinity of chitosan, and the layered porous structure. Moreover, the samples showed good thermal and mechanical stability and retained their structure after several uses. These findings highlight the potential of chitosan-centered green nanocomposites as sustainable materials for passive AWH applications.