Eco‐Friendly Nonfluorinated Coating of Omniphobic Membranes With ZnO Nanoparticles Re‐Entrant Structures: Design, Characterization, and Desalination Performance via Membrane Distillation

ABSTRACT Membrane distillation commonly faces challenges such as wetting, fouling, and scaling, which limit its long‐term desalination performance. In this study, an omniphobic membrane was developed via an ecofriendly coating approach, a nonfluorinated omniphobic PVDF hollow fiber membrane via dip coating of zinc oxide nanoparticles with various concentrations of 1–3 wt% as re‐entrant structures, followed by stearic acid grafting. The proposed strategy enhanced surface roughness, reduced surface free energy, and promoted stable omniphobicity without fluorination. A comprehensive characterization was conducted using SEM, AFM, FTIR, XRD, contact angle goniometry, LEP testing, and ICP‐OES analysis to confirm surface morphology, roughness, chemical bonding, and coating stability. The results show that increasing ZnO NPs concentration up to 3 wt% produced a surface roughness of 100.43 nm and contact angle above 120° for all tested liquids. The best membrane exhibited excellent desalination performance with water flux above 14 L/m 2 h and salt rejection of ~99.97% for five consecutive days under 30,000 ppm NaCl feed and 100 ppm humic acid. Accelerated chemical exposure under hot synthetic seawater showed less than 5% salt deposition while water contact angle remained above 90° after 48 h, demonstrating strong resistance to surface coating degradation.