Fabrication of stable and simple reusable hydrophobic ZIF-8-coated polyurethane sponge for effective oil/water separation.

Industrial oily wastewater and oil spills pose serious environmental threats, demanding efficient and scalable separation materials. In this work, a hydrophobic/oleophilic ZIF-8/polyurethane sponge (ZIF-8/PUS) composite was fabricated via a simple dip-coating and drying process at room temperature. The composite was characterized by X-ray diffraction, FTIR, scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, and Barrett-Joyner-Halenda (BJH) pore size distribution, confirming successful ZIF-8 deposition and a well-developed porous architecture. The water contact angle increased from 96.8 to 148.4°, while the oil contact angle remained 0°. The sponge achieved an oil absorption capacity of 36.1 g g⁻1 for 15W-40 oil and a water flux of 107 L m⁻2 h⁻1. Temperature-dependent separation tests (25-85 °C) yielded COD removal efficiencies of 99.24-97.55% and oil and grease removal of 99.20-97.74%. Statistics on triple experiments validated these results' robustness: One-way ANOVA showed significant differences in COD and oil/grease removal among experimental groups (p < 0.0001), and Tukey's HSD test showed that optimally adjusted samples outperformed controls (p < 0.05). The sponge retained performance after ten absorption-squeezing cycles. Application to real drilling rig wastewater (RIG-69 Fath unit) achieved 94.97% COD removal (6689 to 67 mg L⁻1) and 99.07% oil and grease removal, demonstrating practical potential for industrial oily wastewater treatment.