Superhydrophobic polymer membrane coated by mineralized β-FeOOH nanorods for direct contact membrane distillation

Membrane wetting and fouling represent the foremost concerning issues confining membrane distillation in the treatment of industrial wastewater. This work presents a superhydrophobic poly(vinylidene fluoride) (PVDF) membrane with anti-fouling property, which was derived from the bioinspired adhesive, mineralization and fluorination process for the direct contact membrane distillation (DCMD). The synthesis of membrane was initiated by co-depositing polydopamine/polyethylenimine composite layer onto membrane substrates as “bio-glue” associated with β-FeOOH nanorods as hierarchical structure anchoring to form coordination complexes via the catechol group and Fe³⁺, then proceeded with the fluorination of 1H,1H,2H,2H-perfluorodecyltriethoxysilane to obtain the superhydrophobic PVDF membrane. Due to the unique micro-nano structure obtained, the resulting PVDF membrane, with a low sliding angle of 5.7° and a high water contact angle of 162°, conforms to the Cassie state. The membrane morphology, wetting behaviour, and anti-fouling performance were systematically characterized. The novel mineralized superhydrophobic membrane exhibited a steady flux and an outstanding salt rejection (99.9%) in treating high salinity and hardness containing-wastewater during 60-h-DCMD test, thus showing great potential for practical application in long-term DCMD.