Superwetting ZIF-67-based composite membranes: Synergistic preparation and enhanced underwater superoleophobic performance for oil–water separation

Oily wastewater discharged from industrial production and daily life poses a serious threat to ecological systems such as rivers and soils. Poly(vinylidene fluoride) (PVDF) membranes are inexpensive and exhibit excellent chemical stability, and thus have been widely used in oily wastewater treatment. However, unmodified PVDF membranes are highly hydrophobic and prone to fouling by oil droplets, resulting in low treatment efficiency. Hydrophilic modification can greatly mitigate membrane fouling. In this work, PDA@ZIF-670.7、PDA@ZIF-670.8、and PDA@ZIF-671.0 nanoparticles were synthesized via a hydrothermal method and subsequently deposited onto PVDF membranes by vacuum-assisted filtration to fabricate PDA@ZIF‑67/PVDF composite membranes. The results showed that the PDA@ZIF‑67/PVDF composite membrane prepared using PDA@ZIF-670.8 at a loading of 23.88 g·m−2 exhibited the best overall performance. The wetting time of water droplets on the membrane surface was 1706.67 ms, and the underwater oil droplet contact angle reached 160.34° or the separation of oil-in-water emulsions, the maximum permeation flux was 9235.67 L·m−2·h−1 and the highest separation efficiency was 99.98%. During five consecutive separation cycles, the permeation flux of the composite membrane remained above 8000 L·m−2·h−1bar−1, while the separation efficiency was still higher than 99.9%. The composite membrane also exhibited excellent stability and maintained favorable surface properties even under strong acidic and alkaline conditions. Overall, the PDA@ZIF‑67/PVDF composite membranes prepared by this simple strategy show great potential for oily wastewater treatment.